Search for a three-proton resonance state in d+12C, α+12C and 12C+12C collisions at 3.37AGeV

Abstract

The new experimental results on the search and study of formation of a possible three-proton resonance state in a target fragmentation region in the total ensemble of collisions of deuterons (2H), [Formula: see text]-particles (4He), and carbon-12 nuclei with target carbon-12 nuclei at incident kinetic energy 3.37[Formula: see text]GeV per nucleon are presented. The narrow peak structure of a possible three-proton resonance state was observed with a four-sigma statistical significance in the spectrum of invariant masses of three protons in the analyzed ensemble of collisions in the collision events with four protons in the final state. The peak structure was not visible in the other channels with the number of protons equal 3, 5, and [Formula: see text]. The mass and width of this possible three-proton resonance state were estimated to be [Formula: see text][Formula: see text]MeV/[Formula: see text] and [Formula: see text][Formula: see text]MeV/[Formula: see text]. The inclusive cross-section of formation of this possible resonance state was estimated to be [Formula: see text][Formula: see text]mb. It was deduced that the three-proton resonances could possibly be formed as a result of capture by a two-proton resonance (with mass [Formula: see text][Formula: see text]MeV/[Formula: see text]) of one more proton with a close velocity. The observed three-proton as well as two-proton resonances are likely to be the hadronic molecules. Taking into account an alpha cluster structure of carbon-12 nuclei, one of the possible mechanisms of formation of three-proton resonances could be the effective fusing of pair of protons with opposite spins, from one fragmenting alpha cluster, with a proton, originating from the second fragmenting alpha cluster.