Probing the flavour structure of New Physics with Bs mesons at LHCb

在 LHCb 上用 Bs 介子探索新物理学的味道结构

• 批准号: ST/H006737/1
• 负责人: Matthew Needham
• 金额: $ 61.18万
• 依托单位: University of Edinburgh
• 依托单位国家: 英国
• 项目类别: Fellowship
• 财政年份: 2010
• 资助国家: 英国
• 起止时间: 2010 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=ST%2FH006737%2F1
• 关键词: Probing; flavour; structure; New; Physics

One of the most puzzling and so far unexplained features of the Universe is the absence of anti-matter. During the Big Bang matter and anti-matter were generated in equal quantities. However, from measurements of cosmic rays it is known that our galaxy consists mainly of matter. Furthermore, there is no evidence for the intense gamma ray emission that would follow the annihilation of matter and anti-matter in distance galaxies with clouds of antimatter. In the early Universe processes must have existed that distinguished between matter and anti-matter. The Russian physicist Sakharov showed that three conditions have to be fulfilled. One of these is particles and anti-particle should behave differently under the combined operation of charge conjugation (swapping of particle and anti-particle) and parity (left-right mirror symmetry) called CP. In the Standard Model of particle physics CP violation is predicted to occur. All measurements made so far agree with the Standard Model picture. However, the level of CP violation in the Standard Model is much too small to explain the observed dominance of matter in our Universe. One possibility is that New Physics such as Supersymmetry leads to additional sources of CP violation. In order to resolve this puzzle more precise measurements are needed. If discrepancies, compared to the Standard Model picture, are found this will be strong evidence for New Physics and also constrain its form. The Large Hadron Collider, which is starting operation at CERN, will open a new era in physics. The Large Hadron Collider Beauty Experiment (LHCb) is a special purpose experiment running at the LHC. The collaboration consists of around 400 physicists from 52 institutes world-wide. By studying very precisely differences in the rate of decays containing b and anti-b quarks it will provide insight into the phenomenon of CP asymmetries. CP violation in Bs mixing is a fundamental prediction of the Standard Model. The mixing phase, beta_s, is relatively unconstrained. Recently, first measurements of this parameter have been made by CDF and D0. Though the uncertainties are large they favour values much larger than predicted by the Standard Model. LHCb will make precise measurements of this quantity and will either reveal the presence of New Physics or confirm the Standard Model prediction. Uniquely, the experiment is able to make measurements in many decay modes allowing important cross-checks of the consistency of the data and analysis to be made. The main aim of this proposal is the measurement of the Bs mixing phase at LHCb. I will first measure this quantity using the golden mode Bs->J/psi phi. The statistics in this mode are large and it is relatively easy to trigger and reconstruct. It will be an important early measurement for the experiment. Following this, I will measure this quantity in the mode Bs-> J/Psi eta' and also study the channel Bd -> phi phi. These modes are harder to reconstruct and have lower yields and it will take several years to collect a statistically significant sample. One way to increase the yields will be to run the experiment at higher luminosity. LHCb is planning to upgrade the trigger and electronics of the experiment around 2015 in order to run at higher luminosities and to collect even higher statistics. The higher luminosity will result in a busier environment for triggering and reconstruction as well as increasing the radiation damage suffered by the detector. I will contribute to studies of the global detector optimization with the aim of minimizing the amount of material in the detector.

宇宙最令人费解和迄今未解释的特征之一是没有反物质。在大爆炸期间，物质和反物质的产生数量相等。然而，根据对宇宙线的测量，我们知道我们的星系主要由物质组成。此外，没有证据表明，在有反物质云的遥远星系中，物质和反物质湮灭后会发出强烈的伽马射线。在早期宇宙中，一定存在区分物质和反物质的过程。俄罗斯物理学家萨哈罗夫指出，必须满足三个条件。其中之一是粒子和反粒子在电荷共轭(粒子和反粒子的交换)和宇称(左右镜像对称)的组合作用下应该表现出不同的行为，称为CP。在粒子物理的标准模型中，预测会发生CP破坏。到目前为止所做的所有测量都与标准模型图片一致。然而，标准模型中的CP破坏水平太小，无法解释我们观察到的宇宙中物质的主导地位。一种可能性是，超对称性等新物理学导致了CP破坏的额外来源。为了解决这个难题，需要更精确的测量。如果与标准模型图相比，发现了差异，这将是新物理学的有力证据，也限制了它的形式。在欧洲核子研究中心开始运行的大型强子对撞机将开启物理学的新纪元。大型强子对撞机美容实验(LHCb)是在大型强子对撞机上运行的一个特殊目的的实验。该合作由来自世界各地52个研究所的约400名物理学家组成。通过非常精确地研究包含b夸克和反b夸克的衰变速率的差异，它将提供对CP不对称现象的洞察。BS混合中的CP破坏是标准模型的一个基本预测。混合相β_S相对不受约束。最近，CDF和D0首次对这一参数进行了测量。尽管不确定性很大，但它们倾向于比标准模型预测的值大得多的值。LHCB将对这一量进行精确测量，并将揭示新物理的存在或证实标准模型的预测。独一无二的是，该实验能够在许多衰减模式下进行测量，从而允许对数据的一致性进行重要的交叉检查和分析。这项建议的主要目的是测量LHCb中的BS混合相。我将首先使用金色模式BS-&gt；J/psi Phi来测量这个量。这种模式的统计量大，触发和重构相对容易。这将是实验的一项重要的早期测量。接下来，我将在模式Bs-&gt；J/Psi Eta‘中测量这个量，并研究通道Bd-&gt；Phi Phi。这些模式更难重建，而且收益率较低，需要几年时间才能收集到具有统计意义的样本。增加产量的一种方法是在更高的光度下进行实验。LHCb计划在2015年左右升级该实验的触发器和电子设备，以便在更高的亮度下运行，并收集更高的统计数据。较高的光度将导致触发和重建的环境更加繁忙，以及增加探测器遭受的辐射损伤。我将致力于全球探测器优化的研究，目的是将探测器中的材料数量降至最低。

项目成果

Measurement of the B s 0 ? D s ( * ) + D s ( * ) - branching fractions

B s 0 的测量？

• DOI: 10.1103/physrevd.93.092008
• 发表时间: 2016
• 期刊: Physical Review D
• 影响因子: 5
• 作者: Aaij R