带电多重数赝快度密度对碰撞对心度依赖关系研究

以核-核碰撞的独立源理论为基础，讨论了(S_NN)^1/2＝１３０ GeV的Au+Au碰撞中，中心快度区带电多重数赝快度密度dn_ch/dη对碰撞对心度的依赖关系.理论结果较好地反映了实验事实. 关键词： 重离子碰撞 带电多重数 赝快度密度 碰撞对心度     

Charged-particle multiplicity at mid-rapidity in Au-Au collisions at relativistic heavy-ion collider

The particle density at mid-rapidity is an essential global variable for the characterization of nuclear collisions at ultra-relativistic energies. It provides information about the initial conditions and energy density reached in these collisions. The pseudorapidity densities of charged particles at mid-rapidity in AuAu collisions at √^s _NN = 130 and 200 GeV at RHIC (relativistic heavy ion collider) have been measured with the PHENIX detector. The measurements were performed using sets of wire-chambers with pad readout in the two central PHENIX tracking arms. Each arm covers one quarter of the azimuth in the pseudorapidity interval |η| < 035. Data is presented and compared with results from proton-proton collisions and nucleus-nucleus collisions at lower energies. Extrapolations to LHC energies are discussed.     

Identified hadron production in √s = 130 GeV Au-Au collisions at relativistic heavy-ion collider

Identified π^±,K ^±, p and -p transverse momentum spectra at mid-rapidity in √^sNN = 130 GeV Au-Au collisions were measured by the PHENIX experiment at RHIC as a function of collision centrality. Average transverse momenta increase with the number of participating nucleonsN _part similarly for all particle species. The multiplicity densities scale faster thanN _part. TheK ^± andp ^±yields per participant increase faster than the π^± yields. We combine the PHENIX neutral and charged pion measurement and find that in central collisions forp _T >-2 GeV/c,-p andp yields are comparable to or even exceed the pion yields.     

z-scaling in heavy ion collisions at the RHIC

Experimental data on transverse particle spectra obtained by the STAR, PHENIX, PHOBOS, and BRAHMS collaborations at the RHIC are analyzed in the framework of the generalized concept of z-scaling. It was developed for analysis of inclusive particle production in proton-(anti)proton collisions at high p _T and high multiplicities. The general scheme of the approach based on the physical principles of self-similarity, locality, and fractality is reviewed. Independence of the scaling function ψ(z) from energy, multiplicity, and atomic weight for h ^±, π ^±,0, K _S ⁰ , and Λ hadrons produced in Au-Au and Cu-Cu collisions at √s = 130 and 200 GeV is discussed. Based on z-scaling, the multiplicity dependence of pion transverse spectra up to p _T = 25 GeV/c in Au-Au collisions at √s = 200 GeV for experiments at the RHIC is predicted. The text was submitted by the author in English.     

Pseudorapidity distributions of charged particles in Pb-Pb collisions at super proton synchrotron energies from the NA50 experiment

We present the measurements of charged particle pseudorapidity distributions dN_ch/dη performed by the NA50 experiment in Pb-Pb collisions at the CERN SPS. Measurements were done at incident energies of 40 GeV (√s = 8.77 GeV) and 158 GeV (√s = 17.3 GeV) per nucleon over a broad impact parameter range. The multiplicity distributions are studied as a function of centrality using the number of participating nucleons(N _part ), or the number of binary nucleon-nucleon collisions (N_coll). Their values at midrapidity exhibit a linear scaling withN _part at both energies. Particle yield increases approximately by a factor of 2 betweeny √s = 8.77 GeV and √s = 17.3 GeV.     

Analysis of multi-strange hyperon production in p+p and Au+Au collisions at RHIC

The analysis of multi-strange hyperon production (Ξ^?, Ω^? and their anti-particles) at mid-rapidity is part of the program covered by the STAR experiment at RHIC. We report on preliminary results in Au+Au and p+p collisions at $\sqrt {s_{NN} } = 130$ and 200 GeV. Measurements of particle ratios are presented and production yields and spectra are discussed for both collision systems.     

Three-dimensional kaon and pion emission source extraction from √sNN = 200 GeV Au + Au collisions at RHIC-STAR

Three-dimensional source images for mid-rapidity, low transverse momentum kaon and pion pairs have been extracted from central Au + Au collisions data at √s _NN = 200 GeV by the STAR experiment at RHIC. The pion source function displays significant non-Gaussian features implying a finite pion emission duration. On the other hand, the kaon source function is essentially Gaussian, consistent with instantaneous emission from the fireball.     

Antiproton and charged kaon production in \sqrt {s_{NN} } = 130 GeV Au+Au collisions at RHICGeV Au+Au collisions at RHIC

Preliminary results on antiproton and charged kaon spectra and the net-proton number at mid-rapidity are reported for Au+Au collisions at $\sqrt {s_{NN} } = 130$ GeV as measured by the STAR experiment at RHIC. Inverse slope parameters of the transverse mass distributions increase with the collision centrality, consistent with a strong radial flow. The antiproton and charged kaon extrapolated yields, normalized to the uncorrected negatively charged hadron yield, increase with the collision centrality. A finite but small number of net-baryons is found to be present at mid-rapidity.     

Transverse energy measurement in Au+Au collisions by the STAR experiment

Transverse energy (E _T ) has been measured with both of its components, namely hadronic (E _T ^had ) and electromagnetic (E _T ^em ) in a common phase space at mid-rapidity for 62.4 GeV Au+Au collisions by the STAR experiment. E _T production with centrality and ?{s_NN }\sqrt {s_{NN} } is studied with similar measurements from SPS to RHIC and is compared with a final state gluon saturation model (EKRT). The most striking feature is the observation of a nearly constant value of E _T /N _ch ∼ 0.8 GeV from AGS, SPS to RHIC. The initial energy density estimated by the boost-invariant Bjorken hydrodynamic model, is well above the critical density for a deconfined matter of quarks and gluons predicted by lattice QCD calculations.     

Directed flow of identified particles from Au+Au collisions at RHIC

We present the measurement of directed flow (v ₁) for the identified particles, namely, Λ, $ \bar \Lambda $ \bar \Lambda and K _s ⁰, as a function of rapidity and centrality in Au+Au collisions at $ \sqrt {s_{NN} } $ \sqrt {s_{NN} } = 200 GeV and 62.4 GeV. The measurement is based on the run IV data obtained by the STAR experiment at RHIC. In order to enhance event plane resolution, we use tracks reconstructed from the Forward Time Projection Chambers (FTPCs), together with the sideward deflection of spectator neutrons measured by the STAR’s Shower Maximum Detector at Zero Degree Calorimeters (ZDC-SMDs). We find that for 200 GeV, proton and antiproton v ₁ is less than 1%, the K _s ⁰ Λ, $ \bar \Lambda $ \bar \Lambda v ₁ is less than 2%; for 62 GeV, proton v ₁ is less than 1% and antiproton is less than 2%, v ₁ for K _s ⁰, Λ, $ \bar \Lambda $ \bar \Lambda is less than 2% in Au+Au collisions at 200 GeV.     

Beam-energy and system-size dependence of dynamical net charge fluctuations

We present measurements of net charge fluctuations in Au + Au collisions at ?{s_NN }\sqrt {s_{NN} } = 19.6, 62.4, 130, and 200 GeV, Cu + Cu collisions at ?{s_NN }\sqrt {s_{NN} } = 62.4, 200 GeV, and p + p collisions at ?s\sqrt s = 200 GeV using the net charge dynamical fluctuations measure ν+ −,dyn. The dynamical fluctuations are non-zero at all energies and exhibit a rather modest dependence on beam energy. We find that at a given energy and collision system, net charge dynamical fluctuations violate 1/N _ch scaling, but display approximate 1/N _part scaling. We observe strong dependence of dynamical fluctuations on the azimuthal angular range and pseudorapidity widths.     

Results from the first physics run of PHENIX at RHIC

First results from measurements of Au?Au collisions at $\sqrt {s_{NN} } = 130$ GeV, performed with the PHENIX experiment during the initial physics run of Brookhaven National Laboratory’s Relativistic Heavy Ion Collider in summer 2000, are summarized. Global characterization of the collisions was obtained from charged-particle multiplicity and transverse energy densities. At mid-rapidity, dN _ch /dν and dE _T /dν rise steadily with the event centrality, while the ratio <E _T >/<N _ch > remains constant. Transverse momentum spectra of charged particles up to 5 GeV/c yield a suppression of high-momentum particles in the most central events when compared to a simple scaling of binary nucleon-nucleon collisions. The scaling matches with peripheral collisions. Transverse momentum spectra of identified neutral pions from 1 to 4 GeV/c in peripheral collisions show consistency with point-like scaling with the average number of binary collisions. Yields in central collisions are significantly suppressed. Transverse momentum spectra of identified charged hadrons up to 3.5 GeV/c were measured in minimum bias events. The mass and centrality dependencies of inverse slope parameters and mean transverse momenta were determined. Inclusive spectra of electrons were measured for momenta from a few hundred MeV/c to 4 GeV/c. Inclusive photon spectra from a few hundred MeV/c to 3 GeV/c were obtained from conversion pair measurements.     

Ratios of charged antiparticles-to-particles near mid-rapidity in Au + Au collisions at sqrt[s(NN)]=130 GeV

We have measured the ratios of antiparticles to particles for charged pions, kaons, and protons near mid-rapidity in central Au+Au collisions at sqrt[s(NN)] = 130 GeV. We observe / = 1.00+/-0.01(stat)+/-0.02(syst), / = 0.91+/-0.07(stat)+/-0.06(syst), and

/

= 0.60+/-0.04(stat)+/-0.06(syst). The / and

/

ratios give a consistent estimate of the baryo-chemical potential mu(B) of 45 MeV, a factor of 5-6 smaller than in central Pb+Pb collisions at sqrt[s(NN)] = 17.2 GeV.     

Charged-particle pseudorapidity density distributions from Au+Au collisions at sqrt[s(NN)]=130 GeV

The charged-particle pseudorapidity density dN(ch)/d eta has been measured for Au+Au collisions at sqrt[s(NN)] = 130 GeV at RHIC, using the PHOBOS apparatus. The total number of charged particles produced for the 3% most-central Au+Au collisions for /eta/相似文献   

System size, energy, centrality and pseudorapidity dependence of charged-particle density in Au+Au and Cu+Cu collisions at RHIC

Charged particle pseudorapidity distributions are presented from the PHOBOS experiment at RHIC, measured in Au+Au and Cu+Cu collisions at ?{s_NN }\sqrt {s_{NN} } =19.6, 22.4, 62.4, 130 and 200 GeV, as a function of collision centrality. The presentation includes the recently analyzed Cu+Cu data at 22.4 GeV. The measurements were made by the same detector setup over a broad range in pseudorapidity, |η| < 5.4, allowing for a reliable systematic study of particle production as a function of energy, centrality and system size. Comparing Cu+Cu and Au+Au results, we find that the total number of produced charged particles and the overall shape (height and width) of the pseudorapidity distributions are determined by the number of nucleon participants, N _part. Detailed comparisons reveal that the matching of the shape of the Cu+Cu and Au+Au pseudorapidity distributions over the full range of η is better for the same N _part/2A value than for the same N _part value, where A denotes the mass number. In other words, it is the geometry of the nuclear overlap zone, rather than just the number of nucleon participants that drives the detailed shape of the pseudorapidity distribution and its centrality dependence.     

Charge fluctuations in Au+Au collisions at RHIC energy

A hadron and string cascade model, JPCIAE, together with the corresponding Monte Carlo event generator, has been employed in this paper to investigate further the charge fluctuations in Au+Au collisions at Snn = 130 GeV. The default JPCIAE calculations are in good agreement with PHENIX and STAR data. We found that the thermal predictions for the π gas, the resonance π gas and quark matter deviate, respectively, from the corresponding dynamical simulations from the JPCIAE model. The discrepancies were also found between the π charge fluctuations and the charge fluctuations of all species of hadrons. However the charge fluctuations for "π from ρ and ω decay" and for all the hadrons from resonance decay are close to each other, indicating the correlation between positively and negatively charged hadrons is not sensitive to the species of hadrons. This work shows further that it is questionable to use the charge fluctuations as a signature of QGP.     

Charged kaon spectra from Au+Au collisions at ?{sNN }\sqrt {s_{NN} } = 200 GeV

The Time-of-Flight detector, based on MRPC technology, has greatly enhanced particle identification capability in STAR. By combining dE/dx measured by the TPC and velocity information from the TOF, we have extended the charged kaon transverse momentum spectra measurements up to ρ _T − 5 GeV/c at mid-rapidity for Au+Au collisions at ?{s_NN }\sqrt {s_{NN} } = 200 GeV. Estimation of charged kaon’s contribution factors from K* and ϕ is also made.     

Pseudorapidity and centrality dependence of the collective flow of charged particles in Au+Au collisions at sqrt[s(NN)]=130 GeV

This paper describes the measurement of collective flow for charged particles in Au+Au collisions at sqrt[s(NN)]=130 GeV using the PHOBOS detector at the Relativistic Heavy Ion Collider (RHIC). The measured azimuthal hit anisotropy is presented over a wide range of pseudorapidity (-5.0相似文献   

Global observables at PHENIX

We present PHENIX recent results on charged particle and transverse energy densities measured at mid-rapidity in Au?Au collisions at $\sqrt {s_{NN} } = 130$ GeV and 200 GeV over a broad range of centralities. The mean transverse energy per charged particle is derived. The first PHENIX measurements at $\sqrt {s_{NN} } = 19.6$ GeV are also presented. A comparison with calculations from various theoretical models is performed.     

PHOBOS at RHIC: Some global observations

Particle production in Au+Au collisions has been measured in the PHOBOS experiment at RHIC for a range of collision energies for a large span of pseudorapidities, |η| < 5.4. Three empirical observations have emerged from this data set which require theoretical examination. First, there is clear evidence of limiting fragmentation. Namely, particle production in central Au + Au collisions, when expressed as dN/dη′ ( η′ ≡ – y_beam), becomes energy independent at high energy for a broad region of η′ around η′ = 0. This energy-independent region grows with energy, allowing only a limited region (if any) of longitudinal boost-invariance. Second, there is a striking similarity between particle production in e⁺e⁻and Au + Au collisions (scaled by the number of participating nucleon pairs). Both the total number of produced particles and the longitudinal distribution of produced particles are approximately the same in e⁺e⁻and in scaled Au + Au. This observation This presentation is based in large part on the PHOBOS summary talk by M Baker at the16th Int. Conf. on Ultrarelativistic Nucleus- Nucleus Collisions, Quark Matter 2002, Nantes, France was not predicted and has not been explained. Finally, particle production has been found to scale approximately with the number of participating nucleon pairs for (N _part ) > 65. This scaling occurs both for the total multiplicity and for highp _T particles (3 <p _T < 4.5 GeV/c). This presentation is based in large part on the PHOBOS summary talk by M Baker at the16th Int. Conf. on Ultrarelativistic Nucleus-Nucleus Collisions, Quark Matter 2002, Nantes, France