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Register a new userPseudorapidity distributions of charged particles in pp($rmoverline{p}$), p(d)A and AA collisions using Tsallis thermodynamics
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The pseudorapidity distributions of charged particles measured in p+p($rm overline{p}$) collisions for energies ranging from $sqrt{s_{NN}}=23.6$ GeV to 13 TeV, d+Au collisions at $sqrt{s_{NN}}=200$ GeV, p+Pb collisions at $sqrt{s_{NN}}= 5.02$ TeV and A+A collisions at RHIC and LHC are investigated in the fireball model with Tsallis thermodynamics. We assume that the rapidity axis is populated with fireballs following q-Gaussian distribution and the charged particles follow the Tsallis distribution in the fireball. The theoretical results are in good agreement with the experimental data for all the collision systems and centralities investigated. The collision energy and centrality dependence of the central position $y_0$ and its width $sigma$ of the fireball distribution are also investigated. A possible application of the model to predict the charged particle pseudorapidity distributions for the system size scan program proposed recently for the STAR experiment at RHIC is proposed.
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We study the recent PHOBOS data on the pseudorapidity density of inclusive charged particles in centrality-binned d+Au collisions at sqrt(s_NN) = 200 GeV. It appears that one can understand the increasing forward-backward asymmetry in the data by assuming that the entire distribution shifts backwards in rapidity according to the initial-state kinematics, while the total multiplicity scales linearly with Npart/2. Two models are explored, both of which achieve a reasonable description of the available data for rapidities sufficiently far from the pro jectiles (|eta|< 3 at the top RHIC energy). One model uses PYTHIA as the underlying distribution, to allow a straightforward mapping of a rapidity shift back to pseudorapidity space. The other model is a simple analytic calculation based on functions inspired by Landaus hydrodynamical model. The apparent success of these simple pictures to describe the bulk of particle production over |eta|< 3 suggests that collective effects may be present even in the small systems created in p+p and d+Au reactions, active over the full rapidity range. The relationship between this and other theoretical approaches are discussed.
The transverse momentum distributions of charged particles in p-Pb collisions as sqrt{s_{NN}} = 5.02 TeV measured by the ALICE collaboration are fitted using Tsallis statistics. The use of a thermodynamically consistent form of this distribution leads to an excellent description of the transverse momentum distributions for all rapidity intervals. The values of the Tsallis parameter q, the temperature T and the radius R of the system do not change within the measured pseudorapidity intervall.
Pseudorapidity distributions of charged particles emitted in $Au+Au$, $Cu+Cu$, $d+Au$, and $p+p$ collisions over a wide energy range have been measured using the PHOBOS detector at RHIC. The centrality dependence of both the charged particle distributions and the multiplicity at midrapidity were measured. Pseudorapidity distributions of charged particles emitted with $|eta|<5.4$, which account for between 95% and 99% of the total charged-particle emission associated with collision participants, are presented for different collision centralities. Both the midrapidity density, $dN_{ch}/deta$, and the total charged-particle multiplicity, $N_{ch}$, are found to factorize into a product of independent functions of collision energy, $sqrt{s_{_{NN}}}$, and centrality given in terms of the number of nucleons participating in the collision, $N_{part}$. The total charged particle multiplicity, observed in these experiments and those at lower energies, assumes a linear dependence of $(ln s_{_{NN}})^2$ over the full range of collision energy of $sqrt{s_{_{NN}}}$=2.7-200 GeV.
The charged particles produced in heavy ion collisions consist of two parts: One is from the freeze-out of hot and dense matter formed in collisions. The other is from the leading particles. In this paper, the hot and dense matter is assumed to expand according to the hydrodynamic model including phase transition and decouples into particles via the prescription of Cooper-Frye. The leading particles are as usual supposed to have Gaussian rapidity distributions with the number equaling that of participants. The investigations of this paper show that, unlike low energy situations, the leading particles are essential in describing the pseudorapidity distributions of charged particles produced in high energy heavy ion collisions. This might be due to the different transparencies of nuclei at different energies.
Nuclear gluon modifications are the least constrained component of current global fits to nuclear parton distributions, due to the inadequate constraining power of presently available experimental data from nuclear deep inelastic scattering and nuclear Drell-Yan lepton-pair production. A recent advance is the use of observables from relativistic nucleus-nucleus collisions to supplement the data pool for global fits. It is thus of interest to investigate the sensitivity of various experimental observables to different strengths of nuclear gluon modifications from large to small Bjorken $x$. In this work we utilize three recent global fits with different gluon strengths to investigate the sensitivity of three observables: nuclear modification factor, pseudorapidity asymmetry, and charge ratio. We observe that both nuclear modification factor and pseudorapidity asymmetry are quite sensitive to the strength of gluon modifications in a wide pseudorapidity interval. The sensitivity is greatly enhanced at LHC (Large Hadron Collider) energies relative to that at RHIC (Relativistic Heavy Ion Collider). The charge ratio is mildly sensitive only at large Bjorken x. Thus measurement of these observables in proton-lead collisions at the LHC affords the potential to further constrain gluon modifications in global fits.
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