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Updated: Jun 22, 2026

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Published on: July 19, 2019
Observation of an "ABC" Effect in proton-proton collisions
S Dymov1, M Hartmann, A Kacharava
1Laboratory of Nuclear Problems, Joint Institute for Nuclear Research, RU-141980 Dubna, Russia. s.dymov@fz-juelich.de
Proton-proton collisions were studied at COSY-ANKE, revealing a diproton enhancement consistent with two-pion production via Delta(1232) isobars. This finding offers insights into multipion production mechanisms in nuclear physics.
Area of Science:
- Nuclear Physics
- Particle Physics
Background:
- The study investigates multipion production in proton-proton (pp) collisions.
- Focuses on low excitation energy in the final pp system, specifically the diproton quasiparticle in the 1S0 state.
Purpose of the Study:
- To measure the cross section for inclusive multipion production in the pp-->ppX reaction.
- To analyze the missing-mass spectra and their dependence on beam energy.
- To investigate the role of Delta(1232) isobars in two-pion production.
Main Methods:
- Measurements were conducted at COSY-ANKE using four beam energies: 0.8, 1.1, 1.4, and 2.0 GeV.
- Analysis focused on the missing-mass (MX) spectra of the pp-->ppX reaction.
- The diproton quasiparticle was constrained to the 1S0 state.
Main Results:
- A strong enhancement at low missing mass (MX) was observed at higher energies, attributed to the Abashian-Booth-Crowe effect.
- This enhancement shifted to higher MX values with increasing beam energy.
- The observed energy and MX variations align with two-pion production mediated by two Delta(1232) isobars, coupled to S and D states of the initial pp system.
- No resonance-like structure was found, unlike in related pn reactions.
Conclusions:
- The results support a model of two-pion production involving Delta(1232) isobars in pp collisions.
- The Abashian-Booth-Crowe effect's energy dependence was characterized.
- The findings differentiate from resonance structures observed in other related reactions.
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