Observation of the $X(1840)$ at BESIII

Observation of the $X(1840)$ in the $3(pi^+pi^-)$ invariant mass in $J/psirightarrowgamma 3(pi^+pi^-)$ at BESIII is reviewed. With a sample of $225.3times10^6$ $J/psi$ events collected with the BESIII detector at BEPCII, the $X(1840)$ is observed with a statistical significance of $7.6sigma$. The mass, width and product branching fraction of the $X(1840)$ are determined. The decay $eta^primerightarrow 3(pi^+pi^-)$ is searched for, and the upper limit of the branching fraction is set at the 90% confidence level.