First observations of the rare decays B + → K + π + π − μ + μ − and B +→ ϕK + μ + μ −

Abstract

First observations of the rare decays B + → K + π + π − μ + μ − and B +→ ϕK +μ+μ− are presented using data corresponding to an integrated luminosity of 3.0 fb−1, collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. The branching fractions of the decays are B(B+→K+π+π−μ+μ−)=(4.36−0.29−0.27(stat)±0.21 (syst)±0.18(norm))×10−7,B(B+→ϕK+μ+μ−)=(0.82−0.19−0.17(stat)−0.10−0.04(syst)±0.27(norm))×10−7,

where the uncertainties are statistical, systematic, and due to the uncertainty on the branching fractions of the normalisation modes. A measurement of the differential branching fraction in bins of the invariant mass squared of the dimuon system is also presented for the decay B + → K + π + π − μ + μ −.