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Register a new userCP Violation in Bs->J/psi phi
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Yuehong Xie
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Study of CP violation in the decay channel Bs->J/psi phi is essential to exploring and constraining physics beyond the Standard Model in the quark flavour sector. The experimental progress in this area of activity at the LHC and Tevatron is discussed.
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We briefly discuss measurements of CP violation in Bs --> J/psi phi decay. Both the phenomenology of Bs mixing and the importance of the measurement to searches for new physics, as well as technical details and issues with the analysis are included. While current results are consistent with the standard model, even large contributions from new physics cannot be excluded.
The CP asymmetry predicted by the Standard Model in the decay modes Bs;d -> J/psi eta and Bs -> J/psi phi is very small, and the observation of a sizeable e ect would be a clear indication of new physics beyond the Standard Model. Contrary to the final state J/psi phi, the former final state is a CP eigenstate, and therefore complex angular distribution analyses are not necessary for the asymmetry measurement. In this paper, the approaches for the study of these two decay channels are presented.
Using data collected with the LHCb detector in proton-proton collisions at a centre-of-mass energy of 7 TeV, the hadronic decay Bs -> J/psi f0(980) is observed. This CP eigenstate mode could be used to measure mixing-induced CP violation in the B_s system. Using a fit to the pi+ pi- mass spectrum with interfering resonances gives R_{f0/phi} = [Gamma(Bs -> J/psi f0, f0 -> pi+ pi-)]/[Gamma(Bs -> J/psi phi, phi -> K+K-)] = 0.252^{+0.046+0.027}_{-0.032-0.033}, where the uncertainties are statistical and systematic, respectively.
Measurement of the mixing-induced CP-violating phase phi_s in Bs decays is of prime importance in probing new physics. Here 7421 +/- 105 signal events from the dominantly CP-odd final state J/psi pi+ pi- are selected in 1/fb of pp collision data collected at sqrt{s} = 7 TeV with the LHCb detector. A time-dependent fit to the data yields a value of phi_s=-0.019^{+0.173+0.004}_{-0.174-0.003} rad, consistent with the Standard Model expectation. No evidence of direct CP violation is found.
We present a measurement of the CP-violating parameter betas using approximately 6500 $BsJpsiPhi$ decays reconstructed with the CDF,II detector in a sample of $pbar p$ collisions at $sqrt{s}=1.96$ TeV corresponding to 5.2 fb$^{-1}$ integrated luminosity produced by the Tevatron Collider at Fermilab. We find the CP-violating phase to be within the range $betas in [0.02, 0.52] cup [1.08, 1.55]$ at 68% confidence level where the coverage property of the quoted interval is guaranteed using a frequentist statistical analysis. This result is in agreement with the standard model expectation at the level of about one Gaussian standard deviation. We consider the inclusion of a potential $S$-wave contribution to the $Bsto J/psi K^+K^-$ final state which is found to be negligible over the mass interval $1.009 < m(K^+K^-)<1.028 gevcc$. Assuming the standard model prediction for the CP-violating phase betas, we find the Bs decay width difference to be $deltaG = 0.075 pm 0.035,textrm{(stat)} pm 0.006,textrm{(syst)} ps$. We also present the most precise measurements of the Bs mean lifetime $tau(Bs) = 1.529 pm 0.025,textrm{(stat)} pm 0.012,textrm{(syst)}$ ps, the polarization fractions $|A_0(0)|^2 = 0.524 pm 0.013,textrm{(stat)} pm 0.015,textrm{(syst)}$ and $|A_{parallel}(0)|^2 = 0.231 pm 0.014,textrm{(stat)} pm 0.015,textrm{(syst)}$, as well as the strong phase $delta_{perp}= 2.95 pm 0.64,textrm{(stat)} pm 0.07,textrm{(syst)} textrm{rad}$. In addition, we report an alternative Bayesian analysis that gives results consistent with the frequentist approach.
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