Study of the χ1 and χ2 charmonium states formed in p annihilations

Abstract We report on a study of the χ 1 ( 3 P 1 ) and χ 2 ( 3 P 2 ) states of charmonium formed in antiproton-proton annihilations. An energy scan through the resonances, performed with a very narrow momentum-band beam of antiprotons intersecting a hydrogen jet target, enables us to perform very precise measurements of the mass and the total width of the two resonances. From a sample of 513 χ 1 and 585 χ 2 events we find M χ 1 = (3510.53±0.13) MeV/ c 2 , M χ 2 = (3556.15±0.14) MeV/ c 2 , Γ χ 1 = (0.88±0.14) MeV and Γ χ 2 = (1.98±0.18) MeV. From our measurement of the quantity Γ( R → p p ) × BR(R → J ψ → e + e − ) , using known branching ratios, we obtain Λ(χ 1 → p p) = (69±13) eV and Λ(χ 2 → p p) = (180±31) eV .