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

宇宙中最令人困惑和至今无法解释的特征之一是不存在反物质。在大爆炸期间，物质和反物质以相等的数量产生。然而，通过对宇宙射线的测量，我们知道我们的星系主要由物质组成。此外，也没有证据表明，在有反物质云的遥远星系中，物质和反物质湮灭后会产生强烈的伽马射线辐射。在早期的宇宙中，一定存在着区分物质和反物质的过程。俄国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）的组合操作下应该有不同的行为，称为CP。在粒子物理学的标准模型中，CP破坏被预言会发生。到目前为止，所有的测量结果都与标准模型的图像一致。然而，标准模型中CP破坏的水平太小，无法解释我们宇宙中物质的观测优势。一种可能性是新物理学，如超对称性，导致CP破坏的额外来源。为了解决这个难题，需要更精确的测量。如果与标准模型的图像相比，发现差异，这将是新物理学的有力证据，也限制了它的形式。欧洲核子研究中心的大型强子对撞机即将开始运行，它将开启物理学的新纪元。大型强子对撞机美丽实验（LHC b）是在LHC上运行的一个特殊目的实验。该合作由来自全球52个研究所的约400名物理学家组成。通过非常精确地研究含有B夸克和反B夸克的衰变速率的差异，它将提供对CP不对称现象的深入了解。Bs混合中的CP破坏是标准模型的一个基本预言。混合相β_s相对不受约束。最近，CDF和D 0首次测量了该参数。虽然不确定性很大，但它们倾向于比标准模型预测的值大得多的值。LHCb将对这个量进行精确测量，并将揭示新物理学的存在或证实标准模型的预测。独特的是，该实验能够在许多衰变模式下进行测量，从而可以对数据和分析的一致性进行重要的交叉检查。该建议的主要目的是测量LHCb的Bs混合相。我将首先使用黄金模式Bs->J/psi phi测量这个量。这种模式下的统计量很大，触发和重建相对容易。这将是实验的一个重要的早期测量。在此之后，我将在模式Bs-> J/Psieta '中测量该量，并且还研究通道Bd -> phi phi。这些模式很难重建，产量较低，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年左右升级实验的触发器和电子设备，以便在更高的光度下运行并收集更高的统计数据。更高的亮度将导致触发和重建的繁忙环境，以及增加探测器遭受的辐射损伤。我将有助于研究的全球探测器优化的目的是最大限度地减少在探测器中的材料量。

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.