Constraints on mixing and CP-violation in the neutral charmed meson system at LHCb

Alexander, Michael T. (2012) Constraints on mixing and CP-violation in the neutral charmed meson system at LHCb. PhD thesis, University of Glasgow.

Abstract

This thesis presents measurements of the charm sector mixing and CP-violation parameters yCP and AGamma, made using data collected in 2010 by the LHCb experiment at the LHC at s^1/2 = 7 TeV. yCP is defined as the difference from unity of the ratio of the effective lifetime of the D0 meson decaying to a CP-undefined final state to its lifetime when decaying to a CP-eigenstate. AGamma is the CP-asymmetry of the effective lifetimes of the D0 and D0bar when decaying to a CP-eigenstate. In the absence of CP-violation yCP will be consistent with the mixing parameter y, and AGamma will be consistent with zero.

CP-violation in the charm sector is predicted to be very small in the SM, though first evidence for direct CP-violation in D0 decays has recently been observed by LHCb. Observation of significantly more CP-violation than is allowed in the SM would be a strong indication of new physics. The current world best measurements of yCP and AGamma show no evidence of CP-violation.

The methods used to measure the effective lifetime of the D0 are presented, together with a detailed study of the impact parameter resolutions achieved by Vertex Locator (VELO) sub-detector. A resolution of < 36 μm on the x and y components of impact parameter measurements is measured for particles with pT > 1 GeV. The final dataset on which yCP and AGamma are measured comprises 28.0 +/- 2.8 pb−1, from which 226,110 D0 to Kpi and 30,481 D0 to KK candidates are selected. The dominant sources of systematic uncertainty arise from combinatorial backgrounds and D0 produced in decays of B mesons. The final results are found to be
AGamma = (−5.9 +/- 5.9 (stat.) +/- 2.1 (syst.)) x 10−3,
yCP = (5.5 +/- 6.3 (stat.) +/- 4.1 (syst.)) x 10−3.
yCP is consistent with the world average of y and with zero, and AGamma is consistent with zero. Thus, these results show no evidence for CP-violation or mixing in the D0 system.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: LHCb, charm, CP violation, mixing, yCP, AGamma, D0, lifetime, VELO, impact parameter resolution
• Subjects: Q Science > QC Physics
• Colleges/Schools: College of Science and Engineering > School of Physics and Astronomy
• Supervisor's Name: Chris, Dr. Parkes and Paul, Dr. Soler
• Date of Award: 2012
• Depositing User: Dr M Alexander
• Unique ID: glathesis:2012-3549
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 07 Aug 2012
• Last Modified: 10 Dec 2012 14:08
• URI: https://theses.gla.ac.uk/id/eprint/3549