Observation of a narrow charmonium-like state in exclusive B+ -> K+ pi+pi- J/psi decays

TL;DR

This paper reports the discovery of a narrow charmonium-like state near the D D* threshold in B+ decays, with high statistical significance, providing evidence for exotic quarkonium states.

Contribution

First observation of a narrow charmonium-like state in B+ decays with precise mass measurement near the D D* threshold.

Findings

Mass of the state is 3872.0 MeV with small uncertainties.

Statistical significance exceeds 10 sigma.

Produced in B+ -> K+ pi+pi- J/psi decays.

Abstract

We report the observation of a narrow charmonium-like state produced in the exclusive decay process B+ -> K+ pi+pi- J/psi. This state, which decays into pi+pi- J/psi, has a mass of 3872.0+-0.6(stat)+-0.5(syst) MeV, a value that is very near the M_D + M_D* mass threshold. The results are based on an analysis of 152M B-Bbar events collected at the Upsilon(4S) resonance in the Belle detector at the KEKB collider. The statistical significance of the signal is in excess of 10 sigma.