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The decay , with a 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 and 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 . The asymmetries are determined to be and , and the branching fraction ratio is measured to be , 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 is also performed. No significant signal is observed, and the upper limit on the product of the branching fraction ratio and the fragmentation-fraction ratio is set to be 0.015 (0.016) at the 90% (95%) confidence level.
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