Search for the 1P1 charmonium state in pp annihilations at the CERN intersecting storage rings

Abstract This experiment has been performed at the CERN Intersecting Storage Rings to study the direct formation of charmonium states in antiproton-proton annihilations. The experimental program has partly been devoted to an inclusive scan for p p → J /ψ + X in the range 3520–3530 MeV/ c 2 . A cluster of five events has been observed in a narrow energy band, centred on the centre of gravity of the 3 P J states where the 1 P 1 is expected to be. When interpreted as a new resonace, these data yield a mass m = 3525.4±0.8 MeV/ c 2 .