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Register a new userObservation of $chi_{c1}$ decays into vector meson pairs $phiphi$, $omegaomega$, and $omegaphi$
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Decays of $chi_{c1}$ to vector meson pairs $phiphi$, $omegaomega$ and $omegaphi$ are observed for the first time using $(106pm4)times 10^6$ $psip$ events accumulated at the BESIII detector at the BEPCII $e^+e^-$ collider. The branching fractions are measured to be $(4.4pm 0.3pm 0.5)times 10^{-4}$, $(6.0pm 0.3pm 0.7)times 10^{-4}$, and $(2.2pm 0.6pm 0.2)times 10^{-5}$, for $chi_{c1}to phiphi$, $omegaomega$, and $omegaphi$, respectively. The observation of $chi_{c1}$ decays into a pair of vector mesons $phiphi$, $omegaomega$ and $omegaphi$ indicates that the hadron helicity selection rule is significantly violated in $chi_{cJ}$ decays. In addition, the measurement of $chi_{cJ}to omegaphi$ gives the rate of doubly OZI-suppressed decay. Branching fractions for $chi_{c0}$ and $chi_{c2}$ decays into other vector meson pairs are also measured with improved precision.
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We evaluate ratios of the $chi_{c1}$ decay rates to $eta$ ($eta, K^-$) and one of the $f_0(1370)$, $f_0(1710)$, $f_2(1270)$, $f_2(1525)$, $K^{*}_2(1430)$ resonances, which in the local hidden gauge approach are dynamically generated from the vector-vector interaction. With the simple assumption that the $chi_{c1}$ is a singlet of SU(3), and the input from the study of these resonances as vector-vector molecular states, we describe the experimental ratio $mathcal{B}(chi_{c1} rightarrow eta f_2(1270))/ mathcal{B}(chi_{c1} rightarrow eta f_2(1525))$ and make predictions for six more ratios that can be tested in future experiments.
We report the first observation of the radiative decay of the $Upsilon(1S)$ into a charmonium state. The statistical significance of the observed signal of $Upsilon(1S) to gamma chi_{c1}$ is 6.3 standard deviations including systematics. The branching fraction is calculated to be Br($Upsilon(1S) to gamma chi_{c1}$) = (4.7^{+2.4}_{-1.8} (stat) ^{+0.4}_{-0.5} (sys)) * 10^{-5}. We also searched for $Upsilon(1S)$ radiative decays into $chi_{c0,2}$ and $eta_c(1S,2S)$ and set upper limits on their branching fractions. These results are obtained from a 24.9 fb^{-1} data sample collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider at a center-of-mass energy equal to the $Upsilon(2S)$ mass using $Upsilon(1S)$ tagging by the $Upsilon(2S) to Upsilon(1S) pi^+pi^-$ transitions.
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.
The first observation of the decays $Lambda_b^0 to chi_{c1} p K^-$ and $Lambda_b^0 to chi_{c2} p K^-$ is reported using a data sample corresponding to an integrated luminosity of $3.0$ fb$^{-1}$, collected by the LHCb experiment in $pp$ collisions at centre-of-mass energies of 7 and 8 TeV. The following ratios of branching fractions are measured begin{eqnarray*} frac{{cal B}(Lambda_b^0 to chi_{c1} p K^-)}{{cal B}(Lambda_b^0 to J/psi p K^-)} = 0.242 pm 0.014 pm 0.013 pm 0.009, frac{{cal B}(Lambda_b^0 to chi_{c2} p K^-)}{{cal B}(Lambda_b^0 to J/psi p K^-)} = 0.248 pm 0.020 pm 0.014 pm 0.009, frac{{cal B}(Lambda_b^0 to chi_{c2} p K^-)}{{cal B}(Lambda_b^0 to chi_{c1} p K^-)} = 1.02 pm 0.10 pm 0.02 pm 0.05, end{eqnarray*} where the first uncertainty is statistical, the second systematic and the third due to the uncertainty on the branching fractions of the $chi_{c1}to J/psigamma$ and $chi_{c2} to J/psigamma$ decays. Using both decay modes, the mass of the $Lambda_b^0$ baryon is also measured to be $m_{Lambda_b^0} = 5619.44 pm 0.28 pm 0.26$ MeV/$c^2$, where the first and second uncertainties are statistical and systematic, respectively.
A search for rare lepton decays of the eta meson was performed using the WASA detector at CELSIUS. Two candidates for double Dalitz decay eta->e+e-e+e- events are reported with a background of 1.3+/-0.2 events. This allows to set an upper limit to the branching ratio of 9.7E-5 (90% CL). The branching ratio for the decay eta->e+e-gamma is determined to (7.8+/-0.5 stat+/-0.8 syst)E-3. An upper limit (90% CL) for the branching ratio for the eta->e+e- decay is 2.7E-5 and a limit for the sum of the eta->mu+mu-mu+mu- and eta->pi+pi-mu+mu- decays is 3.6E-4.
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