Precision $b$-hadron lifetime and $CP$-violation measurements with the LHCb experiment

在我的职业生涯中，我一直在努力理解“事物是如何运作的”。粒子物理学致力于通过帮助回答科学中一些最基本的问题，从量子到宇宙尺度，来进一步了解宇宙。此外，粒子物理学与技术和高性能计算有着深刻的联系：CERN开发了灵敏的成像探测器，现在用于医疗应用，也是万维网诞生的地方。这些机会激励我攻读博士学位，并继续激励我的研究生涯。粒子物理学的核心是探索自然界的对称性，以及这些对称性是如何被巧妙打破的。在大爆炸期间，创造了等量的物质和反物质，但它们的性质略有不同，导致一种类型比另一种类型存活得更多，导致我们今天生活的宇宙以物质为主。这种差异可以用电荷宇称（CP）对称性的破坏来解释，CP对称性描述了如果一个粒子与它的反粒子（C）互换，然后左右互换（P），那么物理定律对它来说应该是相同的。基本相互作用的标准模型（SM）预测了CP破坏的存在，但只是在很小的数量上，不足以解释我们在宇宙中观察到的物质-反物质不对称性。因此，CP破坏的新来源必须存在于SM之外。LHCb实验试图通过精确测量重夸克的性质来找到这种新的物理学。夸克是构成原子核的质子和中子的基本构件。对重夸克的研究有着悠久而辉煌的历史，导致了许多重要的发现，并将2008年诺贝尔物理学奖授予了第一个在SM中写下CP破坏数学的理论家。LHCb实验正在通过前所未有的详细研究重夸克来延续这一遗产，这是由于它可以在CERN LHC记录，处理和分析的事件样本的巨大规模。LHC的其他实验还没有发现任何超越SM的新物理的直接证据：他们目前正在将他们的搜索能量边界推进到多TeV的尺度。LHCb可以通过在重夸克衰变过程的量子虚环中存在非SM粒子来间接探测更高的能量。我的建议旨在对CP破坏和重夸克性质进行最精确的测量。要做到这一点，需要我们对LHC中发生的许多不同过程的重建和选择有深刻的理解，需要使用巧妙的算法和现代计算技术来帮助我们从巨大的背景噪声中挖掘出信号。这项技术将用于下一代网格/云计算，并具有它带来的所有创新潜力。我们必须了解我们的实验设备对测量的微妙影响，随着数据样本的增加，这项任务只会变得更加困难。总之，SM为我们提供了宇宙的详细描述，但我们知道它不可能是完整的：新的物理必须在那里，只是等待被发现。我很高兴能成为这段旅程的一部分。

Throughout my career I have been driven to understand "how things work". Particle physics strives to further our understanding of the Universe by helping to answer some of the most fundamental questions in science, ranging from the quantum to cosmological scales. In addition, particle physics has a deep link with technology and high performance computing: CERN has developed sensitive imaging detectors which are now used in medical applications and is where the World Wide Web was born. These opportunities inspired me to study for a PhD and continue to inspire my research career.At its heart, particle physics is all about exploring the symmetries of nature and how these symmetries are subtly broken. During the Big Bang equal quantities of matter and antimatter were created, but slight differences in their properties have caused more of one type to survive than the other, leading to the matter dominated Universe that we live in today. This difference can be explained by the violation of Charge-Parity (CP) symmetry which describes how the laws of physics should be the same for a particle if it were interchanged with its antiparticle (C) and then left and right were interchanged (P). The Standard Model (SM) of fundamental interactions predicts the presence of CP-violation, but only in tiny quantities which are insufficient to explain the matter-antimatter asymmetry we observe in the Universe. Therefore, new sources of CP-violation must exist beyond those in the SM.The LHCb experiment attempts to find this new physics through precision measurements of the properties of heavy quarks. Quarks are the fundamental building blocks of the protons and neutrons which make up atomic nuclei. The study of heavy quarks has a long and illustrious history, leading to many important discoveries and the award of the 2008 Nobel prize in physics to the theorists who first wrote down the mathematics of CP-violation in the SM. The LHCb experiment is continuing this legacy by studying heavy quarks in unprecedented detail due to the huge size of the event samples that it can record, process and analyse at the CERN LHC. Other experiments at the LHC have yet to find any direct evidence of new physics beyond the SM: they are currently pushing the energy boundaries of their searches into the multi-TeV scale. LHCb can indirectly probe to much higher energies via the presence of non-SM particles in the quantum virtual loops of the heavy-quark decay processes.My proposal aims to perform the most precise measurements of CP-violating and heavy-quark properties. To do this requires us to have a deep understanding of the reconstruction and selection of many different processes which occur in the LHC, requiring the use of clever algorithms and modern computing technology to help us dig out signals from the large background noise. This technology will be used in the next generation of grid/cloud computing, with all the potential for innovation that it brings. We have to understand the subtle effects which our experimental apparatus can have on the measurements, a task which only becomes more difficult as the size of the data sample grows.In conclusion, the SM gives us a detailed description of the Universe but we know that it cannot be complete: new physics must be out there, just waiting to be discovered. I am hugely excited to be part of this journey.