Bottomonium spectroscopy and radiative transitions involving the χbJ(1P,2P) states at BABAR

Abstract

We use ( 121 ± 1 ) million Υ ( 3 S ) and ( 98 ± 1 ) million Υ ( 2 S ) mesons recorded by the BABAR detector at the PEP-II e + e − collider at SLAC to perform a study of radiative transitions involving the χ b J ( 1 P , 2 P ) states in exclusive decays with μ + μ − γ γ final states. We reconstruct twelve channels in four cascades using two complementary methods. In the first we identify both signal photon candidates in the electromagnetic calorimeter (EMC), employ a calorimeter timing-based technique to reduce backgrounds, and determine branching-ratio products and fine mass splittings. These results include the best observational significance yet for the χ b 0 ( 2 P ) → γ Υ ( 2 S ) and χ b 0 ( 1 P ) → γ Υ ( 1 S ) transitions. In the second method, we identify one photon candidate in the EMC and one which has converted into an e + e − pair due to interaction with detector material, and we measure absolute product branching fractions. This method is particularly useful for measuring Υ ( 3 S ) → γ χ b 1 , 2 ( 1 P ) decays. Additionally, we provide the most up-to-date derived branching fractions, matrix elements and mass splittings for χ b transitions in the bottomonium system. Using a new technique, we also measure the two lowest-order spin-dependent coefficients in the nonrelativistic QCD Hamiltonian.