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Register a new userEvidence for $eta_{c} rightarrow gammagamma$ and Measurement of $J/psirightarrow 3gamma$
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The decay of $J/psi$ to three photons is studied using $psi(3686)topi^+pi^-J/psi$ in a sample of $1.0641times10^8$ $psi(3686)$ events collected with the BESIII detector. Evidence of the direct decay of $eta_c$ to two photons, $eta_ctogammagamma$, is reported, and the product branching fraction is determined to be $mathcal{B}(J/psitogammaeta_c,eta_cto gammagamma)=(4.5pm1.2pm0.6)times10^{-6}$, where the first error is statistical and the second is systematic. The branching fraction for $J/psito3gamma$ is measured to be $(11.3pm1.8pm2.0)times 10^{-6}$ with improved precision.
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Using the inclusive photon spectrum based on a data sample collected at the $J/psi$ peak with the KEDR detector at the VEPP-4M $e^+e^-$ collider, we measured the rate of the radiative decay $J/psitogammaeta_{rm c}$ as well as $eta_{rm c}$ mass and width. Taking into account an asymmetric photon lineshape we obtained $Gamma^0_{gammaeta_{rm c}}=2.98pm0.18 phantom{|}^{+0.15}_{-0.33}$ keV, $M_{eta_{rm c}} = 2983.5 pm 1.4 phantom{|}^{+1.6}_{-3.6}$ MeV/$c^2$, $Gamma_{eta_{rm c}} = 27.2 pm 3.1 phantom{|}^{+5.4}_{-2.6}$ MeV.
We performed a search for the decay $K_L^0 rightarrow 3gamma$ with the E391a detector at KEK. In the data accumulated in 2005, no event was observed in the signal region. Based on the assumption of $K_L^0 rightarrow 3gamma$ proceeding via parity-violation, we obtained the single event sensitivity to be $(3.23pm0.14)times10^{-8}$, and set an upper limit on the branching ratio to be $7.4times10^{-8}$ at the 90% confidence level. This is a factor of 3.2 improvement compared to the previous results. The results of $K_L^0 rightarrow 3gamma$ proceeding via parity-conservation were also presented in this paper.
We present the first upper-limit measurement of the branching fractions of the isospin-violating transitions $chi_{c0,2} rightarrow pi^{0} eta_{c}$. The measurements are performed using $106times 10^{6}$ $psi(3686)$ events accumulated with the BESIII detector at the BEPCII $e^{+}e^{-}$ collider at a center-of-mass energy corresponding to the $psi(3686)$ mass. We obtained upper limits on the branching fractions at a 90% confidence level of $B(chi_{c0} rightarrow pi^{0} eta_{c}) < 1.6 times 10^{-3}$ and $B(chi_{c2} rightarrow pi^{0} eta_{c}) < 3.2 times 10^{-3}$.
A study of $B^{0}_{s} to eta_{c} phi$ and $B^{0}_{s} to eta_{c} pi^{+}pi^{-}$ decays is performed using $pp$ collision data corresponding to an integrated luminosity of 3.0$,rm fb^{-1}$, collected with the LHCb detector in Run~1 of the LHC. The observation of the decay $B^{0}_{s} to eta_{c} phi$ is reported, where the $eta_{c}$ meson is reconstructed in the $pbar p$, $K^+K^-pi^+pi^-$, $pi^+pi^-pi^+pi^-$ and $K^+K^-K^+K^-$ decay modes and the $phi(1020)$ in the $K^+ K^-$ decay mode. The decay $B^{0}_{s} to J/psi phi$ is used as a normalisation channel. Evidence is also reported for the decay $B^{0}_{s} to eta_{c} pi^{+}pi^{-}$, where the $eta_{c}$ meson is reconstructed in the $pbar p$ decay mode, using the decay $B^{0}_{s} to J/psi pi^+ pi^-$ as a normalisation channel. The measured branching fractions are begin{eqnarray*} {mathcal B (B^{0}_{s} to eta_{c} phi)} &=& left(5.01 pm 0.53 pm 0.27 pm 0.63 right) times 10^{-4} ,, onumber {mathcal B (B^{0}_{s} to eta_{c} pi^+ pi^-)} &=& left(1.76 pm 0.59 pm 0.12 pm 0.29 right) times 10^{-4} ,, end{eqnarray*} where in each case the first uncertainty is statistical, the second systematic and the third uncertainty is due to the limited knowledge of the external branching fractions.
Using a sample of $1.31 times 10^{9}$ $J/psi$ events collected with the BESIII detector at the BEPCII collider, we study the decays of $J/psi rightarrow K_S K_L$ and $K_S K_S$. The branching fraction of$J/psirightarrow K_S K_L$ is determined to be ${cal B}(J/psi rightarrow K_S K_L)=(1.93pm0.01~(rm{stat.})pm0.05~(rm{syst.}))times10^{-4}$, which significantly improves on previous measurements. No clear signal is observed for the $J/psi rightarrow K_S K_S$ process, and the upper limit at the 95% confidence level for its branching fraction is determined to be ${cal B}(J/psi rightarrow K_S K_S)<1.4times10^{-8}$, which improves on the previous searches by two orders in magnitude and reaches the order of the Einstein-Podolsky-Rosen expectation.
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