New Heavy Exotic Hadrons

TL;DR

This paper reviews recent experimental discoveries of exotic hadronic states, including new resonances, bottomonium states, and charged structures, highlighting advances in understanding heavy exotic hadrons at the Belle experiment.

Contribution

It provides new measurements of cross sections, observations of previously unseen resonant structures, and identification of novel heavy exotic states, expanding knowledge of heavy hadron spectroscopy.

Findings

Observation of resonant structures below charmonium threshold

Detection of a new narrow peak at 3823.5 MeV/c^2 (ψ_2)

Discovery of charged Z_b(10610) and Z_b(10650) states

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.