We study the process $e^+e^- to (D^{*} bar{D}^{*})^{pm} pi^mp$ at a center-of-mass energy of 4.26GeV using a 827pb$^{-1}$ data sample obtained with the BESIII detector at the Beijing Electron Positron Collider. Based on a partial reconstruction techn
ique, the Born cross section is measured to be $(137pm9pm15)$pb. We observe a structure near the $(D^{*} bar{D}^{*})^{pm}$ threshold in the $pi^mp$ recoil mass spectrum, which we denote as the $Z^{pm}_c(4025)$. The measured mass and width of the structure are $(4026.3pm2.6pm3.7)$MeV/c$^2$ and $(24.8pm5.6pm7.7)$MeV, respectively. Its production ratio $frac{sigma(e^+e^-to Z^{pm}_c(4025)pi^mp to (D^{*} bar{D}^{*})^{pm} pi^mp)}{sigma(e^+e^-to (D^{*} bar{D}^{*})^{pm} pi^mp)}$ is determined to be $0.65pm0.09pm0.06$. The first uncertainties are statistical and the second are systematic.
The decay of $J/psi$ to three photons is studied using $psi(3686)topi^+pi^-J/psi$ in a sample of $1.0641times10^8$ $psi(3686)$ events collected with the BESIII detector. Evidence of the direct decay of $eta_c$ to two photons, $eta_ctogammagamma$, is
reported, and the product branching fraction is determined to be $mathcal{B}(J/psitogammaeta_c,eta_cto gammagamma)=(4.5pm1.2pm0.6)times10^{-6}$, where the first error is statistical and the second is systematic. The branching fraction for $J/psito3gamma$ is measured to be $(11.3pm1.8pm2.0)times 10^{-6}$ with improved precision.
The two-photon transition $psi(3686)togammagamma J/psi$ is studied in a sample of 106 million $psi(3686)$ decays collected by the BESIII detector. The branching fraction is measured to be $(3.1pm0.6(unit{stat})^{+0.8}_{-1.0}(unit{syst})) times10^{-4}
$ using $J/psito e^+e^-$ and $J/psitomu^+mu^-$ decays, and its upper limit is estimated to be $4.5times10^{-4}$ at the 90% conference level. This work represents the first measurement of a two-photon transition among charmonium states. The orientation of the $psi(3686)$ decay plane and the $J/psi$ polarization in this decay are also studied. In addition, the product branching fractions of sequential $E1$ transitions $psi(3686)togammachi_{cJ}, chi_{cJ}togamma J/psi (J=0,1,2)$ are reported.
