The resonance parameters of the charmonium ground state, ηc(11S0), have been measured by means of the reaction p̄p→ηc→γγ. The mass and total width are determined to be 2984.1 ± 2.1 ± 1.0 MeV/c2 and 20.4-6.7+7.7 ± 2.0 MeV, respectively. The product of branching ratios B(p̄p→ηc)B(ηc→γγ) is determined to be (22.4-3.7+3.8 ± 2.0) × 10-8, from which B(ηc→γγ)=(1.87-0.31-0.50 +0.32+0.95) × 10-4, and Γ(ηc→γγ)=3.8-1.0-1.0 +1.1+1.9 keV are derived using B(ηc→p̄p)= (12 ± 4) × 10-4 from the literature.
|Original language||English (US)|
|Number of pages||6|
|Journal||Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics|
|State||Published - Jul 24 2003|
Bibliographical noteFunding Information:
The authors gratefully acknowledge the technical support provided by Fermilab, in particular by the Antiproton Source Department of the Beams Division and the On-line Support Department of the Computing Division. We also wish to thank the staff, engineers, and technicians at their respective institutions for their help and cooperation. This research was sponsored by the US Department of Energy and the Italian Istituto Nazionale di Fisica Nucleare.