Q. An

We study the process ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}J/\ensuremath{\psi}$ at a center-of-mass energy of 4.260 GeV using a $525\text{ }\text{ }{\mathrm{pb}}^{\ensuremath{-}1}$ data sample collected with the BESIII detector operating at the Beijing Electron Positron Collider. The Born cross section is measured to be $(62.9\ifmmode\pm\else\textpm\fi{}1.9\ifmmode\pm\else\textpm\fi{}3.7)\text{ }\text{ }\mathrm{pb}$, consistent with the production of the $Y(4260)$. We observe a structure at around $3.9\text{ }\text{ }\mathrm{GeV}/{c}^{2}$ in the ${\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}J/\ensuremath{\psi}$ mass spectrum, which we refer to as the ${Z}_{c}(3900)$. If interpreted as a new particle, it is unusual in that it carries an electric charge and couples to charmonium. A fit to the ${\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}J/\ensuremath{\psi}$ invariant mass spectrum, neglecting interference, results in a mass of $(3899.0\ifmmode\pm\else\textpm\fi{}3.6\ifmmode\pm\else\textpm\fi{}4.9)\text{ }\text{ }\mathrm{MeV}/{c}^{2}$ and a width of $(46\ifmmode\pm\else\textpm\fi{}10\ifmmode\pm\else\textpm\fi{}20)\text{ }\text{ }\mathrm{MeV}$. Its production ratio is measured to be $R=(\ensuremath{\sigma}\mathbf{(}{e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}{Z}_{c}(3900{)}^{\ensuremath{\mp}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}J/\ensuremath{\psi}\mathbf{)}/\ensuremath{\sigma}({e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}J/\ensuremath{\psi}))=(21.5\ifmmode\pm\else\textpm\fi{}3.3\ifmmode\pm\else\textpm\fi{}7.5)%$. In all measurements the first errors are statistical and the second are systematic.

We study ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{h}_{c}$ at center-of-mass energies from 3.90 to 4.42 GeV by using data samples collected with the BESIII detector operating at the Beijing Electron Positron Collider. The Born cross sections are measured at 13 energies and are found to be of the same order of magnitude as those of ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}J/\ensuremath{\psi}$ but with a different line shape. In the ${\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}{h}_{c}$ mass spectrum, a distinct structure, referred to as ${Z}_{c}(4020)$, is observed at $4.02\text{ }\text{ }\mathrm{GeV}/{c}^{2}$. The ${Z}_{c}(4020)$ carries an electric charge and couples to charmonium. A fit to the ${\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}{h}_{c}$ invariant mass spectrum, neglecting possible interferences, results in a mass of $(4022.9\ifmmode\pm\else\textpm\fi{}0.8\ifmmode\pm\else\textpm\fi{}2.7)\text{ }\text{ }\mathrm{MeV}/{c}^{2}$ and a width of $(7.9\ifmmode\pm\else\textpm\fi{}2.7\ifmmode\pm\else\textpm\fi{}2.6)\text{ }\text{ }\mathrm{MeV}$ for the ${Z}_{c}(4020)$, where the first errors are statistical and the second systematic. The difference between the parameters of this structure and the ${Z}_{c}(4025)$ observed in the ${D}^{*}{\overline{D}}^{*}$ final state is within $1.5\ensuremath{\sigma}$, but whether they are the same state needs further investigation. No significant ${Z}_{c}(3900)$ signal is observed, and upper limits on the ${Z}_{c}(3900)$ production cross sections in ${\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}{h}_{c}$ at center-of-mass energies of 4.23 and 4.26 GeV are set.

We report an improved measurement of the neutrino mixing angle θ13 from the Daya Bay Reactor Neutrino Experiment. We exclude a zero value for sin22θ13 with a significance of 7.7 standard deviations. Electron antineutrinos from six reactors of 2.9 GWthwere detected in six antineutrino detectors deployed in two near (flux-weighted baselines of 470 m and 576 m) and one far (1648 m) underground experimental halls. Using 139 days of data, 28909 (205308) electron antineutrino candidates were detected at the far hall (near halls). The ratio of the observed to the expected number of antineutrinos assuming no oscillations at the far hall is 0.944±0.007(stat.)±0.003(syst.). An analysis of the relative rates in six detectors finds sin22θ13=0. 089±0.010(stat.)±0.005(syst.) in a three-neutrino framework. © 2013 Chinese Physical Society and the Institute of High Energy Physics of the Chinese Academy of Sciences and the Institute of Modern Physics of the Chinese Academy of Sciences and IOP Publishing Ltd.

We report on a study of the process ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}{(D{\overline{D}}^{*})}^{\ensuremath{\mp}}$ at $\sqrt{s}=4.26\text{ }\text{ }\mathrm{GeV}$ using a $525\text{ }\mathrm{pb}{}^{\ensuremath{-}1}$ data sample collected with the BESIII detector at the BEPCII storage ring. A distinct charged structure is observed in the ${(D{\overline{D}}^{*})}^{\ensuremath{\mp}}$ invariant mass distribution. When fitted to a mass-dependent-width Breit-Wigner line shape, the pole mass and width are determined to be ${M}_{\mathrm{pole}}=\phantom{\rule{0ex}{0ex}}\mathbf{(}3883.9\ifmmode\pm\else\textpm\fi{}1.5\phantom{\rule{0.333em}{0ex}}(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}4.2\phantom{\rule{0.333em}{0ex}}(\mathrm{syst})\mathbf{)}\text{ }\text{ }\mathrm{MeV}/{c}^{2}$ and ${\mathrm{\ensuremath{\Gamma}}}_{\mathrm{pole}}=\mathbf{(}24.8\ifmmode\pm\else\textpm\fi{}3.3\phantom{\rule{0.333em}{0ex}}(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}11.0\phantom{\rule{0.333em}{0ex}}(\mathrm{syst})\mathbf{)}\text{ }\text{ }\mathrm{MeV}$. The mass and width of the structure, which we refer to as ${Z}_{c}(3885)$, are $2\ensuremath{\sigma}$ and $1\ensuremath{\sigma}$, respectively, below those of the ${Z}_{c}(3900)\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}J/\ensuremath{\psi}$ peak observed by BESIII and Belle in ${\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}J/\ensuremath{\psi}$ final states produced at the same center-of-mass energy. The angular distribution of the $\ensuremath{\pi}{Z}_{c}(3885)$ system favors a ${J}^{P}={1}^{+}$ quantum number assignment for the structure and disfavors ${1}^{\ensuremath{-}}$ or ${0}^{\ensuremath{-}}$. The Born cross section times the $D{\overline{D}}^{*}$ branching fraction of the ${Z}_{c}(3885)$ is measured to be ${\ensuremath{\sigma}\mathbf{(}{e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}\phantom{\rule{0ex}{0ex}}{\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}{Z}_{c}(3885)}^{\ensuremath{\mp}}\mathbf{)}\ifmmode\times\else\texttimes\fi{}{\mathcal{B}\mathbf{(}{Z}_{c}(3885)}^{\ensuremath{\mp}}\ensuremath{\rightarrow}{(D{\overline{D}}^{*})}^{\ensuremath{\mp}}\mathbf{)}=\mathbf{(}83.5\ifmmode\pm\else\textpm\fi{}6.6\phantom{\rule{0.333em}{0ex}}(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}22.0\phantom{\rule{0.333em}{0ex}}(\mathrm{syst})\mathbf{)}\text{ }\text{ }\text{ }\mathrm{pb}$. Assuming the ${Z}_{c}(3885)\ensuremath{\rightarrow}D{\overline{D}}^{*}$ signal reported here and the ${Z}_{c}(3900)\ensuremath{\rightarrow}\ensuremath{\pi}J/\ensuremath{\psi}$ signal are from the same source, the partial width ratio $(\mathrm{\ensuremath{\Gamma}}({Z}_{c}(3885)\ensuremath{\rightarrow}D{\overline{D}}^{*})/\mathrm{\ensuremath{\Gamma}}({Z}_{c}(3900)\ensuremath{\rightarrow}\ensuremath{\pi}J/\ensuremath{\psi}))=6.2\ifmmode\pm\else\textpm\fi{}1.1\phantom{\rule{0.333em}{0ex}}(\mathrm{stat})\phantom{\rule{0.333em}{0ex}}\ifmmode\pm\else\textpm\fi{}2.7\phantom{\rule{0.333em}{0ex}}(\mathrm{syst})$ is determined.