Observation of a new chi_b state in radiative transitions to Upsilon(1S) and Upsilon(2S) at ATLAS

TL;DR

This paper reports the observation of a new chi_b state, likely the chi_b(3P), in radiative decays to Upsilon(1S) and Upsilon(2S) using ATLAS data from proton-proton collisions at 7 TeV.

Contribution

First observation of a new chi_b state at 10.530 GeV in radiative transitions to Upsilon states at the LHC.

Findings

Discovery of a new chi_b state at 10.530 GeV

Observation of this state in both Upsilon(1S)gamma and Upsilon(2S)gamma decay modes

Confirmation of the chi_b(1P,2P) states in the same dataset

Abstract

The chi_b(nP) quarkonium states are produced in proton-proton collisions at the Large Hadron Collider (LHC) at sqrt(s) = 7 TeV and recorded by the ATLAS detector. Using a data sample corresponding to an integrated luminosity of 4.4 fb^-1, these states are reconstructed through their radiative decays to Upsilon(1S,2S) with Upsilon->mu+mu-. In addition to the mass peaks corresponding to the decay modes chi_b(1P,2P)->Upsilon(1S)gamma, a new structure centered at a mass of 10.530+/-0.005 (stat.)+/-0.009 (syst.) GeV is also observed, in both the Upsilon(1S)gamma and Upsilon(2S)gamma decay modes. This is interpreted as the chi_b(3P) system.