Observation of the χc2(2P) meson in the reaction γγ→D¯¯¯D at BABAR

Abstract

A search for the Z ( 3930 ) resonance in γ γ production of the D ¯¯¯ D 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 D ¯¯¯ D invariant mass distribution shows clear evidence of the Z ( 3930 ) state with a significance of 5.8 σ . 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 P C = 2 ++ ); therefore we identify the Z ( 3930 ) state as the χ c 2 ( 2 P ) meson. The value of the partial width Γ γ γ × B ( Z ( 3930 ) → D ¯¯¯ D ) is found to be ( 0.24 ± 0.05 ± 0.04 ) keV .