Time dependent studies of B->h+h'- decays and research and operation for the VELO project at LHCb

Dean, Cameron (2019) Time dependent studies of B->h+h'- decays and research and operation for the VELO project at LHCb. PhD thesis, University of Glasgow.

Abstract

The family of B->h+h'- decays, where h refers to protons, pions or kaons, are of great interest to the particle physics community. Two such decays, Bs0->K+K- and B0->pi+pi-, are related by U-spin symmetry with their tree levels decays suppressed, resulting in equal contributions from their loop level decays. Hence they are a good place to search for physics beyond the Standard Model.

This thesis discusses two separate studies of this class of decay. One study measures the effective lifetimes of the decays B0->pi+pi-, B0->K+pi-, Bs0->pi+K-, Bs0->K+K-, Lb0->pK-, and Lb0->ppi- at 7 and 8 TeV which corresponds to an integrated luminosity of 1 fb-1 and 2 fb-1 respectively. The effective lifetime of Bs0->K+K- can be used to constrain the value of the CP observable ADeltaGammaKK.

The other analysis discusses time-dependent measurements of CP violation in B0->pi+pi- and Bs0->K+K- decays at 13 TeV which corresponds to an integrated luminosity of 2fb-1. These decays can be used to place constraints on the Unitarity Triangle angles beta and gamma to test for deviations from inclusive measurements of these angles. The analysis at 13 TeV measured the CP observables for B0->pi+pi- and Bs0->K+K- to be

For B0->pi+pi-, the correlation between Spipi and Cpipi was measured to be -0.15 while, for Bs0->K+K-, the correlation was measured to be -0.012 between SKK and CKK. These results are the most precise from a single experiment to date.

The LHCb detector has performed exceptionally since the start of data taking at the LHC with many important results reported. To ensure the optimal performance it is important to inspect and validate different subdetectors throughout the life of the experiment. The Vertex Locator (VELO) detector surrounds the interaction point of the proton collisions and is the first detector the collision products traverse. To ensure a good signal quality, the silicon strips must be fully depleted. As the detector ages the effective depletion voltage increases so the high voltage system must be qualified to ensure it can cope. Tests of this subsystem were devised to study the high voltage supply at different stages of the system where it was found that the VELO is performing to expectations and that LHCb can meet its physics goals for the foreseen lifetime of the current detector until its replacement by the upgraded LHCb. To ensure that this performance will continue until its end of use, monitoring software was developed and deployed for use by on-call experts to observe the evolution of the leakage currents within the detector.

With the current design of LHCb, it would become prohibitively long to the statistical uncertainties on the physics channels of interest to the collaboration and the current trigger scheme would become saturated in the high-luminosity LHC environment. At the end of Run II of the LHC in 2018, the LHCb collaboration will begin the implementation of an upgraded detector. The current VELO will be removed and replaced with a new design which will improve the physics reach of the collaboration beyond the current limitations.

To this end, studies of the electrical characterisation of high speed transmission lines have been performed on several prototypes to produce the best possible final detector. The signal transmission properties and impedances have been measured and used to define the designs of several components that will be inserted in the final detector. Further to these tests, the bit-error rates, jitter and the effect of bending of the high speed flex cables have been studied with all the properties found to be within the desired constraints. With this knowledge, the design of the VELO is moving to its final stages and should ensure the production of a detector capable of producing the quality of physics expected of the LHCb collaboration within the time frame set out by the upgrade team.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Flavour physics, CP violation, LHCb, VELO, detector development, signal quality.
• Subjects: Q Science > QC Physics
• Colleges/Schools: College of Science and Engineering > School of Physics and Astronomy
• Funder's Name: Science & Technology Facilities Council (STFC)
• Supervisor's Name: Eklund, Prof. Lars
• Date of Award: 2019
• Depositing User: Cameron Dean
• Unique ID: glathesis:2019-40969
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 05 Feb 2019 13:56
• Last Modified: 05 Oct 2021 15:14
• Thesis DOI: 10.5525/gla.thesis.40969
• URI: https://theses.gla.ac.uk/id/eprint/40969