Study of rare FCNC Lambda_b baryon decays.

稀有 FCNC Lambda_b 重子衰变的研究。

• 批准号: 2180607
• 金额: --
• 依托单位: University of Warwick
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2019
• 资助国家: 英国
• 起止时间: 2019 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2180607
• 关键词: Study; rare; FCNC; Lambda_b; baryon

The rare FCNC decays of hadrons containing b quark provide highly sensitive tests of new physics beyond the standard model. In particular semileptonic decays of B mesons to strange meson and pair of oppositely charged leptons like B0 --> K* l+ l- received significant attention in recent years. The Lambda_b baryon decays can provide information complementary to the meson decays. Up to now only Lambda_b --> Lambda mu+ mu- decay was studied in the details. In addition, LHCb experiment performed a search for CP violation in the decay Lambda_b --> p K- mu+ mu-. In this project we aim to perform a more detailed experimental study of the Lambda_b --> p K- mu+ mu- decay. At the start, the differential branching fraction will be measured as a function of the dimuon invariant mass squared. One of the difficulties for interpretation of the measurements performed for the Lambda_b --> p K- mu+ mu- decay comes from the fact that at this stage there is no theoretical prediction or experimental information about the hadronic structure of the pK- system. The second goal of the project will be to exploit angular distributions of the decay with the aim to first contribute to the understanding of the pK- structure of this decay and possibly measure at least some of the angular observables which are sensitive to the new physics.The important aspect of the proposed measurements of Lambda_b --> p K- mu+ mu- decay is that it heavily relies on the positive particle identification of protons and kaons. In the current LHCb detector, this is possible for kaon momentum over 10 GeV/c and proton momentum from about 15 GeV/c. These are relatively high thresholds and significant improvement in the sensitivity could be achieved if the particle identification at lower momenta can be achieved. Such improvement would not only benefit study in this project but large number of measurements in LHCb would benefit from such improvement, with one particular area to point out being flavour tagging. One proposed solution is to install a TORCH detector during LS3 to provide particle identification capability for low momentum tracks. The idea of TORCH detector is to exploit time-of-flight measurement for charged particles by precise timing of the Cherenkov photons emitted in TORCH quartz radiator bar. Preliminary studies suggest that it can provide significant improvement in LHCb detector capabilities. In this project, we will attack question of how to reconstruct information from TORCH detector into high-level quantities on particle identification at the track level. Due to the geometry of the TORCH detector, resulting Cherenkov image seen by photodetectors is complex and currently available reconstruction needs significant speedup for practical use. We will exploit alternative ideas based on machine learning, which could possibly speed up reconstruction to the point that it could be usable at the trigger level.

含有b夸克的强子罕见的fcnc衰变为超越标准模型的新物理提供了高度灵敏的测试。特别是B介子到奇异介子的半轻子衰变和一对带电相反的轻子，如B0-&GT；K*L+L-近年来受到了极大的关注。Lambda_b重子衰变可以为介子衰变提供补充信息。到目前为止，只对Lambda_b--&gt；Lambda Mu+Mu衰变进行了详细的研究。此外，LHCb实验在衰变的Lambda_b--&gt；p K-Mu+Mu-中进行了CP破坏的搜索。在这个项目中，我们的目标是对Lambda_b--&gt；p K-Mu+Mu-衰变进行更详细的实验研究。在开始时，微分分支分数将被测量为双介子不变质量平方的函数。解释Lambda_b--&gt；p K-Mu+Mu衰变的测量的困难之一来自于这样一个事实，即在这个阶段没有关于PK-系统的强子结构的理论预测或实验信息。该项目的第二个目标将是利用衰变的角分布，目的是首先有助于理解这种衰变的pk结构，并可能测量至少一些对新物理敏感的角观测值。拟议的Lambda_b-&gt；p K-Mu+Mu衰变测量的重要方面是，它严重依赖质子和介子的正粒子识别。在目前的LHCb探测器中，K介子动量大于10GeV/c，质子动量大于15GeV/c是可能的。这些都是相对较高的阈值，如果能够在较低动量下实现粒子识别，灵敏度将得到显著提高。这样的改进不仅有利于本项目的研究，而且LHCb中的大量测量也将从这种改进中受益，其中一个特别要指出的领域是风味标签。一种建议的解决方案是在LS3期间安装火炬探测器，为低动量轨迹提供粒子识别能力。火炬探测器的想法是通过对火炬石英辐射器棒中发射的切伦科夫光子进行精确计时，来测量带电粒子的飞行时间。初步研究表明，它可以显著提高LHCb检测器的能力。在本项目中，我们将解决如何将火炬探测器的信息重构为高级别的量在轨迹级进行粒子识别的问题。由于火炬探测器的几何形状，由光电探测器所得到的切伦科夫图像是复杂的，目前可用的重建需要显著的加速才能用于实际应用。我们将开发基于机器学习的替代想法，这可能会加快重建速度，使其能够在触发级别上使用。