Observation of Charmonium $h_{c}$ Radiative Decays to Multiple Light Hadrons and the Tensor State $f_2(1270)$

Abstract

Using $ψ(3686)\rightarrow π^{0} h_{c}$ decays from a data sample of $(27.12\pm0.14)\times10^{8}$ $ψ(3686)$ events collected by the BESIII detector at the BEPCII collider, $h_c$ radiative decays to $γπ^{+}π^{-},~γπ^{+}π^{-}η,~\gamma2(π^{+}π^{-})$, and $γp\bar{p}$ are observed for the first time, each with a significance greater than $5σ$. The corresponding branching fractions are measured. Furthermore, intermediate states below 2.8 GeV/$c^{2}$ are investigated, leading to the first observation of the decay process of $h_c\rightarrowγf_{2}(1270)\rightarrowγπ^{+}π^{-}$ with a significance of $5.5\,σ$. This observation represents the first instance of $h_c$ radiative decay to a tensor state.

Figures (2)

• Figure 1: Fits to the $M(\gamma X)$ invariant mass distributions, where $X$ represents (I) $\pi^{+}\pi^{-}$, (II) $\pi^{+}\pi^{-}\eta$, (III) $2(\pi^{+}\pi^{-})$, and (IV) $p\bar{p}$. The dots with error bars are data, the red solid line is the fitting result, the pink dashed line is the signal shape, the blue dashed line is the smooth background and the other dashed lines represent the peaking backgrounds.
• Figure 2: Fit to the $M(\pi^{+}\pi^{-})$ invariant mass distribution for the process of $h_{c}\rightarrow\gamma\pi^{+}\pi^{-}$ for events in the (top) $h_c$ signal region and (bottom) $h_c$ sideband regions. The dots with error bars are data, the red solid line is the total fitting result, the pink dashed line is the signal of $h_{c}\rightarrow\gamma f_{2}(1270)$ and the green dashed line is the phase space process of $h_{c}\rightarrow\gamma\pi^{+}\pi^{-}$. The blue dashed line denotes the smooth background, and the brown dashed line the background from $h_{c}\rightarrow\pi^{+}\pi^{-}\pi^{0}$. The black dashed line is the $\psi(3686) \to \omega f_2(1270)$ peaking background.