Charged Lepton flavour violation and Optimised 4D Tracking at LHCb

Thompson, Daniel James David ORCID: 0000-0003-1196-5943 (2025). Charged Lepton flavour violation and Optimised 4D Tracking at LHCb. University of Birmingham. Ph.D.

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Abstract

The first estimated upper limit for the branching fraction of the forbidden decay \(\Lambda_b^0\rightarrow\Lambda(1520)\mu^\pm e^\mp\) is presented. This is calculated using data collected by the LHCb experiment in 2011-12 and 2016-18, corresponding to an integrated luminosity of 8.7 fb\(^{-1}\). This decay is forbidden in the Standard Model of particle physics and hence this constitutes a search for Charged Lepton Flavour Violation (cLFV) and an observation of signal would be unequivocal evidence for New Physics.

While any hints or evidence of signal would transform the analysis outlook, the search for \(\Lambda_b^0\rightarrow\Lambda(1520)\mu^\pm e^\mp\) remains blinded and the presented results are based on a background-only dataset assuming no signal. An estimated upper limit of \[\mathcal{B}(\Lambda_b^0\rightarrow\Lambda(1520)\mu^\pm e^\mp) \lesssim 2.8\times 10^{-8}\;@\;95\%\;\mathrm{confidence\;level}\] is evaluated, from an overall low-background analysis strategy. This limit is competitive with other cLFV searches in the decays of \(b\)-hadrons.

During Long-Shutdown 4 of the LHC, a major upgrade to the LHCb experiment is planned, to enable the detector to derive maximum benefit from the High-Luminosity LHC. An investigation of a potential sensor technology for the VELO sub-detector is presented, concluding that the LGADs tested are unable to withstand the high-radiation environment of the HL-LHC. A flexible approach to VELO Upgrade II simulation is also introduced to develop and evaluate performance of candidate designs. This lead to the conclusion that a detector with fast timing, improved spatial resolution and a larger inner radius is essential to meet the requirements of LHCb Upgrade II. Finally, a tool to allow performance optimisation of the entire LHCb Upgrade II detector has been developed, and used for the first investigations of inter-subdetector performance with LHCb core software.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):