Abstract
A flavour-tagged decay-time-dependent amplitude analysis of Bs0 → (K+π−)(K−π+) decays is presented in the K±π∓ mass range from 750 to 1600MeV/c2. The analysis uses pp collision data collected with the LHCb detector at centre-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3.0 fb−1. Several quasi-two-body decay modes are considered, corresponding to K±π∓ combinations with spin 0, 1 and 2, which are dominated by the K0*(800)0 and K0*(1430)0, the K*(892)0 and the K2*(1430)0 resonances, respectively. The longitudinal polarisation fraction for the {B}_s^0to {K}^{ast }(892){}^{circ}{overline{K}}^{ast }{(892)}^0 decay is measured as fL = 0.208 ± 0.032 ± 0.046, where the first uncertainty is statistical and the second is systematic. The first measurement of the mixing-induced CP-violating phase, {phi}_s^{doverline{d}} , in bto doverline{d}s transitions is performed, yielding a value of {phi}_s^{doverline{d}}=-0.10pm 0.13left(mathrm{stat}right)pm 0.14 (syst) rad.
Highlights
K ∗0 s dominated by the gluonic loop diagram shown in figure 1, has been discussed extensively in the literature as a benchmark test for the SM and as an excellent probe for physics beyond the SM [1,2,3,4,5,6,7]
The weak phase φs depends on the Bs0 decay channel under consideration, and can be different between channels as it depends on the contributions from tree- and loop-level processes
The CP -averaged fractions of the contributing amplitudes, fi, as well as their strong-phase differences, δi, are determined together with the CP -violating weak phase φdsd and a parameter that accounts for the amount of CP violation in decay, |λ|
Summary
The phenomenon of quark mixing means that a Bs0 meson can oscillate into its antiparticle equivalent, B0s. The total decay amplitude of the flavour eigenstates at t = 0 into the final state f = (K+π−)(K−π+), denoted by f |Bs0(0) and f |B0s(0) , is a coherent sum of scalar-scalar (SS), scalar-vector (SV), vector-scalar (VS), scalar-tensor (ST), tensor-scalar (TS), vector-vector (VV), vector-tensor (VT), tensor-vector (TV) and tensor-tensor (TT) contributions. Since only the phase evolution of M0 is linked to that of the scattering amplitude (by virtue of Watson’s theorem [18]), its modulus is parameterised with a fourth-order polynomial whose coefficients are determined in the final fit to data. Details of this parameterisation can be found in appendix B.
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