Determination of spin and parity of the $Z_c(3900)$

Abstract

The spin and parity of the $Z_c(3900{)}^{\pm }$ state are determined to be $J^P=1^{+}$ with a statistical significance larger than $7\ddot{I}ƒ$ over other quantum numbers in a partial wave analysis of the process $e^{+}{e}^{-}\to \ddot{I}{€}^{+}\ddot{I}{€}^{-}J/\ddot{I}ˆ$. We use a data sample of 1.92 fb${}^{-1}$ accumulated at $\sqrt{s}=4.23$ and 4.26 GeV with the BESIII experiment. When parameterizing the $Z_c(3900{)}^{\pm }$ with a Flatte-like formula, we determine its pole mass $M_{\text{pole}}=(3881.2\pm 4.2_{\text{stat}}\pm 52.7_{\text{syst}})\text{MeV}/c^2$ and pole width $\hat{I}{“}_{\text{pole}}=(51.8\pm 4.6_{\text{stat}}\pm 36.0_{\text{syst}})\text{MeV}$. We also measure cross sections for the process $e^{+}{e}^{-}\to Z_c(3900{)}^{+}\ddot{I}{€}^{-}+c.c.\to J/\ddot{I}ˆ\ddot{I}{€}^{+}\ddot{I}{€}^{-}$ and determine an upper limit at the 90\% confidence level for the process $e^{+}{e}^{-}\to Z_c(4020{)}^{+}\ddot{I}{€}^{-}+c.c.\to J/\ddot{I}ˆ\ddot{I}{€}^{+}\ddot{I}{€}^{-}$.

8 pages, 2 figures, 1 table