相对论重离子碰撞中直接光子的产生

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1、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2BackgroundLHC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3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、KNOsc

2、aling、…）2.高能PP碰撞可否产生QGP？方法：直接光子、DrellYan…历史：TEVATRON上E735group的失败经验4outline高能pp碰撞所面临的问题：Multiplescattering,manyPomerons/stringsinvolvedHowtotreattheafterwardsecondaryscattering?直接光子的产生（来自RHIC实验的经验）RHICAu+Audataareexplainedwith4sourcesHydrodynamicdescri

3、ptionofthehotdensematterinAAHydrodynamictreatmentofthesecondaryscatteringinpp结果和讨论pQCD+plasmacontributionIsitpossibletoformaQGPinppcollisions?5HadronproductioninppUsually,apairofstringsareformed:PYTHIA,HIJING,DPM,FRITIOF,VENUS,NEXUS,…hadronproduction:s

4、tringfragmentation,i.e.F.M.Liuetal.PRD67,034011(2003)6ppcollisionsathighEProblem:Two-stringpicturecannotexplainobservables(~100GeV)Highmultiplicity(multiplicitydis.predictedistoonarrow)IncreaseofmeanptHighptjetsRiseofcentralrapiditydensitySolution:Mult

5、iplescatteringbecomesimportantathighenergiesMorePomerons/stringsareaddedPomeron=apairofstringsF.M.Liuetal.PRD67,034011(2003)H.J.Drescheretal,Phys.Rept.350,93(2001).7高能极限下的pp碰撞Multipleelementaryinteractions(Pomerons)inNEXUS/EPOS:Question:Howtotreattheaf

6、terwardsecondaryscattering?onpartonlevel?oronhadronlevel?Pomeronnumbermightbeverybig.Rapidity8PresentdataaregenerallyingoodagreementwithNLOQCDprediction.Butatendencyforthedatatobeabove(below)thetheoryforlower(large)pt.Directphotondatainpp(ppbar)LatestP

7、DGreview9pp->gammawithNLOpQCD2.Fragmentationcontribution:Highordercontribution1.LeadingOrdercontributionpreliminaryD0andCDFcanonlymeasurept>10GeV.Shouldthesecondaryinteractionberesponsibleforthisdeviation?Saturationmakesadecreaseatlowx！W.Vogelsang&M.R.

8、Walley1997JPG:23,A1-A6910RHICAuAu碰撞流体力学的应用取得了巨大胜利：1）Jetquenching,高横动量区强子产额的压低2）EllipticFlow（v2)随着碰撞中心度的变化规律低横动量区n_qscaling背对背的关联…QGP产生的证据11HydrodynamictreatmentInitialcondition:thermalizedQCDmatteratrestatEvolution:3Didealhydrodynamice