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Register a new userFirst observation of the M1 transition $psi(3686)to gammaeta_c(2S)$
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Using a sample of 106 million psi(3686) events collected with the BESIII detector at the BEPCII storage ring, we have made the first measurement of the M1 transition between the radially excited charmonium S-wave spin-triplet and the radially excited S-wave spin-singlet states: psi(3686)togammaeta_c(2S). Analyses of the processes psi(2S)to gammaeta_c(2S) with eta_c(2S)to K_S^0 Kpi and K^+K^-pi^0 gave an eta_c(2S) signal with a statistical significance of greater than 10 standard deviations under a wide range of assumptions about the signal and background properties. The data are used to obtain measurements of the eta_c(2S) mass (M(eta_c(2S))=3637.6pm 2.9_mathrm{stat}pm 1.6_mathrm{sys} MeV/c^2), width (Gamma(eta_c(2S))=16.9pm 6.4_mathrm{stat}pm 4.8_mathrm{sys} MeV), and the product branching fraction (BR(psi(3686)to gammaeta_c(2S))times BR(eta_c(2S)to Kbar Kpi) = (1.30pm 0.20_mathrm{stat}pm 0.30_mathrm{sys})times 10^{-5}). Combining our result with a BaBar measurement of BR(eta_c(2S)to Kbar K pi), we find the branching fraction of the M1 transition to be BR(psi(3686)togammaeta_c(2S)) = (6.8pm 1.1_mathrm{stat}pm 4.5_mathrm{sys})times 10^{-4}.
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We report a measurement of the $B^0rightarrowpsi(2S)pi^0$ branching fraction based on the full $Upsilon(4S)$ data set of $772times10^{6}$ $Bbar{B}$ pairs collected by the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. We obtain $B(B^0rightarrowpsi(2S)pi^0) = (1.17pm0.17text{(stat)}pm0.08text{(syst)})times10^{-5}$. The result has a significance of 7.2 standard deviations and is the first observation of the decay $B^0rightarrowpsi(2S)pi^0$.
Using a sample of $448.1times10^{6}$ $psi(3686)$ events collected with the BESIII detector, a search for the isospin violating decay $eta_{c}topi^{+}pi^{-}pi^{0}$ via $psi(3686)togammaeta_{c}$ is presented. No signal is observed, and the upper limit on $mathcal{B}(psi(3686)to gammaeta_{c}to gammapi^{+}pi^{-}pi^{0} )$ is determined to be $1.6times10^{-6}$ at the $90%$ confidence level. In addition, a search for $eta(1405)to f_{0}(980)pi^{0}$ in $psi(3686)$ radiative decays is performed. No signal is observed, and the branching fraction $mathcal{B}(psi(3686)togammaeta(1405)to gamma f_{0}(980)pi^{0}togamma pi^+pi^-pi^0 )$ is calculated to be less than $ 5.0times10^{-7}$ at the $90%$ confidence level.
Using a data sample of $4.48times10^{8}$ $psip$ events collected with the BESIII detector, we present a first observation of $psi(3686)to pbar{p}phi$, and we measure its branching fraction to be $[6.06pm0.38 ($stat.$) pm 0.48 ($syst.$)]times10^{-6}$. In contrast to the earlier discovery of a threshold enhancement in the $pbar{p}$-mass spectrum of the channel $J/psitogamma pbar p$, denoted as $X(pbar{p})$, we do not find a similar enhancement in $psi(3686)to pbar{p}phi$. An upper limit of $1.82times10^{-7}$ at the $90%$ confidence level on the branching fraction of $psi(3686)to X(pbar{p})phito pbar{p}phi$ is obtained.
Using a data sample of $448.1 times 10^6$ $psi(3686)$ events collected with the BESIII detector at the BEPCII collider, we report the first observation of the electromagnetic Dalitz decay $psi(3686) to eta e^+ e^-$, with significances of 7.0$sigma$ and 6.3$sigma$ when reconstructing the $eta$ meson via its decay modes $etatogamma pi^+ pi^-$ and $etatopi^+pi^-eta$ ($eta to gammagamma$), respectively. The weighted average branching fraction is determined to be $mathcal{B}(psi(3686) to eta e^+ e^-)= (1.90 pm 0.25 pm 0.11) times 10^{-6}$, where the first uncertainty is statistical and the second systematic.
We observe the decay $psi(3686) to n bar{n}$ for the first time and measure $psi(3686) to p bar{p}$ with improved accuracy by using $1.07times 10^8$ $psi(3686)$ events collected with the BESIII detector. The measured branching fractions are $mathcal{B}(psi(3686) to n bar{n}) = (3.06 pm 0.06 pm 0.14)times 10^{-4}$ and $mathcal{B}(psi(3686) to p bar{p}) = (3.05 pm 0.02 pm 0.12) times 10^{-4}$. Here, the first uncertainties are statistical and the second ones systematic. With the hypothesis that the polar angular distributions of the neutron and proton in the center-of-mass system obey $1+alpha cos^2theta$, we determine the $alpha$ parameters to be $alpha_{nbar{n}} = 0.68 pm 0.12 pm 0.11$ and $alpha_{pbar{p}} = 1.03 pm 0.06 pm 0.03$ for $psi(3686)to nbar{n}$ and $psi(3686)to pbar{p}$, respectively.
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