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Register a new userBeam energy dependence of strange hadron production from STAR at RHIC
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Xiaoping Zhang
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We present STAR measurements of K^{0}_{S}, phi, Lambda, Xi, and Omega at mid-rapidity from Au+Au collisions at sqrt{s_{NN}} = 7.7, 11.5, 19.6, 27, and 39 GeV from the Beam Energy Scan (BES) program at the BNL Relativistic Heavy Ion Collider (RHIC). Nuclear modification factors and baryon-to-meson ratios are measured to understand recombination and parton energy loss mechanisms. Implications on partonic versus hadronic dynamics at low beam energies are discussed.
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We report the energy dependence of mid-rapidity (anti-)deuteron production in Au+Au collisions at $sqrt{s_text{NN}} = $7.7, 11.5, 14.5, 19.6, 27, 39, 62.4, and 200 GeV, measured by the STAR experiment at RHIC. The yield of deuterons is found to be well described by the thermal model. The collision energy, centrality, and transverse momentum dependence of the coalescence parameter $B_2$ are discussed. We find that the values of $B_2$ for anti-deuterons are systematically lower than those for deuterons, indicating that the correlation volume of anti-baryons is larger than that of baryons at $sqrt{s_text{NN}}$ from 19.6 to 39 GeV. In addition, values of $B_2$ are found to vary with collision energy and show a broad minimum around $sqrt{s_text{NN}}= $20 to 40 GeV, which might imply a change of the equation of state of the medium in these collisions.
The measurements of particle multiplicity distributions have generated considerable interest in understanding the fluctuations of conserved quantum numbers in the Quantum Chromodynamics (QCD) hadronization regime, in particular near a possible critical point and near the chemical freeze-out. We report the measurement of efficiency and centrality bin width corrected cumulant ratios ($C_{2}/C_{1}$, $C_{3}/C_{2}$) of net-$Lambda$ distributions, in the context of both strangeness and baryon number conservation, as a function of collision energy, centrality and rapidity. The results are for Au + Au collisions at five beam energies ($sqrt{s_{NN}}$ = 19.6, 27, 39, 62.4 and 200 GeV) recorded with the Solenoidal Tracker at RHIC (STAR). We compare our results to the Poisson and negative binomial (NBD) expectations, as well as to Ultra-relativistic Quantum Molecular Dynamics (UrQMD) and Hadron Resonance Gas (HRG) model predictions. Both NBD and Poisson baselines agree with data within the statistical and systematic uncertainties. The ratios of the measured cumulants show no features of critical fluctuations. The chemical freeze-out temperatures extracted from a recent HRG calculation, which was successfully used to describe the net-proton, net-kaon and net-charge data, indicate $Lambda$ freeze-out conditions similar to those of kaons. However, large deviations are found when comparing to temperatures obtained from net-proton fluctuations. The net-$Lambda$ cumulants show a weak, but finite, dependence on the rapidity coverage in the acceptance of the detector, which can be attributed to quantum number conservation.
Large proton and antiproton enhancement with respect to pions has been observed at intermediate transverse momentum $p_T approx$ 2-5 GeV/$c$ in Au+Au collisions at RHIC. To investigate the possible source of this anomaly, the production of $phi$ mesons and two particle angular correlations triggered by mid-$p_T$ baryons or mesons are studied. We also present the first measurement of proton and antiproton production at $sqrt{s_{NN}} = 62.4$ GeV in Au+Au collisions, which aims to study the energy dependence of the observed baryon enhancement.
We present a system size and energy dependence of $phi$ meson production in Cu+Cu and Au+Au collisions at $sqrt{s_{NN}}$=62.4 GeV and 200 GeV measured by the STAR experiment at RHIC. We find that the number of participant scaled $phi$ meson yields in heavy ion collisions over that of p+p collisions are larger than 1 and increase with collision energy. We compare the results with those of open-strange particles and discuss the physics implication.
The energy and system size dependence of pseudorapidity ($eta$) and multiplicity distributions of photons are measured in the region -2.3 $leq$ $eta$ $leq$ -3.7 for Cu + Cu collisions at $sqrt{s_{NN}}$ = 200 and 62.4 GeV. Photon multiplicity measurements at forward rapidity have been carried out using a Photon Multiplicity Detector (PMD) in the STAR experiment. Photons are found to follow longitudinal scaling for Cu + Cu collisions for 0-10% centrality. A Comparison of pseudorapidity distributions with HIIJING model is also presented.
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