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Authors
Sadaharu Uehara
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The X(3872) and Z(4430) are candidates of tetraquark state with a ccbar pair. We present results from Belle recently updated for the mass, branching fractions etc. in different production/decay processes of the X(3872). Results from a Dalitz analysis for B --> Z(4430) K --> psi pi^+- K are also presented.
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Search for exotics has increased importance since the observation of the X(3872), 13 years ago, announced by the Belle Collaboration. The observation of pentaquark states by LHCb, and the Z-charged states observed at Belle and BES III have raised even more the attention to the field. Presently several states are observed that do not fit potential models, and looking for them in different production mechanisms and search for their decay modes it is important, as well as to do precise measurement of their mass, width, lineshape. We shortly report in this note about the plan in searching for exotics at Belle II at KEK (Tsukuba, Japan), that just ended the Phase-II running period, and show the first re-discovery results using 5 pb$^{-1}$ integrated luminosity.
We report a search for $X(3872)$ and $X(3915)$ in $B^+ to chi_{c1} pi^0 K^+$ decays. We set an upper limit of $mathcal{B}(B^+ to X(3872) K^+) times mathcal{B}(X(3872) to chi_{c1} pi^0)$ $ < 8.1 times 10^{-6}$ and $mathcal{B}(B^+ to X(3915) K^+) times mathcal{B}(X(3915) to chi_{c1} pi^0)$ $ < 3.8 times 10^{-5}$ at 90% confidence level. We also measure $mathcal{B}(X(3872) to chi_{c1} pi^0)/mathcal{B}(X(3872) to J/psi pi^+ pi^-) < 0.97$ at 90% confidence level. The results reported here are obtained from $772 times 10^{6}$ $Boverline{B}$ events collected at the $Upsilon(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider.
We perform a full amplitude analysis of B0 -> psi K+ pi- decays, with psi -> mu+ mu- or e+ e-, to constrain the spin and parity of the Z(4430)-. The J^P=1+ hypothesis is favored over the 0-, 1-, 2- and 2+ hypotheses at the levels of 3.4 sigma, 3.7 sigma, 4.7 sigma and 5.1 sigma, respectively. The analysis is based on a 711 fb^-1 data sample that contains 772x10^6 B B pairs, collected at the Y(4S) resonance by the Belle detector at the asymmetric-energy e+ e- collider KEKB.
We have searched for exclusive production of exotic charmonia in the reaction $mu^+~N rightarrow mu^+ (J!/!psipi^+pi^-)pi^{pm}~N$ using COMPASS data collected with incoming muons of 160 GeV/$c$ and 200 GeV/$c$ momentum. In the $J!/!psipi^+pi^-$ mass distribution we observe a signal with a statistical significance of 4.1 $sigma$. Its mass and width are consistent with those of the $X(3872)$. The shape of the $pi^+pi^-$ mass distribution from the observed decay into $J!/!psipi^+pi^-$ shows disagreement with previous observations for $X(3872)$. The observed signal may be interpreted as a possible evidence of a new charmonium state. It could be associated with a neutral partner of $X(3872)$ with $C = -1$ predicted by a tetraquark model. The product of cross section and branching fraction of the decay of the observed state into $J!/!psipi^+pi^-$ is determined to be 71$pm$28(stat)$pm$39(syst) pb.
Monte-Carlo simulations for a resonance scan of the charmonium-like state X(3872) at Panda are performed. Final state radiation hadronic background reactions are taken into account. The signal reconstruction uses a realistic pattern recognition (track finder and track fitter) and electron/pion discrimination.
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