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

LHCb实验在研究粲子体系中的混合和CP违背现象方面具有无可比拟的能力。虽然在魅力衰变中混合是在大约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。在与混合有关的现象中还没有发现CP的破坏，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。学生将着手进行魅力混合和使用四体D衰变进行cp破坏测量的项目，特别是单Cabibbo抑制过程D->pi+pi-pi+pi-和K+K-pi+pi-。这些衰变以前还没有被用于这种测量，并且提供了有希望的灵敏度，与迄今为止利用的二体和三体衰变所获得的灵敏度相辅相成。他将采用一种与模型无关的方法，利用北京BESIII实验中测量的强相参数的外部知识来做到这一点。分析将基于LHC运行1和2收集的数据。根据进行分析的速度，他还可以使用升级后的LHCb探测器在Run 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对BESIII数据的分析，从这些数据中确定强相位参数。牛津大学是英国仅有的两个BESIII成员之一，因此拥有对这些数据的独特访问权。TORCH是一种新型的飞行时间切伦科夫探测器，计划在十年内安装在LHCb升级II中。一项强有力的研发计划需要最终设计出具有必要性能的产品。学生将在这一发展过程中发挥核心作用。可能涉及的领域包括对原型和最终探测器的前端电子设备进行评估；参与测试束流的数据采集和分析；以及重构代码的改进。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，并且将与行业密切联系，特别是英国Photek公司，他们一直积极参与TORCH项目的发展，直到现在。

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.