We present the first observation of the singly Cabibbo-suppressed decay \(\Lambda_c^+ \rightarrow \Lambda K^+\pi^0\) with a significance of \(5.7\sigma\) and the first evidence of \(\Lambda_c^+ ...\rightarrow \Lambda K^+\pi^+\pi^-\) decay with a significance of \(3.1\sigma\), based on \(e^+e^-\) annihilation data recorded by the BESIII detector at the BEPCII collider. The data correspond to an integrated luminosity of \(6.4~{\rm fb^{-1}}\), in the center-of-mass energy range from \(4.600~{\rm GeV}\) to \(4.950~{\rm GeV}\). We determine the branching fractions of \(\Lambda_c^+ \rightarrow \Lambda K^+\pi^0\) and \(\Lambda_c^+ \rightarrow \Lambda K^+\pi^+\pi^-\) relative to their Cabibbo-favored counterparts to be \(\frac{\mathcal{B}(\Lambda_c^+ \rightarrow \Lambda K^+\pi^0)}{\mathcal{B}(\Lambda_c^+ \rightarrow \Lambda \pi^+\pi^0)} = (2.09\pm0.39_{\mathrm{stat.}}\pm0.07_{\mathrm{syst.}}) \times 10^{-2}\) and \(\frac{\mathcal{B}(\Lambda_c^+ \rightarrow \Lambda K^+\pi^+\pi^-)}{\mathcal{B}(\Lambda_c^+ \rightarrow \Lambda \pi^+\pi^+\pi^-)} = (1.13\pm0.41_{\mathrm{stat.}}\pm0.06_{\mathrm{syst.}}) \times 10^{-2}\), respectively. Moreover, by combining our measured result with the world average of \(\mathcal{B}(\Lambda^+_c\to \Lambda\pi^+\pi^0)\), we obtain the branching fraction \(\mathcal{B}(\Lambda_c^+ \to \Lambda K^+\pi^0) = (1.49\pm0.27_{\mathrm{stat.}}\pm0.05_{\mathrm{syst.}}\pm0.08_{\mathrm{ref.}}) \times 10^{-3}\). This result significantly departs from theoretical predictions based on quark \(SU(3)\) flavor symmetry, which is underpinned by the presumption of meson pair \(S\)-wave amplitude dominance.
Based on \((27.08\pm 0.14)\times10^{8}\) \(\psi(3686)\) events collected with the BESIII detector operating at the BEPCII collider, the \(\psi(3686)\to\Sigma^{+}\bar{\Sigma}^{-}\omega\) and ...\(\Sigma^{+}\bar{\Sigma}^{-}\phi\) decays are observed for the first time with statistical significances of 13.8\(\sigma\) and 7.6\(\sigma\), respectively. The corresponding branching fractions are measured to be \(\mathcal{B}(\psi(3686)\to\Sigma^{+}\bar{\Sigma}^{-}\omega)=(1.90 \pm 0.18 \pm 0.21) \times 10^{-5}\) and \(\mathcal{B}(\psi(3686)\to\Sigma^{+}\bar{\Sigma}^{-}\phi)=(2.96 \pm 0.54 \pm 0.41) \times 10^{-6}\), where the first uncertainties are statistical and the second systematic.
Using an \(e^+ e^-\) collision data sample of \((10087 \pm 44)\times10^6 ~J/\psi\) events taken at the center-of-mass energy of \(3.097~\rm{GeV}\) by the BESIII detector at the BEPCII collider, the ...process \(\Lambda+N \rightarrow \Sigma^+ + X\) is studied for the first time employing a novel method. The \(\Sigma^{+}\) hyperons are produced by the collisions of \(\Lambda\) hyperons from \(J/\psi\) decays with nuclei in the material of the BESIII detector. The total cross section of \(\Lambda + ^{9}{\rm Be} \rightarrow \Sigma^+ + X\) is measured to be \(\sigma = (37.3 \pm 4.7 \pm 3.5)~{\rm mb}\) at \(\Lambda\) beam momenta within \(1.057, 1.091~{\rm GeV}/c\), where the uncertainties are statistical and systematic, respectively. This analysis is the first study of \(\Lambda\)-nucleon interactions at an \(e^+ e^-\) collider, providing information and constraints relevant for the strong-interaction potential, the origin of color confinement, the unified model for baryon-baryon interactions, and the internal structure of neutron stars.
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.
The Cabbibo-favored decay \(\Lambda_{c}^+ \to \Xi^{0}K^{+}\pi^{0}\) is studied for the first time using 6.1 fb\(^{-1}\) of \(e^+e^-\) collision data at center-of-mass energies between 4.600 and 4.840 ...GeV, collected with the BESIII detector at the BEPCII collider. With a double-tag method, the branching fraction of the three-body decay \(\Lambda_{c}^+ \to \Xi^{0}K^{+}\pi^{0}\) is measured to be \((7.79 \pm 1.46 _{\rm} \pm0.71 _{\rm}) \times 10^{ - 3}\), where the first and second uncertainties are statistical and systematic, respectively. The branching fraction of the two-body decay \(\Lambda_{c}^+ \to \Xi(1530)^{0}K^+\) is \((5.99\pm1.04\pm0.29)\times10^{-3}\), which is consistent with the previous result of \((5.02\pm0.99\pm0.31)\times 10^{-3}\). In addition, the upper limit on the branching fraction of the doubly Cabbibo-suppressed decay \(\Lambda_{c}^+ \to nK^+\pi^0\) is \(7.1 \times 10^{-4}\) at the 90\(\%\) confidence level. The upper limits on the branching fractions of \(\Lambda_{c}^+ \to \Sigma^{0}K^{+}\pi^{0}\) and \(\Lambda K^{+}\pi^{0}\) are also determined to be \(1.8\times 10^{-3}\) and \( 2.0 \times 10^{-3}\), respectively.
By analyzing 7.33\,fb\(^{-1}\) of \(e^+e^-\) collision data collected at center-of-mass energies between 4.128 and 4.226 GeV with the BESIII detector, we search for the semileptonic decays \(D^+_s ...\to K_1(1270)^0 e^+\nu_e\) and \(D^+_s \to b_1(1235)^0 e^+\nu_e\) for the first time. No significant signals are observed for either decay mode. The upper limits on the (product) branching fractions are determined to be \({\mathcal B}D^+_s \to K_1(1270)^0 e^+\nu_e < 4.1\times 10^{-4}\) and \({\mathcal B}D^+_s \to b_1(1235)^0 e^+\nu_e\cdot {\mathcal B}b_1(1235)^0\to \omega\pi^0 < 6.4\times 10^{-4}\) at 90\% confidence level.
We perform a study of the \(X(3872)\) lineshape using the data samples of \(e^+e^-\to\gamma X(3872)\), \(X(3872)\to D^0\bar{D}^0 \pi^0\) and \(\pi^+\pi^- J/\psi\) collected with the BESIII detector. ...The effects of the coupled-channels and the off-shell \(D^{*0}\) are included in the parameterization of the lineshape. The lineshape mass parameter is obtained to be \(M_{X}=(3871.63\pm 0.13^{+0.06}_{-0.05})\) MeV. Two poles are found on the first and second Riemann sheets corresponding to the \(D^{*0}\bar{D}^0\) branch cut. The pole location on the first sheet is much closer to the \(D^{*0}\bar{D}^0\) threshold than the other, and is determined to be \(7.04\pm0.15^{+0.07}_{-0.08}\) MeV above the \(D^0\bar{D}^0\pi^0\) threshold with an imaginary part \(-0.19\pm0.08^{+0.14}_{-0.19}\) MeV.
Phys. Rev. D 99, 012013 (2019) Using a data sample of $(1310.6\pm7.0)\times10^{6}$ $J/\psi$ decay events
collected with the BESIII detector at BEPCII, we study the electromagnetic
Dalitz decay ...$J/\psi \to \eta' e^+e^-$ with two dominant $\eta'$ decay modes,
$\eta' \to \gamma \pi^+ \pi^-$ and $\eta' \to \pi^+\pi^-\eta$. The branching
fraction is determined to be $\mathcal{B}(J/\psi \to \eta' e^+e^-) =
(6.59\pm0.07\pm0.17) \times 10^{-5}$, which improves in precision by a factor
of 2 over the previous BESIII measurement. A search for the dark photon
($\gamma '$) is performed via $J/\psi \to\eta' \gamma ', \gamma' \to
e^{+}e^{-}$. Excluding the $\omega$ and $\phi$ mass regions, no significant
signal is observed in the mass range from 0.1 to 2.1 GeV/$c^{2}$. We set upper
limits at the 90\% confidence level on $\mathcal{B}(J/\psi \to \eta' \gamma
')\times\mathcal{B}(\gamma ' \to e^+e^-)$, $\mathcal{B}(J/\psi \to\eta'
\gamma'$) and the mixing strength as a function of dark photon mass. This is
among the first searches for dark photons in charmonium decays.
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