New Heavy Exotic Hadrons

Abstract

We review recent studies on exotic states at the Belle experiment. The results include: (1) The measurement of the cross sections of $\gamma \gamma \to \omega \phi$, $\phi\phi$, and $\omega \omega$ for masses that range from threshold to 4.0 GeV. In addition to signals from well established spin-zero and spin-two charmonium states, there are clear resonant structures below charmonium threshold, which have not been previously observed. We report a spin-parity analysis for the new structures; (2) No X(3872) signal is observed in $\eta J/\psi$ or $\gamma \chi_{c1}$ mode in B decays. A narrow peak at 3823.5 MeV/$c^2$ (named as $\psi_2$) to $\gamma \chi_{c1}$ with a significance of 4.2 standard deviations including systematic uncertainty is observed in $B^{\pm} \to K^{\pm} \gamma \chi_{c1}$; (3) The bottomonium states $h_b(1P)$, $h_b(2P)$ and $\Upsilon(1D)$ are observed in the reaction $e^+e^- \to \pi^+ \pi^- + X$; (4) The observation of two narrow charged structures (named as $Z_b(10610)$ and $Z_b(10650)$) in the mass spectra of the $\pi^{\pm}\Upsilon(nS) (n=1,2,3)$ and $\pi^{\pm} h_b(mP)$ $(m=1,2)$ pairs that are produced in association with a single charged pion in Y(5S) decays.