Observation of a Neutral Charmoniumlike State ${Z}_{c}(4025{)}^{0}$ in ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}({D}^{*}{\overline{D}}^{*}{)}^{0}{\ensuremath{\pi}}^{0}$

Observation of a Neutral Charmoniumlike State $Z_{c} (4025)^{0}$ in $e^{+} e^{-} \to (D^{} {\bar{D}}^{})^{0} π^{0}$

M. Ablikim et al. (BESIII Collaboration)

Phys. Rev. Lett. 115, 182002 – Published 29 October 2015

Abstract

We report a study of the process $e^{+} e^{-} \to (D^{*} {\bar{D}}^{*})^{0} π^{0}$ using $e^{+} e^{-}$ collision data samples with integrated luminosities of $1092 {pb}^{- 1}$ at $\sqrt{s} = 4.23 GeV$ and $826 {pb}^{- 1}$ at $\sqrt{s} = 4.26 GeV$ collected with the BESIII detector at the BEPCII storage ring. We observe a new neutral structure near the $(D^{*} {\bar{D}}^{*})^{0}$ mass threshold in the $π^{0}$ recoil mass spectrum, which we denote as $Z_{c} (4025)^{0}$ . Assuming a Breit-Wigner line shape, its pole mass and pole width are determined to be $(4025. 5_{- 4.7}^{+ 2.0} \pm 3.1) MeV / c^{2}$ and $(23.0 \pm 6.0 \pm 1.0) MeV$ , respectively. The Born cross sections of $e^{+} e^{-} \to Z_{c} (4025)^{0} π^{0} \to (D^{*} {\bar{D}}^{*})^{0} π^{0}$ are measured to be $(61.6 \pm 8.2 \pm 9.0) pb$ at $\sqrt{s} = 4.23 GeV$ and $(43.4 \pm 8.0 \pm 5.4) pb$ at $\sqrt{s} = 4.26 GeV$ . The first uncertainties are statistical and the second are systematic.