EM Decay of X(3872) as the 11D2(2−+)1{^1D_2}(2^{-+}) charmonium

The recently BaBar results raise the possibility that X(3872) has negative parity. This makes people reconsider assigning X(3872) to the $1{^1D_2}(c\bar c)$ state. In this paper we give a general form of the wave function of $2^{-+}$ mesons. By solving the instantaneous Bethe-Salpeter equation, we get the mass spectrum and corresponding wave functions. We calculate electromagnetic decay widths of the first $2^{-+}$ state which we assume to be the X(3872) particle. The results are $\Gamma(2^{-+}(3872)\rightarrow J/\psi\gamma) = 1.59^{+0.53}_{-0.42}$ keV, $\Gamma(2^{-+}(3872)\rightarrow \psi(2S)\gamma) = 2.87^{+1.46}_{-0.97}$ eV and $\Gamma(2^{-+}(3872)\rightarrow \psi(3770)\gamma) = 0.135^{+0.066}_{-0.047}$ keV. The ratio of branch fractions of the second and first channel is about 0.002, which is inconsistent with the experimental value $3.4\pm 1.4$. So X(3872) is unlikely to be a $2^{-+}$ charmonium state. In addition, we obtain a relatively large decay width for $2^{-+}(3872)\rightarrow h_c\gamma$ channel which is $392^{+62}_{-111}$ keV.Comment: Revised versio

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

Observation of χcJ→ΛΛˉη\chi_{cJ}\to \Lambda\bar \Lambda \eta

By analyzing $(448.1\pm2.9)\times10^6$ $\psi(3686)$ events collected with the BESIII detector operating at the BEPCII collider, the decays of $\chi_{cJ} \to \Lambda\bar \Lambda \eta$ ($J=0$, 1 and 2) are observed for the first time with statistical significances of $13.9\sigma$, $6.7\sigma$, and $8.2\sigma$, respectively. The product branching fractions of $\psi(3686)\to\gamma\chi_{cJ}$ and $\chi_{cJ}\to \Lambda\bar \Lambda \eta$ are measured. Dividing by the world averages of the branching fractions of $\psi(3686)\to\gamma\chi_{cJ}$, the branching fractions of $\chi_{cJ}\to \Lambda\bar \Lambda \eta$ decays are determined to be $(2.31\pm0.30\pm0.21)\times10^{-4}$, $(5.86\pm1.38\pm0.68)\times10^{-5}$, and $(1.05\pm0.21\pm0.15)\times10^{-4}$ for $J=0$, 1 and 2, respectively, where the first uncertainties are statistical and the second systematic.Comment: 9 pages, 4 figure

Evidence for the cusp effect in η′\eta' decays into ηπ0π0\eta\pi^0\pi^0

Using a sample of $4.3\times 10^5$ $\eta'\to\eta\pi^0\pi^0$ events selected from the 10 billion $J/\psi$ event data set collected with the BESIII detector, we study the decay $\eta'\to\eta\pi^0\pi^0$ within the framework of non-relativistic effective field theory. Evidence for a structure at $\pi^+\pi^-$ mass threshold is observed in the invariant mass spectrum of $\pi^0\pi^0$ with a statistical significance of around $3.5\sigma$, which is consistent with the cusp effect as predicted by the non-relativistic effective field theory. After introducing the amplitude for describing the cusp effect, the $\pi\pi$ scattering length combination $a_0-a_2$ is determined to be $0.226\pm0.060_{stat.}\pm0.012_{syst.}$, which is in good agreement with theoretical calculation of $0.2644\pm0.0051$

Measurement of Branching Fractions of Singly Cabibbo-suppressed Decays Λc+→Σ0K+\Lambda_c^+ \rightarrow \Sigma^{0} K^+ and Σ+KS0\Sigma^{+} K_{S}^0

Based on a sample of 4.4 $\mathrm{fb}^{-1}$ of $e^{+}e^{-}$ annihilation data collected in the energy region between 4.6 GeV and 4.7 GeV with the BESIII detector at BEPCII, two singly Cabibbo-suppressed decays $\Lambda_c^+ \rightarrow \Sigma^0 K^+$ and $\Lambda_{c}^{+} \rightarrow \Sigma^+ K_{S}^0$ are studied. The ratio of the branching fraction $\mathcal{B}(\Lambda_c^+ \rightarrow \Sigma^0 K^+)$ relative to $\mathcal{B}(\Lambda_c^+ \rightarrow \Sigma^0 \pi^+)$ is measured to be $0.0361 \pm 0.0073(\mathrm{stat.}) \pm 0.0005(\mathrm{syst.})$, and the ratio of $\mathcal{B}(\Lambda_c^+ \rightarrow \Sigma^+ K_{S}^0)$ relative to $\mathcal{B}(\Lambda_{c}^{+} \rightarrow \Sigma^+ \pi^+ \pi^-)$ is measured to be $0.0106 \pm 0.0031(\mathrm{stat.}) \pm 0.0004(\mathrm{syst.})$. After taking the world-average branching fractions of the reference decay channels, the branching fractions $\mathcal{B}(\Lambda_c^+ \rightarrow \Sigma^0 K^+)$ and $\mathcal{B}(\Lambda_{c}^{+} \rightarrow \Sigma^+ K_{S}^0)$ are determined to be $(4.7\pm 0.9(\mathrm{stat.})\pm 0.1(\mathrm{syst.}) \pm 0.3(\mathrm{ref.}))\times10^{-4}$ and $(4.8\pm 1.4(\mathrm{stat.})\pm 0.2(\mathrm{syst.}) \pm 0.3(\mathrm{ref.}))\times10^{-4}$, respectively. The branching fraction of the $\Lambda_{c}^{+} \rightarrow \Sigma^+ K_{S}^0$ decay is measured for the first time.Comment: 13 pages, 4 figure

First Observation of the Semileptonic Decay Λc+→pK−e+νe\Lambda_c^+\rightarrow pK^- e^+\nu_e

Using $4.5~\mathrm{fb}^{-1}$ of $e^+e^-$ annihilation data samples collected at the center-of-mass energies ranging from 4.600~GeV to 4.699~GeV with the BESIII detector at the BEPCII collider, a first study of the semileptonic decays $\Lambda_c^+\rightarrow pK^-e^+\nu_e$, $\Lambda_c^+\rightarrow \Lambda(1520) e^+\nu_e$ and $\Lambda_c^+\rightarrow \Lambda(1405) e^+\nu_e$ is performed. The $\Lambda_c^+\rightarrow pK^-e^+\nu_e$ decay is observed with a significance of $8.2\sigma$ and the branching fraction is measured to be $\mathcal{B}(\Lambda_c^+\rightarrow pK^- e^+\nu_e)=(0.82\pm0.15_{\rm stat.}\pm0.06_{\rm syst.})\times 10^{-3}$. We also report the first evidence of $\Lambda_c^+\rightarrow \Lambda(1520) e^+\nu_e$ and $\Lambda_c^+\rightarrow \Lambda(1405) e^+\nu_e$ with a significance of $4.0\sigma$, and measure $\mathcal B(\Lambda^+_c\rightarrow \Lambda(1520)e^+\nu_e)=(0.99\pm0.51_{\rm stat.}\pm0.10_{\rm syst.})\times10^{-3}$ as well as $\mathcal B(\Lambda^+_c\rightarrow \Lambda(1405)e^+\nu_e)=(1.69\pm0.76_{\rm stat.}\pm0.16_{\rm syst.})\times10^{-3}$. Combining the inclusive semileptonic $\Lambda_c^+$ branching fraction measured by the BESIII, the relative fraction is determined to be $[\mathcal{B}(\Lambda_c^+\rightarrow pK^-e^+\nu_e)/\mathcal{B}(\Lambda_c^+\rightarrow X e^+\nu_e)]=(2.1\pm0.4_{\rm stat.}\pm0.2_{\rm syst.})\%$, which provides a clear confirmation that semileptonic $\Lambda_c^+$ decays are not saturated by the $\Lambda \ell^+\nu_{\ell}$ final state.Comment: 13 pages, 9 figures and 2 table

Observation of the Y(4230)Y(4230) and evidence for a new vector charmonium-like state Y(4710)Y(4710) in e+e−→KS0KS0J/ψe^{+}e^{-}\to K_{S}^{0} K_{S}^{0} J/\psi

Cross sections for the process $e^{+} e^{-} \to K_{S}^{0} K_{S}^{0} J/\psi$ at center-of-mass energies from $4.128$ to $4.950$ GeV are measured using data samples with a total integrated luminosity of 21.2 fb$^{-1}$ collected by the BESIII detector operating at the BEPCII storage ring. The $Y(4230)$ state is observed in the energy dependence of the $e^{+} e^{-} \to K_{S}^{0} K_{S}^{0} J/\psi$ cross section for the first time with a statistical significance of 26.0$\sigma$. In addition, an enhancement around $4.710$ GeV, called the $Y(4710)$, is seen with a statistical significance of 4.2$\sigma$. There is no clear structure around $4.484$ GeV. Using a fit with a coherent sum of three Breit-Wigner functions, we determine the mass and width of the $Y(4230)$ state to be $4226.9 \pm 6.6 \pm 21.9$ MeV/$c^{2}$ and $71.7 \pm 16.2 \pm 31.4$ MeV, respectively, and the mass and width of the $Y(4710)$ state to be $4704.0 \pm 52.3 \pm 69.5$ MeV/$c^{2}$ and $183.2 \pm 114.0 \pm 90.8$ MeV, respectively, where the first uncertainties are statistical and the second are systematic. In addition, the average Born cross section ratio of $e^{+} e^{-} \to K_{S}^{0} K_{S}^{0} J/\psi$ to $e^{+} e^{-} \to K^{+} K^{-} J/\psi$ is measured to be $0.388_{-0.028}^{+0.035}\pm0.016$, or $0.426_{-0.031}^{+0.038}\pm0.018$ if three-body phase space is considered.Comment: Update draft based the comments from PRD refere