Observation of the Rare Baryonic Decay B+ → pΛ and Measurement of its Weak Decay Parameter

The first observation of the decay B+→p⁢Λ is presented using proton-proton collision data collected by the LHCb experiment between 2016 and 2018 at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5.4 fb−1. The Signal Significance exceeds Seven Standard deviations. Using the B+ →KS0π+ decay as a normalization channel, the branching fraction is measured and combined with previous LHCb results based on data collected at 7 and 8 TeV in 2011 and 2012, yielding B⁡(B+→p⁢Λ )=(1.24±0.17±0.05±0.03)×10−7, where the first uncertainty is Statistical, the Second is Systematic, and the third comes from the uncertainty on the branching fraction of the normalization channel. The B+→pΛ weak decay parameter is measured to be αB=0.8⁢7+0.26 −0.29±0.09, indicating the presence of comparable S-wave and P-wave decay amplitudes.