Study of Charmonium(-like) States via ISR at Belle

TL;DR

This study measures cross sections of various charmonium-related processes at Belle, revealing multiple resonant structures near 4.05 and 4.25 GeV/c^2, indicating complex dynamics of vector charmonium states above open charm threshold.

Contribution

First detailed measurement of cross sections and resonant structures in multiple final states related to charmonium(-like) states at Belle.

Findings

Observation of Y(4260) near 4.25 GeV/c^2

Discovery of two resonant structures at 4361 and 4664 MeV/c^2

Indication of complex dynamics in vector charmonium states

Abstract

The cross sections for e+e- to pi+pi-J/psi, pi+pi-psi(2S), K+K-J/psi, DDbar, DDbar pi, D*Dbar, and D*D*bar are measured using data sample collected on or near the Upsilon(4S) resonance with the Belle detector at KEKB. A peak near 4.25 GeV/c^2, corresponding to the so called Y(4260), is observed in pi+pi-J/psi final state. In addition, there is another cluster of events at around 4.05 GeV/c^2. Two resonant structures are observed in the pi+pi-psi(2S) invariant mass distribution, one at 4361+-9+-9 MeV/c^2 with a width of 74+-15+-10 MeV/c^2, and another at 4664+-11+-5 MeV/c^2 with a width of 48+-15+-3 MeV/c^2. The rich structures observed in all these final states indicate that our understanding of the vector charmonium states above the open charm threshold is still poor, let alone the other possible dynamics such as charmonium hybrids or final state re-scattering and so on.