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1、RHIC和和LHC实验实验中直中直接光子的产生接光子的产生 2010年年7月月 乌兰浩特乌兰浩特 刘复明刘复明 华中师范大学华中师范大学2Background1.LHC加速器正在进行高能pp碰撞2.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物理目标:1.ATLAS、CMS：通过双光子道寻找标准模型Higgs粒子2.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：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
2、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4outline高能高能pppp碰撞所面临的问题：碰撞所面临的问题：Multiple scattering,many Pomerons/strings involvedHow to treat the afterward secondary scattering?直接光子的产生直接光子的产生 （来自（来自RHICRHIC实验的经验实验的经验）RHIC Au+Au data are explained with 4 sourcesHydr
3、odynamic description of the hot dense matter in AA Hydrodynamic treatment of the secondary scattering in pp结果和讨论结果和讨论pQCD+plasma contributionIs it possible to form a QGP in pp collisions?5Hadron production in ppUsually,a pair of strings are formed:PYTHIA,HIJING,DPM,FRITIOF,VENUS,NEXUS,hadron product
4、ion:string fragmentation,i.e.F.M.Liu et al.PRD 67,034011(2003)6pp collisions at high EProblem:Two-string picture can not explain observables(100GeV)1)High multiplicity(multiplicity dis.predicted is too narrow)2)Increase of mean pt3)High pt jets4)Rise of central rapidity densitySolution:Multiple scat
5、tering becomes important at high energies More Pomerons/strings are addedPomeron =a pair of strings F.M.Liu et al.PRD 67,034011(2003)H.J.Drescher et al,Phys.Rept.350,93(2001).7高能极限下的高能极限下的pppp碰撞碰撞Multiple elementary interactions(Pomerons)in NEXUS/EPOS:Question:How to treat the afterward secondary sc
6、attering?on parton level?or on hadron level?Pomeron number might be very big.Rapidity8Present 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 review9pp-gamma with NLO pQ
7、CD2.Fragmentation contribution:High order contribution1.Leading Order contributionpreliminaryD0 and CDF can only measure pt 10GeV.Should the secondary interaction be responsible for this deviation?Saturation makes a decrease at low x！W.Vogelsang&M.R.Walley 1997 JPG:23,A1-A6910RHICRHIC AuAuAuAu碰撞碰撞流体
8、力学的应用取得了巨大胜利：流体力学的应用取得了巨大胜利：1）Jet quenching,高横动量区强子产额的压低2）Elliptic Flow（v2)随着碰撞中心度的变化规律 低横动量区 n_q scaling 3)背对背的关联4)QGP产生的证据产生的证据11Hydrodynamic treatmentInitial condition:thermalized QCD matter at rest atEvolution:3D ideal hydrodynamic equationdescribed with 3+1D ideal hydrodynamicsEoS:1st order pha
9、se transition at QGP phase:3 flavor free Q&G gas HG phase:hadronic gas PCEFreeze-out:Cooper-Fry Formulism,May followed with cascade treatment parameterized based on Glauber model string overlapping and melting 12AuAuAuAu碰撞中直接光子的来源碰撞中直接光子的来源Jets lose energy in plasma1.Leading Order contribution 2.Fra
10、gmentation contribution:3.Thermal contribution4.Jet-photon conversionAu+Au-direct photons at 200AGeVDirect photon production from AuAu collisions at top RHIC energy is well explained in a large pt range at all centralities.FML,T.Hirano,K.Werner,Y.Zhu,Phys.Rev.C79:014905,200914来自来自RHIC实验的经验实验的经验1.热光子
11、会使低横动量区低横动量区直接光子产额明显增加2.能量损失会压低高横动量区高横动量区碎裂光子的产额1)The tendency for the data to be above(below)2)the theory for lower(large)pt 3)高能pp碰撞中可能可能产生了热密物质1.2)采用流体力学方法来处理高能pp碰撞中次级碰撞2.14TeV 50 AuAu 200GeV对对pppp碰撞的启示碰撞的启示:15Plasma evolution in pp(EPOS)16Plasma contribution to direct photonEffect from secondary scattering:光子探测器 Pt range:100Mev100GeV,detectable!Pt=1GeV/c2GeV/c3GeV/cpQCDplasmaplasma pQCDpreliminary17Conclusion1.流体力学可否应用于高能pp碰撞?LHC的直接光子测量将提供参考答案2.高能PP碰撞可否产生QGP？可能：高能、对心（大 事件）18Thank you!
相对论重离子碰撞中直接光子的产生课件
