Study of charm mixing and CP violation with the LHCb experiment

利用 LHCb 实验研究魅力混合和 CP 破坏

• 批准号: 2114891
• 金额: --
• 依托单位: University of Oxford
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2018
• 资助国家: 英国
• 起止时间: 2018 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2114891
• 关键词: Study; charm; mixing; CP; violation

The primary purpose of the thesis research is to perform a measurement of mixing and a search for indirect CP violation in the neutral charm meson ('D') system. This goal will be achieved through a time-dependent Dalitz plot study of multibody decays, initially focusing on the channel D->K^0_S KK. The analysis requires knowledge of the variation of the strong phase over Dalitz space, and this information will be taken from measurements performed by experiments at charm threshold (i.e. CLEO-c and BESIII). This approach will enable the study to avoid any model-dependence, and will allow the results to be interpreted in a clean and straightforward manner.The aims of the measurement are of very high scientific importance. Charm mixing is described by two parameters, x_D and y_D, that are both still poorly known. Indeed it is not yet established whether x_D is even non zero. Indirect CP violation in charm is predicted to be very small in the Standard Model, and any observation made with current experimental precision would have a strong claim to be interpreted as a New Physics driven effect. LHCb has accumulated samples of charm decays much larger than at any previous facility, and hence the opportunities presented for analysis are unprecedented and very exciting.There have been very few previous mixing studies performed with D0->K^0_S KK, and none on LHCb. The resonance structure of the decay is very different to that of D0->K^0_S pipi, which is itself the subject of an ongoing analysis within LHCb, making the two channels complementary in their physics reach. (Indeed the student will collaborate closely with the team working on K^0_S pipi, which will allow ideas and methods to be exchanged between the two analyses). No previous study of D0->K^0_S KK has adopted the model independent approach that will be pursued in the thesis analysis.The possibility exists to extend the measurement programme to other D decay channels, again pursuing the model-independent approach. One good candidate is the mode D->Kpipipi, which has a rich structure of intermediate resonances, and where expertise exists in the host institute from previous studies performed at LHCb and CLEO-c.As stated, the student will work together with a team of other physicists (from Oxford and CERN), who are already embarked on a similar analysis with a sister decay. He will also benefit from the association that Oxford has recently made with the BESIII experiment in Beijing. 'Engineering measurements' performed at BESIII will be invaluable in harnassing the full statistical power of the LHCb data set.Finally, it is possible that the student will develop calibration, reconstruction and analysis tools suitable for analysing first data with the LHCb Upgrade. This experiment will begin data taking in 2021, and it may be feasible for the student to perform one of the first physics measurements with the early data from the Upgrade. A decision will be made late in the second year of the studentship whether this path will be pursued, of whether more studies will be made with the existing data set. This work would count as a secondary project alongside the major thesis goal, described above.

本论文研究的主要目的是在中性粲介子（D）系统中进行混合测量和寻找间接CP破坏。这一目标将通过多体衰变的时间依赖性Dalitz图研究来实现，最初关注通道D->K^0_S KK。分析需要的知识的变化的强相在Dalitz空间，这一信息将采取从实验进行的测量在魅力阈值（即CLEO-C和BESIII）。这种方法将使研究能够避免任何依赖模型的情况，并使结果能够以清晰和直接的方式得到解释。测量的目的具有非常高的科学重要性。魅力混合由两个参数x_D和y_D描述，这两个参数仍然知之甚少。事实上，它还没有确定是否x_D甚至是非零的。在标准模型中，间接CP破坏的魅力预计是非常小的，任何观察与目前的实验精度将有强烈的要求被解释为一个新物理驱动的效果。LHCb积累了比以往任何设施都大得多的粲衰变样本，因此提供的分析机会是前所未有的，非常令人兴奋。以前很少有D 0->K^0_S KK的混合研究，没有LHCb。衰变的共振结构与D 0->K^0_S pipi的共振结构非常不同，这本身就是LHCb内部正在进行的分析的主题，使两个通道在物理范围上互补。（实际上，学生将与K^0_S pipi的团队密切合作，这将允许在两个分析之间交换想法和方法）。以前对D 0->K^0_S KK的研究中没有采用本论文分析中所采用的模型无关方法，因此有可能将测量程序扩展到其他D衰变通道，再次采用模型无关方法。一个很好的候选者是模式D->Kpipipi，它具有丰富的中间共振结构，并且在LHCb和CLEO-c之前进行的研究中，主办机构拥有专业知识。如上所述，学生将与其他物理学家团队（来自牛津大学和欧洲核子研究中心）一起工作，他们已经开始对姐妹衰变进行类似的分析。他还将受益于牛津大学最近与北京BESIII实验的联系。在BESIII进行的“工程测量”对于充分利用LHCb数据集的统计能力将是非常宝贵的。最后，学生将有可能开发适合分析LHCb升级的第一批数据的校准，重建和分析工具。该实验将于2021年开始数据采集，学生可以使用升级的早期数据进行首批物理测量之一。将在学生的第二年晚些时候决定是否继续这条道路，是否会用现有的数据集进行更多的研究。这项工作将算作一个次要项目旁边的主要论文目标，如上所述。