Longitudinal scaling of observables in heavy-ion collision models

Abstract

Longitudinal scaling of pseudorapidity distribution of charged particles ($d{N}_{\mathrm{ch}}/d\eta$) is observed when presented as a function of pseudorapidity ($\eta$) shifted by the beam rapidity ($\eta$ - $y_{\mathrm{beam}}$) for a wide range of collision systems ($e^{+}+e^{-}$, p+p, $d$+A and A+A) and beam energies. Such a scaling is also observed for the elliptic flow ($v_2$) of charged hadrons in A+A collisions. This is a striking observation, as $v_2$ is expected to be sensitive to the initial conditions, the expansion dynamics and the degrees of freedom of the system, all of which potentially varies with collision system and colliding energies. We present a study of the longitudinal scalings of $d{N}_{\mathrm{ch}}/d\eta$, average transverse momentum ($<p_{\mathrm{T}}>$) and $v_2$ using transport models UrQMD and AMPT for Au+Au collisions at center of mass energies ($\sqrt{s_{\mathrm{NN}}}$) of 19.6, 62.4, 200 GeV and Pb+Pb collisions at 2760 GeV. Only the AMPT models which includes partonic effects and quark coalescence as a mechanism of hadronization, shows longitudinal scaling for $d{N}_{\mathrm{ch}}/d\eta$, $<p_{\mathrm{T}}>$ and $v_2$. Whereas the UrQMD and AMPT default versions show longitudinal scaling only for $d{N}_{\mathrm{ch}}/d\eta$ and $<p_{\mathrm{T}}>$. We also discuss the possibility of longitudinal scaling of $v_2$ within two extreme scenarios of models with hydrodynamic and collisionless limits. We find the longitudinal scaling of bulk observables to be an important test for the underlying physics mechanism in models of particle production.

5 pages, 3 figures, accepted for publication in Physical Review C

References in corpus (14)

• Systematic Measurements of Identified Particle Spectra in pp, d+Au and Au+Au Collisions from STAR
• Energy Loss and Flow of Heavy Quarks in Au+Au Collisions at sqrt(s_NN) = 200 GeV
• Measurements of Strange Particle Production in $p+p$ Collisions at $\sqrt{s}$= 200 GeV
• Heavy-Quark Kinetics in the QGP at LHC
• Thermal Dileptons at LHC
• Has the QCD Critical Point been Signaled by Observations at RHIC ?
• Centrality dependence of charged hadron and strange hadron elliptic flow from sqrt(s_NN) = 200 GeV Au+Au collisions
• The centrality dependence of elliptic flow, the hydrodynamic limit, and the viscosity of hot QCD
• Partonic flow and $\varphi$-meson production in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV
• Measuring Shear Viscosity Using Transverse Momentum Correlations in Relativistic Nuclear Collisions
• Elliptic flow for phi mesons and (anti)deuterons in Au+Au collisions at sqrt(s_NN) = 200 GeV
• Hadronic resonance production in $d$+Au collisions at $\sqrt{s_{{}_{NN}}}$ = 200 GeV at RHIC
• System Size, Energy and Centrality Dependence of Pseudorapidity Distributions of Charged Particles in Relativistic Heavy Ion Collisions
• Extended Longitudinal Scaling: direct evidence of saturation