Abstract
The first measurement of decay-time-dependent CP asymmetries in the decay $B_s^0\rightarrow J/\psi K_{\rm S}^0$ and an updated measurement of the ratio of branching fractions $\mathcal{B}(B_s^0\rightarrow J/\psi K_{\rm S}^0)/\mathcal{B}(B_d^0\rightarrow J/\psi K_{\rm S}^0)$} are presented. The results are obtained using data corresponding to an integrated luminosity of 3.0 fb$^{-1}$ of proton-proton collisions recorded with the LHCb detector at centre-of-mass energies of 7 and 8 TeV. The results on the CP asymmetries are $A_{\Delta\Gamma}(B_s^0\rightarrow J/\psi K_{\rm S}^0) = 0.49_{-0.65}^{+0.77}(stat) \pm 0.06(syst)$, $C_{\rm dir}(B_s^0\rightarrow J/\psi K_{\rm S}^0) = -0.28 \pm 0.41(stat) \pm 0.08(syst)$ and $S_{\rm mix}(B_s^0\rightarrow J/\psi K_{\rm S}^0) = -0.08 \pm 0.40(stat) \pm 0.08(syst)$. The ratio $\mathcal{B}(B_s^0\rightarrow J/\psi K_{\rm S}^0)/\mathcal{B}(B_d^0\rightarrow J/\psi K_{\rm S}^0)$ is measured to be $0.0431 \pm 0.0017(stat) \pm 0.0012(syst) \pm 0.0025(f_s/f_d)$, where the last uncertainty is due to the knowledge of the $B_s^0$ and $B_d^0$ production fractions.
Highlights
Forthcoming data from the LHC and KEK e+e− super B factory will lead to an unprecedented precision on the phase φedff
This paper presents the first measurement of the time-dependent CP asymmetries in Bs0 → J/ψ KS0 decays, as well as an updated measurement of the ratio of time-integrated branching fractions B(Bs0 → J/ψ KS0)/B(B0 → J/ψ KS0)
The opposite side (OS) taggers determine the flavour of the non-signal b-hadron [29] while the same side kaon (SSK) tagger exploits the fact that the additional s (s) quark produced in the fragmentation of a Bs0 (B0s) meson often forms a K+ (K−) meson [30]
Summary
The LHCb detector [15, 16] is a single-arm forward spectrometer covering the pseudorapidity range 2 < η < 5, designed for the study of particles containing b or c quarks. The tracking system provides a measurement of momentum, p, of charged particles with a relative uncertainty that varies from 0.5% at low momentum to 1.0% at 200 GeV/c. The minimum distance of a track to a primary vertex, the impact parameter, is measured with a resolution of (15 + 29/pT) μm, where pT is the component of the momentum transverse to the beam, in GeV/c. Electrons and hadrons are identified by a calorimeter system consisting of scintillating-pad and preshower detectors, an electromagnetic calorimeter and a hadronic calorimeter. Decays of hadronic particles are described by EvtGen [20], in which final-state radiation is generated using Photos [21]. The interaction of the generated particles with the detector, and its response, are implemented using the Geant toolkit [22, 23] as described in ref. The interaction of the generated particles with the detector, and its response, are implemented using the Geant toolkit [22, 23] as described in ref. [24]
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