Fine structure of the cross sections of e+e− annihilation near the thresholds of pp¯ and nn

Abstract

The energy dependence of the cross sections of pp, nn, and meson production in e + e − annihilation in the vicinity of the pp and nn thresholds is studied. The proton-neutron mass difference and the pp Coulomb interaction are taken into account. The values of the cross sections are very sensitive to the parameters of the optical potential. It is shown that the commonly accepted factorization approach for the account of the Coulomb interaction does not work well enough in the vicinity of the threshold due to the finite size of the optical potential well. * A.I.Milstein@inp.nsk.su † S.G.Salnikov@inp.nsk.su 1 arXiv:1804.01283v1 [hep-ph]

Measurement of hadronic cross sections at CMD-3

“…4. The fitting curve, taken from the theoretical works [9] and [10], shows a good agreement with data.…”

“…The DM2 experiment observed a "sharp behavior" of the cross section of this process near nucleonantinucleon threshold, confirmed later by the BaBar. The origin of this phenomenon remains unclear, see theoretical papers [8], [9], [10]. The cross section, measured with the CMD-3, is shown in Fig.…”

Common explanation of the behavior of some e+e− annihilation processes around s=1.9 GeV

“…Here are a few examples: (i) the diffractive photoproduction of a six-pion system [14,15]; (ii) the decays B ± → ppK ± [53] andB 0 → D 0 pp [54] with a salient peak just above the pp threshold; (iii) a sudden drop near the pp threshold in the η ′ π + π − mass distribution in the J/ψ → γη ′ π + π − decay [55]; (iv) various quarkonia decays with a pp pair in the final state, thoroughly listed in Ref. [49].…”

“…The authors of Ref. [49] recently explained the results of the NN experiments [26][27][28] using nuclear, rather than particle, phenomenology. A quantitative comparison of the success of their model with ours is not possible, as they did not provide any measure of agreement with the data.…”

Experimental input from $e^+e^-$ machines to hadronic contribution to muon (g-2)

“…The e + e − → pp cross section demonstrates exponentially fast rising in about 1 MeV interval. An explanation of this behavior is suggested in [22].…”