Abstract
The time-dependent CP asymmetry in B_s^0\to J/\psi K^+K^- decays is measured using $pp$ collision data at \sqrt{s}=7TeV, corresponding to an integrated luminosity of 1.0fb^-1, collected with the LHCb detector. The decay time distribution is characterised by the decay widths \Gamma_L and \Gamma_H of the light and heavy mass eigenstates of the B_s^0--\bar{B}_s^0 system and by a CP-violating phase \phi_s. In a sample of 27\,617 B_s^0\to J/\psi K^+K^- decays, where the dominant contribution comes from B_s^0\to J/\psi\phi\ decays, these parameters are measured to be \phi_s = 0.07 \pm 0.09 (stat) \pm 0.01 (syst) rad, \Gamma_s \equiv (\Gamma_L+\Gamma_H)/2 = 0.663 \pm 0.005 (stat) \pm 0.006 (syst) ps^-1, \Delta\Gamma_s \equiv \Gamma_L -\Gamma_H = 0.100 \pm 0.016 (stat) \pm 0.003 (syst) & ps^-1, corresponding to the single most precise determination of \phi_s, \Delta\Gamma_s and \Gamma_s. The result of performing a combined analysis with B_s^{0} \to J/\psi \pi^+\pi^- decays gives \phi_s = 0.01 \pm 0.07 (stat) \pm 0.01 (syst) rad, \Gamma_s = 0.661 \pm 0.004 (stat) \pm 0.006 (syst) ps^-1, \Delta\Gamma_s = 0.106 \pm 0.011 (stat) \pm 0.007 (syst) & ps^-1. All measurements are in agreement with the Standard Model predictions.
Highlights
The interference between B0s meson decay amplitudes to CP eigenstates J=c X directly or via mixing gives rise to a measurable CP-violating phase s
The results of the fit for the principal physics parameters are given in Table VI for the solution with ÁÀs > 0, showing both the statistical and the total systematic uncertainties described in Sec
The B0s ! J=c þÀ analysis used in this paper is unchanged with respect to Ref. [6] except for: (1) the inclusion of the same-side kaon tagger in the same manner as has already been described for the B0s ! J=c KþKÀ sample
Summary
The interference between B0s meson decay amplitudes to CP eigenstates J=c X directly or via mixing gives rise to a measurable CP-violating phase s. The indirect determination via global fits to experimental data gives 2s 1⁄4 0:0364 Æ 0:0016 rad [2] This paper extends previous LHCb measurements in the B0s ! In this analysis the KþKÀ mass range is extended to Æ30 MeV=c2, and the notation B0s ! J=c KþKÀ is used to include explicitly both P- and S-wave decays [12] In both channels additional same-side flavor-tagging information is used.
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