Formation of the χ 1 and χ 2 charmonium resonances in antiproton-proton annihilation and measurements of their masses and total widths

Abstract

In an experiment performed at the CERN-ISR the direct formation is observed of the χ 1 and χ 2 charmonium states in proton-antiproton annihiliation. A novel technique provided excellent energy resolution together with small background and reduced systematics. The following values for the masses and total widths of the states were obtained: Λ χ 1 <3 MeV (95% CL); m χ 1 = (3511.3±0.4±0.4) MeV; Λ χ 2 =(2.6 +1.4−1.0) MeV; m ξ 2 =(3556.9±0.4±0.5) MeV. First measurements of the partial widths to antiproton-proton are also reported: Λ( χ 1 → p p)=57 +13 -11±11) and Λ( χ 2 → p p)=(233 +51 -45±48) eV .