Search for time-dependent CP violation in D0→ π +π −π 0 decays and precision luminosity measurements at LHCb

McHugh, Niall (2024) Search for time-dependent CP violation in D0→ π +π −π 0 decays and precision luminosity measurements at LHCb. PhD thesis, University of Glasgow.

Abstract

The results of an absolute luminosity measurement at the LHCb experiment and a search for time-dependent CP violation in D0 meson decays are presented in this thesis. An overview of the underlying theory relevant to time-dependent CP violation in the neutral meson systems is also provided, with a particular focus on neutral charmed-mesons. The LHCb detector that recorded the data used for these measurements is also described in detail, along with its recent upgrade for Runs 3 and 4 of the LHC.

An absolute determination of the luminosity at the LHCb experiment between 2016 and 2018 in pp collisions at √ s = 13 TeV is obtained by directly reconstructing the beam profiles from beam-gas interactions. A cross section of

σVertex = 58.00 ± 0.02 (stat) ± 0.46 (syst) mb

for the Vertex counter is obtained, with a preliminary relative precision of 0.83%. The largest systematic uncertainties arise from corrections to the beam-gas vertex resolution, measurement spread believed to be caused by an imperfect bunch profile description, and uncertainty on the bunch current measurements. The dominant systematic uncertainties are largely uncorrelated with the complementary van der Meer analysis. The combination of the two measurements therefore has the potential to be the most precise determination of the absolute luminosity at a hadron collider to date.

A measurement of time-dependent CP violation in D0 → π +π −π 0 decays collected by the LHCb experiment in 2012 and from 2015 to 2018, corresponding to an integrated luminosity of 7.7 fb−1 , is also presented. The flavour of each D0 candidate is determined from the decay D∗ (2010)+ → D0π +. Detection asymmetries are corrected with a data-driven weighting procedure. The gradient of the time-dependent CP-asymmetry, ∆Y , is measured to be

∆Y = (−1.3 ± 6.3 (stat) ± 2.4 (syst)) × 10−4 ,

which is compatible with CP conservation. The decay D0 → K−π +π 0 is used as a control channel to validate the measurement procedure. After correcting for detection asymmetries, the control channel is also found to be compatible with no time-dependent CP asymmetry.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Subjects: Q Science > QB Astronomy; Q Science > QC Physics
• Colleges/Schools: College of Science and Engineering > School of Physics and Astronomy
• Supervisor's Name: Soler, Professor Paul
• Date of Award: 2024
• Depositing User: Theses Team
• Unique ID: glathesis:2024-84456
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 08 Jul 2024 15:08
• Last Modified: 10 Jul 2024 13:54
• Thesis DOI: 10.5525/gla.thesis.84456
• URI: https://theses.gla.ac.uk/id/eprint/84456