Shape of proton and the pion cloud

• Published in: The European physical journal. A, Hadrons and nuclei Hadrons and nuclei, 2018-07, Vol.54 (7), p.1-8, Article 116
• Main Authors: Jenkovszky, László, Szanyi, István, Tan, Chung-I
• Format: Article
• Language: English
• Subjects: Coupling; Dependence; Hadrons; Heavy Ions; Nuclear Fusion; Nuclear Physics; Particle and Nuclear Physics; Physics; Physics and Astronomy; Protons; Regge poles; Regular Article - Theoretical Physics
• ISSN: 1434-6001; 1434-601X
• DOI: 10.1140/epja/i2018-12567-5

. Proton-proton differential and total cross sections provide information on the energy dependence of proton shape and size. We show that the deviation from exponential behavior of the diffraction cone observed near t = -0.1 GeV 2 the so-called break) both at the ISR and the LHC follows from the t -channel two-pion loop contributions, imposed by unitarity. By using a simple Regge pole model, we extrapolate the “break” from the ISR energy region to that of the LHC. This allows us to answer two important questions: 1) To what extent is the “break” observed recently at the LHC a “recurrence” of that seen at the ISR (universality)? 2) What is the relative weight of two-pion effect to the vertex coupling (Regge residue) compared to expanding size (pomeron propagator) in producing the “break”? We find that the effect comes both from the Regge residue (proton-pomeron coupling) and from the Regge propagator. A detailed analysis of their balance, including the correlation between the relevant parameters is presented.