O. Albayrak

By analyzing a data sample of $2.93{\mathrm{fb}}^{-1}$ collected at $\sqrt{s}=3.773\mathrm{GeV}$ with the BESIII detector operated at the BEPCII storage rings, we measure the branching fractions $\mathcal{B}(D^0\to \omega \eta )=(2.15\pm 0.17_{\mathrm{stat}}\pm 0.15_{\mathrm{sys}})\times {10}^{-3}$, $\mathcal{B}(D^0\to \eta {\pi }^0)=(0.58\pm 0.05_{\mathrm{stat}}\pm 0.05_{\mathrm{sys}})\times {10}^{-3}$, $\mathcal{B}(D^0\to {\eta }^{\prime }{\pi }^0)=(0.93\pm 0.11_{\mathrm{stat}}\pm 0.09_{\mathrm{sys}})\times {10}^{-3}$, $\mathcal{B}(D^0\to \eta \eta )=(2.20\pm 0.07_{\mathrm{stat}}\pm 0.06_{\mathrm{sys}})\times {10}^{-3}$ and $\mathcal{B}(D^0\to {\eta }^{\prime }\eta )=(0.94\pm 0.25_{\mathrm{stat}}\pm 0.11_{\mathrm{sys}})\times {10}^{-3}$. We note that $\mathcal{B}(D^0\to \omega \eta )$ is measured for the first time and that $\mathcal{B}(D^0\to \eta \eta )$ is measured with much improved precision.

The decay $J/\psi \to \gamma \gamma \varphi$ is studied using a sample of $1.31\times {10}^{9}J/\psi$ events collected with the BESIII detector. Two structures around $1475\mathrm{MeV}/c^2$ and $1835\mathrm{MeV}/c^2$ are observed in the $\gamma \varphi$ invariant mass spectrum for the first time. With a fit on the $\gamma \varphi$ invariant mass, which takes into account the interference between the two structures, and a simple analysis of the angular distribution, the structure around $1475\mathrm{MeV}/c^2$ is found to favor an assignment as the $\eta (1475)$ and the mass and width for the structure around $1835\mathrm{MeV}/c^2$ are consistent with the $X(1835)$. The statistical significances of the two structures are $13.5\sigma$ and $6.3\sigma$, respectively. The results indicate that both $\eta (1475)$ and $X(1835)$ contain a sizeable $s\overline{s}$ component.

Using a data set with an integrated luminosity of $2.93{\mathrm{fb}}^{-1}$ collected at $\sqrt{s}=3.773\mathrm{GeV}$ with the BESIII detector operating at the BEPCII storage rings, we search for the rare decay $D^{+}\to D^0{e}^{+}{\nu }_e$. No signal events are observed. We set the upper limit on the branching fraction for $D^{+}\to D^0{e}^{+}{\nu }_e$ to be $1.0\times 10^{-4}$ at the 90% confidence level.

We study the process $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}\psi (3686)$ using $5.1{\mathrm{fb}}^{-1}$ of data collected at 16 center-of-mass energy ($\sqrt{s}$) points from 4.008 to 4.600 GeV by the BESIII detector operating at the BEPCII collider. The measured Born cross sections for $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}\psi (3686)$ are consistent with previous results, but with much improved precision. A fit to the cross section shows contributions from two structures: the first has $M=4209.5\pm 7.4\pm 1.4\mathrm{MeV}/c^2$ and $\mathrm{\Gamma }=80.1\pm 24.6\pm 2.9\mathrm{MeV}$, and the second has $M=4383.8\pm 4.2\pm 0.8\mathrm{MeV}/{\mathrm{c}}^2$ and $\mathrm{\Gamma }=84.2\pm 12.5\pm 2.1\mathrm{MeV}$, where the first errors are statistical and the second systematic. The lower-mass resonance is observed in the process $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}\psi (3686)$ for the first time with a statistical significance of $5.8\sigma$. A charged charmoniumlike structure is observed in the ${\pi }^{\pm }\psi (3686)$ invariant mass spectrum for data at $\sqrt{s}=4.416\mathrm{GeV}$. A fit with an $S$-wave Breit-Wigner function yields a mass $M=4032.1\pm 2.4\mathrm{MeV}/c^2$, where the errors are statistical only. However, there are still unresolved discrepancies between the fit model and data. The width of the intermediate state varies in a wide range for different kinematic regions within the data set. Therefore, no simple interpretation of the data has been found, and a future data sample with larger statistics and more theoretical input will be required to better understand this issue.

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

Based on a sample of 1.31 billion $J/\psi$ events collected with the BESIII detector, we report the study of the doubly radiative decay ${\eta }^{\prime }\to \gamma \gamma {\pi }^0$ for the first time, where the ${\eta }^{\prime }$ meson is produced via the $J/\psi \to \gamma {\eta }^{\prime }$ decay. The branching fraction of ${\eta }^{\prime }\to \gamma \gamma {\pi }^0$ inclusive decay is measured to be $\mathcal{B}({\eta }^{\prime }\to \gamma \gamma {\pi }^0{)}_{\mathrm{Incl}}=(3.20\pm 0.07(\mathrm{stat})\pm 0.23(\mathrm{sys}))\times {10}^{-3}$, while the branching fractions of the dominant process ${\eta }^{\prime }\to \gamma \omega$ and the nonresonant component are determined to be $\mathcal{B}({\eta }^{\prime }\to \gamma \omega )\times \mathcal{B}(\omega \to \gamma {\pi }^0)=(23.7\pm 1.4(\mathrm{stat})\pm 1.8(\mathrm{sys}))\times {10}^{-4}$ and $\mathcal{B}({\eta }^{\prime }\to \gamma \gamma {\pi }^0{)}_{\mathrm{NR}}=(6.16\pm 0.64(\mathrm{stat})\pm 0.67(\mathrm{sys}))\times {10}^{-4}$, respectively. In addition, the $M_{\gamma \gamma }^2$-dependent partial widths of the inclusive decay are also presented.

We observe for the first time the process $e^{+}{e}^{-}\to \eta h_c$ with data collected by the BESIII experiment. Significant signals are observed at the center-of-mass energy $\sqrt{s}=4.226\mathrm{GeV}$, and the Born cross section is measured to be $(9.5_{-2.0}^{+2.2}\pm 2.7)\mathrm{pb}$. Evidence for $\eta h_c$ is observed at $\sqrt{s}=4.358\mathrm{GeV}$ with a Born cross section of $(10.0_{-2.7}^{+3.1}\pm 2.6)\mathrm{pb}$, and upper limits on the production cross section at other center-of-mass energies between 4.085 and 4.600 GeV are determined.