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Register a new userHigher-order multipole amplitude measurement in $psi(2S)togammachi_{c2}$
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BESIII Collaboration
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Using $106times10^6$ $psi(2S)$ events collected with the BESIII detector at the BEPCII storage ring, the higher-order multipole amplitudes in the radiative transition $psi(2S)togammachi_{c2}togammapipi/gamma KK$ are measured. A fit to the $chi_{c2}$ production and decay angular distributions yields $M2=0.046pm0.010pm0.013$ and $E3=0.015pm0.008pm0.018$, where the first errors are statistical and the second systematic. Here $M2$ denotes the normalized magnetic quadrupole amplitude and $E3$ the normalized electric octupole amplitude. This measurement shows evidence for the existence of the $M2$ signal with $4.4sigma$ statistical significance and is consistent with the charm quark having no anomalous magnetic moment.
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Using 106~million $psi(3686)$ events collected with the BESIII detector, we measure multipole amplitudes for the decay $psi(3686)rightarrowgammachi_{c1,2}togammagamma J/psi$ beyond the dominant electric-dipole amplitudes. The normalized magnetic-quadrupole amplitude for $psi(3686)rightarrowgammachi_{c1,2}rightarrowgammagamma J/psi$ and the normalized electric-octupole amplitudes for $psi(3686)rightarrowgammachi_{c2}$,~$chi_{c2}rightarrowgamma J/psi$ are determined. The M2 amplitudes for $psi(3686)rightarrowgammachi_{c1}$ and $chi_{c1,2}rightarrowgamma J/psi$ are found to differ significantly from zero and are consistent with theoretical predictions. We also obtain the ratios of M2 contributions of $psi(3686)$ and $J/psi$ decays to $chi_{c1,2}$, $b_{2}^{1}/b_{2}^{2} = 1.35pm0.72$ and $a_{2}^{1}/a_{2}^{2} = 0.617pm0.083$, which agree well with theoretical expectations. By considering the multipole contributions of $chi_{c1,2}$, we measure the product branching fractions for the cascade decays $psi(3686)rightarrowgammachi_{c0,1,2}togammagamma J/psi$ and search for the process $eta_{c}(2S)togamma J/psi$ through $psi(3686)rightarrowgammaeta_{c}(2S)$. The product branching fraction for $psi(3686)rightarrowgammachi_{c0}togammagamma J/psi$ is 3$sigma$ larger than published measurements, while those of $psi(3686)rightarrowgammachi_{c1,2}togammagamma J/psi$ are consistent. No significant signal for the decay $psi(3686)togamma eta_c(2S)togamma gamma J/psi$ is observed, and the upper limit of the product branching fraction at the 90% confidence level is determined.
We perform a helicity amplitude analysis for the processes of $e^+e^-$$rightarrow$$J/psi,psi(2S)rightarrowXi(1530)barXi(1530)rightarrowpipiXibarXirightarrowLambdabarLambda4pirightarrow pbar{p}6pi$. The joint angular distribution for these processes are obtained, which allows a proper estimation of the detection efficiency using helicity amplitude information. In addition, the sensitivities of measurement of hyperon asymmetry decay parameters for these processes are discussed.
We measure the mass of the eta meson using psi(2S) --> eta J/psi events acquired with the CLEO-c detector operating at the CESR e+e- collider. Using the four decay modes eta --> gamma gamma, 3pi0, pi+pi-pi0, and pi+pi-gamma, we find M(eta)=547.785 +- 0.017 +- 0.057 MeV, in which the first uncertainty is statistical and the second systematic. This result has an uncertainty comparable to the two most precise previous measurements and is consistent with that of NA48, but is inconsistent at the level of 6.5sigma with the much smaller mass obtained by GEM.
A high-precision determination of the main parameters of the psi(2S) resonance has been performed with the KEDR detector at the VEPP-4M e^{+}e^{-} collider in three scans of the psi(2S) -- psi(3770) energy range. Fitting the energy dependence of the multihadron cross section in the vicinity of the psi(2S) we obtained the mass value M = 3686.114 +- 0.007 +- 0.011 ^{+0.002}_{-0.012} MeV and the product of the electron partial width by the branching fraction into hadrons Gamma_{ee}*B_{h} = 2.233 +- 0.015 +- 0.037 +- 0.020 keV. The third error quoted is an estimate of the model dependence of the result due to assumptions on the interference effects in the cross section of the single-photon e^{+}e^{-} annihilation to hadrons explicitly considered in this work. Implicitly, the same assumptions were employed to obtain the charmonium leptonic width and the absolute branching fractions in many experiments. Using the result presented and the world average values of the electron and hadron branching fractions, one obtains the electron partial width and the total width of the psi(2S): Gamma_{ee} =2.282 +- 0.015 +- 0.038 +- 0.021 keV, Gamma = 296 +- 2 +- 8 +- 3 keV. These results are consistent with and more than two times more precise than any of the previous experiments.
The product of the electronic width of the $psi(2S)$ meson and the branching fraction of its decay to the muon pair was measured in the $e^{+}e^{-} to psi(2S) to mu^{+}mu^{-}$ process using nine data sets corresponding to an integrated luminosity of about 6.5 pb$^{-1}$ collected with the KEDR detector at the VEPP-4M electron-positron collider: [ Gamma_{ee}timesmathcal{B}_{mumu} = 19.3 pm 0.3 pm 0.5 ~text{eV}. ] Adding the previous KEDR results on hadronic and leptonic channels, the values of the $psi(2S)$ electronic width were obtained under two assumptions: either with the assumption of lepton universality [ Gamma_{ee} = 2.279 pm 0.015 pm 0.042 ~text{keV} ] or without it, summing up hadronic and three independent leptonic channels: [ Gamma_{ee} = 2.282 pm 0.015 pm 0.042 ~text{keV}. ]
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