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

Search for the charged lepton flavor violating decay J/ψ→eτJ/\psi\to e\tau

A search for the charged lepton flavor violating decay $J/\psi\to e^{\pm}\tau^{\mp}$ with $\tau^{\mp} \to \pi^{\mp}\pi^0\nu_{\tau}$ is performed with about $10$ billion $J/ \psi$ events collected with the BESIII detector at the BEPCII. No significant signal is observed, and an upper limit is set on the branching fraction $\mathcal{B}(J/\psi\to e^{\pm}\tau^{\mp})<7.5\times10^{-8}$ at the 90$\%$ confidence level. This improves the previously published limit by two orders of magnitude.Comment: 9 pages, 4 figures, 2 table

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

Production of doubly-charged Δ\Delta baryon in e+e−e^{+}e^{-} annihilation at energies from 2.3094 to 2.6464 GeV

The processes $e^{+}e^{-} \to \Delta^{++}\bar{\Delta}^{--}$ and $e^{+}e^{-}\to \Delta^{++} \bar{p} \pi^{-} + c.c.$ are studied for the first time with $179~{\rm pb}^{-1}$ of $e^{+}e^{-}$ annihilation data collected with the BESIII detector at center-of-mass energies from $2.3094$ GeV to $2.6464$ GeV. No significant signal for the $e^{+}e^{-}\to \Delta^{++}\bar{\Delta}^{--}$ process is observed and the upper limit of the Born cross section is estimated at each energy point. For the process $e^{+}e^{-} \to \Delta^{++} \bar{p} \pi^{-} + c.c.$, a significant signal is observed at center-of-mass energies near 2.6454 GeV and the corresponding Born cross section is reported.Comment: 10 pages, 4 figure

Observation of Ξ−\Xi^{-} Hyperon Transverse Polarization in ψ(3686)→Ξ−Ξˉ+\psi(3686)\rightarrow\Xi^{-}\bar\Xi^{+}

Using a sample of $(448.1~\pm~2.9)$ $\times 10^{6}$ $\psi(3686)$ decays collected with the BESIII detector at BEPCII, we report an observation of $\Xi^{-}$ transverse polarization with a significance of $7.3 \sigma$ in the decay $\psi(3686)\rightarrow\Xi^{-}\bar\Xi^{+}$ ($\Xi^{-}\rightarrow\pi^{-}\Lambda$, $\bar\Xi^{+}\rightarrow\pi^{+}\bar\Lambda$, $\Lambda\to p\pi^{-}$, $\bar\Lambda\to\bar{p}\pi^{+}$). The relative phase of the electric and magnetic form factors is determined to be $\Delta\Phi = (0.667 \pm 0.111 \pm 0.058)$ rad. This is the first measurement of the relative phase for a $\psi(3686)$ decay into a pair of $\Xi^{-}\bar\Xi^{+}$ hyperons. The $\Xi^{-}$ decay parameters ($\alpha_{\Xi^{-}}$, $\phi_{\Xi^-}$) and their conjugates ($\alpha_{\bar\Xi^{+}}$, $\phi_{\bar{\Xi}^{+}}$), the angular-distribution parameter $\alpha_{\psi}$, and the strong-phase difference $\delta_{p}-\delta_{s}$ for $\Lambda$-$\pi^-$ scattering are measured to be consistent with previous BESIII results.Comment: 8 pages, 3 figures, consistent with paper published in Phys. Rev. D (Letter) 106, L091101 (2022

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

Measurement of the C ⁣PC\!P-even fraction of D0→K+K−π+π−D^0\to K^+K^-\pi^+\pi^-

A determination of the $C\!P$-even fraction $F_+$ in the decay $D^0 \to K^+K^-\pi^+\pi^-$ is presented. Using $2.93$ fb$^{-1}$ of $e^+e^-\to\psi(3770)\to D\bar{D}$ data collected by the BESIII detector, one charm meson is reconstructed in the signal mode and the other in a $C\!P$ eigenstate or the decay $D\to K_{S, L}^0\pi^+\pi^-$. Analysis of the relative rates of these double-tagged events yields the result $F_+ = 0.730 \pm 0.037 \pm 0.021$, where the first uncertainty is statistical and the second is systematic. This is the first model-independent measurement of $F_+$ in $D^0 \to K^+K^-\pi^+\pi^-$ decays.Comment: 13 pages, 5 figure

Measurement of the absolute branching fraction of the inclusive decay Ds+→π+π+π−XD_s^+\to \pi^+\pi^+\pi^- X

Using an $e^+ e^-$ collision data sample with a total integrated luminosity of $3.19$ fb$^{-1}$ collected with the BESIII detector at a center-of-mass energy of 4.178 GeV, the branching fraction of the inclusive decay of the $D_s^+$ meson to final states including at least three charged pions is measured for the first time to be ${\cal B}(D_s^+\to\pi^+ \pi^+ \pi^- X) = (32.81 \pm 0.35_{\rm stat} \pm {0.82_{\rm syst}})\%$. In this measurement the charged pions from $K_S^0$ meson decays are excluded. The partial branching fractions of $D_s^+\to\pi^+ \pi^+ \pi^- X$ are also measured as a function of the $\pi^+ \pi^+ \pi^-$ invariant mass.Comment: 13 pages, 4 figure