Observation of the chi_c2(2P) meson in the reaction gamma gamma -> D Dbar at BABAR

TL;DR

This paper reports the observation of the chi_c2(2P) meson in gamma gamma collisions producing D Dbar pairs, confirming its quantum numbers and measuring its mass, width, and two-photon partial width with high significance.

Contribution

First observation of the chi_c2(2P) meson in gamma gamma to D Dbar production, with detailed measurements of its properties and quantum numbers.

Findings

Z(3930) observed with 5.8 sigma significance

Mass and width measured as 3926.7 MeV/c^2 and 21.3 MeV

Identified as tensor state with J^PC = 2^++

Abstract

A search for the Z(3930) resonance in gamma gamma production of the DDbar system has been performed using a data sample corresponding to an integrated luminosity of 384 fb^-1 recorded by the BABAR experiment at the PEP-II asymmetric-energy electron-positron collider. The DDbar invariant mass distribution shows clear evidence of the Z(3930) state with a significance of 5.8 sigma. We determine mass and width values of (3926.7 +- 2.7 +- 1.1) MeV/c^2 and (21.3 +- 6.8 +- 3.6) MeV, respectively. A decay angular analysis provides evidence that the Z(3930) is a tensor state with positive parity and C-parity (J^PC = 2^++); therefore we identify the Z(3930) state as the chi_c2(2P) meson. The value of the partial width Gamma_(gamma gamma)xB(Z(3930)-> DDbar) is found to be (0.24 +- 0.05 +- 0.04) keV.