Search for b → sττ decays at the LHCb experiment
File(s)
Author(s)
Tilquin, Hanae
Type
Thesis
Abstract
Several measurements of decays of b-hadrons underpinned by flavour changing neutral currents show deviations with their Standard Model predictions. New physics models that explain these anomalous results could feature enhanced couplings to third generation fermions, leading to sizeable branching fractions for b → sττ decays. However, b → sττ decays have never been observed. They are experimentally difficult to detect, and have a small branching fraction in the Standard Model. This thesis reports a novel search for b → sττ transitions with two muonic tau decays. The search is made with pp collision data at a centre-of-mass energy of 13 TeV corresponding to an integrated luminosity of 5.6 fb−1, recorded by the LHCb experiment between 2016 and 2018. The searches are carried out for Bs → K+K−τ+τ− and B0 → K+π−τ+τ− decays, as well as for the b → dτ τ process Bs → K−π+τ+τ−, in the entire
dihadron mass ranges. No signal is found and so upper limits for the branching fractions of
these decays are set, which are an order of magnitude more stringent than the current world’s best results. The resulting upper limits on the branching fractions of B0 → K∗(892)ττ and Bs → ϕ(1020)ττ are 2.5 × 10−4 at 95% CL and 5.5 × 10−4 at 95% CL respectively.
dihadron mass ranges. No signal is found and so upper limits for the branching fractions of
these decays are set, which are an order of magnitude more stringent than the current world’s best results. The resulting upper limits on the branching fractions of B0 → K∗(892)ττ and Bs → ϕ(1020)ττ are 2.5 × 10−4 at 95% CL and 5.5 × 10−4 at 95% CL respectively.
Version
Open Access
Date Issued
2024-09-09
Date Awarded
2025-01-01
Copyright Statement
Creative Commons Attribution NonCommercial Licence
License URL
Advisor
Patel, Mitesh
Smith, Mark
Sponsor
Science and Technology Facilities Council (Great Britain)
Publisher Department
Physics
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)