Longitudinal Flow of Protons from(2–8)AGeVCentralAu+AuCollisions

Abstract

Experimental heavy ion programs from the Bevalac, SIS, the AGS and the CERN SPS have attempted to characterize the distributions of particles emerging from high energy collisions in terms of simple thermodynamic principles. Testing the underlying assumptions of chemical and thermal equilibrations at different stages of the collision has been attempted by comparing model expectations to many different experimental observables. Static isotropic thermal emission models applied to observed particle rapidity distributions from experiments at all beam energies consistently fail to describe the observed shape; such model predictions being too narrow. Thermal models which include collective longitudinal expansion have been much more successful at reproducing the observed rapidity distributions [1,2]. The additional collective motion is attributed to intense pressure gradients which develop in the very hot, compressed nuclear matter fireballs created in heavy ion collisions.At the AGS, rapidity distributions of multiple particle species, including pions, kaons, protons and lambda hyperons from central collisions have been simultaneously described by a thermal distribution with a common longitudinal expansion velocity [2,3]. The agreement between the proton and other particle distributions suggests a high degree of stopping of the incident nucleons at the top AGS energy, which implies even more stopping at lower beam energies. However, recent investigations of the centrality dependence of the proton rapidity distributions from 6-11 AGeV Au+Au collisions by E917 suggest that the degree of nucleon stopping may be less than previously considered [4]. Nevertheless, their flat dN/dy for central collisions at all beam energies, fitted by sources distributed uniformly in rapidity to y-y cm = 0, could also be interpreted in the manner presented herein.For the asymptotic case at extremely high beam energies, Bjorken proposed [5] that nuclear transparency would evacuate the central rapidity region of all of the initial nucleons, leaving a hot, high-energy density region in which a Quark Gluon Plasma might form. In 160 AGeV Pb+Pb collisions at the CERN SPS, observed net proton ((+)-(-)) rapidity distributions [6] exhibit a double-humped character which is consistent with this transparency. At SPS energies, the nucleon distributions are not describable by a simple thermal model with only collective longitudinal flow, but rather need additional theoretical consideration of transparency. However, the negative hadron (mostly pions) rapidity distributions are well-described by this model, which might be interpreted as suggesting a significant amount of collective longitudinal flow for produced particles [2].

Novel scheme for parametrizing the chemical freeze-out surface in heavy ion collision experiments

“…Data Analysis: − We have used AGS [57][58][59][60][61][62][63][64][65], SPS [66][67][68][69][70][71][72][73][74][75], RHIC [76][77][78][79][80][81][82][83][84][85][86][87][88][89][90][91] and LHC [92][93][94][95] data for our analysis. STAR BES data has been used following [49,96,97].…”

On Descriptions of Particle Transverse Momentum Spectra in High Energy Collisions

“…, andp produced at mid-y or mid-η in central Au-Au collisions at different √ s N N , where the particle types, y or η intervals, centrality classes, and collision energies are marked in the panels. The closed and open symbols represent respectively the experimental data of positively and negatively charged particles measured by the E866 [24], E895 [25,26], E802 [27,28], STAR [29,30,31], and PHENIX [32,33] Collaborations marked in the panels, where in Figs. 1(a)-1(d) the data for π ± and K + are taken from the E866 Collaboration [24] and the data for p are taken from the E895 Collaboration [25,26].…”

“…The closed and open symbols represent respectively the experimental data of positively and negatively charged particles measured by the E866 [24], E895 [25,26], E802 [27,28], STAR [29,30,31], and PHENIX [32,33] Collaborations marked in the panels, where in Figs. 1(a)-1(d) the data for π ± and K + are taken from the E866 Collaboration [24] and the data for p are taken from the E895 Collaboration [25,26]. The solid and dashed curves are our results fitted by Eqs.…”

“…In this work, the p T (m T ) spectra of positively and negatively charged pions (π + and π − ), positively and negatively charged kaons (K + and K − ), protons and antiprotons (p andp) produced at mid-(pseudo)rapidity (mid-y or mid-η) measured in central gold-gold (Au-Au) collisions at the Alternating Gradient Synchrotron (AGS) by the E866 [24], E895 [25,26], and E802 [27,28] Collaborations and at the Relativistic Heavy Ion Collider (RHIC) by the STAR [29,30,31] and PHENIX [32,33] Collaborations, in central leadlead (Pb-Pb) collisions at the Super Proton Synchrotron (SPS) by the NA49 Collaboration [34,35,36] and at the Large Hadron Collider (LHC) by the ALICE Collaboration [37], as well as in inelastic (INEL) proton-proton (pp) collisions at the SPS by the NA61/SHINE Collaboration [38,39], at the RHIC by the PHENIX Collaboration [40], and at the LHC by the CMS Collaboration [41,42] are studied. The (two-component) standard distribution is used to fit the data and to extract T , T i , T 0 , and β T , as well as the excitation functions of parameters (the energy dependent parameters).…”

Systematics of chemical freeze-out parameters in heavy-ion collision experiments

“…We have used AGS [62][63][64][65][66][67][68][69][70], SPS [71][72][73][74][75][76][77][78][79][80], RHIC [81][82][83][84][85][86][87][88][89][90][91][92][93][94][95][96] and LHC [97][98][99][100] data for our analysis. The data for STAR BES is obtained from Ref [48,55,101].…”