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Register a new userTwo-photon widths of the $chi_{c0, 2}$ states and helicity analysis for $chi_{c2}argammagamma$}
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BESIII Collaboration: M. Ablikim
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Based on a data sample of 106 M $psi^{prime}$ events collected with the BESIII detector, the decays $psi^{prime}argammachi_{c0, 2}$,$chi_{c0, 2}argammagamma$ are studied to determine the two-photon widths of the $chi_{c0, 2}$ states. The two-photon decay branching fractions are determined to be ${cal B}(chi_{c0}argammagamma) = (2.24pm 0.19pm 0.12pm 0.08)times 10^{-4}$ and ${cal B}(chi_{c2}argammagamma) = (3.21pm 0.18pm 0.17pm 0.13)times 10^{-4}$. From these, the two-photon widths are determined to be $Gamma_{gamma gamma}(chi_{c0}) = (2.33pm0.20pm0.13pm0.17)$ keV, $Gamma_{gamma gamma}(chi_{c2}) = (0.63pm0.04pm0.04pm0.04)$ keV, and $cal R$ $=Gamma_{gamma gamma}(chi_{c2})/Gamma_{gamma gamma}(chi_{c0})=0.271pm 0.029pm 0.013pm 0.027$, where the uncertainties are statistical, systematic, and those from the PDG ${cal B}(psi^{prime}argammachi_{c0,2})$ and $Gamma(chi_{c0,2})$ errors, respectively. The ratio of the two-photon widths for helicity $lambda=0$ and helicity $lambda=2$ components in the decay $chi_{c2}argammagamma$ is measured for the first time to be $f_{0/2} =Gamma^{lambda=0}_{gammagamma}(chi_{c2})/Gamma^{lambda=2}_{gammagamma}(chi_{c2}) = 0.00pm0.02pm0.02$.
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Based on $448.1 times 10^6$ $psi(3686)$ events collected with the BESIII detector, the decays $psi(3686)togammachi_{cJ}, chi_{cJ} to gammagamma~(J=0, 1, 2)$ are studied. The decay branching fractions of $chi_{c0,c2} to gammagamma$ are measured to be $mathcal{B}(chi_{c0}togammagamma) = (1.93 pm 0.08 pm 0.05 pm 0.05)times 10^{-4}$ and $mathcal{B}(chi_{c2}togammagamma) = (3.10 pm 0.09 pm 0.07 pm 0.11)times 10^{-4} $, which correspond to two-photon decay widths of $Gamma_{gammagamma}(chi_{c0}) = 2.03 pm 0.08 pm 0.06 pm 0.13 ~rm{keV}$ and $Gamma_{gammagamma}(chi_{c2}) = 0.60 pm 0.02 pm 0.01 pm 0.04 ~rm{keV}$ with a ratio of $mathcal{R}=Gamma_{gammagamma}(chi_{c2})/Gamma_{gammagamma}(chi_{c0})= 0.295 pm 0.014 pm 0.007 pm 0.027$, where the uncertainties are statistical, systematic and associated with the uncertainties of $mathcal{B}(psi(3686)togammachi_{c0,c2})$ and the total widths $Gamma(chi_{c0,c2})$, respectively. For the forbidden decay of $chi_{c1}togammagamma$, no signal is observed, and an upper limit on the two-photon width is obtained to be $Gamma_{gammagamma}(chi_{c1})<5.3 ~rm{eV}$ at the 90% confidence level. The ratio of the two-photon widths between helicity-zero and helicity-two components in the decay $chi_{c2}togammagamma$ is also measured to be $f_{0/2} = Gamma^{lambda=0}_{gammagamma}(chi_{c2})/Gamma^{lambda=2}_{gammagamma}(chi_{c2}) = (0.0 pm 0.6 pm 1.2)times 10^{-2}$, where the uncertainties are statistical and systematic, respectively.
Using a sample of 1.06 times 10^8 psi^{prime} decays collected by the BESIII detector, chi_{c0} and chi_{c2} decays into pi^0pi^0 and etaeta are studied. The branching fraction results are Br(chi_{c0}topi^0pi^0)=(3.23pm 0.03pm0.23 pm 0.14)times 10^{-3}, Br(chi_{c2}topi^0pi^0)=(8.8pm 0.2pm 0.6pm0.4)times 10^{-4}, Br(chi_{c0}toetaeta)=(3.44pm 0.10pm0.24 pm0.2)times 10^{-3}, and Br(chi_{c2}toetaeta)=(6.5pm 0.4pm 0.5pm 0.3)times 10^{-4}, where the uncertainties are statistical, systematic due to this measurement, and systematic due to the branching fractions of psi^{prime}togammachi_{cJ}, respectively. The results provide information on the decay mechanism of chi_c states into pseudoscalars.
Prompt production of charmonium $chi_{c0}$, $chi_{c1}$ and $chi_{c2}$ mesons is studied using proton-proton collisions at the LHC at a centre-of-mass energy of $sqrt{s}=7$TeV. The $chi_{c}$ mesons are identified through their decay to $J/psigamma$, with $J/psitomu^+mu^-$ using photons that converted in the detector. A data sample, corresponding to an integrated luminosity of $1.0mathrm{fb}^{-1}$ collected by the LHCb detector, is used to measure the relative prompt production rate of $chi_{c1}$ and $chi_{c2}$ in the rapidity range $2.0<y<4.5$ as a function of the $J/psi$ transverse momentum from 3 to 20 GeV$/c$. First evidence for $chi_{c0}$ meson production at a high-energy hadron collider is also presented.
The decays $chi_{c1} rightarrow J/psi mu^+ mu^-$ and $chi_{c2} rightarrow J/psi mu^+ mu^-$ are observed and used to study the resonance parameters of the $chi_{c1}$ and $chi_{c2}$ mesons. The masses of these states are measured to be m(chi_{c1}) = 3510.71 pm 0.04(stat) pm 0.09(syst)MeV,, m(chi_{c2}) = 3556.10 pm 0.06(stat) pm 0.11(syst)MeV,, where the knowledge of the momentum scale for charged particles dominates the systematic uncertainty. The momentum-scale uncertainties largely cancel in the mass difference m(chi_{c2}) - m(chi_{c1}) = 45.39 pm 0.07(stat) pm 0.03(syst)MeV,. The natural width of the $chi_{c2}$ meson is measured to be $$Gamma(chi_{c2}) = 2.10 pm 0.20(stat) pm 0.02(syst)MeV,.$$ These results are in good agreement with and have comparable precision to the current world averages.
Using a sample of $447.9times 10^6$ $psi(3686)$ events collected with the BESIII detector in 2009 and 2012, we study the decays $chi_{c0,2}to$ $etaeta$ and $etaeta$. The decays $chi_{c2}toetaeta$, $chi_{c0}toetaeta$ and $chi_{c2}toetaeta$ are observed for the first time with statistical significances of $9.6sigma$, $13.4sigma$ and $7.5sigma$, respectively. The branching fractions are determined to be $mathcal{B}(chi_{c0}toetaeta) =(2.19pm0.03pm0.14)times10^{-3}$, $mathcal{B}(chi_{c2}toetaeta) = (4.76pm0.56pm0.38)times10^{-5}$, $mathcal{B}(chi_{c0}toetaeta) = (8.92pm0.84pm0.65)times10^{-5}$ and $mathcal{B}(chi_{c2}toetaeta) = (2.27pm0.43pm0.25)times10^{-5}$, where the first uncertainties are statistical and the second systematic. The precision for the measurement of $mathcal{B}(chi_{c0}toetaeta)$ is significantly improved compared to previous measurements. Based on the measured branching fractions, the role played by the doubly and singly Okubo-Zweig-Iizuka disconnected transition amplitudes for $chi_{c0,2}$ decays into pseudoscalar meson pairs can be clarified.
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