Searches for CP violation in D+ to K-K+pi+ decays at the LHCb experiment

Thesis

This thesis documents searches for direct CP violation in the Cabibbo-suppressed D+ to K-K+pi+ decay at the LHCb experiment. Two complementary analyses are described. Direct CP-violating asymmetries are predicted to exist in singly Cabibbo-suppressed charm decays with magnitudes of up to O(0.001) in the Standard Model, and can be enhanced to the percent level by contributions from new physics. No such asymmetry has yet been observed.

The LHCb detector is a forward spectrometer with a precise vertex detector and powerful particle identification capabilities, designed to collect large, pure samples of charm and $B$ decays. Data collected at LHCb in 2010 corresponding to an integrated luminosity of 35pb^-1 are used to perform a model-independent search for direct CP violation in the D+ to K-K+pi+ decay. The Dalitz plot is divided into bins and a chi^2 test of the compatibility of the dataset with no CP violation is performed. No evidence of CP violation is found.

A second search for CP violation in the region of the D+ to K-K+pi+ Dalitz plot around the phi resonance is described. The charge asymmetry in this decay is calculated and compared to that in the control channel D+ to Ks(pi+pi-)pi+. The 1.0fb^-1 of data collected at LHCb in 2011 are used. The CP-violating asymmetry is found to be (-0.04+/-0.14+/-0.14)% where the uncertainties are statistical and systematic, respectively. A new observable sensitive to CP violation that varies across the phi resonance is defined and measured, and is consistent with no CP violation at the current level of sensitivity. In addition, the CP-violating asymmetry in the decay Ds+ to Ks pi+ is determined to be (0.61+/-0.83+/-0.14)%. There is no evidence for CP violation in either channel. The prospects for new results using data collected in 2012 are very promising and a significant improvement in our understanding of these decays is anticipated.

Authors: Gordon, H

• Publication date: 2013
• DOI: 10.5287/ora-mv6jayb18
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: charm; flavour physics; CP violation
• Subjects: Particle physics