RHIC上200GeV Au+Au碰撞中直接虚光子的测量
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摘要
大爆炸理论预言在大爆炸发生后约几十微秒的宇宙早期可能会产生一种特殊的物质形态-夸克胶子等离子体(QGP)。格点QCD计算预言了在高温和低重子密度的条件下的从普通强子物质到这种夸克解禁闭的局部热平衡物质的相变。位于美国布鲁克海文国家实验室(BNL)的相对论重离子对撞机(RHIC)通过高能重离子碰撞提供了寻找QGP物质形态,研究其行为和性质的实验环境。这种物质会以直接光子和双轻子的方式发射热辐射。作为电弱相互作用探针,因为不参与强相互作用,直接光子和轻子一旦产生在穿越相对论重离子碰撞产生的高温高密物质时只受到很小的相互作用。它们被认为能够携带从各个碰撞演化过程中的信,对其的研究能够反映碰撞系统最直接最纯净的信息。
本文给出了位于RHIC的螺旋管径迹探测器(STAR)中直接虚光子的首次研究结果。这也是在高横动量下首次基于虚光子方法的直接光子测量。测量是基于2010年与2011年采集的每核子对质心能量200GeV的金核金核碰撞数据,给出了直接虚光子的不变产额及其与单举光子的比例。这种基于虚光子方法测量的直接光子被称为直接虚光子。在横动量区间1的飞行时间谱仪(TOF)提供了从低到中横动量区间的干净的电子鉴别,使得双电子的测量成为可能。
数据分析结果显示直接虚光子的产额谱在低横动量区间比从质子质子碰撞结果得到的预期有明显的升高。这种升高说明了在此区间中存在物质热化的贡献。不变产额谱与理论计算得到的预期相符合,其包含QGP,强子气体(hadron gas)和原初产生的贡献。在高横动量区间,直接虚光子的产额谱符合从质子质子碰撞结果得到的预期。这说明在此区间来自于物质热辐射的贡献非常微弱。对直接虚光子的测量提供了两个动力学区间：1)可以对热化物质进行研究的低横动量区间；2)可以研究原初过程中部分子的硬散射的高横动量区间。一个与初始温度相关的逆坡度参数(inverse slope parameter)也可以从不变产额谱中得到。
The Big-Bang theory indicates that the Quark Gluon Plasma (QGP) is formed at the very universe in a few tens of microseconds. Lattic QCD predicts a phase transition from hadronic matter to this deconfined and locally thermalized matter at high temperature and low baryon density. Relativistic Heavy Ion Col-lider (RHIC) at Brookhaven National Laboratory (BNL) provides an opportunity to study this strongly coupled QGP. The research of the behavior and proper-ty of QGP is a very interesting topic for physicist. This medium is expected to emit thermal radiation which is in the form of direct photons and dileptons. As electroweak probes, which do not suffer strong interaction, direct photon and lep-ton will traverse the hot and dense medium created by heavy ion collisions with minimal interactions once they are produced. They are believed to bring the in-formation from all the evolution steps. The research on these probes will provide the most direct and pure information.
In this thesis, the first measurement on direct virtual photon from Solenoidal Tracker at RHIC (STAR) is reported. This measurement is also the first high transverse momentum(pT) result on direct photon via virtual photon method. This analysis is based on the data of sNN=200GeV Au+Au collisions taken from year2010run and year2011run (Run10and Runll). The invariant yield of direct virtual photon and the fraction of direct virtual photon versus inclusive photon are presented. This direct photon measured by virtual photon method is called direct virtual photon. Its production in the range of1 From the direct virtual photon invariant yield spectra, a significant en-hancement compared to the prediction based on p+p results is observed for1
本文给出了位于RHIC的螺旋管径迹探测器(STAR)中直接虚光子的首次研究结果。这也是在高横动量下首次基于虚光子方法的直接光子测量。测量是基于2010年与2011年采集的每核子对质心能量200GeV的金核金核碰撞数据,给出了直接虚光子的不变产额及其与单举光子的比例。这种基于虚光子方法测量的直接光子被称为直接虚光子。在横动量区间1
数据分析结果显示直接虚光子的产额谱在低横动量区间比从质子质子碰撞结果得到的预期有明显的升高。这种升高说明了在此区间中存在物质热化的贡献。不变产额谱与理论计算得到的预期相符合,其包含QGP,强子气体(hadron gas)和原初产生的贡献。在高横动量区间,直接虚光子的产额谱符合从质子质子碰撞结果得到的预期。这说明在此区间来自于物质热辐射的贡献非常微弱。对直接虚光子的测量提供了两个动力学区间：1)可以对热化物质进行研究的低横动量区间；2)可以研究原初过程中部分子的硬散射的高横动量区间。一个与初始温度相关的逆坡度参数(inverse slope parameter)也可以从不变产额谱中得到。
The Big-Bang theory indicates that the Quark Gluon Plasma (QGP) is formed at the very universe in a few tens of microseconds. Lattic QCD predicts a phase transition from hadronic matter to this deconfined and locally thermalized matter at high temperature and low baryon density. Relativistic Heavy Ion Col-lider (RHIC) at Brookhaven National Laboratory (BNL) provides an opportunity to study this strongly coupled QGP. The research of the behavior and proper-ty of QGP is a very interesting topic for physicist. This medium is expected to emit thermal radiation which is in the form of direct photons and dileptons. As electroweak probes, which do not suffer strong interaction, direct photon and lep-ton will traverse the hot and dense medium created by heavy ion collisions with minimal interactions once they are produced. They are believed to bring the in-formation from all the evolution steps. The research on these probes will provide the most direct and pure information.
In this thesis, the first measurement on direct virtual photon from Solenoidal Tracker at RHIC (STAR) is reported. This measurement is also the first high transverse momentum(pT) result on direct photon via virtual photon method. This analysis is based on the data of sNN=200GeV Au+Au collisions taken from year2010run and year2011run (Run10and Runll). The invariant yield of direct virtual photon and the fraction of direct virtual photon versus inclusive photon are presented. This direct photon measured by virtual photon method is called direct virtual photon. Its production in the range of1
引文
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[33]Ruan L, et al. Perspectives of a Midrapidity Dimuon Program at RHIC:A Novel and Compact Muon Telescope Detector. J. Phys.,2009, G36:095001.
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[43]Agostinelli S, et al. GEANT4:A simulation toolkit. Nucl. Instrum. Meth.,2003, A506:250-303.
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[46]Tang Z, et al. Spectra and radial flow at RHIC with Tsallis statistics in a Blast-Wave description. Phys. Rev.,2009, C79:051901.
[47]Amsler C, et al. Review of particle physics. Phys. Lett.,2008, B667:1.
[48]Kroll N M, Wada W. Internal Pair Production Associated with the Emission of High-Energy Gamma Rays. Phys. Rev.,1955,98(5):1355-1359.
[49]Adams J, et al. Identified particle distributions in pp and AuAu collisions at sqrt(NN)= 200 GeV. Phys. Rev. Lett.,2004,92:112301.
[50]Abelev B I, et al. Identified baryon and meson distributions at large transverse momenta from Au +Au collisions at sSNN=200 GeV. Phys. Rev. Lett.,2006,97:152301.
[51]Adare A, et al. Detailed measurement of the e+e-pair continuum in p+p and Au+Au collisions at sNN=200 GeV and implications for direct photon production. Phys.Rev.,2010, C81:034911.
[52]STAR collaboration B H.J/ψproduction in Au+ Aucollisions at center of mass energy=200-GeV. Acta Phys. Pol. B Proc.5,471, (2012).
[53]Adams J, et al. Phi meson production in Au+ Au and p+p collisions at s**(1/2)=200-GeV. Phys. Lett.,2005, B612:181-189.
[54]Adare A, et al. J/ψ) production vs centrality, transverse momentum, and rapidity in Au+Au col-lisions at sNN=200 GeV. Phys. Rev. Lett.,2007,98:232301.
[55]Gavai R, Kharzeev D, Satz H, et al. Quarkonium production in hadronic collisions. Int.J.Mod.Phys., 1995, A10:3043-3070.
[56]Silva C L. Quarkonia measurement in p+p and d+Au collisions at s**(1/2)=200- GeV by PHENIX Detector. Nucl.Phys.,2009, A830:227C-230C.
[57]Adamczyk L, et al. Measurements of D0 and D* Production in p+p Collisions at s=200 GeV. Phys.Rev.,2012, D86:072013.
[58]Lichard P. Formalism for dilepton production via virtual photon bremsstrahlung in hadronic reac-tions. Phys. Rev. D,1995,51:6017-6035.
[59]Landsberg L G. Electromagnetic Decays of Light Mesons. Phys. Rept.,1985,128:301-376.
[60]Afanasiev S, et al. Measurement of Direct Photons in Au+Au Collisions at sNN=200 GeV. Phys.Rev.Lett.,2012,109:152302.
[61]Gordon L, Vogelsang W. Polarized and unpolarized prompt photon production beyond the leading order. Phys.Rev.,1993, D48:3136-3159.
[62]Adler S, et al. Measurement of direct photon production in p+p collisions at s**(1/2)=200-GeV. Phys.Rev.Lett.,2007,98:012002.
[63]d'Enterria D G, Peressounko D. Probing the QCD equation of state with thermal photons in nucleus-nucleus collisions at RHIC. Eur.Phys.J.,2006,C46:451-464.
[2]Gross D J, Wilczek F. Ultraviolet Behavior of Non-Abelian Gauge Theories. Phys. Rev. Lett., 1973,30:1343-1346.
[3]Politzer H D. Reliable Perturbative Results for Strong Interactions? Phys. Rev. Lett.,1973, 30:1346-1349.
[4]Gross D J, Wilczek F. Asymptotically Free Gauge Theories. I. Phys. Rev. D,1973,8:3633-3652.
[5]H, Politzer D. Asymptotic freedom:An approach to strong interactions. Physics Reports,1974, 14(4):129-180.
[6]Bethke S. The 2009 world average of as. The European Physical Journal C-Particles and Fields, 2009,64:689-703.10.1140/epjc/s10052-009-1173-1.
[7]Gupta R. Introduction to Lattice QCD.1998..
[8]Das D. Recent results from STAR experiment in Au+Au collisions at sNN=9.2 GeV.2009..
[9]Hering G. Dielectron production in heavy ion collisions at 158-GeV/c per nucleon.2001. Ph.D. Thesis (Advisor:Peter Braun-Munzinger).
[10]Pisarski R D. Phenomenology of the Chiral Phase Transition. Phys.Lett.,1982, B110:155.
[11]Rapp R, Wambach J. Chiral symmetry restoration and dileptons in relativistic heavy ion collisions. Adv.Nucl.Phys.,2000,25:1.
[12]Rapp R. Thermal lepton production in heavy ion collisions.2002..
[13]Arleo F. Hard pion and prompt photon at RHIC, from single to double inclusive production. JHEP, 2006,0609:015.
[14]Engelen J. The LHC project:Overview and status. Czech.J.Phys.,2005,55:B13-B21.
[15]Chatrchyan S, et al. The CMS experiment at the CERN LHC. JINST,2008,3:S08004.
[16]Vercellin E. The ALICE experiment:Overview and status. AIP Conf.Proc.,2009,1120:151-156.
[17]Ludlam T. Overview of experiments and detectors at RHIC. Nucl.Instrum.Meth.,2003, A499:428-432.
[18]Adcox K, et al. PHENIX detector overview. Nucl.Instrum.Meth.,2003, A499:469-479.
[19]Adare A, et al. Enhanced production of direct photons in Au+Au collisions at sNN=200 GeV and implications for the initial temperature. Phys.Rev.Lett.,2010,104:132301.
[20]Vitev I, Zhang B W. A Systematic study of direct photon production in heavy ion collisions. Phys.Lett.,2008, B669:337-344.
[21]Adare A, Adler S, Afanasiev S, et al. Direct photon production in d+Au collisions at sNN=200 GeV. Phys.Rev.,2013, C87:054907.
[22]Wilde M. Measurement of Direct Photons in pp and Pb-Pb Collisions with ALICE. Nucl.Phys., 2013, A904-905:573c-576c.
[23]Chatrchyan S, et al. Measurement of isolated photon production in pp and PbPb collisions at sNN=2.76 TeV. Phys.Lett.,2012, B710:256-277.
[24]Harrison M, Ludlam T, Ozaki S. RHIC project overview. Nucl. Instrum. Meth.,2003, A499:235-244.
[25]Ackermann K H, et al. STAR detector overview. Nucl. Instrum. Meth.,2003, A499:624-632.
[26]Bergsma F, et al. The STAR detector magnet subsystem. Nucl. Instrum. Meth.,2003, A499:633-639.
[27]Simon F, et al. The Forward GEM Tracker of STAR at RHIC.2008..
[28]Shao M, et al. Extensive particle identification with TPC and TOF at the STAR experiment. Nucl. Instrum. Meth.,2006, A558:419-429.
[29]Dong X. The time-Of-flight detector for RHIC/STAR and the related physics. AIP Conf. Proc., 2006,865:332-337.
[30]Llope W J. The large-area time-of-flight upgrade for STAR. Nucl. Instrum. Meth.,2005, B241:306-310.
[31]Beddo M, et al. The STAR barrel electromagnetic calorimeter. Nucl. Instrum. Meth.,2003, A499:725-739.
[32]Allgower C E, et al. The STAR endcap electromagnetic calorimeter. Nucl. Instrum. Meth.,2003, A499:740-750.
[33]Ruan L, et al. Perspectives of a Midrapidity Dimuon Program at RHIC:A Novel and Compact Muon Telescope Detector. J. Phys.,2009, G36:095001.
[34]Llope W, Zhou J, Nussbaum T, et al. The STAR Vertex Position Detector.2014..
[35]Anderson M, et al. The STAR time projection chamber:A unique tool for studying high multiplicity events at RHIC. Nucl. Instrum. Meth.,2003, A499:659-678.
[36]Shao M. et al. Extensive particle identification with TPC and TOF at the STAR experiment. Nucl. Instrum. Meth.,2006, A558:419-429.
[37]Xu Y c, et al. Calibration of ionization energy loss at relativistic rise with STAR Time Projection Chamber.2008..
[38]Cerron Zeballos E, Crotty I, Hatzifotiadou D, et al. A New type of resistive plate chamber:The Multigap RPC. Nucl.Instrum.Meth.,1996, A374:132-136.
[39]collaboration S. proposal for alarge area time of flight system for STAR..
[40]Adams J, et al. Experimental and theoretical challenges in the search for the quark gluon plasma: The STAR collaboration's critical assessment of the evidence from RHIC collisions. Nucl. Phys., 2005, A757:102-183.
[41]Miller M L, Reygers K, Sanders S J, et al. Glauber modeling in high energy nuclear collisions. Ann.Rev.Nucl.Part.Sci.,2007,57:205-243.
[42]Bichsel H. A method to improve tracking and particle identification in TPCs and silicon detectors. Nucl. Instrum. Meth.,2006, A562:154-197.
[43]Agostinelli S, et al. GEANT4:A simulation toolkit. Nucl. Instrum. Meth.,2003, A506:250-303.
[44]Allison J, et al. Geant4 developments and applications. IEEE Trans. Nucl. Sci.,2006,53:270.
[45]Sjostrand T, Mrenna S, Skands P. PYTHIA 6.4 physics and manual. JHEP,2006,05:026.
[46]Tang Z, et al. Spectra and radial flow at RHIC with Tsallis statistics in a Blast-Wave description. Phys. Rev.,2009, C79:051901.
[47]Amsler C, et al. Review of particle physics. Phys. Lett.,2008, B667:1.
[48]Kroll N M, Wada W. Internal Pair Production Associated with the Emission of High-Energy Gamma Rays. Phys. Rev.,1955,98(5):1355-1359.
[49]Adams J, et al. Identified particle distributions in pp and AuAu collisions at sqrt(NN)= 200 GeV. Phys. Rev. Lett.,2004,92:112301.
[50]Abelev B I, et al. Identified baryon and meson distributions at large transverse momenta from Au +Au collisions at sSNN=200 GeV. Phys. Rev. Lett.,2006,97:152301.
[51]Adare A, et al. Detailed measurement of the e+e-pair continuum in p+p and Au+Au collisions at sNN=200 GeV and implications for direct photon production. Phys.Rev.,2010, C81:034911.
[52]STAR collaboration B H.J/ψproduction in Au+ Aucollisions at center of mass energy=200-GeV. Acta Phys. Pol. B Proc.5,471, (2012).
[53]Adams J, et al. Phi meson production in Au+ Au and p+p collisions at s**(1/2)=200-GeV. Phys. Lett.,2005, B612:181-189.
[54]Adare A, et al. J/ψ) production vs centrality, transverse momentum, and rapidity in Au+Au col-lisions at sNN=200 GeV. Phys. Rev. Lett.,2007,98:232301.
[55]Gavai R, Kharzeev D, Satz H, et al. Quarkonium production in hadronic collisions. Int.J.Mod.Phys., 1995, A10:3043-3070.
[56]Silva C L. Quarkonia measurement in p+p and d+Au collisions at s**(1/2)=200- GeV by PHENIX Detector. Nucl.Phys.,2009, A830:227C-230C.
[57]Adamczyk L, et al. Measurements of D0 and D* Production in p+p Collisions at s=200 GeV. Phys.Rev.,2012, D86:072013.
[58]Lichard P. Formalism for dilepton production via virtual photon bremsstrahlung in hadronic reac-tions. Phys. Rev. D,1995,51:6017-6035.
[59]Landsberg L G. Electromagnetic Decays of Light Mesons. Phys. Rept.,1985,128:301-376.
[60]Afanasiev S, et al. Measurement of Direct Photons in Au+Au Collisions at sNN=200 GeV. Phys.Rev.Lett.,2012,109:152302.
[61]Gordon L, Vogelsang W. Polarized and unpolarized prompt photon production beyond the leading order. Phys.Rev.,1993, D48:3136-3159.
[62]Adler S, et al. Measurement of direct photon production in p+p collisions at s**(1/2)=200-GeV. Phys.Rev.Lett.,2007,98:012002.
[63]d'Enterria D G, Peressounko D. Probing the QCD equation of state with thermal photons in nucleus-nucleus collisions at RHIC. Eur.Phys.J.,2006,C46:451-464.