Observation of candidate exotic mesons containing heavy quarks with Belle

TL;DR

This paper reports the discovery of two resonance-like structures near 4.1 GeV in the $hi_{c1}$ invariant mass, suggesting possible tetraquark states, along with new measurements of other exotic mesons using Belle data.

Contribution

It provides the first observation of these structures and analyzes their nature, proposing they could be tetraquark states, and includes updated measurements of known exotic mesons.

Findings

Two resonance-like structures near 4.1 GeV in $hi_{c1}$ mass.

Structures unlikely to be reflections from known resonances.

Possible tetraquark interpretation for the new states.

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.