Observation of new excited Bs0 states using the LHCb Detector

Date of Award

December 2020

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physics

Advisor(s)

Matthew Rudolph

Subject Categories

Physical Sciences and Mathematics

Abstract

In this thesis, the observation of new excited Bs0 states in the B+K- spectrum is presented. The dataset was collected by the LHCb detector at CERN, with 7 TeV centre-of-mass energy in 2011, 8 TeV in 2012, and 13 TeV in 2015-2018. The corresponding total integrated luminosity is around 9 fb-1. The structure is interpreted as the result of overlapping excited Bs0 states with a global significance better than 20 sigma. With high significance of at least 8 sigma with respect to the one peak hypothesis, a two-peak hypothesis provides a better description of the data than a single resonance. Under this hypothesis the masses and widths of the two states, assuming they decay directly to B+K-, are determined to be:

m1 = 6062.7 +- 1.0 (stat) +- 0.4 (syst) MeV,

Gamma1 = 20.2 +- 3.9 (stat) +- 2.7 (syst) MeV,

m2 = 6107.7 +- 5.2 (stat) +- 2.0 (syst) MeV,

Gamma2 = 81.9 +- 17.0 (stat) +- 27.8 (syst) MeV.

Alternative values assuming a decay through B*+K-, with a missing photon from the B*+ -> B+ gamma decay, are also determined. The ratio of the total production cross-section times branching fraction of the new states relative to the previously observed Bs2* state is determined to be 0.791 +- 0.075 (stat) +- 0.091 (syst). Additionally, measurements on silicon sensors for the LHCb Upstream Tracker (UT) upgrade are also presented in this thesis.

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