Beautiful Flavours: Discovering New Physics with B-hadrons and Tau-leptons

Particle Physics is the study of the fundamental nature of the universe. We have known for decades that our best theory to describe physics at large energies and small lengths, the Standard Model, is incomplete. The theory lacks, for example, any particle that can explain the dark matter that we know exists from astrophysics research. The fundamental nature of the physics beyond the Standard Model - the particles and forces involved - is unknown. Despite the Standard Model being nearly 50 years old the key open question in the field remains 'what physics lies beyond the Standard Model?'. The Large Hadron Collider (LHC) collides proton beams at high energies with the goal of exposing this new physics for dedicated, controlled study; I will collect data at the LHC-beauty (LHCb) detector at the LHC and address this crucial question, seeking to discover new fundamental particles. I will use innovative new techniques to provide a greater understanding of the physics that governs the universe around us.

Recently, a series of measurements have provided hints for deviations from Standard Model predictions in very rare processes that consider how often specific particles ('beauty quarks') decay into other particles ('strange quarks' and 'muons' or 'electrons'). Proposed explanations for these effects require additional fundamental particles not present in the Standard Model. I will search for the effects of these new particles in related beauty quark decays; specifically, I will study decays of beauty quarks that involve particles known as 'tau-leptons' (which can be thought of as a heavier version of muons and electrons). Proposed theories that explain the existing anomalous results typically predict much larger effects in these tau-lepton processes. My research therefore offers the opportunity to discover new particles and the physics beyond the Standard Model, offering a potential revolution in the way we understand the universe.

However, detecting and measuring these tau-leptons is extremely challenging; innovative new techniques are crucial. To date, measurements of tau-leptons in similar processes have relied on finding the individual particles that the tau-leptons themselves decay to. I will instead apply Machine Learning techniques that will enable me to reconstruct the properties of the tau-leptons themselves and the full system under study, making use of a holistic approach that combines additional output from the LHCb detector alongside the more traditional information. This will enable me to find interesting signals in the data more effectively, and better reject background that can mimic the signal processes. I will use these methods to make a series of measurements of beauty quark decays that involve tau-leptons and achieve high sensitivity to the presence of new phenomena. I will integrate this approach into the data acquisition and recording philosophy of LHCb, searching explicitly for the first time for these beauty quark decays to tau-leptons in every proton-proton collision at LHCb.

My studies will provide new knowledge and let us understand nature better. If my results are inconsistent with the Standard Model, I will have observed the effects of new particles; my measurements will be sensitive to new particles much heavier than the currently known fundamental particles. Such a discovery would reshape the way we view the universe, potentially offering new insight into the nature of matter itself. However, should my results prove consistent with the Standard Model, I will still have explored a vast landscape of physics across many different energies and masses, and will have placed extremely strong constraints on the behaviour of the physics that lies beyond the Standard Model. My research will give us a new and greater understanding of how the universe works.