# Observation of $e^{+}e^{-}\rightarrow \pi^{+}\pi^{-}\psi(3770)$ and $D_{1}(2420)^{0}\bar{D}^{0} + c.c.$

## TL;DR

This study reports the first observation of the process $e^{+}e^{-}
ightarrow \pi^{+}\pi^{-}\psi(3770)$ and investigates intermediate states, including the $D_{1}(2420)$, revealing new insights into charmonium-like states and their production mechanisms.

## Contribution

First observation of $e^{+}e^{-}
ightarrow \pi^{+}\pi^{-}\psi(3770)$ and detailed analysis of $D_{1}(2420)$ production at BESIII energies.

## Key findings

- $e^{+}e^{-}
ightarrow \pi^{+}\pi^{-}\psi(3770)$ observed at 4.42 GeV with 5.2$\sigma$ significance.
- Evidence for $D_{1}(2420)^{0} o D^{0}\pi^{+}\pi^{-}$ at 4.42 GeV with 7.4$\sigma$ significance.
- No significant signal for $X_{2}(4013)$ in $Dar{D}$ spectra.

## Abstract

Several intermediate states of the reaction channels $e^{+}e^{-} \rightarrow \pi^{+} \pi^{-} D^{0} \bar{D}^{0}$ and $e^{+}e^{-} \rightarrow \pi^{+} \pi^{-} D^{+}D^{-}$ are studied using the data samples collected with the BESIII detector at center-of-mass energies above 4.08 GeV. For the first time in this final state, a $\psi(3770)$ signal is seen in the $D\bar{D}$ invariant mass spectrum, with a statistical significance of $5.2\sigma$ at $\sqrt{s} = 4.42$ GeV. There is also evidence for this resonance at $\sqrt{s}$ = 4.26 and 4.36 GeV with statistical significance of 3.2$\sigma$ and 3.3$\sigma$, respectively. In addition, the Born cross section of $e^{+}e^{-}\to \pi^{+}\pi^{-}\psi(3770)$ is measured. The proposed heavy-quark-spin-symmetry partner of the $X(3872)$, the state $X_{2}(4013)$, is also searched for in the $D\bar{D}$ invariant mass spectra. No obvious signal is found. The upper limit of the Born cross section of the process $e^{+}e^{-}\to \rho^{0}X_{2}(4013)$ combined with the branching fraction is measured. Also, the processes $e^{+}e^{-}\to D_{1}(2420)\bar{D} + c.c.$ are investigated. The neutral mode with $D_{1}(2420)^{0}\to D^{0}\pi^{+}\pi^{-}$ is reported with statistical significance of 7.4$\sigma$ at $\sqrt{s} = 4.42$ GeV for the first time, and evidence with statistical significance of 3.2$\sigma$ and 3.3$\sigma$ at $\sqrt{s}$ = 4.36 and 4.60 GeV is seen, respectively. No evident signal for the process $e^{+}e^{-}\to D_{1}(2420)^{0}\bar{D}^{0} + c.c., D_{1}(2420)^{0}\to D^{*+}\pi^{-}$ is reported. Evidence for $e^{+}e^{-}\to D_{1}(2420)^{+}D^{-} +~c.c., D_{1}(2420)^{+}\to D^{+}\pi^{+}\pi^{-}$ is reported with statistical significance of 3.1$\sigma$ and 3.0$\sigma$ at $\sqrt{s}$ = 4.36 and 4.42 GeV, respectively.