Measurement of $e^+e^- \to \gamma\chi_{cJ}$ via initial state radiation at Belle

TL;DR

This study searches for the process $e^+e^- o \gamma\chi_{cJ}$ using initial state radiation at Belle, setting upper limits on cross sections and decay rates due to lack of significant signals, contributing to understanding charmonium states.

Contribution

First measurement setting upper limits on $e^+e^- o \gamma\chi_{cJ}$ cross sections and charmonium-like state decays at various energies using Belle data.

Findings

No significant signals observed except from $\psi(2S)$ decays.

Upper limits on cross sections range from a few pb to tens of pb.

Constraints on decay rates of specific charmonium and charmonium-like states.

Abstract

The process $e^+e^- \to \gamma\chi_{cJ}$ ($J$=1, 2) is studied via initial state radiation using 980 fb$^{-1}$ of data at and around the $\Upsilon(nS)$ ($n$=1, 2, 3, 4, 5) resonances collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. No significant signal is observed except from $\psi(2S)$ decays. Upper limits on the cross sections between $\sqrt{s}=3.80$ and $5.56~{\rm GeV}$ are determined at the 90% credibility level, which range from few pb to a few tens of pb. We also set upper limits on the decay rate of the vector charmonium [$\psi(4040$), $\psi(4160)$, and $\psi(4415)$] and charmoniumlike [$Y(4260)$, $Y(4360)$, and $Y(4660)$] states to $\gamma\chi_{cJ}$.