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Event-by-event fluctuations in the multiplicities of charged particles and photons at SPS energies are discussed. Fluctuations are studied by controlling the centrality of the reaction and rapidity acceptance of the detectors. Results are also presented on the event-by-event study of correlations between the multiplicity of charged particles and photons to search for DCC-like signals.
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arxiv:nucl-ex/0208019
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The ^18F(p, alpha)^15O reaction is recognized as one of the most important reaction for nova gamma-ray astronomy as it governs the early =< 511 keV emission. However, its rate remains largely uncertain at nova temperatures due to unknown low-energy resonance strengths. In order to better constrain this reaction rate, we have studied the one-nucleon transfer reaction, D(^18F,p alpha)^15N, at the CRC-RIB facility at Louvain La Neuve.
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arxiv:nucl-ex/0209017
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Recent results on identified hadrons from the PHENIX experiment in Au+Au collisions at mid-rapidity at $\sqrt{s_{NN}}$ = 200 GeV are presented. The centrality dependence of transverse momentum distributions and particle ratios for identified charged hadrons are studied. The transverse flow velocity and freeze-out temperature are extracted from $p_{T}$ spectra within the framework of a hydrodynamic collective flow model. Two-particle HBT correlations for charged pions are measured in different centrality selections for a broad range of transverse momentum of the pair. Results on elliptic flow measurements with respect to the reaction plane for identified particles are also presented.
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arxiv:nucl-ex/0209027
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Enhanced production of events with almost equal-sized fragments is experimentally revealed by charge correlations in the multifragmentation of a finite nuclear system selected in $^{129}$Xe central collisions on $^{nat}$Sn. The evolution of their weight with the incident energy: 32, 39, 45, 50 AMeV, is measured.Dynamical stochastic mean field simulations performed at 32 AMeV, in which spinodal instabilities are responsible for multifragmentation, exhibit a similar enhancement of this kind of events. The above experimental observation evidences the spinodal decomposition of hot finite nuclear matter as the origin of multifragmentation in the Fermi energy regime.
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arxiv:nucl-ex/0212018
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Non-identical two particle correlation functions probe asymmetries between the average space-time emission points of different particle species. The system collective expansion would produce such asymmetry because massive particles, such as protons, are on average more pushed towards the edge of the system, than lighter ones, i.e. pions. Measuring pion-kaon, pion-proton and kaon-proton correlation functions, using the STAR detector, we show that the data are consistent with the effect of transverse flow in Au-Au collisions at $\sqrt{s_{NN}} = 130$ GeV.
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arxiv:nucl-ex/0212026
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Beam polarization asymmetries for the p(gamma,K+)Lambda and p(gamma,K+)sigma0 reactions are measured for the first time for Egamma=1.5-2.4 GeV and 0.6<cos(theta_cm(K+))<1.0 by using linearly polarized photons at the Laser-Electron-Photon facility at SPring-8 (LEPS). The observed asymmetries are positive and gradually increase with rising photon energy. The data are not consistent with theoretical predictions based on tree-level effective Lagrangian approaches. Including the new results in the development of the models is, therefore, crucial for understanding the reaction mechanism and to test the presence of baryon resonances which are predicted in quark models but are sofar undiscovered.
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arxiv:nucl-ex/0302005
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At the internal facility COSY-11 a first measurement of the reaction p(pol)p -> pp eta near the production threshold has been performed. Results for the analysing power will be presented and a comparison with one meson exchange models will be discussed.
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arxiv:nucl-ex/0302010
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The background induced by radioactive impurities of $^{208}\rm Tl$ and $^{214}\rm Bi$ in the source of the double beta experiment NEMO-3 has been investigated. New methods of data analysis which decrease the background from the above mentioned contamination are identified. The techniques can also be applied to other double beta decay experiments capable of measuring independently the energies of the two electrons.
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arxiv:nucl-ex/0302022
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The charge form factor of the neutron has been determined from asymmetries measured in quasi--elastic pol.3He(pol e,e'n) at a momentum transfer of 0.67(GeV/c)^2. In addition, the target analyzing power, A_y^o, has been measured to study effects of final state interactions and meson exchange currents.
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arxiv:nucl-ex/0303015
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We present the results of the experimental study on synthesis of a wide range of isotopes in a superdense plasma. The initial conditions necessary for plasma bunch formation were provided by specially organized coherent impact on a solid target with a total energy up to 1 kJ. More than 4000 shots were performed with various targets made of light, medium, and heavy elements. Subsequent analysis of the products of the target explosion reveals the presence of a wide range of elements absent in the initial materials. Elements with nuclei three and more times heavier than the nucleus of the target main element are detected in the products. The isotopic composition of the produced elements significantly differs from the natural one. The presence of unknown superheavy elements at the border of the periodic table and beyond it was detected by several different spectroscopic methods of elemental and isotopic analyzes.
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arxiv:nucl-ex/0304018
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First results on the production of Xi and AntiXi hyperons in Pb+Pb interactions at 40 AGeV are presented. The AntiXi/Xi ratio at midrapidity is studied as a function of collision centrality. The ratio shows no significant centrality dependence within statistical errors; it ranges from 0.07 to 0.15. The AntiXi/Xi ratio for central Pb+Pb collisions increases strongly with the collision energy.
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arxiv:nucl-ex/0305021
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The level densities and radiative strength functions (RSFs) in 160,161Dy have been extracted using the (3He,alpha gamma) and (3He,3He' gamma) reactions, respectively. The data are compared to previous measurements on 161,162Dy. The energy distribution in the canonical ensemble is discussed with respect to the nucleon Cooper pair breaking process. The gross properties of the RSF are described by the giant electric dipole resonance. The RSF at low gamma-ray energies is discussed with respect to temperature dependency. Resonance parameters of a soft dipole resonance at Egamma = 3 MeV are deduced.
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arxiv:nucl-ex/0307009
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We report on the first detailed measurements of electron backscattering from low Z targets at energies up to 124 keV. Both energy and angular distributions of the backscattered electrons are measured and compared with electron transport simulations based on the Geant4 and Penelope Monte Carlo simulation codes. Comparisons are also made with previous, less extensive, measurements and with measurements at lower energies.
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arxiv:nucl-ex/0310002
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Event-by-event fluctuations of the average transverse momentum of produced particles near mid-rapidity have been measured by the PHENIX Collaboration in sqrt(s_NN)=200 GeV Au+Au and p+p collisions at the Relativistic Heavy Ion Collider. The fluctuations are observed to be in excess of the expectation for statistically independent particle emission for all centralities. The excess fluctuations exhibit a dependence on both the centrality of the collision and on the transverse momentum window over which the average is calculated. Both the centrality and p_T dependence can be well reproduced by a simulation of random particle production with the addition of contributions from hard scattering processes.
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arxiv:nucl-ex/0310005
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A comparison of the close-to-threshold total cross sections for the eta-prime meson production in both the pp --> pp eta-prime and pn --> pn eta-prime reactions should provide insight into the flavour-singlet (perhaps also into gluonium) content of the eta-prime meson and the relevance of quark-gluon or hadronic degrees of freedom in the creation process. The excitation function for the reaction pp --> pp eta-prime has been already established. At present, experimental investigations of the quasi-free pn --> pn X reactions are carried out at the COSY-11 facility using a beam of stochastically cooled protons and the deuteron cluster target. A method of measurement and preliminary results from the test experiments of the pn --> pn eta reaction are presented in this report.
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arxiv:nucl-ex/0311003
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A non-monotonic energy dependence of the $K^{+} / \pi^{+}$ ratio with a sharp maximum close to 30 A$\cdot$GeV is observed in central Pb+Pb collisions. Within a statistical model of the early stage, this is interpreted as a sign of the phase transition to a QGP, which causes a sharp change in the energy dependence of the strangeness to entropy ratio. This observation naturally motivates us to study the production of multistrange hyperons ($\Xi$, $\Omega$) as a function of the beam energy. Furthermore it was suggested that the kinematic freeze-out of $\Omega$ takes place directly at QGP hadronization. If this is indeed the case, the transverse momentum spectra of the $\Omega$ directly reflect the transverse expansion velocity of a hadronizing QGP. In this report we show preliminary NA49 results on $\Omega^{-}$ and $\bar{\Omega}^{+}$ production in central Pb+Pb collisions at 40 and 158 A$\cdot$GeV and compare them to measurements of $\Xi^{-}$ and $\bar{\Xi}^{+}$ production in central Pb+Pb collisions at 30, 40, 80 and 158 A$\cdot$GeV.
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arxiv:nucl-ex/0312022
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Bose-Einstein correlations of identically charged pion pairs were measured by the PHENIX experiment at mid-rapidity in Au+Au collisions at $\sqrt{s_{\rm NN}}$ = 200 GeV. The Bertsch-Pratt radius parameters were determined as a function of the transverse momentum of the pair and as a function of the centrality of the collision. Using the \it{full} Coulomb correction, the ratio $R_{\rm out}/R_{\rm side}$ is smaller than unity for $<k_{\rm T}>$ from 0.25 to 1.2 GeV/c and for all measured centralities. However, using recently developed partial Coulomb correction methods, we find that $R_{\rm out}/R_{\rm side}$ is 0.8-1.1 for the measured $<k_{\rm T}>$ range, and approximately constant at unity with the number of participants.
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arxiv:nucl-ex/0401003
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We report the first inclusive photon measurements about mid-rapidity (|y|<0.5) from Au+Au collisions at sqrt(s_{NN}) = 130 GeV at RHIC. Photon pair conversions were reconstructed from electron and positron tracks measured with the Time Projection Chamber (TPC) of the STAR experiment. With this method, an energy resolution of Delta(E)/E = 2% at 0.5 GeV has been achieved. Reconstructed photons have also been used to measure the transverse momentum (pt) spectra of pi0 mesons about mid-rapidity (|y|<1) via the pi0 -> photon photon decay channel. The fractional contribution of the pi0 -> photon photon decay to the inclusive photon spectrum decreases by 20% +/- 5% between pt = 1.65 GeV/c and pt = 2.4 GeV/c in the most central events, indicating that relative to pi0 -> photon photon decay the contribution of other photon sources is substantially increasing.
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arxiv:nucl-ex/0401008
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The understanding of few-nucleon systems at low energies is essential, e.g. for accurate predictions of element abundances in big-bang and stellar fusion. Novel effective field theories, taking only nucleons, or nucleons and pions as explicit degrees of freedom, provide a systematic approach, permitting an estimate of theoretical uncertainties. Basic constants parameterising the short range physics are derived from only a handful of experimental values. The doublet neutron scattering length a_2 of the deuteron is particularly sensitive to a three-nucleon contact interaction, but experimentally known with only 6% accuracy. It can be deduced from the two experimentally accessible parameters of the nd scattering length. We plan to measure the poorly known "incoherent" nd scattering length a_{i,d} with 10^{-3} accuracy, using a Ramsey apparatus for pseudomagnetic precession with a cold polarised neutron beam at PSI. A polarised target containing both deuterons and protons will permit a measurement relative to the incoherent np scattering length, which is know experimentally with an accuracy of 2.4\times 10^{-4}.
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arxiv:nucl-ex/0401029
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We show that the centrality dependence of charged particle and photon pseudorapidity density at midrapidity along with the transverse energy pseudorapidity density at SPS and RHIC energies scales with the number of participating constituent quarks. The number of charged particles and transverse energy per participant constituent quark is found to increase with increase in beam energy.
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arxiv:nucl-ex/0401036
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A study of the interaction of loosely bound nuclei 6,7Li at 9 and 19 AMeV with light targets has been undertaken. With the determination of unambiguous optical potentials in mind, elastic data for four projectile-target combinations and one neutron transfer reaction 13C(7Li,8Li)12C have been measured on a large angular range. The kinematical regime encompasses a region where the mean field (optical potential) has a marked variation with mass and energy, but turns out to be sufficiently surface transparent to allow strong refractive effects to be manifested in elastic scattering data at intermediate angles. The identified exotic feature, a "plateau" in the angular distributions at intermediate angles, is fully confirmed in four reaction channels and interpreted as a pre-rainbow oscillation resulting from the interference of the barrier and internal barrier farside scattering subamplitudes.
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arxiv:nucl-ex/0402011
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Preliminary results on pion-pion Bose-Einstein correlations in central Pb+Pb collisions measured by the NA49 experiment are presented. Rapidity as well as transverse momentum dependence of the HBT-radii are shown for collisions at 20, 30, 40, 80, and 158 AGeV beam energy. Including results from AGS and RHIC experiments only a weak energy dependence of the radii is observed. Based on hydrodynamical models parameters like lifetime and geometrical radius of the source are derived from the dependence of the radii on transverse momentum.
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arxiv:nucl-ex/0403034
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We have measured the rapidity distributions dN/dy of pi+/-, K+/- and p,pbar in central Au+Au collisions at sqrt(s_nn) = 200 GeV. The average rapidity loss per participant nucleon is 2.0 +/- 0.2 units of rapidity. The strange to non--strange meson ratios K/pi are found to track variations of the baryo--chemical potential in energy and rapidity.
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arxiv:nucl-ex/0403049
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An overview of the most important experimental results obtained in the first three running years with the BRAHMS experiment from Brookhaven National Laboratory(USA) is presented. The design of the experiment permits to measure the interesting physical quantities in a large ranges of rapidity and transverse momentum. Therefore, properties of hadron production vs rapidity and transverse momenta are presented.
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arxiv:nucl-ex/0404011
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We present transverse momentum spectra from d+Au collisions at sqrt(s_NN) = 200 GeV for identified hadrons at mid-rapidity and unidentified hadrons in the forward rapidity region using the Solenoidal Tracker at RHIC. We scale these spectra by the mean number of binary collisions to form a transverse momentum dependent ratio to spectra from p+p collisions, showing that the Cronin effect measured at lower centre-of-mass energies is also present at this higher energy. The data also suggest a dependence of the Cronin effect on the hadron species. We also compare central d+Au collisions to more peripheral ones, contrasting the behaviour to that observed in Au+Au collisions and remark on unidentified hadrons at forward rapidities which show a qualitatively different behaviour.
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arxiv:nucl-ex/0404027
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The future accelerator facility for beams of ions and antiprotons at Darmstadt will provide antiproton beams of intensities that are two orders of magnitude higher than currently available. Within the foreseen scheme, antiprotons can be decelerated to 30 MeV. The low-energy antiproton community has recently formed a users group to make use of this opportunity to create a next-generation low-energy antiproton facility called FLAIR, which will be able to provide cooled antiproton beams well below 100 keV kinetic energy. This talk gives an overview of the layout and physics program of the proposed facility.
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arxiv:nucl-ex/0406018
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An experiment on the radiative pi^+ meson photoproduction from the proton (gamma p->gamma pi^+ n) was carried out at the Mainz Microtron MAMI in the kinematic region 537 MeV <E_{gamma}<817 MeV, 140^o<theta_{gamma-gamma'}^cm<180^o. The pi^+ meson polarizabilities have been determined from a comparison of the data with the predictions of two different theoretical models, the first one being based on an effective pole model with pseudoscalar coupling while the second one is based on diagrams describing both resonant and nonresonant contributions. The validity of the models has been verified by comparing the predictions with the present experimental data in the kinematic region where the pion polarizability contribution is negligible (s_1<5 mu^2) and where the difference between the predictions of the two models does not exceed 3%. In the region, where the pion polarizability contribution is substantial (5<s_1/mu^2<15, -12<t/mu^2<-2), the difference (alpha-beta)_{pi^+} of the electric (alpha) and the magnetic (beta) polarizabilities has been determined. As a result we find: (alpha-beta)_{pi^+}=(11.6\pm 1.5_{stat}\pm 3.0_{syst}\pm 0.5_{mod})x10^-4fm^3. This result is at variance with recent calculations in the framework of chiral perturbation theory.
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arxiv:nucl-ex/0407011
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The polarized longitudinal-transverse structure function $\sigma_{LT^\prime}$ has been measured using the $p(\vec e,e'\pi^+)n$ reaction in the $\Delta(1232)$ resonance region at $Q^2=0.40$ and 0.65 GeV$^2$. No previous $\sigma_{LT^\prime}$ data exist for this reaction channel. The kinematically complete experiment was performed at Jefferson Lab with the CEBAF Large Acceptance Spectrometer (CLAS) using longitudinally polarized electrons at an energy of 1.515 GeV. A partial wave analysis of the data shows generally better agreement with recent phenomenological models of pion electroproduction compared to the previously measured $\pi^0 p$ channel. A fit to both $\pi^0 p$ and $\pi^+ n$ channels using a unitary isobar model suggests the unitarized Born terms provide a consistent description of the non-resonant background. The $t$-channel pion pole term is important in the $\pi^0 p$ channel through a rescattering correction, which could be model-dependent.
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arxiv:nucl-ex/0407013
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The 3He(4He,gamma)7Be reaction plays an important role in determining the high energy solar neutrino flux and in understanding the abundances of primordial 7Li. The present paper reports a new precision measurement of the cross sections of this direct capture reaction, determined by measuring the ensuing 7Be activity in the region of Ec.m.=400 keV to 950 keV. Various recent theoretical fits to our data result in a consistent extrapolated value of S34(0)=0.53(2)(1).
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arxiv:nucl-ex/0407017
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The 18F(p,a)15O reaction is recognized as one of the most important reaction for nova gamma-ray astronomy as it governs the early <= 511 keV emission. However, its rate remains largely uncertain at nova temperatures due to unknown low-energy resonance strengths. We report here on our last results concerning the study of the D(18F,pa)15N reaction, as well as on the determination of the 18F(p,a)15O reaction rate using the R-matrix theory. Remaining uncertainties are discussed.
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arxiv:nucl-ex/0408001
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Measurements of the production of high energy pi0 mesons at large pseudorapidity, coincident with charged hadrons at mid-rapidity, for proton+proton and deuteron+gold collisions at sqrt(s)_NN=200 GeV are reported. The p+p cross section for inclusive pi0 production follows expectations from next-to-leading order perturbative QCD. Both the inclusive cross section and the di-hadron azimuthal correlations are consistent with a model where parton showers supplement leading-order pQCD. A suppression of the back-to-back azimuthal correlations was observed in d+Au, qualitatively consistent with the gluon saturation picture.
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arxiv:nucl-ex/0408004
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We have measured the 14N(p,g)15O excitation function for energies in the range E_p = 155--524 keV. Fits of these data using R-matrix theory yield a value for the S-factor at zero energy of 1.64(17) keV b, which is significantly smaller than the result of a previous direct measurement. The corresponding reduction in the stellar reaction rate for 14N(p,g)15O has a number of interesting consequences, including an impact on estimates for the age of the Galaxy derived from globular clusters.
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arxiv:nucl-ex/0408018
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The formulae for calculating jet fragmentation momentum, $<j_T^2>$, and parton transverse momentum, $<k_T^2>$, and conditional yield are discussed in two particle correlation framework. Additional corrections are derived to account for the limited detector acceptance and inefficiency, for cases when the event mixing technique is used. The validity of our approach is confirmed with Monte-carlo simulation.
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arxiv:nucl-ex/0409024
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Excitation functions of the spin correlation coefficients A_{NN}(p_{lab},theta_{c.m.}), A_{SS}(p_{lab},theta_{c.m.}), and A_{SL}(p_{lab},theta_{c.m.}) have been measured with the polarized proton beam of the Cooler Synchrotron COSY and an internal polarized atomic beam target. Data were taken continuously during the acceleration for proton momenta p_{lab} ranging from 1000 to 3300 MeV/c (kinetic energies T_{lab} 450 - 2500 MeV) as well as for discrete momenta of 1430 MeV/c and above 2000 MeV/c covering angles theta_{c.m.} between 30 deg and 90 deg. The data are of high internal consistency. Whereas A_{SL}(p_{lab,}theta_{c.m.}) is small and without structures in the whole range, A_{NN} and even more A_{SS} show a pronounced energy dependence. The angular distributions for A_{SS} are at variance with predictions of existing phase shift analyses at energies beyond 800 MeV. The impact of our results on phase shift solutions is discussed. The direct reconstruction of the scattering amplitudes from all available pp elastic scattering data considerably reduces the ambiguities of solutions.
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arxiv:nucl-ex/0412014
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This article reviews the research program and efforts for the TEXONO Collaboration on neutrino and astro-particle physics. The ``flagship'' program is on reactor-based neutrino physics at the Kuo-Sheng (KS) Power Plant in Taiwan. A limit on the neutrino magnetic moment of munuebar < 1.3 times 10^{-10} mub at 90% confidence level was derived from measurements with a high purity germanium detector. Other physics topics at KS, as well as the various R&D program, are discussed.
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arxiv:nucl-ex/0412057
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At ELSA interesting results on baryon resonances have been obtained by the CB-ELSA, the CBELSA/TAPS and the SAPHIR collaborations. New resonances were found, in particular a new $\rm D_{15}(2070)$ decaying into $p\eta$, was recently observed by the CB-ELSA experiment. The availability of a polarized beam and a polarized target did allow to measure the GDH sum rule up to 2.9 GeV. In the future double polarization experiments will be performed using the Crystal Barrel detector together with new forward detector components. These polarization observables will provide important additional information for the partial wave analyses performed to extract the contributing resonances and their parameters from the data.
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arxiv:nucl-ex/0501024
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The nucleon elastic form factors are of fundamental interest, provide a unique testing ground for QCD motivated models of nucleon structure and are of critical importance to our understanding of the electromagnetic properties of nuclei. Even after an experimental effort spanning nearly 50 years the nucleon form factors are still the subject of active investigation. Advances in polarized beams, polarized targets and recoil polarimetry have been exploited over the last decade to produce an important and precise set of data. I review the status of the experimental efforts to measure the nucleon elastic form factors.
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arxiv:nucl-ex/0502003
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We present the preliminary results from our analysis of event by event fluctuation in K/pi ratio in Au+Au collision at \sqrt s_{NN} = 200 GeV and at 62.4 GeV using STAR detector at RHIC. Two different methods have been used to extract the strength of dynamical fluctuation and the centrality dependence of that. The results from the study of energy and centrality dependence of the dynamical fluctuation are presented. From the excitation function it is seen that at two RHIC energies the measure of dynamical fluctuation is constant with values very close to that at 12.3 GeV at SPS. The dynamical fluctuation is found to be positive and decreasing with increasing centrality at RHIC. The results are compared with HIJING model calculation with jets. Results from HIJING are found to be very close to data from central collisions whereas it over predicts the data for peripheral events.
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arxiv:nucl-ex/0503023
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We have searched for particle-bound 26-O and 28-F isotopes in the reaction products of secondary 27-F and 29-Ne beams, respectively. No events have been observed. Upper limits for the respective production cross sections by one-p-stripping reactions are established under the assumption that 26-O and 28-F are particle bound. Since the experimental upper limits are much lower than common estimates we conclude that neither 26-O nor 28-F are likely particle bound.
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arxiv:nucl-ex/0504007
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The RIKEN data on the Coulomb Dissociation (CD) of 8B were shown to be in good agreement with the Direct Capture (DC) data on the 7Be(p,g)8B reaction (that were known at that time) of Filippone {\em et al.} Yet recently it was claimed that the RIKEN2 CD data must be corrected in order to be reconciled with the slope of DC data. Considering the (correct) so called scale independent b-slope parameter of the RIKEN2 CD data, the resultant corrected b-slope parameter suggested by Esbensen, Bertsch and Snover is shown to be considerably smaller than the so called average b-slope parameter of DC data. The suggested corrections of the b-slope parameter lead to a large disagreement with DC data, in sharp contrast to the claim. The slope corrections are only significant for the RIKEN2 CD data. For the GSI kinematics, where in fact one may observe slope different than for DC (at least for the GSI1 data), they find a fortuitous cancellation that leads to a vanishingly small slope correction. Hence the validity of these correction based on the observed slopes can not be substantiated.
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arxiv:nucl-ex/0504008
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Experimental results for identified hadron spectra in AA collisions at RHIC are reviewed. Jet suppression in central AuAu collisions at 200 GeV is seen in leading meson and baryon spectra at high p_t. Enhanced baryon production at intermediate p_T (2<p_t<5 GeV/c) is related to quark content but not its mass.In d+Au collisions Cronin enhancement is observed with larger magnitude for baryons than for mesons, but this difference can not explain the baryon-to-meson ratio in Au+Au collisions. In Au+Au the observations at 62.4 GeV and 200 GeV are very similar, but smaller suppresion of the leading particles is seen at low beam energy, which is evidence for a smooth beam energy dependence of the effect. Near and away side jets seen in two-particle correlations are very similar for the leading baryons and mesons.
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arxiv:nucl-ex/0505013
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We measure cross sections for residual nuclide formation in the mass range 6 < A < 97 caused by bombardment with protons and deuterons of 3.65 GeV/nucleon energy of enriched tin isotopes (112-Sn, 118-Sn, 120-Sn, 124-Sn). The experimental data are compared with calculations by the codes FLUKA, LAHET, CEM03, and LAQGSM03. Scaling behavior is observed for the whole mass region of residual nuclei, showing a possible multifragmentation mechanism for the formation of light products (6 < A < 31). Our analysis of the isoscaling dependence also shows a possible contribution of multifragmentation to the production of heavier nuclides, in the mass region 39 < A < 81.
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arxiv:nucl-ex/0506024
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The work is aimed at experimental determination of the independent and cumulative yields of radioactive residual nuclei produced in intermediate-energy proton-irradiated thin targets made of highly isotopic enriched and natural lead (206,207,208,natPb) and 209Bi. 5972 radioactive product nuclide yields have been measured in 55 thin targets induced by 0.04, 0.07, 0.10, 0.15, 0.25, 0.6, 0.8, 1.2, 1.4, 1.6, and 2.6 GeV protons extracted from the ITEP U-10 proton synchrotron. The measured data have been compared with data obtained at other laboratories as well as with theoretical simulations by seven codes. We found that the predictive power of the tested codes is different but is satisfactory for most of the nuclides in the spallation region, though none of the codes agree well with the data in the whole mass region of product nuclides and all should be improved further.
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arxiv:nucl-ex/0507009
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Measured hard photon multiplicities from second-chance nucleon-nucleon collisions are used in combination with a kinetic thermal model, to estimate the break-up times of excited nuclear systems produced in nucleus-nucleus reactions at intermediate energies. The obtained nuclear break-up time for the $^{129}${Xe} + $^{nat}${Sn} reaction at 50{\it A} MeV is $\Delta$$\tau$ $\approx$ 100 -- 300 fm/$c$ for all reaction centralities. The lifetime of the radiating sources produced in seven other different heavy-ion reactions studied by the TAPS experiment are consistent with $\Delta$$\tau$ $\approx$ 100 fm/$c$, such relatively long thermal photon emission times do not support the interpretation of nuclear breakup as due to a fast spinodal process for the heavy nuclear systems studied.
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arxiv:nucl-ex/0508032
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The 44Ti(t1/2 = 59 y) nuclide, an important signature of supernova nucleosynthesis, has recently been observed as live radioactivity by gamma-ray astronomy from the Cas A remnant. We investigate in the laboratory the major 44Ti production reaction, 40Ca(alpha,gamma)44Ti (E_cm = 0.6-1.2 MeV/u), by direct off- line counting of 44Ti nuclei. The yield, significantly higher than inferred from previous experiments, is analyzed in terms of a statistical model using microscopic nuclear inputs. The associated stellar rate has important astrophysical consequences, increasing the calculated supernova 44Ti yield by a factor ~2 over previous estimates and bringing it closer to Cas A observations.
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arxiv:nucl-ex/0509006
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We performed a coincidence measurement of two nucleons emitted from the nonmesonic weak decay (NMWD) of ^{5}_{\Lambda}He formed via the ^{6}Li(\pi^+,K^+) reaction. The energies of two nucleons and the pair number distributions in the opening angle between them were measured. In both np and nn pairs, we observed a clean back-to-back correlation coming from the two-body decay of \Lambda p --> n p and \Lambda n --> n n, respectively. The ratio of the nucleon pair numbers was N_{nn}/N_{np}=0.45 \pm 0.11(stat)\pm 0.03(syst) in the kinematic region of cos(theta_{NN}) < -0.8. Since each decay mode was exclusively detected, the measured ratio should be close to the ratio of \Gamma(\Lambda p --> np)/\Gamma(\Lambda n --> nn). The ratio is consistent with recent theoretical calculations based on the heavy meson/direct quark exchange picture.
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arxiv:nucl-ex/0509015
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We present the latest results on event-by-event fluctuations of charged particle multiplicity in Au+Au and Cu+Cu collisions at $\sqrt{s_{NN}} = 200$ GeV and 62.4 GeV measured by PHENIX experiment at RHIC. The two particle correlation length to discuss order parameters, which can be extracted from scale dependence of the fluctuations, is supposed to be sensitive to the critical points of QCD phase transition. The obtained correlation length with respect to the pseudo rapidity gap indicates the power law behavior as a function of the number of participant nucleons for Au+Au collisions at $\sqrt{s_{NN}} = 200$ GeV.
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arxiv:nucl-ex/0510043
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A Large Ion Collider Experiment (ALICE) is the only experiment at the Large Hadron Collider (LHC) dedicated to the study of heavy ion collisions. The Time Projection Chamber (TPC) is the main tracking detector covering the pseudo rapidity range $|\eta|< 0.9$. It is designed for a maximum multiplicity \dNdy = 8000. The aim of the laser system is to simulate ionizing tracks at predifined positions throughout the drift volume in order to monitor the TPC response to a known source. In particular, the alignment of the read-out chambers will be performed, and variations of the drift velocity due to drift field imperfections can be measured and used as calibration data in the physics data analysis. In this paper we present the design of the pulsed UV laser and optical system, together with the control and monitoring systems.
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arxiv:nucl-ex/0511014
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The measurement of direct photons in s(NN)**1/2 = 200 GeV p+p and Au+Au collisions is presented. The signal is compared to NLO pQCD calculations, which, in case of Au+Au, are scaled with the number of underlying nucleon-nucleon collisions. The agreement of the calculation with the data in both cases confirms the scaling of hard processes with the number of nucleon-nucleon collisions and supports the explanation of the earlier-observed pion suppression as a final-state effect.
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arxiv:nucl-ex/0511041
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The cluster structures of the excited states in $^{11}$B are studied by analyzing the isoscalar monopole and quadrupole strengths in the $^{11}$B($d$,$d'$) reaction at $E_d=200$ MeV. The excitation strengths are compared with the predictions by the shell-model and antisymmetrized molecular-dynamics (AMD) calculations. It is found that the large monopole strength for the $3/2^-_3$ state at $E_x=8.56$ MeV is well described by the AMD calculation and is an evidence for a developed $2\alpha+t$ cluster structure.
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arxiv:nucl-ex/0512040
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We present results on two-particle azimuthal correlations of high-$p_T$ neutral strange baryons ($\Lambda$,$\bar{\Lambda}$) and mesons ($K^0_S$) associated with non-identified charged particles in d+Au and Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV. In particular, we discuss properties of the near-side yield of associated charged particles as a function of centrality, transverse momentum and $z_T$, as well as possible baryon/meson and particle/antiparticle differences. The results are compared to the proton and pion triggered correlations and to fragmentation and recombination models.
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arxiv:nucl-ex/0603008
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We present preliminary results from dp --> 3He X (X=pi0,eta) measurements near the eta production threshold. The data were taken during a slow ramping of the COSY internal deuteron beam scattered on a proton target. The 3He ejectiles were registered with the COSY-11 detection setup. The ongoing data analysis should deliver high precision data for the dp --> 3He eta total and differential cross sections for the excess energies in the range from threshold up to 9 MeV. The preliminary excitation function for the reaction dp --> 3He pi0 does not show any structure which could originate from the decay of 3He-eta bound state. We present also a threshold excitation curve for the dp --> 3He X channel. Contrary to corresponding results from SATURNE we see no cusp in the vicinity of the eta threshold.
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arxiv:nucl-ex/0603023
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Recent results of $\Lambda$(1520) resonance production in d+Au collisions at $\sqrt{s_{\rm NN}} = $ 200 GeV are presented and discussed in terms of the evolution and freeze-out conditions of a hot and dense fireball medium. Yields and spectra are compared to results from p+p and Au+Au collisions. The $\Lambda$(1520)/$\Lambda$ ratio in d+Au collisions ratio is consistent with the ratio in p+p collisions. This suggests a short time for elastic interactions between chemical and thermal freeze-out. One can conclude that the interaction volume in d+Au collisions is small.
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arxiv:nucl-ex/0603031
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We argue for a cost-effective, long-term North American underground science strategy based on partnership with Canada and initial construction of a modest U.S. Stage I laboratory designed to complement SNOLab. We show, by reviewing the requirements of detectors now in the R&D phase, that SNOLab and a properly designed U.S. Stage I facility would be capable of meeting the needs of North America's next wave of underground experiments. We discuss one opportunity for creating a Stage I laboratory, the Pioneer tunnel in Washington State, a site that could be developed to provide dedicated, clean, horizontal access. This unused tunnel, part of the deepest (1040 m) tunnel system in the U.S., would allow the U.S. to establish, at low risk and low cost, a laboratory at a depth (2.12 km.w.e., or kilometers of water equivalent) quite similar to that of the Japanese laboratory Kamioka (2.04 km.w.e.). We describe studies of cosmic ray attenuation important to properly locating such a laboratory, and the tunnel improvements that would be required to produce an optimal Stage I facility. We also discuss possibilities for far-future Stage II (3.62 km.w.e.) and Stage III (5.00 km.w.e.) developments at the Pioneer tunnel, should future North American needs for deep space exceed that available at SNOLab.
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arxiv:nucl-ex/0604004
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The PHENIX experiment has measured direct photons at $\sqrt{s_{NN}}$ = 200 GeV in $p+p$, $d$+Au and Au+Au collisions. For $p_{T}$ $<$ 4 GeV/$c$, the internal conversion into $e^{+}e^{-}$ pairs has been used to measure the direct photons in Au+Au.
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arxiv:nucl-ex/0605005
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Evidence for the existence of long-lived neutron-deficient isotopes has been found in a study of naturally-occurring Th using iductively coupled plasma-sector field mass spectrometry. They are interpreted as belonging to the recently discovered class of long-lived high spin super- and hyperdeformed isomers.
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arxiv:nucl-ex/0605008
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We discuss several observables measured by PHOBOS that show common scaling features in Cu+Cu and Au+Au collisions at RHIC energies. In particular, we examine the centrality and energy dependence of the charged particle multiplicity, as well as the centrality dependence of the elliptic flow at mid-rapidity. The discrepancy between Cu+Cu and Au+Au of the final state azimuthal asymmetry (elliptic flow), relative to the initial state geometry of the collision, can be resolved by accounting for fluctuations in the description of the initial geometry.
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arxiv:nucl-ex/0605012
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Measurements of azimuthal anisotropy for strange and multi-strange hadrons are presented for the first time in their centrality dependence. The high statistics results of v2(pT) allow for a more detailed comparison to hydrodynamical model calculations. Number-of-constituent-quark scaling was tested for different centrality classes separately. Higher order anisotropies like v4(pT) are measured for multi-strange hadrons. While we observe agreement between measured data and models a deeper understanding and refinement of the models seem to be necessary in order to fully understand the details of the data.
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arxiv:nucl-ex/0607021
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We have examined the spin structure of the proton in the region of the nucleon resonances (1.085 GeV < W < 1.910 GeV) at an average four momentum transfer of Q^2 = 1.3 GeV^2. Using the Jefferson Lab polarized electron beam, a spectrometer, and a polarized solid target, we measured the asymmetries A_parallel and A_perp to high precision, and extracted the asymmetries A_1 and A_2, and the spin structure functions g_1 and g_2. We found a notably non-zero A_perp, significant contributions from higher-twist effects, and only weak support for polarized quark--hadron duality.
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arxiv:nucl-ex/0608003
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The possible sources of systematic uncertainties in the hyperons global polarization measurement are discussed. The equation with detector acceptance effects taken into account is provided. Contribution of the hyperons directed flow into the hyperons global polarization measurement is shown. The systematic uncertainties of the Lambda hyperons global polarization measurement in Au+Au collisions with the STAR detector at RHIC are calculated.
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arxiv:nucl-ex/0608034
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It has been established that "hard probes", observables involving high-momentum transfer, provide useful tools for studying the hot, dense medium created in nucleus-nucleus collisions at RHIC. The nuclear modification factor, azimuthal correlations, direct photon production, as well as the dependence of the nuclear modificaton factor on centrality and angle with respect to the reaction plane are critical for understanding the early dynamics of such heavy-ion collisions. We will review recent results from PHENIX for particle production at high-pT and discuss their implications.
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arxiv:nucl-ex/0609018
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The structure of the unbound proton-rich isotope 19Na was studied in resonance elastic scattering of a radioactive 18Ne beam on a proton target using the thick-target inverse-kinematics method. The experiment covered excitation energy range from 0.5 to 2.7 MeV in c.m.s. Only one state of 19Na (the second excited state) was observed. A combined R-matrix and potential-model analysis was performed. The spin and parity assignment of this second excited state was confirmed to be 1/2+. We showthat the position of the 1/2+ state significantly affects the reaction rate through that state but the total reaction rate remains unchanged since the 18Ne(2p,gamma) proceeds mostly via the ground and first excited states in 19Na at stellar temperatures.
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arxiv:nucl-ex/0609040
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A high purity germanium crystal was operated in liquid argon as a Compton suppressed radiation spectrometer. Spectroscopic quality resolution of less than 1% of the full-width half maximum of full energy deposition peaks was demonstrated. The construction of the small apparatus used to obtain these results is reported. The design concept is to use the liquid argon bath to both cool the germanium crystal to operating temperatures and act as a scintillating veto. The scintillation light from the liquid argon can veto cosmic-rays, external primordial radiation, and gamma radiation that does not fully deposit within the germanium crystal. This technique was investigated for its potential impact on ultra-low background gamma-ray spectroscopy. This work is based on a concept initially developed for future germanium-based neutrinoless double-beta decay experiments.
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arxiv:nucl-ex/0610018
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Particle correlations at small relative velocities can be used to study the space-time evolution of hot and expanding system created in heavy ion collisions. Baryon and antibaryon source sizes extracted from baryon-baryon correlations complement the information deduced from the correlation studies of identical pions. Correlations of non-identical particles are sensitive also to the space-time asymmetry of their emission. High statistics data set of STAR experiment allows us to present the results of baryon-baryon correlation measurements at various centralities and energies, as well as to take carefully into account the particle identification probability and the fraction of primary baryons and antibaryons. Preliminary results show significant contribution of annihilation channel in baryon-antibaryon correlations.
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arxiv:nucl-ex/0610030
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The NA49 fixed-target experiment studied high energy-density matter produced in nucleus-nucleus reactions at the CERN SPS. In central Pb+Pb collisions at 158A GeV the energy density at the early stage substantially exceeds the threshold for quark deconfinement predicted by lattice QCD. The produced matter shows strong transverse and longitudinal flow. Ratios of yields of produced particles are approximately consistent with statistical equilibration. An energy scan through the SPS range revealed structure in the energy dependence of pion and kaon yields as well as of the inverse slopes of transverse mass distributions. These features suggest that a deconfined phase starts to be produced at around 30A GeV in central Pb+Pb collisions. The analysis of fluctuations and correlations has not yet provided evidence for the predicted critical point of QCD.
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arxiv:nucl-ex/0612008
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Rare isotope beams of neutron-deficient $^{106,108,110}$Sn nuclei from the fragmentation of $^{124}$Xe were employed in an intermediate-energy Coulomb excitation experiment yielding $B(E2, 0^+_1 \to 2^+_1)$ transition strengths. The results indicate that these $B(E2,0^+_1 \to 2^+_1)$ values are much larger than predicted by current state-of-the-art shell model calculations. This discrepancy can be explained if protons from within the Z = 50 shell are contributing to the structure of low-energy excited states in this region. Such contributions imply a breaking of the doubly-magic $^{100}$Sn core in the light Sn isotopes.
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arxiv:nucl-ex/0612011
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The neutron-proton bremsstrahlung process $(np \to np\gamma)$ is known to be sensitive to meson exchange currents in the nucleon-nucleon interaction. The triply differential cross section for this reaction has been measured for the first time at the Los Alamos Neutron Science Center, using an intense, pulsed beam of up to 700 MeV neutrons to bombard a liquid hydrogen target. Scattered neutrons were observed at six angles between 12$^\circ$ and 32$^\circ$, and the recoil protons were observed in coincidence at 12$^\circ$, 20$^\circ$, and 28$^\circ$ on the opposite side of the beam. Measurement of the neutron and proton energies at known angles allows full kinematic reconstruction of each event. The data are compared with predictions of two theoretical calculations, based on relativistic soft-photon and non-relativistic potential models.
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arxiv:nucl-ex/0701009
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This work evaluates the model dependence of the electric and Coulomb quadrupole amplitudes (E2, C2) in the predominantly M1 (magnetic dipole-quark spin flip) gamma* N -> Delta transition. Both the model-to-model dependence and the intrinsic model uncertainties are evaluated and found to be comparable to each other and no larger than the experimental errors. It is confirmed that the quadrupole amplitudes have been accurately measured indicating significant non-zero angular momentum components in the proton and Delta.
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arxiv:nucl-ex/0701024
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When studying the initial state and evolution of the matter created in relativistic heavy ion collisions, high-pT direct photons are a powerful probe. They are created in initial hard processes and in parton fragmentation, and possibly in interactions of partons with the hot and dense medium. We present systematic measurements of high-pT direct photon production in \sqrt{s_{NN}} = 200 GeV p+p and Au+Au collisions. The nuclear modification factor of direct photons is shown for 5 < pT < 18 GeV/c, and at very high transverse momenta it seems to be below unity in the most central Au+Au collisions.
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arxiv:nucl-ex/0701040
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We present results on two-particle angular correlations in p+p and Cu+Cu collisions over a broad range of ($\eta$,$\phi$). The PHOBOS detector has a uniquely large angular coverage for inclusive charged particles. This allows for the study of correlations on both long and short range pseudorapidity scales. A complex two-dimensional correlation structure emerges which is interpreted in the context of a cluster model. The cluster size and its decay width are extracted from the two-particle pseudorapidity correlation function. Relative to p+p collisions, Cu+Cu reactions show a non-trivial decrease of cluster size with increasing centrality. These results may provide insight into the hadronization stage of the hot and dense medium created in heavy ion collisions.
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arxiv:nucl-ex/0701055
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Transverse momentum spectra of pi^{+/-} at midrapidity are measured at high p_T in p+p and p+Pb collisions at 158 GeV/nucleon beam energy by the NA49 experiment. This study is complementary to our previous results on the same spectra from Pb+Pb collisions. The nuclear modification factors R_{A+A/p+p}, R_{p+A/p+p} and R_{A+A/p+A} as a function of p_T are extracted and compared to RHIC measurements, thus providing insight into the energy dependence of nuclear modification. The modification factor R_{A+A/p+A} proved to be consistent with our previous results on the central to peripheral modification factor R_{CP}. The limitation of our current p_T range is discussed and planned future upgrades are outlined. Some aspects of the FAIR-CBM experiment are also presented as a natural future continuation of the measurements at very high p_T.
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arxiv:nucl-ex/0702044
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The silicon pixel detector of the ALICE experiment at LHC comprises the two innermost layers of the inner tracking system of the apparatus. It contains 1200 readout chips, each of them corresponding to a 8192 pixel matrix. The single chip outputs a digital Fast-OR signal which is active whenever at least one of the pixels in the matrix records a hit. The 1200 Fast-OR output signals can be used to implement a unique triggering capability: few details on the pixel trigger system and some of the possible applications for p-p collisions are presented.
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arxiv:nucl-ex/0703019
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We report a measurement of dressed-spin effects of polarized 3He atoms from a cold atomic source traversing a region of constant magnetic field B0 and a transverse oscillatory dressing field Bd cos(omega * t). The observed effects are compared with a numerical simulation using the Bloch equation as well as a calculation based on the dressed-atom formalism. An application of the dressed spin of 3He for a proposed neutron electric dipole moment measurement is also discussed.
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arxiv:nucl-ex/0703029
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The NA60 experiment studies dimuon production in In-In and p-A collisions at the CERN SPS. We report recent results on \jpsi production, measured through its muon pair decay. As a function of centrality, we show that in In-In the \jpsi yield is suppressed beyond expectations from nuclear absorption. We present also for the first time results on \jpsi production in p-A collisions at 158 GeV, the same energy of the nucleus-nucleus data. For both p-A and In-In we show preliminary results on \psip suppression. Finally, we have studied the kinematical distributions of the \jpsi produced in In-In collisions. We present results on transverse momentum and rapidity, as well as on the angular distribution of the \jpsi decay products.
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arxiv:nucl-ex/0703030
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Design studies for a second generation Dilepton Spectrometer to be built at the SIS accelerator of GSI are presented. The basic design parameters of this system are specified and the different detector components for charged particle tracking and for lepton identification are described. The geometrical acceptance for lepton pairs is given. Results on single track momentum resolution and on lepton pair mass resolution are reported.
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arxiv:nucl-ex/9605004
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Signatures of critical behaviour in nuclear fragmentation are often based on arguments from percolation theory. We demonstrate with general thermodynamic considerations and studies of the Ising model that the reliance on percolation as a reference model bears the risk of missing parts of the essential physics.
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arxiv:nucl-ex/9607002
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The coincidence cross-section and the interference structure function, R_LT, were measured for the 12C(e,e'p) 11B reaction at quasielastic kinematics and central momentum transfer of q=400 MeV/c. The measurement was at an opening angle of theta_pq=11 degrees, covering a range in missing energy of E_m = 0 to 65 MeV. The R_LT structure function is found to be consistent with zero for E_m > 50 MeV, confirming an earlier study which indicated that R_L vanishes in this region. The integrated strengths of the p- and s-shell are compared with a Distorted Wave Impulse Approximation calculation. The s-shell strength and shape are compared with a Hartree Fock-Random Phase Approximation calculation. The DWIA calculation overestimates the cross sections for p- and s-shell proton knockout as expected, but surprisingly agrees with the extracted R_LT value for both shells. The HF-RPA calculation describes the data more consistently, which may be due to the inclusion of 2-body currents in this calculation.
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arxiv:nucl-ex/9709003
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Azimuthal distributions of particles produced in nucleus-nucleus collisions are measured with respect to an estimated reaction plane which, because of finite multiplicity fluctuations, differs in general from the true reaction plane. It follows that the measured distributions do not coincide with the true ones. I propose a general method of reconstructing the Fourier coefficients of the true azimuthal distributions from the measured ones. This analysis suggests that the Fourier coefficients are the best observables to characterize azimuthal anisotropies because, unlike other observables such as the in-plane anisotropy ratio or the squeeze-out ratio, they can be reconstructed accurately.
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arxiv:nucl-ex/9711003
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The first measurements of the induced proton polarization, P_n, for the 12C (e,e'\vec{p}) reaction are reported. The experiment was performed at quasifree kinematics for energy and momentum transfer (\omega,q) \approx (294 MeV, 756 MeV/c) and sampled a recoil momentum range of 0-250 MeV/c. The induced polarization arises from final-state interactions and for these kinematics is dominated by the real part of the spin-orbit optical potential. The distorted-wave impulse approximation provides good agreement with data for the 1p_{3/2} shell. The data for the continuum suggest that both the 1s_{1/2} shell and underlying l > 1 configurations contribute.
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arxiv:nucl-ex/9712001
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Constraints on the spin-averaged $\Lambda p$ scattering length and effective range have been obtained from measurements of the $pp\to pK^+\Lambda$ reaction close to the production threshold by comparing model phase-space Dalitz plot occupations with experimental ones. The data fix well the position of the virtual bound state in the $\Lambda p$ system. Combining this with information from elastic $\Lambda p$ scattering measurements at slightly higher energies, together with the fact that the hyperdeuteron is not bound, leads to a new determination of the low energy $\Lambda p$ scattering parameters.
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arxiv:nucl-ex/9803008
|
We outline the motivation and conceptual design for a new experiment aimed at a 10-fold improvement in the accuracy of the parity-violating asymmetry A_gamma in the angular distribution of 2.2 MeV gamma rays from the n+p-->d+gamma reaction. This observable is primarily sensitive to the weak pion-nucleon coupling H_pi^1. A proof-of-principle experiment using unpolarized low-energy neutron capture on polyethylene and an array of 12 CsI detectors operated in current mode has been performed. Results of this test experiment including the current mode signal, electronic noise and detector sensitivity to magnetic fields are reported.
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arxiv:nucl-ex/9804001
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The use of an ultracold neutron interferometer incorporating an electrostatic accelerator having a strong electric field gradient to accelerate neutrons by their possible electric moments is proposed as a method of measuring the neutron electric dipole moment. Such electrical acceleration, followed by an amplifier and a generator of phase difference, could develop relatively large phase differences and these could be measured by a Mach-Zehnder interferometer. This method might extend the sensitivity of the measurement by several orders of magnitude beyond the current limit of 10^{-25} e.cm. Furthermore the systematic errors in such a measurement could be significantly different from those of the current EDM experiments.
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arxiv:nucl-ex/9804003
|
We report measurements of Xi and Xi-bar hyperon absolute yields as a function of rapidity in 158 GeV/c Pb+Pb collisions. At midrapidity, dN/dy = 2.29 +/- 0.12 for Xi, and 0.52 +/- 0.05 for Xi-bar, leading to the ratio of Xi-bar/Xi = 0.23 +/- 0.03. Inverse slope parameters fitted to the measured transverse mass spectra are of the order of 300 MeV near mid-rapidity. The estimated total yield of Xi particles in Pb+Pb central interactions amounts to 7.4 +/- 1.0 per collision. Comparison to Xi production in properly scaled p+p reactions at the same energy reveals a dramatic enhancement (about one order of magnitude) of Xi production in Pb+Pb central collisions over elementary hadron interactions.
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arxiv:nucl-ex/9810005
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With the aim to study spin dependence of pion production near threshold, an internal target facility and a forward detector have been installed in the Cooler synchrotron ring at IUCF. The detector system comprises scintillators and wire chambers. The target consists of a thin-walled open-ended storage cell into which polarized atomic hydrogen is injected. Using a stored and cooled, polarized proton beam, polarization observables of the reaction pp -> pp pi0 have been studied at energies between 21 and 55 MeV above the pion production threshold in the center of mass system. We report here measurements of the spin correlation parameters Axx and Ayy, and the analyzing power Ay, integrated over the pion polar angle.
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arxiv:nucl-ex/9810013
|
Inclusive electron scattering is measured with 4.045 GeV incident beam energy from C, Fe and Au targets. The measured energy transfers and angles correspond to a kinematic range for Bjorken $x > 1$ and momentum transfers from $Q^2 = 1 - 7 (GeV/c)^2$. When analyzed in terms of the y-scaling function the data show for the first time an approach to scaling for values of the initial nucleon momenta significantly greater than the nuclear matter Fermi-momentum (i.e. $> 0.3$ GeV/c).
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arxiv:nucl-ex/9811008
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The reactions p+d-> p+pX and p+d-> p+dX at 305 MeV are studied with the aim to search for supernarrow dibaryons, decay of which into two nucleons is suppressed by the Pauli principle. The experiment was carried out at the Moscow Meson Factory using a spectrometer TAMS, which detected the scattered proton in coincidence with the second charged particle (the proton or deuteron) at various angles. Narrow peaks at 1905 and 1924 MeV with widths less than the experimental resolution (3 MeV) have been observed in missing- mass spectra of the process pd->pX. An analysis of the angular dependence of the experimental data shows that the resonance at $M$=1905 MeV most likely corresponds to the production of the isovector supernarrow dibaryon.
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arxiv:nucl-ex/9902002
|
The multiplicity of inclusive photons has been measured on an event-by-event basis for 158 AGeV Pb induced reactions on Ni, Nb, and Pb targets. The systematics of the pseudorapidity densities at midrapidity (rho_max) and the width of the pseudorapidity distributions have been studied for varying centralities for these collisions. A power law fit to the photon yield as a function of the number of participating nucleons gives a value of 1.13+-0.03 for the exponent. The mean transverse momentum, <p_T>, of photons determined from the ratio of the measured electromagnetic transverse energy and photon multiplicity, remains almost constant with increasing rho_max. Results are compared with model predictions.
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arxiv:nucl-ex/9903006
|
The study of spherical-deformed ground--state phase transitions in finite nuclei as a function of N and Z is hindered by the discrete values of the nucleon number. A resolution of the integer nucleon number problem, and evidence relating to phase transitions in finite nuclei, are discussed from the experimental point of view and interpreted within the framework of the interacting boson model.
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arxiv:nucl-ex/9905002
|
In this paper we have analyzed samples of Neolithic ceramics from Cucuteni-Scanteia - Vaslui county and Neolithic and Dacian ceramics from Magurele - Bucharest, by the method of neutron activation analysis. The following elements have been observed: Fe, K, La, Mn, Na, Sc and Sm. It has been noticed a relative and a slight clusterization of the analyzed items on the ratios of concentrations Na/Mn, La/Sc and La/Sm.
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arxiv:nucl-ex/9908018
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The PINTEX facility at the IUCF Cooler ring, dedicated to the study of spin dependence in nucleon-nucleon interactions, has been used to measure polarization observables of the reaction pp -> pp pi0 at beam energies between 325 and 400 MeV. The stored polarized proton beam had spin projections both in the longitudinal and the transverse directions with respect to the beam momentum. We report here on the measurements of the relative transverse and longitudinal spin-dependent cross sections, deltasigma_T/sigma_tot and deltasigma_L/sigma_tot, and how from these observables the initial spin singlet and triplet cross sections are obtained. Considering angular momentum states less or equal to one, the contribution of the Ps partial waves to the cross section can be extracted.
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arxiv:nucl-ex/9908024
|
Inclusive as well as exclusive energy spectra of the light charged particles emitted in the $^{28}$Si ($E_{lab}$=112.6 MeV) + $^{12}$C reaction has been measured using the {\bf ICARE} multidetector array. The data have been analysed by statistical-model calculations using a spin-dependent level density parametrization. The results suggest significant deformation effects at high spin and cluster emission of $^8$Be.
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arxiv:nucl-ex/9909008
|
Isotopic distributions for light particles and intermediate mass fragments have been measured for 112Sn+112Sn, 112Sn+124Sn, 124Sn+112Sn and 124Sn+124Sn collisions at E/A=50 MeV. Isotope, isotone and isobar yield ratios are utilized to obtain an estimate of the isotopic composition of the gas phase, i.e., the relative abundance of free neutrons and protons at breakup. Within the context of equilibrium calculations, these analyses indicate that the gas phase is enriched in neutrons relative to the liquid phase represented by bound nuclei.
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arxiv:nucl-ex/9910019
|
We present a superior proof that the results for summed strength isovector dipole, spin dipole, and orbital dipole excitations are independent of deformations at the Delta N = 0 level.
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arxiv:nucl-th/0001021
|
We calculate the Wilson coefficients of all dimension 6 gluon operators with non zero spin in the correlation function between two heavy vector currents. For the twist-4 part, we first identify the three independent gluon operators, and then proceed with the calculation of the Wilson coefficients using the fixed point gauge. Together with the previous calculation of the Wilson coefficients for the dimension 6 scalar gluon operators by Nikolaev and Radyushkin, our result completes the list of all the Wilson coefficients of dimension 6 gluon operators in the correlation function between heavy vector currents. We apply our results to investigate the mass of $J/\psi$ in nuclear matter using QCD sum rules. Using an upper bound estimate on the matrix elements of the dimension 6 gluon operators to linear order in density, we find that the density dependent contribution from dimension 6 operators is less than 40% of the dimension 4 operators with opposite sign. The final result gives about -4 MeV mass shift for the charmonium at rest in nuclear matter.
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arxiv:nucl-th/0002002
|
Elastic ed scattering, with deuteron polarization, up to high momentum transfer provides detailed information on the deuteron wave function. This determines the range dependence of the orbital and spin components of the one- and two-body currents, restricting contributions of isobar and meson-exchange currents and of quark/gluon degrees of freedom, as well as the nucleon component. The R-matrix boundary condition model combines all these effects, predicting nucleon-nucleon reactions and the deuteron form-factors simultaneously. A brief description of the model is followed by a comparison of its results with data, emphasizing the restrictions placed on the model by ed elastic form-factors.
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arxiv:nucl-th/0002026
|
Equilibration times for nuclear matter configurations -- modelling intermediate and high energy nucleus-nucleus collisions -- are evaluated within the semiclassical off-shell transport approach developed recently. The transport equations are solved for a finite box in coordinate space employing periodic boundary conditions. The off-shell transport model is shown to give proper off-shell equilibrium distributions in the limit $t \to \infty$ for the nucleon and $\Delta$-resonance spectral functions. We find that equilibration times within the off-shell approach are only slightly enhanced as compared to the on-shell limit for the momentum configurations considered.
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arxiv:nucl-th/0003002
|
We show that a nearly perfect SU(3) symmetry emerges from an extended Projected Shell Model. Starting from a deformed potential we construct separate bases for neutron and proton collective rotational states by exact angular momentum projection. These rotational states are then coupled by diagonalizing a residual pairing plus quadrupole interaction. The states obtained exhibit a one-to-one correspondence with an SU(3) spectrum up to high angular momentum and excitation, and their wave functions have a near-maximal overlap with the SU(3) states. They can also be classified as rotational bands built on spin-1$\hbar$ phonon excitations, which may correspond to a geometrical scissors mode and its generalizations. This work is a direct demonstration that numerical angular momentum projection theory extends the Elliott's original idea to heavy nuclear systems.
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arxiv:nucl-th/0003011
|
We estimate the ratio $R=g_{3}/g_{2}$ of the critical coupling constants $g_{2}$ and $g_{3}$ which are required to achieve binding of 2 or 3 bosons, respectively, with a short-range interaction, and examine how this ratio depends on the shape of the potential. Simple monotonous potentials give $R\simeq 0.8$. A wide repulsive core pushes this ratio close to R=1. On the other hand, for an attractive well protected by an external repulsive barrier, the ratio approaches the rigorous lower bound $R=2/3$. We also present results for N=4 bosons, sketch the extension to $N>4$, and discuss various consequences.
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arxiv:nucl-th/0003026
|
The structure of the second 0^+ state of ^{10}Be is investigated using a microscopic $\alpha+\alpha+n+n$ model based on the molecular-orbit (MO) model. The second 0^+ state, which has dominantly the (1/2^+)^2 configuration, is shown to have a particularly enlarged $\alpha-\alpha$ structure. The kinetic energy of the two valence neutrons occupying along the $\alpha-\alpha$ axis is reduced remarkably due to the strong $\alpha$ clustering and, simultaneously, the spin-orbit interaction unexpectedly plays important role to make the energy of this state much lower. The mixing of states with different spin structure is shown to be important in negative-parity states. The experimentally observed small-level spacing between 1^- and 2^- (~ 300 keV) is found to be an evidence of this spin-mixing effect. ^{12}{Be} is also investigated using $\alpha+\alpha+4n$ model, in which four valence neutrons are considered to occupy the (3/2^-)^2(1/2^+)^2 configuration. The energy surface of ^{12}Be is shown to exhibit similar characteristics, that the remarkable $\alpha$ clustering and the contribution of the spin-orbit interaction make the binding of the state with (3/2^-)^2(1/2^+)^2 configuration properly stronger in comparison with the closed p-shell (3/2^-)^2(1/2^-)^2 configuration.
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arxiv:nucl-th/0003059
|
The neutron distributions of Cs, Ba, Yb and Pb isotopes are described in the framework of relativistic mean-field theory. The self-consistent ground state proton and neutron density distributions are calculated with the relativistic Hartree-Bogoliubov model. The binding energies, the proton and neutron radii, and the quadrupole deformations are compared with available experimental data, as well as with recent theoretical studies of the nuclear structure corrections to the weak charge in atomic parity nonconservation experiments.
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arxiv:nucl-th/0004018
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