RHIC和LHC试验中直接光子的产生.PPT

SQM2008 Beijing Hefei SQM2008 Beijing RHIC和LHC实验中直接光子的产生 2010年7月 乌兰浩特 刘复明 华中师范大学 * Background LHC加速器正在进行高能pp碰撞 LHC上的四个实验组都安装了高性能的光子探测器 物理目标: ATLAS、CMS：通过双光子道寻找标准模型Higgs粒子 ALICE: pp　通过gamma事件测量碎裂函数　　 　　　　　 AA　研究QGP性质 * 这里我想探索的问题是： 1. 流体力学可否应用于高能pp碰撞? 反方：流体力学应用要求系统尺度远大于平均自由程 正方：Landau建议 应用于强子－强子碰撞 已取得巨大成功 (ISR能区： 快度分布、KNO scaling、…） 2. 高能PP碰撞可否产生QGP？ 方法：直接光子、Drell Yan … 历史：TEVATRON上 E735 group 的失败经验 * outline 高能pp碰撞所面临的问题： Multiple scattering, many Pomerons / strings involved How to treat the afterward secondary scattering? 直接光子的产生 （来自RHIC实验的经验） RHIC Au+Au data are explained with 4 sources Hydrodynamic description of the hot dense matter in AA Hydrodynamic treatment of the secondary scattering in pp 结果和讨论 pQCD + plasma contribution Is it possible to form a QGP in pp collisions? * Hadron production in pp Usually, a pair of strings are formed: PYTHIA, HIJING, DPM, FRITIOF, VENUS, NEXUS,… hadron production: string fragmentation, i.e. F.M.Liu et al. PRD 67, 034011 (2003) * pp collisions at high E Problem: Two-string picture can not explain observables (~100GeV) High multiplicity (multiplicity dis. predicted is too narrow) Increase of mean pt High pt jets Rise of central rapidity density Solution: Multiple scattering becomes important at high energies More Pomerons/strings are added Pomeron = a pair of strings F.M.Liu et al. PRD 67, 034011 (2003) H.J.Drescher et al, Phys.Rept.350,93(2001). * 高能极限下的pp碰撞 Multiple elementary interactions (Pomerons) in NEXUS/EPOS: Question: How to treat the afterward secondary scattering ? on parton level ? or on hadron level? Pomeron number might be very big. Rapidity * Present data are generally in good agreement with NLO QCD prediction. But a tendency for the data to be above (below) the theory for lower (large) pt. Direct photon data in pp (ppbar) Latest PDG review * pp- gamma with NLO