Search for an axion-like particle in J/ψJ/\psi radiative decays

We search for an axion-like particle (ALP) $a$ through the process $\psi(3686)\rightarrow\pi^+\pi^-J/\psi$, $J/\psi\rightarrow\gamma a$, $a\rightarrow\gamma\gamma$ in a data sample with $(2708.1\pm14.5)\times10^6$ $\psi(3686)$ events collected by the BESIII detector. No significant ALP signal is observed over the expected background, and the upper limits on the branching fraction of the decay $J/\psi\rightarrow\gamma a$ and the ALP-photon coupling constant $g_{a\gamma\gamma}$ are set at the 95\% confidence level in the mass range of 0.165\leq m_a\leq2.84\,\mbox{GeV}/c^2. The limits on $\mathcal{B}(J/\psi\rightarrow\gamma a)$ range from $8.3\times10^{-8}$ to $1.8\times10^{-6}$ over the search region, and the constraints on the ALP-photon coupling are the most stringent to date for 0.165\leq m_a\leq1.468\,\mbox{GeV}/c^2.Comment: 10 pages, 5 figure

Measurements of the electric and magnetic form factors of the neutron for time-like momentum transfer

We present the first measurements of the electric and magnetic form factors of the neutron in the time-like (positive $q^2$) region as function of four-momentum transfer. We explored the differential cross sections of the reaction $e^+e^- \rightarrow \bar{n}n$ with data collected with the BESIII detector at the BEPCII accelerator, corresponding to an integrated luminosity of 354.6 pb$^{-1}$ in total at twelve center-of-mass energies between $\sqrt{s} = 2.0 - 2.95$ GeV. A relative uncertainty of 18% and 12% for the electric and magnetic form factors, respectively, is achieved at $\sqrt{s} = 2.3935$ GeV. Our results are comparable in accuracy to those from electron scattering in the comparable space-like (negative $q^2$) region of four-momentum transfer. The electromagnetic form factor ratio $R_{\rm em}\equiv |G_E|/|G_M|$ is within the uncertainties close to unity. We compare our result on $|G_E|$ and $|G_M|$ to recent model predictions, and the measurements in the space-like region to test the analyticity of electromagnetic form factors.Comment: main paper: 9 pages, 6 figures, 3 tables; supplement: 9 pages, 28 table

Measurements of the branching fractions of the inclusive decays D0(D+)→π+π+π−X

Using eþe− annihilation data corresponding to an integrated luminosity of 2.93 fb−1 taken at a center-of mass energy of 3.773 GeV with the BESIII detector, we report the first measurements of the branching fractions of the inclusive decays D0 → πþπþπ−X and Dþ → πþπþπ−X, where pions from K0 S decays have been excluded from the πþπþπ− system and X denotes any possible particle combination. The branching fractions of D0ðDþÞ → πþπþπ−X are determined to be BðD0 → πþπþπ−XÞ¼ð17.60 0.11 0.22Þ% and BðDþ → πþπþπ−XÞ¼ð15.25 0.09 0.18Þ%, where the first uncertainties are statistical and the second systematic

Search for an invisible muon philic scalar X0X_{0} or vector X1X_{1} via J/ψ→μ+μ−+invisibleJ/\psi\to\mu^+\mu^-+\rm{invisible} decay at BESIII

A light scalar $X_{0}$ or vector $X_{1}$ particles have been introduced as a possible explanation for the $(g-2)_{\mu}$ anomaly and dark matter phenomena. Using $(8.998\pm 0.039)\times10^9$ \jpsi events collected by the BESIII detector, we search for a light muon philic scalar $X_{0}$ or vector $X_{1}$ in the processes $J/\psi\to\mu^+\mu^- X_{0,1}$ with $X_{0,1}$ invisible decays. No obvious signal is found, and the upper limits on the coupling $g_{0,1}'$ between the muon and the $X_{0,1}$ particles are set to be between $1.1\times10^{-3}$ and $1.0\times10^{-2}$ for the $X_{0,1}$ mass in the range of $1<M(X_{0,1})<1000$~MeV$/c^2$ at 90$\%$ confidence level.Comment: 9 pages 7 figure

Observation of J/ψJ/\psi decays to e+e−e+e−e^{+}e^{-}e^{+}e^{-} and e+e−μ+μ−e^{+}e^{-}\mu^{+}\mu^{-}

Using a data sample of $4.481\times 10^8$ $\psi(3686)$ events collected with the BESIII detector, we report the first observation of the four-lepton-decays $J/\psi\to e^+e^-e^+e^-$ and $J/\psi\to e^+e^-\mu^+\mu^-$ utilizing the process $\psi(3686)\to \pi^+\pi^- J/\psi$. The branching fractions are determined to be $[4.32\pm0.26~(\rm stat)\pm0.19~(\rm syst)]\times 10^{-5}$ and $[2.45~\pm0.21~(\rm stat)\pm0.10~(\rm syst)]\times 10^{-5}$, respectively. The results deviate from theoretical predictions, by 2.8 and 5.2 $\sigma$, respectively. No significant signal is observed for $J/\psi\to \mu^+\mu^-\mu^+\mu^-$, and an upper limit on the branching fraction is set at $1.6\times 10^{-6}$ at the 90$\%$ confidence level. A CP asymmetry observable is constructed for the first two channels, which is measured to be $(-0.019\pm0.067\pm0.025)$ and $(-0.016\pm0.081\pm0.003)$, respectively. No evidence for CP violation is observed in this process.Comment: 9 pages, 1 figur

First Observation of a Three-Resonance Structure in e+e−→e^+e^-\rightarrow{non-open} Charm Hadrons

We report the measurement of the cross sections for $e^+e^-$$\rightarrow${nOCH} (nOCH stands for non-open charm hadrons) with improved precision at center-of-mass energies from 3.645 to 3.871 GeV. We observe for the first time a three-resonance structure in the energy-dependent lineshape of the cross sections, which are $\mathcal R(3760)$, $\mathcal R(3780)$ and $\mathcal R(3810)$ with significances of $9.4\sigma$, $15.7\sigma$, and $9.8\sigma$, respectively. The $\mathcal R(3810)$ is observed for the first time. We found two solutions in analysis of the cross sections. For solution I [solution II], we measure the mass, the total width and the product of electronic width and nOCH decay branching fraction to be $(3805.8 \pm 1.1 \pm 2.7)$ [$(3805.8 \pm 1.1 \pm 2.7)$] MeV/$c^2$, $(11.6 \pm 2.6 \pm 1.9)$ [$(11.5 \pm 2.5 \pm 1.8)$] MeV, and $(10.8\pm 3.2\pm 2.3)$ [$(11.0\pm 2.9\pm 2.4)$] eV for the $\mathcal R(3810)$, respectively. In addition, we measure the branching fractions ${\mathcal B}({\mathcal R}(3760)$$\rightarrow${nOCH}$)=(24.5 \pm 13.4 \pm 27.4)\% [(6.8 \pm 5.4 \pm 7.6)\%]$ for the first time, and ${\mathcal B}(\mathcal R(3780)$$\rightarrow${nOCH}$)=(11.6 \pm 5.8 \pm 7.8)\% [(10.3 \pm 4.5 \pm 6.9)\%]$. Moreover, we determine the open-charm (OC) branching fraction ${\mathcal B}({\mathcal R}$$(3760)\rightarrow${OC}$)=(75.5 \pm 13.4 \pm 27.4)\% [(93.2 \pm 5.4 \pm 7.6)\%]$, which supports the interpretation of $\mathcal R(3760)$ as an OC pair molecular state, but contained a simple four-quark state component. The first uncertainties are from fits to the cross sections, and the second are systematic