Investigation of the Decay of Orbitally-Excited B Mesons and First Measurement of the Branching Ratio BR(B*_J->B*pi(X))

TL;DR

This paper reports the first measurement of the branching ratio of orbitally-excited B mesons decaying into B pi, along with mass and width determinations of the B1(3/2) state, based on a large dataset from the OPAL detector.

Contribution

It provides the first experimental measurement of the branching ratio BR(B*J->B*pi) and detailed properties of the B1(3/2) state using a large sample of reconstructed B mesons.

Findings

Measured BR(B*J->B*pi(X)) = 0.85 +0.36-0.37 +- 0.12

Determined B1(3/2) mass as 5.738 GeV/c2

Estimated B1(3/2) width as 18 MeV/c

Abstract

From about 4 million hadronic Z decays recorded by the OPAL detector on and near to the Z resonance, we select a sample of more than 570000 inclusively reconstructed B mesons. Orbitally-excited mesons B*J are reconstructed using Bpi+- combinations. Independently, B* mesons are reconstructed using the decay B* -> Bgamma. The selected B* candidates are used to obtain samples enriched or depleted in the decay B*J -> B*pi+-(X), where (X) refers to decay modes with or without additional accompanying decay particles. From the number of signal candidates in the Bpi+- mass spectra of these two samples, we perform the first measurement of the branching ratio of orbitally-excited B mesons decaying into B*pi(X): BR(B*J ->B*pi(X)) = 0.85 +0.36-0.37 +- 0.12, where the first error is statistical and the second systematic. If B*J decay modes other than single pion transitions can be neglected the measured ratio corresponds to the branching ratio BR(B*J->B*pi). In the framework of Heavy Quark Symmetry, a simultaneous fit to the Bpi+- mass spectra of the samples enriched or depleted in B*J->B*pi+-(X) decays yields the mass and the width of the B1(3/2) state, as well as the branching ratio of B*J mesons decaying into B*pi: M(B1(3/2)) = (5.738 +0.005-0.006 +-0.007) GeV/c2 G(B1(3/2)) = (18 +15-13 +29-23) MeV/c BR(B*J->B*pi) = 0.74 +0.12-0.10 +0.21-0.15, where the uncertainties are statistical and systematic, respectively.