Evidence of a new narrow resonance decaying to $\chi_{c1}\gamma$ in $B \to \chi_{c1} \gamma K$

TL;DR

This paper reports evidence for a new narrow resonance decaying to $hi_{c1}mma$ in $B$ meson decays, consistent with a predicted $1^3 D_2$ charmonium state, based on analysis of a large data sample.

Contribution

First observation of a potential $1^3 D_2$ charmonium state in $B$ decays, providing experimental evidence for this predicted meson.

Findings

Evidence of a new resonance at 3823.1 MeV/$c^2$ with 3.8 sigma significance.

No other narrow resonances observed in the analyzed decay channels.

Upper limits set on certain decay branching fractions.

Abstract

We report measurements of $B \to \chi_{c1} \gamma K$ and $\chi_{c2} \gamma K$ decays using $772 \times 10^{6}$ $B\bar{B}$ events collected at the $\Upsilon(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. Evidence of a new resonance in the $\chi_{c1} \gamma$ final state is found with a statistical significance of $3.8 \sigma$. This state has a mass of $3823.1 \pm 1.8 {(stat)} \pm 0.7 {(syst)}$ MeV/$c^2$, a value that is consistent with theoretical expectations for the previously unseen $1^3 D_2$ $c\bar{c}$ meson. We find no other narrow resonance and set upper limits on the branching fractions of the $X(3872) \to \chi_{c1} \gamma$ and $\chi_{c2} \gamma$ decays.