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

点击翻译按钮获取中文摘要

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.