We report measurements of $B\to {\chi }_{c1}\gamma K$ and ${\chi }_{c2}\gamma K$ decays using $772\times {10}^6$ $B\overline{B}$ events collected at the ${\rm Y}(4S)$ 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 $3823.1\pm 1.8(\mathrm{stat})\pm 0.7(\mathrm{syst})\mathrm{MeV}/c^2$, a value that is consistent with theoretical expectations for the previously unseen $1{}^{3}D_2$ $c\overline{c}$ 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.

• Received 15 April 2013

DOI:https://doi.org/10.1103/PhysRevLett.111.032001