Search for B+ --> X(3872) K+, X(3872) --> J/psi gamma

TL;DR

This paper reports evidence for the radiative decay of X(3872) in B+ decays, measuring its branching fraction and providing insights into its nature, based on a large dataset from the BaBar experiment.

Contribution

First measurement of X(3872) --> J/psi gamma decay in B+ decays, with quantified branching fractions and statistical significance.

Findings

Evidence for X(3872) --> J/psi gamma decay at 3.4 sigma significance.

Measured product of branching fractions: (3.3 +/- 1.0 +/- 0.3) x 10^-6.

Measured BF(B+ --> chi_c1 K+): (4.9 +/- 0.2 +/- 0.4) x 10^-4.

Abstract

In a study of B+ --> J/psi gamma K+ decays, we find evidence for the radiative decay X(3872) --> J/psi gamma with a statistical significance of 3.4 sigma. We measure the product of branching fractions BF(B+ --> X(3872) K+).BF(X(3872) --> J/psi gamma) = (3.3 +/- 1.0 +/- 0.3) x 10^-6, where the uncertainties are statistical and systematic, respectively. We also measure the branching fraction BF(B+ --> chi_c1 K+) = (4.9 +/- 0.2 +/- 0.4) x 10^-4. These results are obtained from (287+/-3) million BBar decays collected at the Y(4S) resonance with the BaBar detector at the PEP-II B Factory at SLAC.