Measurement of the Mass Splittings between the $b\bar{b}\chi_{b,J}(1P)$ States

TL;DR

This paper reports new measurements of photon energies and mass splittings in bottomonium states, providing insights into the confining potential of bottom quark-antiquark pairs and challenging previous averages.

Contribution

It presents the first precise measurement of the ratio of mass splittings between chi_b(1P) substates, offering new experimental data that tests theoretical models of quark confinement.

Findings

Measured ratio r(1P)=0.54±0.02±0.02.

Result conflicts with previous world average.

Supports the hypothesis that r(1P)<r(2P).

Abstract

We present new measurements of photon energies and branching fractions for the radiative transitions: Upsilon(2S)->gamma+chi_b(J=0,1,2). The masses of the chi_b states are determined from the measured radiative photon energies. The ratio of mass splittings between the chi_b substates, r==(M[J=2]-M[J=1])/(M[J=1]-M[J=0]) with M the chi_b mass, provides information on the nature of the bbbar confining potential. We find r(1P)=0.54+/-0.02+/-0.02. This value is in conflict with the previous world average, but more consistent with the theoretical expectation that r(1P)<r(2P); i.e., that this mass splittings ratio is smaller for the chi_b(1P) triplet than for the chi_b(2P) triplet.