Observation of candidate exotic mesons containing heavy quarks with Belle

Abstract

We report the observation of two resonance-like structures in the $\pi^+ \chi_{c1}$ invariant mass distribution near 4.1 GeV in exclusive $B\to K\pi^+\chi_{c1}$ decays. A detailed Dalitz-plot analysis demonstrates that these structures cannot be produced by reflections from any known and possibly unknown resonances in the $K\pi$ channel. If these two peaks are produced by resonances in the $\pi^+\chi_{c1}$ channel, their minimal quark structure would have to be a $c\bar{c}u\bar{d}$ tetraquark arrangement, similar to that proposed for the $Z^+(4430)$ structure reported by Belle last year in the $\pi^+\psi^{'}$ mass distribution produced in $B\to K\pi^+\psi^{'}$ decays. In addition, we report some new measurements on the properties of the X(3872) meson and the $1^{--}$ $Y$ states that are produced with initial state radiation. %and also other latest XYZ results. The analyses are based on a large data sample recorded at the $\Upsilon(4S)$ resonances and nearby continuum with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider.