Measurements of the branching fractions of the $P$-wave charmonium spin-singlet state $h_c(^1P_1) \to h^+ h^-\pi^0/\eta$

TL;DR

This study measures the branching fractions of various hadronic decay modes of the $h_c$ charmonium state using a large data sample, providing new insights into its decay properties and testing theoretical models.

Contribution

First measurement of several $h_c$ decay branching fractions, including evidence for specific modes, using a large dataset from BESIII.

Findings

$h_c o ext{pi}^+ ext{pi}^- ext{pi}^0$ observed with 9.6$\sigma$ significance

Evidence for $h_c o K^+ K^- ext{pi}^0$ and $h_c o K^+ K^- ext{eta}$ with over 3$\sigma$ significance

Upper limit set for $h_c o ext{pi}^+ ext{pi}^- ext{eta}$ decay branching fraction

Abstract

Based on $(2712.4\pm 14.3)\times10^{6}$ $\psi(3686)$ events, we investigate four hadronic decay modes of the $P$-wave charmonium spin-singlet state $h_c(^1P_1) \to h^+ h^- \pi^0/\eta$ ($h=\pi$ or $K$) via the process $\psi(3686) \to \pi^{0}h_c$ at BESIII. The $h_c \to \pi^+ \pi^- \pi^0$ decay is observed with a significance of 9.6$\sigma$ after taking into account systematic uncertainties. Evidences for $h_c \to K^+ K^- \pi^0$ and $h_c \to K^+ K^- \eta$ are found with significances of $3.5\sigma$ and $3.3\sigma$, respectively, after considering the systematic uncertainties. The branching fractions of these decays are measured to be $\mathcal{B}(h_c \to \pi^+ \pi^- \pi^0)=(1.36\pm0.16\pm0.14)\times10^{-3}$, $\mathcal{B}(h_c \to K^+ K^- \pi^0)=(3.26\pm0.84\pm0.36)\times10^{-4}$, and $\mathcal{B}(h_c \to K^+ K^- \eta)=(3.13\pm1.08\pm0.38)\times10^{-4}$, where the first uncertainties are statistical and the second are systematic. No significant signal of $h_c\to\pi^+\pi^-\eta$ is found, and the upper limit of its decay branching fraction is determined to be $\mathcal{B}(h_c\to\pi^+\pi^-\eta) < 4.0 \times 10^{-4}$ at 90% confidence level.