First observation of the decay B→ppbarμν and measurement of its differential branching fraction

Abstract

This work presents the discovery of the decay B→ppbarμν. Additionally, this thesis includes a measurement of its differential branching fraction as a function of ppbar mass. The decay B→ppbarμν is observed with a significance in excess of 5sigma using data collected at the LHCb experiment in 2011, 2012 and 2016. The decay is suppressed by the smallest and least well known element of the CKM matrix, |Vub|. The work presented in this thesis also constitutes the first observation of a semileptonic decay of a meson to baryons. An enhancement effect at the ppbar mass threshold is observed, consistent with observations from other decays with a ppbar pair in the final state. In contrast to other observed B decays such as B→ppbarπ , the decay B→ppbarμν is a clean environment to study the mass of the ppbar system, without QCD interference from an additional hadron. The total branching fraction normalised to the decay B→J/psiK is measured to be BF(B→ppbarμν) = (5.27^(+0.23)_(-0.24)+-0.21+-0.15)x10^(-6), where the first uncertainty is statistical, the second is systematic and the third is from the normalisation branching fraction.

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