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Abstract:

A time- and flavor-integrated amplitude analysis of $B^0$ and $B_s^0$ decays to the $(K^{+}{\mathrm{Ï€}}^{−})(K^{−}{\mathrm{Ï€}}^{+})$ final state in the $K^{*}(892{)}^0{\stackrel{¯}{K}}^{*}(892{)}^0$ region is presented, using $pp$ collision data recorded with the LHCb detector in 2011–2018, corresponding to an integrated luminosity of $9{\mathrm{fb}}^{−1}$ . The branching fractions of the $B^0$ and $B_s^0$ decays are measured relative to the $B^0→D^{−}{\mathrm{Ï€}}^{+}$ and $B_s^0→D_s^{−}{\mathrm{Ï€}}^{+}$ modes, respectively. The corresponding longitudinal polarization fractions are found to be $f_L^d=0.600Â\pm 0.022Â\pm 0.017$ and $f_L^s=0.159Â\pm 0.010Â\pm 0.007$ , where the uncertainties are statistical and systematic, respectively. The theory-motivated ratio of the squared $B_s^0$ to $B^0$ longitudinally polarized decay amplitudes is found to be $L_{K^{*0}{\stackrel{¯}{K}}^{*0}}=4.92Â\pm 0.55Â\pm 0.48Â\pm 0.02Â\pm 0.10$ , where the uncertainties are statistical, systematic, due to uncertainty of external mass and lifetime measurements, and due to knowledge of the fragmentation fraction ratio, respectively. This confirms the previously reported tension between experimental determinations and theoretical predictions of longitudinal polarization in $B→VV$ decays at the level of 4.4 standard deviations.

Abstract:

A search is performed for lepton-number-violating $B^{−}→D^{(*)+}{\mathrm{μ}}^{−}{\mathrm{μ}}^{−}$ decays, using data collected by the LHCb experiment in proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of $5.4{\mathrm{fb}}^{−1}$ . No significant signal is observed, and upper limits are set on the branching fractions, $\mathcal{B}(B^{−}→D^{+}{\mathrm{μ}}^{−}{\mathrm{μ}}^{−})<4.6×{10}^{−8}$ and $\mathcal{B}(B^{−}→D^{*+}{\mathrm{μ}}^{−}{\mathrm{μ}}^{−})<5.9×{10}^{−8}$ , at the 95% confidence level.

Abstract:

The decay $B^{Â\pm }→K_{\mathrm{S}}^0{\mathrm{Ï€}}^{Â\pm }$ , with a $CP$ asymmetry expected to be close to zero in the standard model, is theoretically clean and sensitive to potential new physics. An analysis of the decays $B^{Â\pm }→K_{\mathrm{S}}^0{\mathrm{Ï€}}^{Â\pm }$ and $B^{Â\pm }→K_{\mathrm{S}}^0{K}^{Â\pm }$ is performed using proton-proton collision data collected by the LHCb experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of $5.4{\mathrm{fb}}^{−1}$ . The $CP$ asymmetries are determined to be ${\mathcal{A}}^{CP}(B^{Â\pm }→K_{\mathrm{S}}^0{\mathrm{Ï€}}^{Â\pm })=−0.028Â\pm 0.009Â\pm 0.009$ and ${\mathcal{A}}^{CP}(B^{Â\pm }→K_{\mathrm{S}}^0{K}^{Â\pm })=0.118Â\pm 0.062Â\pm 0.031$ , and the branching fraction ratio is measured to be $\mathcal{B}(B^{Â\pm }→K_{\mathrm{S}}^0{K}^{Â\pm })/\mathcal{B}(B^{Â\pm }→K_{\mathrm{S}}^0{\mathrm{Ï€}}^{Â\pm })=0.055Â\pm 0.004Â\pm 0.002$ , where the first uncertainties are statistical and the second are systematic. These results are the most precise measurements of these quantities to date. A search for the rare decay $B_c^{Â\pm }→K_{\mathrm{S}}^0{K}^{Â\pm }$ is also performed. No significant signal is observed, and the upper limit on the product of the branching fraction ratio $\mathcal{B}(B_c^{Â\pm }→K_{\mathrm{S}}^0{K}^{Â\pm })/\mathcal{B}(B^{Â\pm }→K_{\mathrm{S}}^0{\mathrm{Ï€}}^{Â\pm })$ and the fragmentation-fraction ratio $f_c/f_u$ is set to be 0.015 (0.016) at the 90% (95%) confidence level.