Observation of a neutral charmoniumlike state $Z_c(4025)^0$ in $e^{+} e^{-} \to (D^{*} \bar{D}^{*})^{0} \pi^0$

TL;DR

This paper reports the discovery of a new neutral charmoniumlike state, $Z_c(4025)^0$, observed in $e^{+} e^{-}$ collisions, with measured mass, width, and production cross sections at specific energies, indicating a potential exotic hadron.

Contribution

First observation of the neutral $Z_c(4025)^0$ state in $e^{+} e^{-} o (D^{*} ar{D}^{*})^{0} o ext{final state}$, providing new insights into exotic charmoniumlike states.

Findings

Observation of a new neutral structure near the $(D^{*} ar{D}^{*})^{0}$ threshold.

Measured mass and width of $Z_c(4025)^0$ as approximately 4025.5 MeV/c^2 and 23 MeV.

Determined production cross sections at two different energies.

Abstract

We report a study of the process $e^{+} e^{-} \to (D^{*} \bar{D}^{*})^{0} \pi^0$ using $e^+e^-$ collision data samples with integrated luminosities of $1092 \rm{pb}^{-1}$ at $\sqrt{s}=4.23 \rm{GeV}$ and $826 \rm{pb}^{-1}$ at $\sqrt{s}=4.26 \rm{GeV}$ 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 $\pi^0$ 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 $(4025.5^{+2.0}_{-4.7}\pm3.1) \rm{MeV}/c^2$ and $(23.0\pm 6.0\pm 1.0) \rm{MeV}$, respectively. The Born cross sections of $e^{+}e^{-}\to Z_{c}(4025)^{0} \pi^0\to (D^{*} \bar{D}^{*})^{0}\pi^0$ are measured to be $(61.6\pm8.2\pm9.0) \rm{pb}$ at $\sqrt{s}=4.23 \rm{GeV}$ and $(43.4\pm8.0\pm5.4) \rm{pb}$ at $\sqrt{s}=4.26 \rm{GeV}$. The first uncertainties are statistical and the second are systematic.