Search for the radiative transitions $\psi(3770)\to\gamma\eta_c$ and $\gamma\eta_c(2S)$

TL;DR

This study searches for specific radiative transitions from $ ext{psi}(3770)$ to $ ext{eta}_c$ and $ ext{eta}_c(2S)$, setting upper limits on their branching fractions due to no significant signal detection.

Contribution

First search for $ ext{psi}(3770)$ radiative transitions to $ ext{eta}_c$ and $ ext{eta}_c(2S)$ with BESIII data, establishing upper limits on their branching fractions.

Findings

No significant signal observed.

Upper limits set on product branching fractions.

Branching fractions constrained at 90% confidence level.

Abstract

By using a 2.92 fb$^{-1}$ data sample taken at $\sqrt{s} = 3.773$ GeV with the BESIII detector operating at the BEPCII collider, we search for the radiative transitions $\psi(3770)\to\gamma\eta_c$ and $\gamma\eta_c(2S)$ through the hadronic decays $\eta_c(\eta_c(2S))\to K^0_SK^\pm\pi^\mp$. No significant excess of signal events above background is observed. We set upper limits at a 90% confidence level for the product branching fractions to be $\mathcal{B}(\psi(3770)\to\gamma\eta_c)\times \mathcal{B}(\eta_c\to K^0_SK^\pm\pi^\mp) < 1.6\times10^{-5}$ and $\mathcal{B}(\psi(3770)\to\gamma\eta_c(2S))\times \mathcal{B}(\eta_c(2S)\to K^0_SK^\pm\pi^\mp) < 5.6\times10^{-6}$. Combining our result with world-average values of $\mathcal{B}(\eta_c(\eta_c(2S))\to K^0_SK^\pm\pi^\mp)$, we find the branching fractions $\mathcal{B}(\psi(3770)\to\gamma\eta_c) < 6.8\times10^{-4}$ and $\mathcal{B}(\psi(3770)\to\gamma\eta_c(2S)) < 2.0\times10^{-3}$ at a 90% confidence level.