Abstract
A flavour-tagged time-dependent angular analysis of {{B} ^0_{s}} !rightarrow {{J /psi }} phi decays is presented where the {J /psi } meson is reconstructed through its decay to an e ^+e ^- pair. The analysis uses a sample of pp collision data recorded with the LHCb experiment at centre-of-mass energies of 7 and 8text {,Te V} , corresponding to an integrated luminosity of 3 text {,fb} ^{-1} . The C!P-violating phase and lifetime parameters of the {B} ^0_{s} system are measured to be {phi _{{s}}} =0.00pm 0.28pm 0.07text {,rad}, {Delta Gamma _{{s}}} =0.115pm 0.045pm 0.011text {,ps} ^{-1} and {Gamma _{{s}}} =0.608pm 0.018pm 0.012text {,ps} ^{-1} where the first uncertainty is statistical and the second systematic. This is the first time that C!P-violating parameters are measured in the {{B} ^0_{s}} !rightarrow {{J /psi }} phi decay with an e ^+e ^- pair in the final state. The results are consistent with previous measurements in other channels and with the Standard Model predictions.
Highlights
The phase difference φs between direct decays and decays through mixing of Bs0 mesons to Charge-Parity (CP) eigenstates is a CP-violating observable
This paper presents a measurement of φs using a flavourtagged time-dependent angular analysis of the Bs0 → J/ψφ mode with J/ψ → e+e− and φ → K + K − decays
The assumed decay-time resolution model, R, consists of a sum of two Gaussian distributions with their widths depending on the per-candidate decay-time uncertainty determined by the vertex fit as detailed in Ref. [18]. The parameters of this model are loosely constrained in the fit of the Bs0 → J/ψ(e+e−)K + K − decay to the values determined using an identical model from a sample of J/ψ → μ+μ− candidates produced at the pp collision vertex (PV)
Summary
The phase difference φs between direct decays and decays through mixing of Bs0 mesons to Charge-Parity (CP) eigenstates is a CP-violating observable. This paper presents a measurement of φs using a flavourtagged time-dependent angular analysis of the Bs0 → J/ψφ mode with J/ψ → e+e− and φ → K + K − decays.1 This is the first time that the Bs0 → J/ψ(e+e−)φ decay is used to measure CP-violating observables, and in particular the phase φs. A comparison of the two results is of interest given the different main sources of systematic uncertainties induced by the markedly different reconstruction of decays with muons in the final state compared to decays with electrons. These differences arise from the significant bremsstrahlung emission of the electrons and the different signatures exploited in the online trigger selection [19–21]. The relevant inputs to the analysis, namely the resolution, efficiency and the flavour tagging, are
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