CP-violating phases in neutral meson oscillations

Abstract

LHCb is one of the four large experiments at the Large Hadron Collider (LHC) at CERN, Geneva, Switzerland and is dedicated to heavy flavour physics. LHCb searches for New Physics (NP) by performing precision measurements of CP-violating parameters.One of the key measurements of LHCb is the extraction of the CP-violating weak phase ϕs. The Standard Model (SM) prediction for this parameter is small: ϕsSM=2arg(VtbVts⁎VcbVcs⁎)=−0.0364±0.0016 [J. Charles, et al., CKMfitter Group, European Physical Journal C 41 (2005) 1–131, updated results and plots available at: http://ckmfitter.in2p3.fr. arXiv:hep-ph/0406184.]. Possible deviations from this SM prediction may be attributed to NP. The parameter ϕs is measured by performing a time-dependent angular analysis of Bs0→J/ψϕ decays and independently by a time-dependent analysis of Bs0→J/ψππ decays. A simultaneous fit to both decays yields ϕs=−0.002±0.083(stat.)±0.027(syst.). The fitted values of ϕs and the lifetime difference ΔΓs exhibit a phase ambiguity, which is resolved by performing fits in bins of the K+K− invariant mass and looking at the difference in fitted strong phases of P-wave and S-wave contributions. Finally, as a first step towards controlling penguin contributions to b→c(c¯s) transitions such as Bs0→J/ψϕ decays, a branching ratio measurement of Bs0→J/ψK¯⁎0 decays is presented.In addition to the ϕs measurement, two other analyses are presented here. Firstly, preliminary results of the LHCb asls measurement are presented. The second analysis is the measurement of triple product asymmetries in Bs0→ϕϕ decays.The branching ratio measurement of Bs0→J/ψK¯⁎0 decays is extracted from a dataset with an integrated luminosity of 0.37 fb−1. The results from all other aforementioned analyses are extracted from the full 2011 LHCb data set which has an integrated luminosity of 1.0 fb−1.