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We report a search for $B$ decays to selected final states with the $eta_c$ meson: $B^{pm}to K^{pm}eta_cpi^+pi^-$, $B^{pm}to K^{pm}eta_comega$, $B^{pm}to K^{pm}eta_ceta$ and $B^{pm}to K^{pm}eta_cpi^0$. The analysis is based on $772times 10^6$ $Bbar{B}$ pairs collected at the $Upsilon(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. We set 90% confidence level upper limits on the branching fractions of the studied $B$ decay modes, independent of intermediate resonances, in the range $(0.6-5.3)times 10^{-4}$. We also search for molecular-state candidates in the $D^0bar{D}^{*0}-bar{D}^0D^{*0}$, $D^0bar{D}^0+bar{D}^0D^0$ and $D^{*0}bar{D}^{*0}+bar{D}^{*0}D^{*0}$ combinations, neutral partners of the $Z(3900)^{pm}$ and $Z(4020)^{pm}$, and a poorly understood state $X(3915)$ as possible intermediate states in the decay chain, and set 90% confidence level upper limits on the product of branching fractions to the mentioned intermediate states and decay branching fractions of these states in the range $(0.6-6.9)times 10^{-5}$.
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We report a search for $B^{0}$ decays into invisible final states using a data sample of $657 times 10^{6}$ $Bbar{B}$ pairs collected at the $Upsilon(4S)$ resonance with the Belle detector at the KEKB $e^{+}e^{-}$ collider. The signal is identified by fully reconstructing a hadronic decay of the accompanying $B$ meson and requiring no other particles in the event. No significant signal is observed, and we obtain an upper limit of $1.3 times 10^{-4}$ at the 90% confidence level for the branching fraction of invisible $B^{0}$ decay.
We report searches for $B^0torm{invisible}$ and $B^0torm{invisible}+gamma$ decays, where the energy of the photon is required to be larger than 0.5 GeV. These results are obtained from a $711,{rm fb}^{-1}$ data sample that contains $772 times 10^6 Bbar{B}$ pairs and was collected near the $Upsilon,(4S)$ resonance with the Belle detector at the KEKB $e^+ e^-$ collider. We observe no significant signal for either decay and set upper limits on their branching fractions at $90%$ confidence level of $mathcal{B},(B^0torm{invisible}) < 7.8times10^{-5}$ and $mathcal{B},(B^0torm{invisible}+gamma) < 1.6times10^{-5}$.
We report the result from the first search for $D^0$ decays to invisible final states. The analysis is performed on a data sample of 924 $rm{fb}^{-1}$ collected at and near the $Upsilon(4S)$ and $Upsilon(5S)$ resonances with the Belle detector at the KEKB asymmetric-energy $e^{+}e^{-}$ collider. The absolute branching fraction is determined using an inclusive $D^0$ sample, obtained by fully reconstructing the rest of the particle system including the other charmed particle. No significant signal yield is observed and an upper limit of $9.4times 10^{-5}$ is set on the branching fraction of $D^0$ to invisible final states at 90% confidence level.
A Dalitz plot analysis of $B^0 to eta_c(1S) K^+pi^-$ decays is performed using data samples of $pp$ collisions collected with the LHCb detector at centre-of-mass energies of $sqrt{s}=7,~8$ and $13$ TeV, corresponding to a total integrated luminosity of $4.7~text{fb}^{-1}$. A satisfactory description of the data is obtained when including a contribution representing an exotic $eta_c(1S) pi^-$ resonant state. The significance of this exotic resonance is more than three standard deviations, while its mass and width are $4096 pm 20~^{+18}_{-22}$ MeV and $152 pm 58~^{+60}_{-35}$ MeV, respectively. The spin-parity assignments $J^P=0^+$ and $J^{P}=1^-$ are both consistent with the data. In addition, the first measurement of the $B^0 to eta_c(1S) K^+pi^-$ branching fraction is performed and gives $displaystyle mathcal{B}(B^0 to eta_c(1S) K^+pi^-) = (5.73 pm 0.24 pm 0.13 pm 0.66) times 10^{-4}$, where the first uncertainty is statistical, the second systematic, and the third is due to limited knowledge of external branching fractions.
Using a sample of 2.59 times 10^7 psi(2S) decays collected by the CLEO--c detector, we present results of a study of chi_{c0} and chi_{c2} decays into two-meson final states. We present the worlds most precise measurements of the chi_{cJ,(J=0,2)} -> pi^+pi^-, pi^0 pi^0, K^+K^-, K^0_S K^0_S, eta eta and eta^{prime} eta^{prime} branching fractions, and a search for chi_c decays into eta eta^{prime}. These results shed light on the mechanism of charmonium decays into pseudoscalar mesons.
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