Particle Physics - Measuring Charm Mixing Parameters in D-4h

LHCb实验对于研究粲系统中的混合和CP破坏现象具有无与伦比的能力。虽然粲衰变中的混合是在大约15年前首次观察到的，但人们非常希望提高对驱动这一过程的参数的了解。在混合相关的现象中还没有发现CP破坏，在目前的精度水平上的任何观测都将是新物理学的一个指标。学生将开始一个使用四体D衰变测量魅力混合和CP破坏的计划，特别是单独的Cabibbo抑制过程D->pi+pi-pi+pi-和K+K-pi+pi-。这些衰变以前没有被用于这种测量，并提供了有前途的灵敏度，是互补的，可从两个和三体衰变，迄今已被利用。他将通过一种独立于模型的方法来做到这一点，该方法使用在北京BESIII实验中测量的强相参数的外部知识。该分析将基于LHC 1991年和1992年收集的数据。根据分析的速度，他还可以使用升级的LHCb探测器在运行3中收集的早期数据进行试点测量，但这目前不构成基线计划的一部分。论文工作的另一个可能的扩展将有助于分析的BESIII数据的强相参数的确定。牛津大学是英国仅有的两个BESIII成员之一，因此可以获得这些数据。TORCH是一种新型的飞行时间切伦科夫探测器，计划在十年后安装在LHCb升级II中。为了达到具有必要性能的最终设计，需要一个强有力的研发计划。学生将在这一发展中发挥核心作用。可能参与的领域包括原型和最终探测器前端电子设备的评估;参与测试束活动中的数据采集和分析;以及重建代码的改进。他还将对TORCH探测器对LHCb物理范围的影响进行基准测试。TORCH成功的核心是其光电探测器的性能，并将与工业界密切联系，特别是英国公司Photek，该公司迄今为止一直积极参与TORCH项目的发展。

The LHCb experiment has unsurpassed capabilities for studying the phenomena of mixing and CP violation in the charm system. Although mixing in charm decays was first observed around 15 years ago, it is highly desirable to improve the knowledge of the parameters that drive this process. CP violation in mixing-related phenomena has not been seen, and any observation at the current level of precision would be an indicator of New Physics.The student will embark on a programme of charm mixing and CP-violation measurements using four-body D decays, in particular the singly Cabibbo suppressed processes D->pi+pi-pi+pi- and K+K-pi+pi-. These decays have not been previously harnessed for such measurement, and offer promising sensitivity that is complementary to that obtainable from the two and three-body decays that have so far been exploited. He will do this with a model-independent approach that uses external knowledge of strong-phase parameters that are measured at the BESIII experiment in Beijing. The analysis will be based on data collected in Runs 1 and 2 of the LHC. Depending on the speed with which the analysis is conducted, he may also make a pilot measurement with early data collected in Run 3 with the upgraded LHCb detector, but this does not currently form part of the baseline plan. Another possible extension of the thesis work would be to contribute to the analysis of the BESIII data from which the strong-phase parameters are determined. Oxford is one of only two UK groups that are members of BESIII, and thus have unique access to these data.The TORCH is a novel time-of-flight Cherenkov detector that is proposed for installation in LHCb Upgrade II in a decade's time. A vigorous programme of R&D is required to arrive at a final design that will have the necessary performance. The student will play a central role in this development. Likely areas of involvement include the evaluation of front end electronics for prototypes and the final detector; participation in data taking and analysis in test beam campaigns; and the improvement of reconstruction code. He will also benchmark the impact that the TORCH detector will have on the physics reach of LHCb. Central to the success of TORCH is the performance of its photodetectors, and there will be close association with industry, in particular the UK firm Photek who have been heavily involved in the evolution of the TORCH project until now.