LHC Physics with Electrons and Photons and the Achievement of the Full Performance Potential of the CMS Electromagnetic Calorimeter

位于瑞士日内瓦附近的欧洲核子研究中心的大型强子对撞机（LHC）将成为世界上最大的粒子加速器。这台机器将于2007年夏天开始运行，它将使沿相反方向运行的高能质子在一个27公里长的环周围发生碰撞。紧凑型μ子螺线管（CMS）是一种通用探测器，是定位在环周围碰撞点的四个大型粒子探测器之一。CMS探测器的关键部件之一是电磁量热计（ECAL）。它由超过75000个钨酸铅晶体组成，旨在精确测量电子和光子的位置和能量。该项目旨在确保CMS ECAL的设计性能潜力得到充分发挥，并在大型强子对撞机的新物理发现中发挥决定性和主导作用，重点是电磁量热计的使用。大型强子对撞机实验项目的主要目标之一是阐明质量的起源，特别是通过发现希格斯玻色子，这是粒子物理学标准模型所预测的一种基本粒子。这种粒子是不稳定的，在大型强子对撞机的质子-质子碰撞中产生时，会立即衰变成质量较小的粒子。它是处于最终状态的稳定粒子，如电子、介子或光子，它们将被探测器观察到。母希格斯玻色子的质量可以由最终态粒子的组合动量重建。在大型强子对撞机上发现的灵敏度最高的希格斯玻色子的衰变通道都有可能包含电子或光子的最终状态。因此，CMS ECAL的完整设计性能的实现对希格斯玻色子的发现具有至关重要的意义。在过去的两年里，我的主要任务是开发第一个完整的物理分析，完全模拟CMS探测器，为发现希格斯玻色子的最重要的通道之一。任何大型强子对撞机物理分析的先决条件之一是最终态粒子的精确重建。CMS ECAL面临的挑战是精确重建电子和光子的位置和能量，并准确有效地识别和选择它们。我现在是这些领域的主要专家，我在项目的头一到两年的目标是继续专注于开发健壮的重建软件，为实验的开始做准备。在项目的第二年或第三年，我的目标是在ECAL方面担任CMS探测器调试的领导角色。执行75000个ECAL晶体的相对校准的主要任务将是我在早期数据采集期间的下一个重点领域。我的下一个目标是研究关键的标准模型信号，特别是W玻色子衰变产生的电子。作为校准ECAL的主要通道，该通道提供了探测器性能的详细探测，并将成为理解许多新物理信号的关键。在精确校准的ECAL中对电子和光子进行精确和有效的重建，将为发现可能通过大型强子对撞机实现的新物理提供最大可能的潜力。随着CMS收集的数据的积累，我从目前的希格斯分析和以前的分析中获得的经验将使我在使用CMS数据发现和研究新的物理信号方面发挥重要作用。我的目标是在许多物理分析中处于领先地位，将我的专业知识扩展到其他希格斯玻色子衰变通道。最后，我将能够利用我在OPAL实验中的知识和经验来开发技术，将不同搜索渠道的结果结合起来，以确保及时发现希格斯玻色子和其他新物理。

The Large Hadron Collider (LHC), located at CERN near Geneva, Switzerland, will be the world's largest particle accelerator. The machine, which is due to begin operation in summer 2007 will collide high energy protons travelling in opposite directions around a 27 km ring. The Compact Muon Solenoid (CMS) is a general purpose detector and is one of four large particle detectors to be positioned at collision points around the ring. One of the key components of the CMS detector is the Electromagnetic Calorimeter (ECAL). This is composed of over 75000 lead tungstate crystals and is designed to accurately measure the positions and energies of electrons and photons. The proposed project is to ensure that the design performance potential of the CMS ECAL is fully exploited, and to play a decisive and leading role in the discovery of new physics at the LHC, focusing on the use of the electromagnetic calorimeter. One of the primary objectives of the LHC experimental program is to elucidate the origin of mass, in particular through the discovery the Higgs boson, an elementary particle predicted by the Standard Model of particle physics. The particle is unstable and when produced in proton-proton collisions at the LHC will immediately decay into less massive particles. It is the stable particles in the final state, such as electrons, muons or photons, which will be observed by the detector. The mass of the parent Higgs boson can be reconstructed from the combined momenta of the final state particles. The decay channels of the Higgs boson which yield the highest sensitivity for discovery at the LHC all have final states which may contain electrons or photons. The achievement of the full design performance of the CMS ECAL is therefore of crucial importance to the discovery of the Higgs boson. My primary task over the last two years has been to develop the first complete physics analysis with full simulation of the CMS detector for one of the most important channels for the discovery of the Higgs boson. One of the pre-requisites for any LHC physics analysis is accurate reconstruction of final state particles. The challenge for the CMS ECAL concerns the precise reconstruction of the positions and energies of electrons and photons and their accurate and efficient identification and selection. I am now the leading expert in these areas, and my objective for the first one to two years of the project will be to continue to focus on the development of robust reconstruction software in preparation for the start of the experiment. In the second or third year of the project I aim to take up a leading role, concerning the ECAL, in the commissioning of the CMS detector. The major task of performing the relative calibration of the 75000 ECAL crystals would be my next area of focus during early data taking. My next objective will be to study key Standard Model signals, and in particular, electrons produced from the decay of the W boson. As well as being the main channel used to calibrate the ECAL, this channel provides a detailed probe of the detector performance, and will be a key to understanding many new physics signals. The accurate and efficient reconstruction of electrons and photons in a precisely calibrated ECAL will provide the maximum possible potential for the discovery of new physics which may become accessible through the LHC. As the data taken by CMS accumulates, my experience from my current Higgs analysis and from previous analyses will place me in a strong position to act as a key player in the discovery and study of new physics signals using CMS data. I aim to take the lead in a number of physics analyses, extending my expertise to other Higgs boson decay channels. Finally, I will be able to use my knowledge and experience from the OPAL experiment to develop techniques to combine results from the different search channels to ensure the timely discovery of the Higgs boson and other new physics.