E835 at FNAL: Charmonium Spectroscopy in $\bar p p$ Annihilations

TL;DR

This paper reports preliminary evidence for the h_c charmonium state in proton-antiproton annihilations, observing an excess near 3526 MeV in the η_cγ decay mode with specific resonance parameters, but no excess in the J/ψπ^0 mode.

Contribution

First experimental search for h_c in p̄p annihilations with observed resonance parameters in η_cγ decay mode, providing new insights into charmonium spectroscopy.

Findings

Observed η_cγ event excess near 3526 MeV with high significance

Resonance mass measured at 3525.8 MeV with narrow width

No excess found in J/ψπ^0 decay mode

Abstract

I present preliminary results on the search for $h_c$ in its $\eta_c\gamma$ and $J/\psi\pi^0$ decay modes. We observe an excess of \eta_c\gamma$ events near 3526 MeV that has a probability ${\cal P} \sim 0.001$ to arise from background fluctations. The resonance parameters are $M=3525.8 \pm 0.2 \pm 0.2 $MeV, $\Gamma\leq$ 1 MeV, and $10.6\pm 3.7\pm3.4(br) < \Gamma_{\bar{p}p}B_{\eta_c\gamma} < 12.8\pm 4.8\pm4.5(br) $eV. We find no event excess within the search region in the $J/\psi\pi^0$ mode.