LHC/ALICE中的双粒子关联测量及介质效应的研究
|
摘要
在现代自然科学研究中,一项极具挑战性的研究目标是在最小尺度上探索物质的构成。一种描述基本粒子与作用力的理论标准模型,假定物质的基本结构是由夸克和轻子通过规范粒子的相互作用而组成的,认为组成物质结构的最小单元是夸克(u,d；c,s；t,b)、轻子(e,νρei；μ,νμ；τ,ντ),以及传递相互作用力的媒介子,即玻色子(W±和Z0)、胶子(g)和光子(γ)。基本作用力根据规范粒子的不同划分为电磁相互作用,弱相互作用和强相互作用。正是这些基本粒子和相互作用力构建了亚原子世界。然而,这个理论并不十分完备,因为它依然无法解释某些基本的问题,比如：基本粒子质量的起源、宇宙的真实真空、以及宇宙中物质远比反物质多的问题..
人们普遍认为,强相互作用由量子色动力学(Quantum Chromodynamics, QCD)描述。量子色动力学的重要特性是渐近自由性质,即随着相互作用的动量标度的变大,强相互作用的耦合常数(αs)趋于零。在渐近自由状态下,部分子间的相互作用是微扰的。QCD预言,在相对论重离子碰撞下,部分子可以达到这种状态,形成夸克胶子等离子体(QGP)。美国布鲁海文国家实验室(BNL)利用相对论重离子对撞机(RHIC)来寻找这种新的物质形态。位于欧洲核子研究中心(CERN)的大型强子对撞机(LHC)于2009年正式启动运行,实现了前所未有的TeV能区的高能重离子碰撞,LHC上的大型重离子对撞机实验(ALICE)合作组专门致力于高温高能量密度的极端条件下强相互作用的基本性质及其物理真空的研究。
基于量子色动力学(QCD),利用格点计算方法,人们成功地预言了夸克从禁闭的普通强子物质中退禁闭到QGP相的临界温度。实验上,该临界温度首先在CERN(?)=17.2 GeV下的SPS重离子碰撞实验中达到。进而在美国布鲁海文国家实验室(BNL)运行的质心能量(?)=60-200 GeV下的相对论重离子对撞机(RHIC)实验中,证实了从强子物质到夸克物质的相变能在高温高密条件下发生。位于欧洲核子研究中心(CERN)的大型强子对撞机LHC实现了质心能量(?)=2.76 TeV下的铅-铅碰撞,该能量高于RHIC碰撞能量的～14倍,使其在更高温度下形成的热密QCD物质持续更长时间。另外,LHC能区的重离子碰撞诱导产生的硬散射过程更加丰富,这些敏锐的硬探针将提供TeV能区下细致研究QGP性质的机会。比如,在核-核中心碰撞中高横动量强子产额的压低和背对背喷注之间的关联消失。ALICE探测器就是为了更加系统的测量核-核碰撞中产生的末态粒子,由此反映碰撞初期出现的热密物质相的性质。特别是,通过测量相空间中强子谱的改变,可以研究硬散射部分子在穿越密度物质时的能量损失效应及碎裂函数性质。在重离子碰撞中,由于喷注淬火效应,硬散射过程产生的大横动量部分子穿越密度物质时会因为多重散射而损失能量,导致高横动量的强子产额减少,低动量强子数目会增多,引起强子谱在相空间中的重新分布。因此,通过测量核环境下部分子的碎裂函数(FF),即测量部分子喷注产生的强子携带喷注动量份额z=PTh／ETjct的分布函数,将真空中的碎裂函数(质子-质子碰撞或核-核边沿碰撞中的碎裂函数)与被介质修正后的碎裂函数(核-核中心碰撞下的碎裂函数)分布进行比较,就可以推断核-核碰撞中的密度物质及其性质。
本论文主要目的是利用光子-强子的关联测量来研究部分子的碎裂函数,即通过测量高能直接光子与散射到光子背面强子之间的关联来研究喷注的碎裂函数。高能直接光子在碰撞初期的硬散射过程中直接产生,主要来自康普顿散射(qg→γq)和湮灭过程(qq→γg)。由于光子的平均自由程很大,在碰撞区域内与其他粒子只有电磁相互作用,因此光子携带了它们初始产生时刻的信息。而与该光子产生于同一硬散射过程的部分子会碎裂为末态强子,通过对强子的测量,就能获得部分子在穿越密度物质后的信息。将产生于同一事件中的光子和强子关联,我们就能得到密度物质作用于部分子喷注上的效应。我选择了高横动量的喷注作为对介质作断层扫描的探针：观测量是高动量直接光子与在其相反方向上的强子的关联。在这一测量中，直接光子标记了同样作为在初始碰撞中硬过程产生的部分子的初始能量,而强子,作为该部分子碎裂出的末态粒子,描述了穿越介质的部分子的属性。通过比较这两种碰撞系统下的光子-强子关联测量,我们可以得到介质效应对末态运动学和喷注碎裂的修正。然而,在碰撞中来自强子和中性介子(主要是π0和η)的衰变光子是直接光子信号提取过程中的主要背景,因此光子信号的提取在本工作中显得至关重要。
本论文着重开展如下两方面的工作。第一部分是关于光子测量,鉴别效率以及直接光子的提取研究,估计来自衰变光子误判引起的系统误差,并研究利用光子—强子关联及强子—强子关联方法在ALICE实验中测量的可行性。利用Monte-Carlo模拟数据,我们研究了ALICE实验中电磁量能器(PHOS和EMCAL)在探测和鉴别光子时的性能表现。由于有限的接受度,在碰撞过程中产生的某些光子落在探测器边缘使得沉积在晶体上的能量不能获得完整的重建,这些光子将不能被正确探测到。同时,光子在穿越位于量能器之前的其它探测器时与探测器物质发生相互作用而使光子转换成正负电子对(γ→e+e-)。模拟结果表明,不同探测器对光子探测效率的影响程度不-样。例如,光子在时间投影室(TPC)和内部径迹系统(ITS)的转换几率约为10%,而在跃迁辐射探测器(TRD)和时间飞行探测器(TOF)中的转换几率接近20%。本文首先报告了在LHC能区中的质子-质子和铅-铅碰撞过程中利用ALICE实验探测器通过直接光子-强子关联测量的方法研究喷注碎裂函数和介质效应的可行性。光子-强子关联测量在质子-质子碰撞中是必须的,因为该测量能够为我们提供有关重离子碰撞下的关联测量的基线参考。我研究了介质可能引起的一系列效应。对于第一个相关的参数就是kT,即部分子层次上的有效横动量。基于国际上己有的实验数据测量值,我们将其延伸外推到LHC能区,从而预测LHC能区上的kT值。本文估计了光子-强子关联测量对于高温热密物质的敏感度及光子-强子关联函数的重新分布,从而提取热密物质的性质。另外,我还通过光子-喷注产生机制研究了喷注在穿越热密物质里产生的过程进行层析结构分析。
该工作的第二部分,主要聚焦在LHC于2010年首次运行的质子-质子碰撞下质心能量(?)=7TeV下的ALICE数据分析工作。该工作从真实数据入手,采用我们在前面已经建立的可行性研究方法,旨在测量质子-质子碰撞下的喷注碎裂函数,为铅-铅数据分析提供基线测量。鉴于当前ALICE有限的统计量和不完整的电磁量能器接收度,本工作的测量集中在小于20GeV/c的横动量区域进行,由于在该横动量范围内大量来自衰变光子的背景贡献使得该测量在此区间特别具有难度和挑战性。由于当前探测器的校准工作依然在进行之中,我无法利用粒子鉴别的方法来区分光子和π0作为触发粒子,而是直接利用在量能器上形成的电磁簇射团簇和利用不变质量方法重建出的π0作为触发粒子进行两粒子关联。而后对触发粒子进行孤立截断的判选,从而提高直接瞬时光子数据样本的机率。双喷注结构与单光子/π0-喷注的运动学结构通过以上研究观测到。同时,利用孤立光子-强子的方位角关联我们提取了部分子层次上的横动量kT值,该测量值与我之前利用蒙特卡罗数据预言的kT结果一致,更进一步,我尝试了构建20GeV以下的喷注在质子-质子(?)=7TcV下的碎裂函数。但展开实际数据分析的时间之短让我无法对该项研究进入到更深的地步。
对于在2010年底LHC首次运行铅-铅碰撞下的质心能量(?)=2.76 TeV下的数据,我做了同样的数据分析,但时间之仓促不允许我将该数据分析部分纳入该论文之中。鉴于电磁量能器覆盖范围的增加以及高横动量光子触发判选能力的实现,2011,2012年LHC运行获取的数据无疑会提供更大的统计量,让该项研究的有效测量范围达到更高,从而获得更多有趣的物理现象和物理结果。
最后,为了论文的完整性,对于我在博士期间对于整个ALICE实验合作组中的主要贡献简要概括如下：
利用光子-强子关联测量的可行性研究。该项可行性研究是本人硕士论文的延续,我在硕士论文研究出的测量和分析方法基础之上,发展和延伸了该观测量对于核核碰撞下形成的热密物质的敏感度。通过各项细致研究,总结出利用光子-强子关联方法测量介质效应是敏感而且有效的,我们甚至可以通过该关联测量提取部分子层次上的运动学量kT,并对形成的热密物质介质本身进行层析扫描。这些研究结果均在ALICE国际合作组中广泛讨论并得到认同,并在大型国际学术会议上报告。
·EMCal探测器校准工作。为了获得一个较好的能量和位置分辨率,我参加了在格勒诺布尔利用宇宙射线和在CERN利用高能电子束流对EMCal探测器进行校准的工作。
EMCal在线数据质量监控(DQM)。为了检测在数据获取过程中的探测器质量,自LHC准备运行以来,我担任了EMCal探测器数据质量检测的任务,并开发和提供了数据检测的软件工具并且保持维护和更新。还开发了数据监控的算法和质量检测的标准,并将其补充到ALICE数据获取系统的在线数据监测框架之下。
电磁量能器EMCal和PHOS的离线数据监测和质量认证(QA)。我负责运行每周从LHC上取得的ALICE数据,对量能器的离线数据质量检验,并将质量检验结果在每周ALICE数据质量检验和数据分析会议-上报告,为实验合作组的量能器数据物理分析提供有效数据库。
中性介子和光子-强子关联的数据分析工作。自2009年LHC开始采集数据以来,我一直致力于探测器的校准和实验数据的分析工作(数据分析现在依然进行之中)。其中包括π0的重建,以及光子-强子的关联测量。我被相应的ALICE物理工作组推选为光子/π0-强子关联测量的数据分析协调人,每周召集两次课题讨论会,并定期在ALICE合作组内报告工作进展。
With the advent of the Large Hadron Collider (LHC) end of 2009, the new accelerator at CERN collides protons and heavy-ions at unprecedented high energies. ALICE, one of the major exper-iment installed at LHC, is dedicated to the study of nuclear matter under extreme conditions of energy density with the opportunity of creating a partonic medium called the Quark-Gluon-Plasma (QGP). This new experimental facility opens new avenues for the understanding of fundamental properties of the strong interaction and its vacuum.
The reach the objectives of this scientific program, it is required to select a set of appropriate probes carrying relevant information on the properties of the medium created in ultra-relativistic heavy-ion collisions. Based on the information delivered by all the observables and guided by modelization of the fundamental principles in action, a coherent picture will emerge to interpret the observed phenomena. In the first part of the present document I describe the context of the scientific program, the general concepts involved in heavy-ion collisions at ultra relativistic energies, and the main results obtained so far in the field.
Among the observables of interest, the production of hadrons jets is particularly attractive. Jets are the result of the hadronisation process of high transverse momentum partons and are observed in the detectors as a beam of collimated hadrons. High transverse momentum partons are created by hard scattering of partons (2→2 type of processes) constituting the colliding projectiles. The jet structure measured, for example as the distribution of the factional jet energy carried by the individual hadrons inside the jet, is the observable of choice. In heavy ion collisions, high transverse momentum partons are created concurrently with the hot and dense medium of interest and their kinematical properties are modified as they traverse the medium. This modification, imprinted in the jet structure, is observed by comparing the jet structure measured in heavy-ion collisions (in medium jet structure) with the jet structure measured in proton-proton collisions (vacuum jet structure). Such a measurement raises however a technical difficulty:whereas jets can be easily identified and measured in proton-proton collisions, in heavy-ion collisions the large hadronic background from the underlying event (the underlying event is everything except the two hard scattered jets and is generated by the beams particle break up and by initial and final state radiation) makes the jet identification measurement quite challenging. In addition the initial momentum of the hard scattered parton is unknown since only the final jet momentum can be measured i.e. the momentum of the parton as it emerges from the medium. This complicates the interpretation of the measurement.
To overcome these difficulties, I have selected a particular 2→2 process which creates a direct photon (direct photon at variance with decay photon) in the final state together with a high transverse momentum parton. The momentum of the photon ((?)), since it does not interact strongly with the medium, calibrates the momentum of the parton((?)=-(?)).Therefore the photon momentum is a measure of the parton momentum when created and the jet momentum the momentum of the parton after it has traversed the medium. In addition since the photon momentum (energy and direction) defines also the jet momentum, jet reconstruction algorithms are not required anymore. Instead of studying photon-jet correlations (where the jet is fully reconstructed), it is sufficient to study photon-hadron correlations from all the hadrons in the event. However, the relatively weak cross section for the production of these particular hard scattering processes makes the measurement quite challenging. An introduction to 2 particle correlations is given in the second part of this document followed by a description of the ALICE detection systems used for this measurement.
The strategy I have followed for this study starts with a validation of the measurement. It consists first in studying with the help of Monte Carlo simulations the accuracy of the selected ob-servable in revealing and quantifying the phenomenon under study. Second, it consists in verifying the ability to measure the observable and its robustness with the detectors setup of the ALICE experiment. The validation procedure and results are discussed in the third part of this document. I have particularly studied the possibility to extract two quantities from the 2 particle azimuthal correlation measured in proton-proton collisions:(ⅰ) the average total transverse momentum () generated at the partonic level by the Fermi motion and initial and final state radiation, and (ⅱ) the per trigger yield of jet hadrons as a function of the fractional jet energy(xE) they carry each (correlation function). The same quantities have been studied from simulated heavy-ion collisions with the objective to analyze the effects due to the presence of highly dense color medium. The distribution of kT values becomes broader in a way that can be directly related to the transport properties of the medium and the correlation function is modified so that the number of high xE hadrons are suppressed (jet quenching) and the number of low xE hadrons is increased (radiative gluon production) with an amplitude proportional to the transport coefficient and to distance tra-versed inside the medium. To finish this part of the document dedicated to Monte Carlo studies (on which I have spent most of my time as a PhD student) with another detailed study n the possibility to exploit the photon-jet observable as a tomographic tool (following a suggestion by X.N. Wang). The idea is to localize the hard scattering well inside the medium (by selecting hadrons with low xE values) or on the surface of the medium (by selecting hadrons with large xE values). One would therefore choose the distance in the medium through which the hard scattered parton travels and probe the medium from its densest part (center) to its less dense part (surface). I found that such a measurement will be quite challenging.
In the forth part of the present document, I address the analysis of the data collected in 2010 for proton-proton collisions at (?)= 7 TcV. During this first long data taking period at LHC, the ALICE detection system was not yet complete. In particular, the incomplete coverage of the electromagnetic calorimeters and the absence of a selective photon trigger was a severe handicap for the photon-jet measurement. The resulting event statistics available for the measurement of this observable was limited to the photon energy range-below 10 GeV. This low energy domain is not well suited for the identification of direct photons because of their scarcity in the overwhelming background generated by decay photons. On top of that, the time between the availability of the data and the scheduled time for my defense was too short to perform an in-depth analysis. Most of the results presented from this analysis in the present document must therefore to be considered as very preliminary, but the key features are there. The results concern the 2 jet and mono jet structure observed in the photon-jet azimuthal correlation, the measured value of (kT) and the xE distributions.
This very preliminary analysis of the first data collected at LHC and presented in this document is the first only toward a comprehensive study of the photon-jet observable. Since the writing of the document, the analysis has progressed and provided a few results which were considered ripe by the collaboration to be presented at the Quark Matter conference in May 2011. The data which will be collected in 2011 in proton-proton and Pb-Pb collisions will be much richer in photon-jet events thanks to the complete coverage of the ALICE electromagnetic calorimeter and thansk to a very high energy photon trigger provided by the calorimeter as well.
For completeness, I finish the present document with the description of my contribution, as the main person in charge, to the quality assurance and monitoring tasks for the two ALICE electromagnetic calorimeters during data taking.
人们普遍认为,强相互作用由量子色动力学(Quantum Chromodynamics, QCD)描述。量子色动力学的重要特性是渐近自由性质,即随着相互作用的动量标度的变大,强相互作用的耦合常数(αs)趋于零。在渐近自由状态下,部分子间的相互作用是微扰的。QCD预言,在相对论重离子碰撞下,部分子可以达到这种状态,形成夸克胶子等离子体(QGP)。美国布鲁海文国家实验室(BNL)利用相对论重离子对撞机(RHIC)来寻找这种新的物质形态。位于欧洲核子研究中心(CERN)的大型强子对撞机(LHC)于2009年正式启动运行,实现了前所未有的TeV能区的高能重离子碰撞,LHC上的大型重离子对撞机实验(ALICE)合作组专门致力于高温高能量密度的极端条件下强相互作用的基本性质及其物理真空的研究。
基于量子色动力学(QCD),利用格点计算方法,人们成功地预言了夸克从禁闭的普通强子物质中退禁闭到QGP相的临界温度。实验上,该临界温度首先在CERN(?)=17.2 GeV下的SPS重离子碰撞实验中达到。进而在美国布鲁海文国家实验室(BNL)运行的质心能量(?)=60-200 GeV下的相对论重离子对撞机(RHIC)实验中,证实了从强子物质到夸克物质的相变能在高温高密条件下发生。位于欧洲核子研究中心(CERN)的大型强子对撞机LHC实现了质心能量(?)=2.76 TeV下的铅-铅碰撞,该能量高于RHIC碰撞能量的～14倍,使其在更高温度下形成的热密QCD物质持续更长时间。另外,LHC能区的重离子碰撞诱导产生的硬散射过程更加丰富,这些敏锐的硬探针将提供TeV能区下细致研究QGP性质的机会。比如,在核-核中心碰撞中高横动量强子产额的压低和背对背喷注之间的关联消失。ALICE探测器就是为了更加系统的测量核-核碰撞中产生的末态粒子,由此反映碰撞初期出现的热密物质相的性质。特别是,通过测量相空间中强子谱的改变,可以研究硬散射部分子在穿越密度物质时的能量损失效应及碎裂函数性质。在重离子碰撞中,由于喷注淬火效应,硬散射过程产生的大横动量部分子穿越密度物质时会因为多重散射而损失能量,导致高横动量的强子产额减少,低动量强子数目会增多,引起强子谱在相空间中的重新分布。因此,通过测量核环境下部分子的碎裂函数(FF),即测量部分子喷注产生的强子携带喷注动量份额z=PTh／ETjct的分布函数,将真空中的碎裂函数(质子-质子碰撞或核-核边沿碰撞中的碎裂函数)与被介质修正后的碎裂函数(核-核中心碰撞下的碎裂函数)分布进行比较,就可以推断核-核碰撞中的密度物质及其性质。
本论文主要目的是利用光子-强子的关联测量来研究部分子的碎裂函数,即通过测量高能直接光子与散射到光子背面强子之间的关联来研究喷注的碎裂函数。高能直接光子在碰撞初期的硬散射过程中直接产生,主要来自康普顿散射(qg→γq)和湮灭过程(qq→γg)。由于光子的平均自由程很大,在碰撞区域内与其他粒子只有电磁相互作用,因此光子携带了它们初始产生时刻的信息。而与该光子产生于同一硬散射过程的部分子会碎裂为末态强子,通过对强子的测量,就能获得部分子在穿越密度物质后的信息。将产生于同一事件中的光子和强子关联,我们就能得到密度物质作用于部分子喷注上的效应。我选择了高横动量的喷注作为对介质作断层扫描的探针：观测量是高动量直接光子与在其相反方向上的强子的关联。在这一测量中，直接光子标记了同样作为在初始碰撞中硬过程产生的部分子的初始能量,而强子,作为该部分子碎裂出的末态粒子,描述了穿越介质的部分子的属性。通过比较这两种碰撞系统下的光子-强子关联测量,我们可以得到介质效应对末态运动学和喷注碎裂的修正。然而,在碰撞中来自强子和中性介子(主要是π0和η)的衰变光子是直接光子信号提取过程中的主要背景,因此光子信号的提取在本工作中显得至关重要。
本论文着重开展如下两方面的工作。第一部分是关于光子测量,鉴别效率以及直接光子的提取研究,估计来自衰变光子误判引起的系统误差,并研究利用光子—强子关联及强子—强子关联方法在ALICE实验中测量的可行性。利用Monte-Carlo模拟数据,我们研究了ALICE实验中电磁量能器(PHOS和EMCAL)在探测和鉴别光子时的性能表现。由于有限的接受度,在碰撞过程中产生的某些光子落在探测器边缘使得沉积在晶体上的能量不能获得完整的重建,这些光子将不能被正确探测到。同时,光子在穿越位于量能器之前的其它探测器时与探测器物质发生相互作用而使光子转换成正负电子对(γ→e+e-)。模拟结果表明,不同探测器对光子探测效率的影响程度不-样。例如,光子在时间投影室(TPC)和内部径迹系统(ITS)的转换几率约为10%,而在跃迁辐射探测器(TRD)和时间飞行探测器(TOF)中的转换几率接近20%。本文首先报告了在LHC能区中的质子-质子和铅-铅碰撞过程中利用ALICE实验探测器通过直接光子-强子关联测量的方法研究喷注碎裂函数和介质效应的可行性。光子-强子关联测量在质子-质子碰撞中是必须的,因为该测量能够为我们提供有关重离子碰撞下的关联测量的基线参考。我研究了介质可能引起的一系列效应。对于第一个相关的参数就是kT,即部分子层次上的有效横动量。基于国际上己有的实验数据测量值,我们将其延伸外推到LHC能区,从而预测LHC能区上的kT值。本文估计了光子-强子关联测量对于高温热密物质的敏感度及光子-强子关联函数的重新分布,从而提取热密物质的性质。另外,我还通过光子-喷注产生机制研究了喷注在穿越热密物质里产生的过程进行层析结构分析。
该工作的第二部分,主要聚焦在LHC于2010年首次运行的质子-质子碰撞下质心能量(?)=7TeV下的ALICE数据分析工作。该工作从真实数据入手,采用我们在前面已经建立的可行性研究方法,旨在测量质子-质子碰撞下的喷注碎裂函数,为铅-铅数据分析提供基线测量。鉴于当前ALICE有限的统计量和不完整的电磁量能器接收度,本工作的测量集中在小于20GeV/c的横动量区域进行,由于在该横动量范围内大量来自衰变光子的背景贡献使得该测量在此区间特别具有难度和挑战性。由于当前探测器的校准工作依然在进行之中,我无法利用粒子鉴别的方法来区分光子和π0作为触发粒子,而是直接利用在量能器上形成的电磁簇射团簇和利用不变质量方法重建出的π0作为触发粒子进行两粒子关联。而后对触发粒子进行孤立截断的判选,从而提高直接瞬时光子数据样本的机率。双喷注结构与单光子/π0-喷注的运动学结构通过以上研究观测到。同时,利用孤立光子-强子的方位角关联我们提取了部分子层次上的横动量kT值,该测量值与我之前利用蒙特卡罗数据预言的kT结果一致,更进一步,我尝试了构建20GeV以下的喷注在质子-质子(?)=7TcV下的碎裂函数。但展开实际数据分析的时间之短让我无法对该项研究进入到更深的地步。
对于在2010年底LHC首次运行铅-铅碰撞下的质心能量(?)=2.76 TeV下的数据,我做了同样的数据分析,但时间之仓促不允许我将该数据分析部分纳入该论文之中。鉴于电磁量能器覆盖范围的增加以及高横动量光子触发判选能力的实现,2011,2012年LHC运行获取的数据无疑会提供更大的统计量,让该项研究的有效测量范围达到更高,从而获得更多有趣的物理现象和物理结果。
最后,为了论文的完整性,对于我在博士期间对于整个ALICE实验合作组中的主要贡献简要概括如下：
利用光子-强子关联测量的可行性研究。该项可行性研究是本人硕士论文的延续,我在硕士论文研究出的测量和分析方法基础之上,发展和延伸了该观测量对于核核碰撞下形成的热密物质的敏感度。通过各项细致研究,总结出利用光子-强子关联方法测量介质效应是敏感而且有效的,我们甚至可以通过该关联测量提取部分子层次上的运动学量kT,并对形成的热密物质介质本身进行层析扫描。这些研究结果均在ALICE国际合作组中广泛讨论并得到认同,并在大型国际学术会议上报告。
·EMCal探测器校准工作。为了获得一个较好的能量和位置分辨率,我参加了在格勒诺布尔利用宇宙射线和在CERN利用高能电子束流对EMCal探测器进行校准的工作。
EMCal在线数据质量监控(DQM)。为了检测在数据获取过程中的探测器质量,自LHC准备运行以来,我担任了EMCal探测器数据质量检测的任务,并开发和提供了数据检测的软件工具并且保持维护和更新。还开发了数据监控的算法和质量检测的标准,并将其补充到ALICE数据获取系统的在线数据监测框架之下。
电磁量能器EMCal和PHOS的离线数据监测和质量认证(QA)。我负责运行每周从LHC上取得的ALICE数据,对量能器的离线数据质量检验,并将质量检验结果在每周ALICE数据质量检验和数据分析会议-上报告,为实验合作组的量能器数据物理分析提供有效数据库。
中性介子和光子-强子关联的数据分析工作。自2009年LHC开始采集数据以来,我一直致力于探测器的校准和实验数据的分析工作(数据分析现在依然进行之中)。其中包括π0的重建,以及光子-强子的关联测量。我被相应的ALICE物理工作组推选为光子/π0-强子关联测量的数据分析协调人,每周召集两次课题讨论会,并定期在ALICE合作组内报告工作进展。
With the advent of the Large Hadron Collider (LHC) end of 2009, the new accelerator at CERN collides protons and heavy-ions at unprecedented high energies. ALICE, one of the major exper-iment installed at LHC, is dedicated to the study of nuclear matter under extreme conditions of energy density with the opportunity of creating a partonic medium called the Quark-Gluon-Plasma (QGP). This new experimental facility opens new avenues for the understanding of fundamental properties of the strong interaction and its vacuum.
The reach the objectives of this scientific program, it is required to select a set of appropriate probes carrying relevant information on the properties of the medium created in ultra-relativistic heavy-ion collisions. Based on the information delivered by all the observables and guided by modelization of the fundamental principles in action, a coherent picture will emerge to interpret the observed phenomena. In the first part of the present document I describe the context of the scientific program, the general concepts involved in heavy-ion collisions at ultra relativistic energies, and the main results obtained so far in the field.
Among the observables of interest, the production of hadrons jets is particularly attractive. Jets are the result of the hadronisation process of high transverse momentum partons and are observed in the detectors as a beam of collimated hadrons. High transverse momentum partons are created by hard scattering of partons (2→2 type of processes) constituting the colliding projectiles. The jet structure measured, for example as the distribution of the factional jet energy carried by the individual hadrons inside the jet, is the observable of choice. In heavy ion collisions, high transverse momentum partons are created concurrently with the hot and dense medium of interest and their kinematical properties are modified as they traverse the medium. This modification, imprinted in the jet structure, is observed by comparing the jet structure measured in heavy-ion collisions (in medium jet structure) with the jet structure measured in proton-proton collisions (vacuum jet structure). Such a measurement raises however a technical difficulty:whereas jets can be easily identified and measured in proton-proton collisions, in heavy-ion collisions the large hadronic background from the underlying event (the underlying event is everything except the two hard scattered jets and is generated by the beams particle break up and by initial and final state radiation) makes the jet identification measurement quite challenging. In addition the initial momentum of the hard scattered parton is unknown since only the final jet momentum can be measured i.e. the momentum of the parton as it emerges from the medium. This complicates the interpretation of the measurement.
To overcome these difficulties, I have selected a particular 2→2 process which creates a direct photon (direct photon at variance with decay photon) in the final state together with a high transverse momentum parton. The momentum of the photon ((?)), since it does not interact strongly with the medium, calibrates the momentum of the parton((?)=-(?)).Therefore the photon momentum is a measure of the parton momentum when created and the jet momentum the momentum of the parton after it has traversed the medium. In addition since the photon momentum (energy and direction) defines also the jet momentum, jet reconstruction algorithms are not required anymore. Instead of studying photon-jet correlations (where the jet is fully reconstructed), it is sufficient to study photon-hadron correlations from all the hadrons in the event. However, the relatively weak cross section for the production of these particular hard scattering processes makes the measurement quite challenging. An introduction to 2 particle correlations is given in the second part of this document followed by a description of the ALICE detection systems used for this measurement.
The strategy I have followed for this study starts with a validation of the measurement. It consists first in studying with the help of Monte Carlo simulations the accuracy of the selected ob-servable in revealing and quantifying the phenomenon under study. Second, it consists in verifying the ability to measure the observable and its robustness with the detectors setup of the ALICE experiment. The validation procedure and results are discussed in the third part of this document. I have particularly studied the possibility to extract two quantities from the 2 particle azimuthal correlation measured in proton-proton collisions:(ⅰ) the average total transverse momentum (
In the forth part of the present document, I address the analysis of the data collected in 2010 for proton-proton collisions at (?)= 7 TcV. During this first long data taking period at LHC, the ALICE detection system was not yet complete. In particular, the incomplete coverage of the electromagnetic calorimeters and the absence of a selective photon trigger was a severe handicap for the photon-jet measurement. The resulting event statistics available for the measurement of this observable was limited to the photon energy range-below 10 GeV. This low energy domain is not well suited for the identification of direct photons because of their scarcity in the overwhelming background generated by decay photons. On top of that, the time between the availability of the data and the scheduled time for my defense was too short to perform an in-depth analysis. Most of the results presented from this analysis in the present document must therefore to be considered as very preliminary, but the key features are there. The results concern the 2 jet and mono jet structure observed in the photon-jet azimuthal correlation, the measured value of (kT) and the xE distributions.
This very preliminary analysis of the first data collected at LHC and presented in this document is the first only toward a comprehensive study of the photon-jet observable. Since the writing of the document, the analysis has progressed and provided a few results which were considered ripe by the collaboration to be presented at the Quark Matter conference in May 2011. The data which will be collected in 2011 in proton-proton and Pb-Pb collisions will be much richer in photon-jet events thanks to the complete coverage of the ALICE electromagnetic calorimeter and thansk to a very high energy photon trigger provided by the calorimeter as well.
For completeness, I finish the present document with the description of my contribution, as the main person in charge, to the quality assurance and monitoring tasks for the two ALICE electromagnetic calorimeters during data taking.
引文
[1]M. J. Herrero, The standard model (1998). hep-ph/9812242. Lectures presentated at the NATO ASI 98 School, Techniques and Concepts of High Energy Physics; St. Croix, Virgin Islands, USA, June 18-29.
[2]V. Barger, R. Phillips Collider Physics (1997) ISBN 0201149451.
[3]S. F. Novaes, standard model:An introduction (2000). hep-ph/0001283. Published in "Particle and Fields".
[4]G. Dissertori, I. Knowles, and M. Schmelling, Quantum Chromodynamics-High Energy Experiments and Theory. Oxford University Press,2003.
[5]Feynman, Richard Phillips (1998). Quantum Electrodynamics. Westview Press; New Ed edition. ISBN 978-0201360752
[6]B. Jager, A. Schafer, et al., Phys. Rev. D67 (2003) 054005.
[7]D. J. Gross and F. Wilczek, Phys. Rev. Lett.30 (1973) 1343.
[8]E. V. Shuryak, Phys. Rep.61 (1980) 71.
[9]S. Hands, Contemp. Phys.42 (2001) 209.
[10]R. J. Fries and B. Muller, Eur. Phys. J. C34 (2004) S279.
[11]T. D. Lee, in Proceedings of the XVII International Conference on High Energy Physics, 1974.
[12]U. W. Heinz and M. Jacob, arXiv:nucl-th/0002042.
[13]RHIC, URL http://www.bul.gov/rhic. BNL, URL http://www.bnl.gov/.
[14]http://www.bnl.gov/rhic/news2/news.asp?a=05-38&t=pr.
[15]L. Evans and P. Bryant, JINST 3 (2008) S08001.
[16]S. Grinstein, PhD thesis:The Inclusive Jet Cross Section using the kT Algorithm (2003).
[17]Y. X. Mao et al., ALICE-INT-2007-021, Euro. Phys. J. C 57 (2008) 613.
[18]Y. X. Mao et al., ALICE-INT-2007-017, Chinese Physics C 32(07) (2008).
[19]Time Magazine (1957), http://www.lbl.gov/Science-Articles/Research-Review/Magazine/1997-fall/contents.html.
[20]U. Yves, http://www-subatech.in2p3.fr/photons/subatech/physics/potpourri/physics.html.
[21]J. D. Bjorken, Phys. Rev. D27 (1983) 140.
[22]K. Miki, PhD thesis:Azimuthal Anisotropy Measurement of Neutral Pion and Direct Photon in (?)=200 GeV Au+Au collisions at RHIC-PHENIX (2009).
[23]Z. Yin, Ph. D. Thesis:High pT physics in heavy ion collisions at (?)=200 GeV (2004).
[24]R. Glauber and G. Matthias, Nucl. Phys. B21 (1970) 135. T. Wibig and D. Sobezynska, J. Phys. G:Nucl. Part. Pyhs.24 (1998) 2037.
[25]A. Kiyomichi, PhD thesis:Study of identified hadron spectra and yields at mid-rapidity in Au+Au collisions at (?)=200 GeV (2005).
[26]P. Braun-Munzinger, D. Magestro, K. Redlich and J. Stahel, Phys. Lett. B 518 (2001) 41.
[27]Yu. L. Dokshitzer, Sov. Phys. JETP 46 (1977) 416; V. N. Gribov and L. P. Lipatov, Sov. J. Nucl. Phys.15 (1972) 438; G. Altarelli and G. Parisi, Nucl. Phys. B 126 (1977) 298.
[28]M. Gluck, E. Reya and A. Vogt, Z. Phys. C 67 (1995) 433.
[29]G. Sterman et al., CTEQ Collaboration, Rev. Mod. Phys.67 (1995) 157.
[30]J. Pumplin et al., JHEP,07 (2002) 012.
[31]J. Binnewies, B. A. Kniehl and G. Kramer, Phys. Rev. D 52 (1995) 4947.
[32]P. Aurenche, et al., Euro. Phys. J. C 13 (2000) 347.
[33]B. A. Knirhl, G. Kramer and B. Potter, Nucl. Phys. B 597 (2001) 337.
[34]J. W. Cronin et al., Phys. Rev. D11 (1975) 3105.
[35]J. J. Aubert et al., Phys. Lett. B123 (1983) 275.
[36]M. Arneodo et al., Nucl. Phys. B441 (1995) 12-30.
[37]Y. X. Mao, W. C. Xiang and D. C. Zhou, International Journal Modern Physics E, Vol.16, Nos.7-8 (2007) 2130. J. Liu, Y. X. Mao, W. C. Xiang and D. C. Zhou, Chinese Science Bulletin Vol.51,No.2 (2006) 139. D. C. Zhou, W. C. Xiang and Y. X. Mao, Journal of Central China Normal University (Natural Sciences) 39 (2005) 482.
[38]X. N. Wang and M. Gyulassy, Phys. Rev. Lett 68 (1992) 1480. M. Gyulassy and X. N. Wang, Nucl. Phys. B420 (1994) 583. X. N. Wang, Phys. Lett. B579 (2004) 299 nucl-th/0307036.
[39]M. Gyulassy, P. Levai and I. Vitev, Phys. Lett. B 538 (2002) 282.
[40]R. Baier, Y. L. Dokshitzer, S. Peigne and D. Schiff, Phys. Lett. B 345 (1995) 277.
[41]R. Baier, D. Schiff and B. G. Zakharov, Ann. Rev. Nucl. Part. Sci 50 (2000) 37.
[42]K. Aamodt, et al., ALICE Collaboration, Phys. Rev. Lett.105 (2010) 252301.
[43]M. C. Abreu, et al., NA50 Collaboration, Phys. Lett. B 530 (2002) 43.
[44]C. Adler, et al., STAR Collaboration, Phys. Rev. Lett 87 (2001) 112303.
[45]I. G. Bearden, et al., BRAHMS Collaboration, Phys. Rev. Lett.88 (2002) 202301.
[46]K. Adcox, et al., PHENIX Collaboration, Phys. Rev. Lett.88 (2001) 3500.
[47]B.B.Back, et al., PHOBOS Collaboration, Phys. Rev. Lett.87 (2001) 102303.
[48]K. Aamodt, et al., ALICE Collaboration, Euro. Phys. J. C 68 (2010) 89.
[49]V. Khachatryan, et al., CMS Collaboration, JHEP 02 (2010) 041.
[50]R. Hanbury Brown and R. Q. Twiss, Nature (London) 178 (1956) 1046.
[51]A.N. Makhlin, Y. M. Sinyukov, Z. Phys. C 39 (1988) 69.
[52]K. Aamodt, et al., ALICE Collaboration, Phys. Lett. B 696 (2011) 328.
[53]M. A. Lisa, et. al., E895 Collaboration, Phys. Rev. Lett.84 (2000) 2798.
[54]C. Alt, et. al., NA49 Collaboration, Phys. Rev. C 66 (2008) 064908.
[55]D. Adamova, et.al., CERES Collaboration, Nucl. Phys. A 714 (2003) 124.
[56]B.I. Abelev, et al., STAR Collaboration, Phys. Rev. C 80 (2009) 024905.
[57]B.B.Back, et al., PHOBOS Collaboration, Phys. Rev. C.73 (2006) 031901.
[58]H. sorge, Phys. Rev. Lett.82 (1999) 2048.
[59]K. Aamodt, et al., ALICE Collaboration, Phys. Rev. Lett.105 (2010) 252302.
[60]Y. Bai, PhD thesis, Nikhef and Utrecht University (2007).
[61]B. I. Abelev et al., STAR Collaboration, Phys. Rev. C 77 (2008) 054901.
[62]A. Adare, et al., PHENIX Collaboration, Phys. Rev. Lett.98 (2007) 162301.
[63]S. M. Dogra, PhD thesis:Particle Production and Correlations in Ultra-Rrelativeistic Nucleus-Nucleus Collisions (2008).
[64]K. Aamodt, et al., ALICE Collaboration, Phys. Lett. B 696 (2011) 30.
[65]S.S. Adler, et al., PHENIX Collaboration, Phys. Rev. C.69 (2004) 034910.
[66]J. Adams et al., STAR Collaboration, Phys. Rev. Lett.91 (2003) 172302.
[67]J. Adams et al., STAR Collaboration, Phys. Rev. Lett.91 (2003) 072302.
[68]D. Magestro, Nucl. Phys. A 774 (2006) 573.
[69]http://xxx.lanl.gov/pdf/nucl-th/0610051.
[70]R. Feynman, R. Field and G. Fox, Nucl. Phys. B128 (1977) 1.
[71]S. S. Adler et al., PHENIX Collaboration, Phys. Rev. D74 (2006) 072002.
[72]L. Apanascvich, et. al., Phys. Rev. D 59 (1999) 074007.
[73]R. Baier, Y. L. Dokshitzer, S. Peigne and D. Schiff, Phys. Lett. B 345 (1995) 277.
[74]T. Horaguchi, Ph. D. Thesis:Prompt Photon Production in Proton-Proton Collitions at (?)=200 GeV (2005).
[75]E. V. Shuryak, Sov. J. Nucl. Phys.28 (1978) 408.
[76]R. J. Fries, B. Muller and D. K. Srivastava, Phys. Rev. Lett.90 (2003) 132301.
[77]M. M. Aggarwal et al., (WA98 Collaboration), Phys. Rev. Lett.85 (2000) 3595.
[78]S. Turbide, R. Rapp and C. Gale, Phys. Rev. D56 (2004) 014903.
[79]S. S. Adler et al., (PHENIX Collaboration), Phys. Rev. Lett.94 (2005) 232301.
[80]L. E. Gordon and W. Vogelsang, Phys. Rev. D (1993) 3136.
[81]A. Adare, et al., PHENIX Collaboration, Phys. Rev. Lett.104 (2010) 132301.
[82]X. N. Wang, Z. Huang and I. Sarcevic, Phys. Rev. Lett.77 (1996) 231.
[83]F. Arleo, J. Phys. G:Nuclear and Particle Physics,34,8 (2007) S1037. F. Arleo, P. Aurenche, Z, Belghobsi, J.-P. Guillet, JHEP 11 (2004) 009. F. Arleo, JHEP 09 (2006) 015.
[84]M. Nguyen, PhD thesis:Two particle correlations with direct photon and π0 triggers in 200 GeV p+p and Au+Au collisions (2009).
[85]M. Connors, PHENIX Collaboration, nucl-ex/0907.4571v2 (2009).
[86]H. Zhang, J. F. Owens, E. Wang and X. N. Wang, hep-ph/0907.4816v2 (2009).
[87]L. Evans and P. Bryant, JINST 3 (2008) S08001.
[88]K. Aamodt, et al., ALICE Collaboration, JINST 3 (2008) S08002. ALICE, URL http://aliceinfo.cern.ch/.
[89]http://13.web.cern.ch/13/.
[90]ALICE Collaboration, ALICE TDR 4 (1999).
[91]ALICE Collaboration, ALICE TDR 7 (2000).
[92]ALICE Collaboration, J. Phys. G:Nucl. Part. Phys.,32 (2006) 1295.
[93]ALICE Collaboration, CERN/LHCC 99-4, http://alice.web.cern.ch/Alice/TDR/.
[94]T. M. Cormier, Eur. Phys. J C34 (2004) s333.
[95]Test Beam, URL http://aliceinfo.cern.ch/Collaboration.
[96]offline, URL http://aliceinfo.cern.ch/Offline/.
[97]AliRoot, URL http://pcaliwcb02.cern.ch/Offline/AliRoot/.
[98]Root, URL http://root.cern.ch.
[99]T. Sjostrand, L. Loonnblad and S. Mrenna, hep-ph/0108264 (2001). T. Sjostrand et al., Comput. Phys. Commun.135 (2001) 238.
[100]M. Gyulassy and X. N. Wang, Comput. Phys. Commun.83 (1994) 307.
[101]R, Brun et al., GEANT3 User Guide, (1985) CERN Data Handling Division DD/EE/84-1. GEANT3, URL http://wwwasd.web.cern.ch/wwasd/geant/.
[102]GEANT4, URL http://wwasd.web.cern.ch/wwasd/geant4/geant4.html.
[103]A. Fasso et al., FLUKA:Status and Prospective for Hadronic Applications (Springer-Verlag Berlin,2001)955.
[104]Lai, H.L. et al., Phys. Rev. D55 (1997) 1280-1296. e-Print Archive:hep-ph/9606399.
[105]P. Aurenche, et al., arXiv:hep-ph/9811382 (1998).
[106]G. Conesa, Ph. D. Thesis:Identification of particles and hard processes with the spec-trometer PHOS of the ALICE experiment (2005).
[107]G. Conesa et al., Nucl. Instr. and Meth. Nucl. Res. A580 (2007) 1446.
[108]G. Conesa et al., ALICE-INT-2005-16.
[109]Y. Mao, Master thesis.
[110]Y. L. Dokshitzer, V. A. Khoze and S. I. Troian, Z. Phys. C55 (1992) 107.
[111]U. Abeysekara, et al., ALICE/EMCAL Collaboration, arXiv:hep-ph/10080413v1 (2010).
[112]C. Albajar et al., UA1 Collaboration, Nucl. Phys. B309 (1988) 405.
[113]N. Armesto, L. Cunqueiro, C. A. Salgado, arXiv:hep-ph/0907.1014.
[114]C. A. Salgado and U. A. Wiedemann, Phys. Rev. D68 (2003) 014008, hep -ph/0302184.
[115]A. Dainese, C. Loizides and G. Paic, hep-ph/0406201v3 (2004).
[116]K. Aamodt, et al., ALICE Collaboration, Euro. Phys. J. C 65 (2010) 111.
[117]https://twiki.cern.ch/twiki/bin/viewauth/AliceEVE/EVEEMC.
[118]https://twiki.cern.ch/twiki/bin/viewauth/ALICE/CaloQA.
[119]K. Aamodt, et al., ALICE Collaboration, Phys. Lett. R 693 (2011) 53.
[120]J. Allen et al., ALICE/EMCAL Collaboration, Nucl. Instr. and Meth. Nucl. Res. A615 (2010) 6.
[121]S. S. Adler et al., PHENIX Collaboration, Phys. Rev. D81 (2010) 072001.
[122]http://qm09.phys.utk.edu/indico/getFile.py/ access?contribld=745&sessionld=44&resId=0&materialId=poster&confId=1
[123]F. Poukoutakis et al., Proceedings of the Computing in High Energy Physics (CHEP 2007), http://cdsweb.cern.ch/record/1066450.
[2]V. Barger, R. Phillips Collider Physics (1997) ISBN 0201149451.
[3]S. F. Novaes, standard model:An introduction (2000). hep-ph/0001283. Published in "Particle and Fields".
[4]G. Dissertori, I. Knowles, and M. Schmelling, Quantum Chromodynamics-High Energy Experiments and Theory. Oxford University Press,2003.
[5]Feynman, Richard Phillips (1998). Quantum Electrodynamics. Westview Press; New Ed edition. ISBN 978-0201360752
[6]B. Jager, A. Schafer, et al., Phys. Rev. D67 (2003) 054005.
[7]D. J. Gross and F. Wilczek, Phys. Rev. Lett.30 (1973) 1343.
[8]E. V. Shuryak, Phys. Rep.61 (1980) 71.
[9]S. Hands, Contemp. Phys.42 (2001) 209.
[10]R. J. Fries and B. Muller, Eur. Phys. J. C34 (2004) S279.
[11]T. D. Lee, in Proceedings of the XVII International Conference on High Energy Physics, 1974.
[12]U. W. Heinz and M. Jacob, arXiv:nucl-th/0002042.
[13]RHIC, URL http://www.bul.gov/rhic. BNL, URL http://www.bnl.gov/.
[14]http://www.bnl.gov/rhic/news2/news.asp?a=05-38&t=pr.
[15]L. Evans and P. Bryant, JINST 3 (2008) S08001.
[16]S. Grinstein, PhD thesis:The Inclusive Jet Cross Section using the kT Algorithm (2003).
[17]Y. X. Mao et al., ALICE-INT-2007-021, Euro. Phys. J. C 57 (2008) 613.
[18]Y. X. Mao et al., ALICE-INT-2007-017, Chinese Physics C 32(07) (2008).
[19]Time Magazine (1957), http://www.lbl.gov/Science-Articles/Research-Review/Magazine/1997-fall/contents.html.
[20]U. Yves, http://www-subatech.in2p3.fr/photons/subatech/physics/potpourri/physics.html.
[21]J. D. Bjorken, Phys. Rev. D27 (1983) 140.
[22]K. Miki, PhD thesis:Azimuthal Anisotropy Measurement of Neutral Pion and Direct Photon in (?)=200 GeV Au+Au collisions at RHIC-PHENIX (2009).
[23]Z. Yin, Ph. D. Thesis:High pT physics in heavy ion collisions at (?)=200 GeV (2004).
[24]R. Glauber and G. Matthias, Nucl. Phys. B21 (1970) 135. T. Wibig and D. Sobezynska, J. Phys. G:Nucl. Part. Pyhs.24 (1998) 2037.
[25]A. Kiyomichi, PhD thesis:Study of identified hadron spectra and yields at mid-rapidity in Au+Au collisions at (?)=200 GeV (2005).
[26]P. Braun-Munzinger, D. Magestro, K. Redlich and J. Stahel, Phys. Lett. B 518 (2001) 41.
[27]Yu. L. Dokshitzer, Sov. Phys. JETP 46 (1977) 416; V. N. Gribov and L. P. Lipatov, Sov. J. Nucl. Phys.15 (1972) 438; G. Altarelli and G. Parisi, Nucl. Phys. B 126 (1977) 298.
[28]M. Gluck, E. Reya and A. Vogt, Z. Phys. C 67 (1995) 433.
[29]G. Sterman et al., CTEQ Collaboration, Rev. Mod. Phys.67 (1995) 157.
[30]J. Pumplin et al., JHEP,07 (2002) 012.
[31]J. Binnewies, B. A. Kniehl and G. Kramer, Phys. Rev. D 52 (1995) 4947.
[32]P. Aurenche, et al., Euro. Phys. J. C 13 (2000) 347.
[33]B. A. Knirhl, G. Kramer and B. Potter, Nucl. Phys. B 597 (2001) 337.
[34]J. W. Cronin et al., Phys. Rev. D11 (1975) 3105.
[35]J. J. Aubert et al., Phys. Lett. B123 (1983) 275.
[36]M. Arneodo et al., Nucl. Phys. B441 (1995) 12-30.
[37]Y. X. Mao, W. C. Xiang and D. C. Zhou, International Journal Modern Physics E, Vol.16, Nos.7-8 (2007) 2130. J. Liu, Y. X. Mao, W. C. Xiang and D. C. Zhou, Chinese Science Bulletin Vol.51,No.2 (2006) 139. D. C. Zhou, W. C. Xiang and Y. X. Mao, Journal of Central China Normal University (Natural Sciences) 39 (2005) 482.
[38]X. N. Wang and M. Gyulassy, Phys. Rev. Lett 68 (1992) 1480. M. Gyulassy and X. N. Wang, Nucl. Phys. B420 (1994) 583. X. N. Wang, Phys. Lett. B579 (2004) 299 nucl-th/0307036.
[39]M. Gyulassy, P. Levai and I. Vitev, Phys. Lett. B 538 (2002) 282.
[40]R. Baier, Y. L. Dokshitzer, S. Peigne and D. Schiff, Phys. Lett. B 345 (1995) 277.
[41]R. Baier, D. Schiff and B. G. Zakharov, Ann. Rev. Nucl. Part. Sci 50 (2000) 37.
[42]K. Aamodt, et al., ALICE Collaboration, Phys. Rev. Lett.105 (2010) 252301.
[43]M. C. Abreu, et al., NA50 Collaboration, Phys. Lett. B 530 (2002) 43.
[44]C. Adler, et al., STAR Collaboration, Phys. Rev. Lett 87 (2001) 112303.
[45]I. G. Bearden, et al., BRAHMS Collaboration, Phys. Rev. Lett.88 (2002) 202301.
[46]K. Adcox, et al., PHENIX Collaboration, Phys. Rev. Lett.88 (2001) 3500.
[47]B.B.Back, et al., PHOBOS Collaboration, Phys. Rev. Lett.87 (2001) 102303.
[48]K. Aamodt, et al., ALICE Collaboration, Euro. Phys. J. C 68 (2010) 89.
[49]V. Khachatryan, et al., CMS Collaboration, JHEP 02 (2010) 041.
[50]R. Hanbury Brown and R. Q. Twiss, Nature (London) 178 (1956) 1046.
[51]A.N. Makhlin, Y. M. Sinyukov, Z. Phys. C 39 (1988) 69.
[52]K. Aamodt, et al., ALICE Collaboration, Phys. Lett. B 696 (2011) 328.
[53]M. A. Lisa, et. al., E895 Collaboration, Phys. Rev. Lett.84 (2000) 2798.
[54]C. Alt, et. al., NA49 Collaboration, Phys. Rev. C 66 (2008) 064908.
[55]D. Adamova, et.al., CERES Collaboration, Nucl. Phys. A 714 (2003) 124.
[56]B.I. Abelev, et al., STAR Collaboration, Phys. Rev. C 80 (2009) 024905.
[57]B.B.Back, et al., PHOBOS Collaboration, Phys. Rev. C.73 (2006) 031901.
[58]H. sorge, Phys. Rev. Lett.82 (1999) 2048.
[59]K. Aamodt, et al., ALICE Collaboration, Phys. Rev. Lett.105 (2010) 252302.
[60]Y. Bai, PhD thesis, Nikhef and Utrecht University (2007).
[61]B. I. Abelev et al., STAR Collaboration, Phys. Rev. C 77 (2008) 054901.
[62]A. Adare, et al., PHENIX Collaboration, Phys. Rev. Lett.98 (2007) 162301.
[63]S. M. Dogra, PhD thesis:Particle Production and Correlations in Ultra-Rrelativeistic Nucleus-Nucleus Collisions (2008).
[64]K. Aamodt, et al., ALICE Collaboration, Phys. Lett. B 696 (2011) 30.
[65]S.S. Adler, et al., PHENIX Collaboration, Phys. Rev. C.69 (2004) 034910.
[66]J. Adams et al., STAR Collaboration, Phys. Rev. Lett.91 (2003) 172302.
[67]J. Adams et al., STAR Collaboration, Phys. Rev. Lett.91 (2003) 072302.
[68]D. Magestro, Nucl. Phys. A 774 (2006) 573.
[69]http://xxx.lanl.gov/pdf/nucl-th/0610051.
[70]R. Feynman, R. Field and G. Fox, Nucl. Phys. B128 (1977) 1.
[71]S. S. Adler et al., PHENIX Collaboration, Phys. Rev. D74 (2006) 072002.
[72]L. Apanascvich, et. al., Phys. Rev. D 59 (1999) 074007.
[73]R. Baier, Y. L. Dokshitzer, S. Peigne and D. Schiff, Phys. Lett. B 345 (1995) 277.
[74]T. Horaguchi, Ph. D. Thesis:Prompt Photon Production in Proton-Proton Collitions at (?)=200 GeV (2005).
[75]E. V. Shuryak, Sov. J. Nucl. Phys.28 (1978) 408.
[76]R. J. Fries, B. Muller and D. K. Srivastava, Phys. Rev. Lett.90 (2003) 132301.
[77]M. M. Aggarwal et al., (WA98 Collaboration), Phys. Rev. Lett.85 (2000) 3595.
[78]S. Turbide, R. Rapp and C. Gale, Phys. Rev. D56 (2004) 014903.
[79]S. S. Adler et al., (PHENIX Collaboration), Phys. Rev. Lett.94 (2005) 232301.
[80]L. E. Gordon and W. Vogelsang, Phys. Rev. D (1993) 3136.
[81]A. Adare, et al., PHENIX Collaboration, Phys. Rev. Lett.104 (2010) 132301.
[82]X. N. Wang, Z. Huang and I. Sarcevic, Phys. Rev. Lett.77 (1996) 231.
[83]F. Arleo, J. Phys. G:Nuclear and Particle Physics,34,8 (2007) S1037. F. Arleo, P. Aurenche, Z, Belghobsi, J.-P. Guillet, JHEP 11 (2004) 009. F. Arleo, JHEP 09 (2006) 015.
[84]M. Nguyen, PhD thesis:Two particle correlations with direct photon and π0 triggers in 200 GeV p+p and Au+Au collisions (2009).
[85]M. Connors, PHENIX Collaboration, nucl-ex/0907.4571v2 (2009).
[86]H. Zhang, J. F. Owens, E. Wang and X. N. Wang, hep-ph/0907.4816v2 (2009).
[87]L. Evans and P. Bryant, JINST 3 (2008) S08001.
[88]K. Aamodt, et al., ALICE Collaboration, JINST 3 (2008) S08002. ALICE, URL http://aliceinfo.cern.ch/.
[89]http://13.web.cern.ch/13/.
[90]ALICE Collaboration, ALICE TDR 4 (1999).
[91]ALICE Collaboration, ALICE TDR 7 (2000).
[92]ALICE Collaboration, J. Phys. G:Nucl. Part. Phys.,32 (2006) 1295.
[93]ALICE Collaboration, CERN/LHCC 99-4, http://alice.web.cern.ch/Alice/TDR/.
[94]T. M. Cormier, Eur. Phys. J C34 (2004) s333.
[95]Test Beam, URL http://aliceinfo.cern.ch/Collaboration.
[96]offline, URL http://aliceinfo.cern.ch/Offline/.
[97]AliRoot, URL http://pcaliwcb02.cern.ch/Offline/AliRoot/.
[98]Root, URL http://root.cern.ch.
[99]T. Sjostrand, L. Loonnblad and S. Mrenna, hep-ph/0108264 (2001). T. Sjostrand et al., Comput. Phys. Commun.135 (2001) 238.
[100]M. Gyulassy and X. N. Wang, Comput. Phys. Commun.83 (1994) 307.
[101]R, Brun et al., GEANT3 User Guide, (1985) CERN Data Handling Division DD/EE/84-1. GEANT3, URL http://wwwasd.web.cern.ch/wwasd/geant/.
[102]GEANT4, URL http://wwasd.web.cern.ch/wwasd/geant4/geant4.html.
[103]A. Fasso et al., FLUKA:Status and Prospective for Hadronic Applications (Springer-Verlag Berlin,2001)955.
[104]Lai, H.L. et al., Phys. Rev. D55 (1997) 1280-1296. e-Print Archive:hep-ph/9606399.
[105]P. Aurenche, et al., arXiv:hep-ph/9811382 (1998).
[106]G. Conesa, Ph. D. Thesis:Identification of particles and hard processes with the spec-trometer PHOS of the ALICE experiment (2005).
[107]G. Conesa et al., Nucl. Instr. and Meth. Nucl. Res. A580 (2007) 1446.
[108]G. Conesa et al., ALICE-INT-2005-16.
[109]Y. Mao, Master thesis.
[110]Y. L. Dokshitzer, V. A. Khoze and S. I. Troian, Z. Phys. C55 (1992) 107.
[111]U. Abeysekara, et al., ALICE/EMCAL Collaboration, arXiv:hep-ph/10080413v1 (2010).
[112]C. Albajar et al., UA1 Collaboration, Nucl. Phys. B309 (1988) 405.
[113]N. Armesto, L. Cunqueiro, C. A. Salgado, arXiv:hep-ph/0907.1014.
[114]C. A. Salgado and U. A. Wiedemann, Phys. Rev. D68 (2003) 014008, hep -ph/0302184.
[115]A. Dainese, C. Loizides and G. Paic, hep-ph/0406201v3 (2004).
[116]K. Aamodt, et al., ALICE Collaboration, Euro. Phys. J. C 65 (2010) 111.
[117]https://twiki.cern.ch/twiki/bin/viewauth/AliceEVE/EVEEMC.
[118]https://twiki.cern.ch/twiki/bin/viewauth/ALICE/CaloQA.
[119]K. Aamodt, et al., ALICE Collaboration, Phys. Lett. R 693 (2011) 53.
[120]J. Allen et al., ALICE/EMCAL Collaboration, Nucl. Instr. and Meth. Nucl. Res. A615 (2010) 6.
[121]S. S. Adler et al., PHENIX Collaboration, Phys. Rev. D81 (2010) 072001.
[122]http://qm09.phys.utk.edu/indico/getFile.py/ access?contribld=745&sessionld=44&resId=0&materialId=poster&confId=1
[123]F. Poukoutakis et al., Proceedings of the Computing in High Energy Physics (CHEP 2007), http://cdsweb.cern.ch/record/1066450.