Repository logo
 

Tests of lepton universality in $B^{0} \to K_{S}^{0} l^{+} l^{-}$ and $B^{+} \to K^{*+} l^{+} l^{-}$ decays at the LHCb experiment


Type

Thesis

Change log

Authors

Smeaton, John 

Abstract

The decays B0KS0l+l and B+K∗+l+l - where l+l represents an electron-positron or muon-antimuon pair - are examples of bsl+l processes. Numerous analyses of such decays have found tensions with predictions under the Standard Model (SM) of particle physics. These tensions form a coherent pattern, which could be caused by a novel physical effect.

Ratios of branching fractions for muon-mode and electron-mode bsl+l processes can be predicted with O(1%) precision under the SM, and can provide stringent experimental tests for novel physical processes which violate lepton universality. This dissertation presents new measurements of such ratios using B0KS0l+l and B+K∗+l+l decays, denoted RKS0−1 and RK∗+−1. These measurements used data from pp collisions collected using the LHCb detector between 2011 and 2018, with a total sample size of 9fb−1 . The results are:

RKS0−1=1.51−0.35+0.40(stat.)−0.04+0.09(syst.)

RK∗+−1=1.44−0.29+0.32(stat.)−0.06+0.09(syst.)

Here, the first uncertainties are statistical, and the second systematic. Both RKS0−1 and RK∗+−1 consistent with SM expectations, at significances of 1.5σ and 1.4σ , respectively. In addition, differential branching fractions for the decays B0KS0e+e and B+K∗+e+e are measured in bins of the dilepton invariant mass squared. The first ever observations of these decays are reported.

Description

Date

2022-03-01

Advisors

Gibson, Valerie

Keywords

B Physics, CERN, Flavour Physics, High-Energy Physics, Large Hadron Collider, LHCb Experiment, Particle Physics

Qualification

Doctor of Philosophy (PhD)

Awarding Institution

University of Cambridge
Sponsorship
STFC (1948363)
Science and Technology Facilities Council (1948363)
Science and Technology Facilities Council (STFC)

Collections