arXiv 0810.30402008-10-16nucl-exhep-ex

RHIC中p+p和Au+Au碰撞的双轻子谱

Dilepton spectra in p+p and Au+Au collisions at RHIC

Torsten Dahms

备注：: 215 pages, 121 figures, Ph.D. Dissertation submitted to Stony Brook University (abstract shortened, for full abstract see dissertation)

摘要：

这项工作提出了在2005年RHIC运行期间收集的sqrt（s）= 200 GeV的p+p碰撞的电子-正电子对的测量，并将其与2004年PHENIX探测器在sqrt（s_NN）= 200 GeV的Au+Au碰撞的结果进行比较。p+p中e+e-对的不变质量分布与轻强子的Dalitz衰变、矢量介子的双电子衰变和相关粲产生的预期贡献一致。从测得的双电子产率中提取的粲截面和底截面为sigma_cc = 544 +/- 39（stat.）+/- 142（系统）+/- 200（模型）微仓和sigma_bb = 3.9 +/- 2.4（统计）+3/-2（系统）微生物分别在最小偏压Au+Au碰撞中，低质量区的双电子产额增加了4.0 +/- 0.3倍（统计）。+/- 1.5（系统）+/- 0.8（模型）与已知的强子源相比。在低于1GeV/c的横动量区，过剩的能量占主导地位，并且平均p_T比预期的源要低得多。低p_T增强目前还没有被任何重离子碰撞的理论模型所理解。增强延伸到更大的横向动量，它也被观察到在p+p和虚拟直接光子解释。p+p测量作为一个重要的测试pQCD计算的直接光子生产从硬散射过程中，在这个动量范围。具有反斜率T_eff = 221 +/- 23（stat.）+/- 18（系统）在p+ p中的二元标度直接光子产额之上的中心Au+Au碰撞中观察到MeV。这可以通过流体动力学模型定性地解释，包括初始温度为300 - 600 MeV、形成时间为0.12 - 0.6 fm/c的热光子辐射。

英文摘要：

This work presents measurements of electron-positron pairs from p+p collisions at sqrt(s) = 200 GeV collected during the 2005 RHIC run and compares them to results from Au+Au collisions at sqrt(s_NN) = 200 GeV taken in 2004 with the PHENIX detector. The invariant mass distribution of e+e- pairs in p+p is consistent with the expected contributions from Dalitz decays of light hadrons, dielectron decays of vector mesons and correlated charm production, which have been measured in the same experiment. The charm and bottom cross section extracted from the measured dielectron yield are sigma_cc = 544 +/- 39(stat.) +/- 142(syst.) +/- 200(model) microbarns and sigma_bb = 3.9 +/- 2.4(stat.) +3/-2(syst.) microbarns, respectively. In min. bias Au+Au collisions the yield of dielectrons in the low mass region is enhanced by a factor of 4.0 +/- 0.3(stat.) +/- 1.5(syst.) +/- 0.8(model) compared to the known hadronic sources. The excess dominates the yield in the transverse momentum region below 1 GeV/c and shows significantly lower average p_T than the expected sources. The low p_T enhancement is currently not understood by any theoretical model of heavy ion collisions. The enhancement extends to larger transverse momenta where it is also observed in p+p and explained by virtual direct photons. The p+p measurement serves as an important test to pQCD calculations of direct photon production from hard scattering processes in this momentum range. An excess with an inverse slope of T_eff = 221 +/- 23(stat.) +/- 18(syst.) MeV is observed in central Au+Au collisions above the binary scaled direct photon yield in p+p. This can be qualitatively explained by hydrodynamical models including thermal photon radiation with initial temperatures of 300 - 600 MeV and formation times of 0.12 - 0.6 fm/c.

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