Excited Upsilon Radiative Decays

TL;DR

This paper investigates bottomonium S-wave states and their radiative M1 transitions using lattice NRQCD, providing new calculations of transition matrix elements and comparing them with experimental data.

Contribution

It presents the first lattice NRQCD calculations of M1 transition matrix elements for excited bottomonium states, revealing larger values than experimental inferences.

Findings

Robust signals for excited state transitions were obtained.

Transition matrix elements qualitatively agree with theoretical expectations.

Calculated matrix elements for Y(2S) and Y(3S) are larger than experimental estimates.

Abstract

Bottomonium S-wave states were studied using lattice NRQCD. Masses of ground and excited states were calculated using multiexponential fitting to a set of correlation functions constructed using both local and wavefunction-smeared operators. Three-point functions for M1 transitions between vector and pseudoscalar states were computed. Robust signals for transitions involving the first two excited states were obtained. The qualitative features of the transition matrix elements are in agreement with expectations. The calculated values of matrix elements for Y(2S) and Y(3S) decay are considerably larger than values inferred from measured decay widths.