Rapidity Distributions Of Net Protons Research Articles

Limiting fragmentation in heavy-ion stopping?

Based on a nonequilibrium–statistical relativistic diffusion model that is consistent with quantum chromodynamics (QCD), we investigate baryon stopping in relativistic heavy-ion collisions at SPS, RHIC, and LHC energies. The net-proton rapidity distributions of the individual fragments exhibit a scaling behaviour similar to limiting fragmentation (LF) that is related to geometric scaling in the colour-glass condensate (CGC) and depends upon the gluon saturation scale. Forward-angle net-proton data at energies reached at the LHC are required to verify the prediction.

Longitudinal dynamics and particle production in relativistic nuclear collisions

This work presents a three-dimensional dynamical initialization model for relativistic heavy-ion collisions, implementing local energy-momentum conservation and baryon charge fluctuations at string junctions. Constraining parameters using experimental data from p+p collisions at various collision energies, the model provides a very good description of the charged hadron and net proton rapidity distributions in Au+Au collisions from 7.7 to 200 GeV and Pb+Pb collisions at 8.77 and 17.3 GeV. We demonstrate the importance of fluctuations of baryon densities to string junctions for describing net-proton distributions at collision energies of 62.4 and 200 GeV. Including this improved baryon stopping description along with the requirement of strangeness neutrality also yields a good description of identified particle yields as functions of the collision energy above 7.7 GeV. We further study asymmetric p+Al and (p, d, $^3$He)+Au collisions at the top RHIC energy and p+Pb, Xe+Xe, and Pb+Pb collisions at LHC energies. We identify the produced particle rapidity distributions in asymmetric collision systems as particularly useful for constraining models of the early-time longitudinal dynamics.

Dependence on beam energy and nuclear equation of state of anisotropic flow and particle production in low-energy heavy-ion collisions

We analyze various flow coefficients of anisotropic momentum distribution of final state particles in mid-central ($b=5\text{--}9\phantom{\rule{0.16em}{0ex}}\mathrm{fm}$) $\mathrm{Au}\phantom{\rule{4pt}{0ex}}+\phantom{\rule{4pt}{0ex}}\mathrm{Au}$ collisions in the beam energy range ${E}_{\mathrm{Lab}}=1A\text{--}158A$ GeV. Different variants of the ultrarelativistic quantum molecular dynamics (UrQMD) model, namely the pure transport (cascade) mode and the hybrid mode, are employed for this investigation. In the hybrid UrQMD model, the ideal hydrodynamical evolution is integrated with the pure transport calculation for description of the evolution of the fireball. We opt for the different available equations of state (EoS) replicating the hadronic as well as partonic degrees of freedom together with possible phase transitions, viz., hadron gas, chiral $+$ deconfinement EoS, and bag model EoS, to investigate their effect on the properties of the final state particles. We also attempt to gain insights about the dynamics of the medium by studying different features of particle production such as particle ratios and net-proton rapidity distribution. The results and conclusions drawn here would be useful to understand the response of various observables to the underlying physics of the model as well as to make comparisons with the upcoming measurements of the future experiments at the Facility for Antiproton and Ion Research (FAIR) and the Nuclotron-based Ion Collider fAcility (NICA).

Radiative Parton Energy Loss and Baryon Stopping in AA Collisions

We study the radiative energy loss contribution to proton stopping in $AA$ collisions. The analyses is performed within the light-cone path integral approach to induced gluon emission. We have found that the radiative correction can fill in partly the midrapidity dip in the net proton rapidity distribution in $AA$ collisions at $\sqrt{s}\sim 10$ GeV. We argue that at $\sqrt{s}\sim 10$ GeV the net proton fluctuations at midrapidity may be dominated by the initial fluctuations of the proton flow, which, to a good accuracy, should be binomial.

Relativistic diffusion model with nonlinear drift

The nonequilibrium-statistical Relativistic Diffusion Model (RDM) is extended to include a nonlinear drift term such that its stationary solution agrees exactly with the thermal equilibrium distribution. The underlying Fokker-Planck equation cannot be solved analytically in this case and we present a numerical solution in rapidity space. The difference to the analytical RDM solution is discussed, and the numerical result is compared to data for net-proton rapidity distributions in \(\sqrt{s_{NN}} = 17.3\) GeV PbPb and 200 GeV AuAu collisions.

Robustness of the baryon-stopping signal for the onset of deconfinement in relativistic heavy-ion collisions

The impact of the experimental acceptance, i.e. transverse-momentum ($p_T$) cut-off and limited rapidity region, on the earlier predicted irregularity in the excitation function of the baryon stopping is studied. This irregularity is a consequence of the onset of deconfinement occurring in the compression stage of a nuclear collision and manifests itself as a wiggle in the excitation function of the reduced curvature ($C_y$) of the net-proton rapidity distribution at midrapidity. It is demonstrated that the wiggle is a very robust signal of a first-order phase transition that survives even under conditions of a very limited acceptance. At the same time the $C_y$ for pure hadronic and crossover transition scenarios become hardly distinguishable, if the acceptance cuts off too much of the low-$p_T$ proton spectrum and/or puts too narrow rapidity window around midrapidity. It is found that the shape of the net-proton rapidity distribution near midrapidity depends on the $p_T$ cut-off. This implies that the measurements should be taken at the same acceptance for all collision energies in order to reliably conclude on the presence or absence of the irregularity.

Alternative scenarios of relativistic heavy-ion collisions. I. Baryon stopping

Simulations of relativistic heavy-ion collisions within the three-fluid model employing a purely hadronic equation of state (EoS) and two versions of the EoS involving deconfinement transition are presented. The latter are an EoS with the first-order phase transition and that with a smooth crossover transition. The model setup is described in detail. The analysis is performed in a wide range of incident energies 2.7 GeV $< \sqrt{s_{NN}} <$ 39 GeV in terms of the center-of-mass energy. Results on proton and net-proton rapidity distributions are reported. Comparison with available data indicate certain preference of the crossover EoS. It is found that predictions within deconfinement-transition scenarios exhibit a "peak-dip-peak-dip" irregularity in the incident energy dependence of the form of the net-proton rapidity distributions in central collisions. This irregularity is a signal of deconfinement onset occurring in the hot and dense stage of the nuclear collision.

Baryon stopping as a probe of deconfinement onset in relativistic heavy-ion collisions

It is argued that an irregularity in the baryon stopping is a natural consequence of onset of deconfinement occurring in the compression stage of a nuclear collision. It is a combined effect of the softest point inherent in an equation of state (EoS) with a deconfinement transition and a change in the nonequilibrium dynamics from hadronic to partonic transport. Thus, this irregularity is a signal from a hot and dense stage of the nuclear collision. In order to illustrate this proposition, calculations within the three-fluid model were performed with three different EoSʼs: a purely hadronic EoS, an EoS with a first-order phase transition and that with a smooth crossover transition. It is found that predictions within the first-order-transition scenario indeed reveal a strong irregularity in the incident energy dependence of the form of the net-proton rapidity distributions in central collisions. This behavior is in contrast to that for the hadronic scenario, where the distribution form gradually evolves, displaying no irregularity. The case of the crossover EoS is intermediate. Only a weak irregularity takes place. Experimental data also exhibit a trend of similar irregularity, which is however based on still preliminary data at energies of 20A GeV and 30A GeV.

Heavy ions at the LHC: Selected predictions

Baryon transport in relativistic heavy-ion collisions is investigated within a gluon saturation model. The theoretical results are compared with Pb + Pb data at SPS, and Au + Au data at RHIC energies. Predictions are made for net-baryon and net-proton rapidity distributions in central Pb + Pb collisions at CERN LHC energies of up to TeV both at forward rapidities, and in the central rapidity region where data will soon be available.

RAPIDITY SPECTRA FOR NET PROTON PRODUCTION AT LHC

Net proton rapidity distributions are calculated, reproduce very well data obtained at AGS, SPS, RHIC and predict results for the LHC experiment.1 Presence of non-ideal plasma effects due to strongly coupled plasma in the early stage of relativistic heavy-ion collisions is investigated in the framework of non-conventional statistical mechanics.

Predictions for net-proton and net-kaon distributions at LHC energies

We investigate baryon and charge transport in relativistic heavy-ion collisions, compare with Au+Au RHIC data at sNN=0.2 TeV, and make predictions for net-proton rapidity distributions in central Pb+Pb collisions at CERN LHC energies of sNN=2.8, 3.9, and 5.5 TeV. We use the gluon saturation model and put special emphasis on the midrapidity valley |y|⩽2. Net-kaon distributions are calculated and compared to BRAHMS Au+Au data at RHIC energies of sNN=0.2 TeV, and predicted for Pb+Pb at 5.5 TeV.

Widths of charged particle pseudorapidity density distributions in high energy [formula omitted] and AA collisions

The paper presents a fit to pseudorapidity distributions of final-state charged particles produced in hadron and heavy ion experiments at different center-of-mass energies. Distributions of charged particles measured in p p ¯ , p ( d ) A , and AA collisions at high energies are presented and good agreement between the fit and the data is found. The basis of the fits is a semi-empirical formula which is obtained from a simple Feynman gas model, namely the two-cylinder gas model. For p p ¯ and AA collisions, the dependence of the width of charged particle pseudorapidity density distributions on logarithmic center-of-mass energy is studied and found to be a linear relationship. Meanwhile, the dependences of the two-cylinder length, single cylinder length, and gap width between the two cylinders on logarithmic center-of-mass energy are found to be linear relationships. As another check and application of the semi-empirical formula, the rapidity distributions of net-protons emitted in AA collisions at high energies are studied. Similar conclusions are obtained.

From RHIC to LHC: a relativistic diffusion approach

We investigate stopping and particle production in heavy-ion collisions in a Relativistic Diffusion Model (RDM). Using three sources for particle production, the energy- and centrality dependence of rapidity distributions of net protons, and pseudorapidity distributions of charged hadrons in heavy systems at RHIC energies are precisely reproduced in the analytical model. The transport coefficients are then extrapolated from Au + Au at RHIC energies (OsNN=19.6 - 200 GeV) to Pb + Pb at LHC energies of OsNN= 5.52 TeV. Rapidity distributions for net protons, and pseudorapidity spectra for produced charged particles are obtained and discussed in a three-sources model at LHC energies.

From RHIC to LHC: A relativistic diffusion approach

Stopping and particle production in heavy-ion collisions are investigated in a Relativistic Diffusion Model (RDM). Using three sources for particle production, the energy- and centrality dependence of rapidity distributions of net protons, and pseudorapidity distributions of charged hadrons in heavy systems at RHIC energies are precisely reproduced in the analytical model. The gradual approach to local thermal equilibrium is discussed. The transport coefficients are then extrapolated from Au + Au at RHIC energies ( s N N = 19.6 − 200 GeV ) to Pb + Pb at LHC energies of s N N = 5.52 TeV . Rapidity distributions fot net protons, and pseudorapidity spectra for produced charged particles are obtained and discussed in a three-sources model at LHC energies.

Diffusion in relativistic systems

Abstract A Relativistic Diffusion Model (RDM) for high-energy heavy-ion collisions is outlined and used to investigate stopping and particle production. With three sources for particle production, the energy- and centrality dependence of rapidity distributions of net protons, and pseudorapidity distributions of charged hadrons in heavy systems at RHIC energies are precisely reproduced in the analytical model. The gradual approach to local thermal equilibrium is discussed for symmetric and asymmetric (d+Au) systems. The transport coefficients are extrapolated from Au+Au at RHIC energies ( s N N = 19.6 – 200 GeV ) to Pb+Pb at LHC energies of s N N = 5.52 TeV . Rapidity distributions for net protons, and pseudorapidity spectra for the produced charged particles are obtained and discussed in a three-sources model at LHC energies.

Strangeness production at RHIC: recent results from BRAHMS

The BRAHMS experiment at RHIC has measured pions, kaons and protons and their antiparticles over a wide range of rapidity and transverse momenta. Au+Au collisions, d+Au and p+p interactions have been studied. From the net-proton rapidity distribution, a stopping power of 73% can be deduced for central Au+Au collisions. The rapidity distributions of produced particles exhibit Gaussian shapes. The full phase-space K+/π+ ratio is 0.173 ± 0.003 ± 0.014 and the value for K−/π− is 0.143 ± 0.003 ± 0.011. At forward rapidities, the ratios for the positively and negatively charged mesons diverge and approach values similar to the ones measured at the SPS. New data at 62.4 GeV promise to shed light on the nature of the sharp maximum of the K+/π+ ratio observed at low SPS energies. At midrapidity, the nuclear modification factor for central Au+Au collisions shows a strong pion suppression at intermediate transverse momenta; a suppression which is even stronger at forward rapidities. The nuclear modification factor for d+Au changes from a Cronin-like enhancement of charged hadrons at midrapidity to a suppression at forward rapidities.

Properties of matter at forward rapidities at RHIC

The BRAHMS experiment at RHIC has measured pions, kaons and protons and their antiparticles over a wide range of rapidity and transverse momenta. Au+Au collisions, d+Au and p+p interactions have been studied. From the net-proton rapidity distribution a stopping power of 73% can be deduced for central Au+Au collisions. The rapidity distributions of produced particles exhibit Gaussian shapes. At midrapidity the nuclear modification factor for central Au+Au collisions shows a strong pion suppression at intermediate transverse momenta; a suppression which is even stronger at forward rapidities. The nuclear modification factor for d+Au changes from a Cronin-like enhancement of charged hadrons at midrapidity to a suppression at forward rapidities.

Baryon stopping and valence quark distribution at small x

We argue that the amount of baryon stopping observed in the central rapidity region of heavy-ion collisions at RHIC is proportional to the nuclear valence quark distributions at small x. By generalizing Mueller's dipole model to describe reggeons we construct a non-linear evolution equation for the valence quark distributions at small x in the leading double-logarithmic approximation. The equation includes the effects of gluon saturation in it. The solution of the evolution equation gives a valence quark distribution function dn val/ dy∼ e −(0.4÷0.5) y . We show that this y-dependence as well as the predictions of regge theory are consistent with the net-proton rapidity distribution reported by BRAHMS.

Results from the BRAHMS experiment at RHIC

Results from the BRAHMS collaboration for Au+Au collisions at √ S NN = 200 GeV are presented, focussing on the measurement of the net-proton rapidity distribution, the determination of the pseudorapidity distribution of charged particles and on the rapidity distributions of pions and kaons.

Charged particle production in proton-, deuteron-, oxygen- and sulphur-nucleus collisions at 200 GeV per nucleon

The transverse momentum and rapidity distributions of net protons and negatively charged hadrons have been measured for minimum bias proton–nucleus and deuteron–gold interactions, as well as central oxygen–gold and sulphur–nucleus collisions at 200 GeV per nucleon. The rapidity density of net protons at midrapidity in central nucleus–nucleus collisions increases both with target mass for sulphur projectiles and with the projectile mass for a gold target. The shape of the rapidity distributions of net protons forward of midrapidity for d+Au and central S+Au collisions is similar. The average rapidity loss is larger than 2 units of rapidity for reactions with the gold target. The transverse momentum spectra of net protons for all reactions can be described by a thermal distribution with ‘temperatures’ between $145 \pm 11$ MeV (p+S interactions) and $244 \pm 43$ MeV (central S+Au collisions). The multiplicity of negatively charged hadrons increases with the mass of the colliding system. The shape of the transverse momentum spectra of negatively charged hadrons changes from minimum bias p+p and p+S interactions to p+Au and central nucleus-nucleus collisions. The mean transverse momentum is almost constant in the vicinity of midrapidity and shows little variation with the target and projectile masses. The average number of produced negatively charged hadrons per participant baryon increases slightly from p+p, p+A to central S+S,Ag collisions.