作者机构：
Argonne Natl Lab, Argonne, IL 60439 USA.;Brookhaven Natl Lab, Upton, NY 11973 USA.;Univ Birmingham, Birmingham, W Midlands, England.;Univ Calif Davis, Davis, CA 95616 USA.;Univ Calif Los Angeles, Los Angeles, CA 90095 USA.
通讯机构：
[Adams, J] A;Argonne Natl Lab, 9700 S Cass Ave, Argonne, IL 60439 USA.
摘要：
We present the first large-acceptance measurement of event-wise mean transverse momentum < p(t)> fluctuations for Au-Au collisions at nucleon-nucleon center-of-momentum collision energy root s(NN) = 130 GeV. The observed nonstatistical < p(t)> fluctuations substantially exceed in magnitude fluctuations expected from the finite number of particles produced in a typical collision. The r.m.s. fractional width excess of the event-wise < p(t)> distribution is 13.7 +/- 0.1(stat) +/- 1.3(syst)% relative to a statistical reference, for the 15% most-central collisions and for charged hadrons within pseudorapidity range vertical bar eta vertical bar < 1,2 pi azimuth, and 0.15 <= p(t) <= 2 GeV/c. The width excess varies smoothly but nonmonotonically with collision centrality and does not display rapid changes with centrality which might indicate the presence of critical fluctuations. The reported < p(t)> fluctuation excess is qualitatively larger than those observed at lower energies and differs markedly from theoretical expectations. Contributions to < p(t)> fluctuations from semihard parton scattering in the initial state and dissipation in the bulk colored medium are discussed.
摘要：
We report the STAR measurement of phi meson production in Au + Au and p + p collisions at root s(NN) = 200 GeV. Using the event mixing technique, the phi spectra and yields are obtained at mid-rapidity for five centrality bins in Au + Au collisions and for non-singly-diffractive p + p collisions. It is found that the phi transverse momentum distributions from Au + An collisions are better fitted with a single-exponential while the p + p spectrum is better described by a double-exponential distribution. The measured nuclear modification factors indicate that phi production in central An + An collisions is suppressed relative to peripheral collisions when scaled by the number of binary collisions (< N-bin>). The systematics of < p(t)> versus centrality and the constant phi/K- ratio versus beam species, centrality, and collision energy rule out kaon coalescence as the dominant mechanism for phi production. (c) 2005 Elsevier B.V. All rights reserved.
摘要：
The short-lived K(892)* resonance provides an efficient tool to probe properties of the hot and dense medium produced in relativistic heavy-ion collisions. We report measurements of K* in root s(NN)=200 GeV Au+Au and p+p collisions reconstructed via its hadronic decay channels K(892)*(0)-> K pi and K(892)*(+/-)-> K(S)(0)pi(+/-) using the STAR detector at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory. The K*(0) mass has been studied as a function of p(T) in minimum bias p+p and central Au+Au collisions. The K-* p(T) spectra for minimum bias p+p interactions and for Au+Au collisions in different centralities are presented. The K*/K yield ratios for all centralities in Au+Au collisions are found to be significantly lower than the ratio in minimum bias p+p collisions, indicating the importance of hadronic interactions between chemical and kinetic freeze-outs. A significant nonzero K*(0) elliptic flow (v(2)) is observed in Au+Au collisions and is compared to the K-S(0) and Lambda v(2). The nuclear modification factor of K* at intermediate p(T) is similar to that of K-S(0) but different from Lambda. This establishes a baryon-meson effect over a mass effect in the particle production at intermediate p(T) (2 < p(T)<= 4 GeV/c).
作者机构：
[Hallman, TJ] Brookhaven Natl Lab, Upton, NY 11973 USA.;Argonne Natl Lab, Argonne, IL 60439 USA.;Univ Bern, CH-3012 Bern, Switzerland.;Univ Birmingham, Birmingham B15 2TT, W Midlands, England.;CALTECH, Pasadena, CA 91125 USA.
通讯机构：
[Hallman, TJ] B;Brookhaven Natl Lab, Upton, NY 11973 USA.
摘要：
We review the most important experimental results from the first three years of nucleus-nucleus collision studies at RHIC, with emphasis on results from the STAR experiment, and we assess their interpretation and comparison to theory. The theory-experiment comparison suggests that central Au + Au collisions at RHIC produce dense, rapidly thermalizing matter characterized by: (1) initial energy densities above the critical values predicted by lattice QCD for establishment of a quark-gluon plasma (QGP); (2) nearly ideal fluid flow, marked by constituent interactions of very short mean free path, established most probably at a stage preceding hadron formation; and (3) opacity to jets. Many of the observations are consistent with models incorporating QGP formation in the early collision stages, and have not found ready explanation in a hadronic framework. However, the measurements themselves do not yet establish unequivocal evidence for a transition to this new form of matter. The theoretical treatment of the collision evolution, despite impressive successes, invokes a suite of distinct models, degrees of freedom and assumptions of as yet unknown quantitative consequence. We pose a set of important open questions, and suggest additional measurements, at least some of which should be addressed in order to establish a compelling basis to conclude definitively that thermalized, deconfined quark-gluon matter has been produced at RHIC. (c) 2005 Published by Elsevier B.V.
摘要：
Identified mid-rapidity particle spectra of pi(+/-), K+/-, and p((p) over bar) from 200 GeV p + p and d + Au collisions are reported. A time-of-flight detector based on multi-gap resistive plate chamber technology is used for particle identification. The particle-species dependence of the Cronin effect is observed to be significantly smaller than that at lower energies. The ratio of the nuclear modification factor (R-dAu) between protons (p + (p) over bar) and charged hadrons (h) in the transverse momentum range 1.2 < p(T) < 3.0 GeV/c is measured to be 1.19 +/- 0.05(stat) +/- 0.03(syst) in minimum-bias collisions and shows little centrality dependence. The yield ratio of (p + (p) over bar)/h in minimum-bias d + Au collisions is found to be a factor of 2 lower than that in Au + Au collisions, indicating that the Cronin effect alone is not enough to account for the relative baryon enhancement observed in heavy ion collisions at RHIC. (c) 2005 Elsevier B.V. All rights reserved.
作者机构：
[Ablikim, M] Inst High Energy Phys, Beijing 100039, Peoples R China.;China Ctr Adv Sci & Technol, Beijing 100080, Peoples R China.;Guangxi Normal Univ, Guilin 541004, Peoples R China.;Henan Normal Univ, Xinxiang 453002, Peoples R China.;Huazhong Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.
通讯机构：
[Ablikim, M] I;Inst High Energy Phys, Beijing 100039, Peoples R China.
摘要：
The cross sections for D-0(D) over bar (0) and D+D- production at 3.773 GeV have been measured with BES-II detector at BEPC. These measurements are made by analyzing a data sample of about 17.3 pb(-1) collected at the center-of-mass energy of 3.773 GeV. Observed cross sections for the charm pair production are radiatively corrected to obtain the tree level cross section for DD production. A measurement of the total tree level hadronic cross section is obtained from the tree level DD cross section and an extrapolation of the R-uds below the open charm threshold. (C) 2004 Elsevier B.V. All rights reserved.
