Observation of eta_b(2S) in Upsilon(2S) -> gamma eta_b(2S), eta_b(2S) -> hadrons, and Confirmation of eta_b(1S)

TL;DR

This study reports the observation of the eta_b(2S) state in Upsilon(2S) decays and confirms the eta_b(1S) state, providing precise measurements of their masses and hyperfine splittings using data from the CLEO III detector.

Contribution

First observation of eta_b(2S) in Upsilon(2S) decays and confirmation of eta_b(1S) with precise mass measurements and hyperfine splitting values.

Findings

eta_b(2S) observed at 9974.6 MeV with 5 sigma significance

Hyperfine splitting of eta_b(2S) is 48.7 MeV

eta_b(1S) confirmed at 3 sigma, consistent with known values

Abstract

The data for 9.3 million Upsilon(2S) and 20.9 million Upsilon(1S) taken with the CLEO III detector has been used to study the radiative population of states identified by their decay into twenty six different exclusive hadronic final states. In the Upsilon(2S) decays an enhancement is observed at a ~5 sigma level at a mass of 9974.6+-2.3(stat)+-2.1(syst) MeV. It is attributed to eta_b(2S), and corresponds to the Upsilon(2S) hyperfine splitting of 48.7+-2.3(stat)+-2.1(syst) MeV. In the Upsilon(1S) decays, the identification of eta_b(1S) is confirmed at a ~3 sigma level with M(eta_b(1S)) in agreement with its known value.