Analysis of charged hadron multiplicity distributions at RHIC

It is demonstrated that with Heinz's collective flow model charged particle distributions at AGS and lower SPS energies (less than 20 GeV/n) ,can successfully be analyzed,but that the model fails for the RHIC data.Heinz's model calculation underestimates the tails of the charged particle distributions from RHIC,the discrepancy becoming bigger as the energy increases.To study the multiplicity distributions at RHIC we develop the so-cailed"Thermalization Component Model",which is based on Heinz's collective flow model.It is realized that the limitation of phase space of collective flow can be reflected in that of the thermalization region.By comparing the contributions of particle production from the thermalization regions at different energies and different centralities,we can deepen our understanding of the features of collective motion at RHIC.     

Dependence of multiplicity and transverse energy distributions on nuclear geometry at RHIC

We study the dependence of multiplicity and transverse energy on nuclear geometry at RHIC at SNN^1/2 =19.6,130,and 200 GeV basing on ellipsoidal decay model.It is found that the ellipsoidal decay model can describe the data well.     

Dependence of multiplicity and transverse energy distributions on nuclear geometry at RHIC

We study the dependence of multiplicity and transverse energy on nuclear geometry at RHIC at √s_NN=19.6, 130, and 200 GeV basing on ellipsoidal decay model. It is found that the ellipsoidal decay model can describe the data well.     

Multiplicity distributions of charged hadrons at AGS, SPS and RHIC

It is found that Collective Flow Model (CFM) which can successfully analyze charged particle distributions at AGS and lower SPS (less than 20 GeV/n), fails to analyze that of RHIC. The tail of distribution of charged particle at RHIC has a jump away from the collective model calculation as the energy increase. Thermalization Component Model (TCM) is presented basing on collective flow to study the multiplicity distributions at RHIC in this paper. It is realized that the limitation of phase space of collective flow can denote that of thermalization region. By comparing the contributions of particle productions from thermalization region at different energies and different centrality, we can deep our study on the feature of collective movement at RHIC.     

Comparative study of charged multiplicity distributions

A compilation is made of charged multiplicity distributions for $\text{π}{}^{\mathrm{\pm }}\text{,}\text{K}{}^{\mathrm{\pm }}\text{,}\text{p and}\text{p}$ interactions on hydrogen. Besides the usually studied parameters 〈 n_c〉 and D, the skewness γ₁, the kurtosis γ₂ and the mode are closely examined. It is found that γ₁ and γ₂ may be considered as constant for p_lab > 10 GeV/c. As a consequence, all the data are well parametrized by means of the Edgeworth expansion, describing the approach to a Gaussian when the number of production centres is increased. The constancy of γ₁ would indicate that this number does not grow in the energy domain studied. Limited to the first order, the Edgeworth expansion is a useful alternative to the Czyzewski-Rybicki formula for expressing all the regularities of the multiplicity distributions.     

Energy dependent growth of nucleon and inclusive charged hadron distributions

In the Color Glass Condensate formalism, charged hadron p T spectra in p+p and p+Pb collisions are studied by considering an energy-dependent broadening of nucleon density distribution. Then, in the glasma flux tube picture, the n-particle multiplicity distributions at different pseudo-rapidity ranges are investigated. Both the theoretical results show good agreement with the recent experimental data from ALICE and CMS at LHC energies.The predictive results for p T or multiplicity distributions in p+p and p+Pb collisions at the Large Hadron Collider are also given in this paper.     

Centrality dependences of the pseudorapidity distributions of charged particles in Au+Au collisions at RHIC energies

By employing the Glauber model, we give the centrality dependences of the numbers of participants and binary nucleon-nucleon collisions in nucleus-nucleus collisions. By taking into account the energy loss of the participants in their multiple collisions, we then present the pseudorapidity distributions of charged particles in nucleus-nucleus collisions as a function of beam energy and impact parameter. Finally, we analyze the centrality dependence of the pseudorapidity of the charged particles in Au＋Au collisions at energies from √SNN=19.6 to 200 GeV. The theoretical results are in good agreement with the experimental observations of the RHIC-PHOBOS collaboration.     

Centrality dependences of the pseudorapidity distributions of charged particles in Au+Au collisions at RHIC energies

By employing the Glauber model, we give the centrality dependences of the numbers of participants and binary nucleon-nucleon collisions in nucleus-nucleus collisions. By taking into account the energy loss of the participants in their multiple collisions, we then present the pseudorapidity distributions of charged particles in nucleus-nucleus collisions as a function of beam energy and impact parameter. Finally, we analyze the centrality dependence of the pseudorapidity of the charged particles in Au+Au collisions at energies from √sNN=19.6 to 200 GeV.The theoretical results are in good agreement with the experimental observations of the RHIC-PHOBOS collaboration.     

The determination of total multiplicity distribution ine + e − annihilation via charged hadron multiplicity distribution

The correspondence between the moments of distribution of primary particles total multiplicity and the moments of partial distribution of charged hadrons multiplicity is obtained. This dependence permits to describe the data on the charged hadrons multiplicity moments by means of negative binomial distribution (NBD) for total hadron multiplicity. The NBD parameterk is fitted as a rational function of c.m. energy.     

Charged-particle pseudorapidity distributions in Au+Au collisions at RHIC

Using the Glauber model, we present the formulas for calculating the numbers of participants,spectators and binary nucleon-nucleon collisions. Based on this work, we get the pseudorapidity distributions of charged particles as the function of the impact parameter in nucleus-nucleus collisions. The theoretical results agree well with the experimental observations made by the BRAHMS Collaboration in Au+Au collisions at √SNN=200 GeV in different centrality bins over the whole pseudorapidity range.     

Charged-particle pseudorapidity distributions in Au+Au collisions at RHIC

Using the Glauber model, we present the formulas for calculating the numbers of participants, spectators and binary nucleon-nucleon collisions. Based on this work, we get the pseudorapidity distributions of charged particles as the function of the impact parameter in nucleus-nucleus collisions. The theoretical results agree well with the experimental observations made by the BRAHMS Collaboration in Au＋Au collisions at √^SNN=200 GeV in different centrality bins over the whole pseudorapidity range.     

Anisotropic flow at RHIC

STAR’s measurement of directed flow for pions,kaons（K 0 S ）,protons and anti-protons,for Au＋Au collisions at 200 GeV obtained in Run7 are presented,as well as elliptic flow for identified particles measured in Au＋Au（Run7） and Cu＋Cu（Run5） collisions.It is found that the slope of proton v 1 （y） at midrapidity is extremely small.Elliptic flow results are compared to Hydro calculation and the discrepancy is discussed.     

Study of charged multiplicity distributions in high energy particle collisions

Data on hadron-proton collisions ranging from 1 to 300 GeV/c in incident momentum show evidence for an energy-dependent approach to a single semi-inclusive scaling curve for the charged multiplicity cross sections as predicted by Koba, Nielsen and Olesen. The onset of this scaling behavior is shown to depend on the initial state hadrons. The relation between the onset of this apparent scaling and the approach to a constant value of 〈n〉/D is suggestive of a two-component process.     

Anisotropic flow at RHIC

STAR’s measurement of directed flow for pions,kaons(K 0 S ),protons and anti-protons,for Au+Au collisions at 200 GeV obtained in Run7 are presented,as well as elliptic flow for identified particles measured in Au+Au(Run7) and Cu+Cu(Run5) collisions.It is found that the slope of proton v 1 (y) at midrapidity is extremely small.Elliptic flow results are compared to Hydro calculation and the discrepancy is discussed.     

RHIC能量多粒子产生的双源统计模型分析

用双源统计模型分析研究了SNN=130 GeV Au+Au反应中的多粒子产生并与单源统计模型的结果进行了比较.研究表明,该反应有一个高温且大体积的内源.这个源的温度比SPS能量的内源至少高15MeV,体积至少大2倍,文中给出了分析     

Cross sections and charged multiplicity distributions for π−p and K−p interactions at 147 GeV/c

The results presented in this paper were obtained from a 105 000 frame exposure of the FNAL Hybrid Proportional Wire Chamber-30 inch Bubble Chamber System, in a tagged beam of 147 GeV/c negative particles. Elastic, total and topological cross sections were obtained for both π^?p and K^?p interactions. Comparisons with other data, taken with various beam particles over large momentum intervals, show good agreement with KNO scaling, and similarity in the scaling behavior of σ_n for the different beam particles.     

Analysis of one-and two-particle spectra at RHIC based on a hydrodynamical model

We calculate the one-particle hadronic spectra and correlation functions of pions based on a hydrodynamical model. Parameters in the model are so chosen that the one-particle spectra reproduce experimental results of √s= 130 AGeV Au + Au collisions at RHIC. Based on the numerical solution, we discuss the space-time evolution of the fluid. Two-pion correlation functions are also discussed. Our numerical solution suggests the formation of the quark-gluon plasma with large volume and low net baryon density.     

Optimisation of variables for studying dilepton transverse momentum distributions at hadron colliders

In future measurements of the dilepton (Z/γ ^∗) transverse momentum, Q _T , at both the Tevatron and LHC, the achievable bin widths and the ultimate precision of the measurements will be limited by experimental resolution rather than by the available event statistics. In a recent paper the variable a _T , which corresponds to the component of Q _T that is transverse to the dilepton thrust axis, has been studied in this regard. In the region, Q _T < 30 GeV, a _T has been shown to be less susceptible to experimental resolution and efficiency effects than the Q _T . Extending over all Q _T , we now demonstrate that dividing a _T (or Q _T ) by the measured dilepton invariant mass further improves the resolution. In addition, we propose a new variable, f_h^*phi _{rm eta }^{*}, that is determined exclusively from the measured lepton directions; this is even more precisely determined experimentally than the above variables and is similarly sensitive to the Q _T . The greater precision achievable using such variables will enable more stringent tests of QCD and tighter constraints on Monte Carlo event generator tunes.