Di-electrons from η -meson Dalitz decay in proton-proton collisions

Abstract

The reaction pp → ppη → ppγe + e − is discussed within a covariant effective meson-nucleon theory. The model is adjusted to data of the subreaction pp → ppη. Our focus is on di-electrons from Dalitz decays of η mesons, η → γγ * → γe + e − , and the role of the corresponding transition form factor F ηγγ * . Numerical results are presented for the intermediate energy kinematics of HADES experiments.

η′ meson production in nucleon-nucleon collisions near the threshold

“…The invariant amplitude T is evaluated here within a phenomenological meson-nucleon theory based on effective interaction Lagrangians (see [26,27,29,32,33]) which include (i) isoscalar mesons: scalar (σ), pseudo-scalar (η), vector (ω), (ii) isovector mesons: scalar (a 0 ), pseudo-scalar (π) and vector (ρ): 8) where N and Φ denote the nucleon and meson fields, respectively, and bold face letters stand for iso-vectors. All couplings with off-mass shell particles are dressed by monopole …”

“…For such factorized Feynman diagrams one can separate, in the cross section, the dependence on the variables connected with the Dalitz decay vertex and perform the integration analytically [26,27]. Then, formally, Eq.…”

“…Hence, at s γ * close to the η pole mass the invariant mass distribution, for the specified final state with one real photon and one di-electron, is entirely governed by the η Dalitz decay. However, at larger di-electron masses, where the (virtual) η meson is highly off-mass shell, this contribution rapidly vanishes [27] and, consequently, beyond the η pole mass the distribution is governed by the η ′ Dalitz decay.…”

Ω and Η (Η') Mesons From Nn and Nd Collisions at Intermediate Energies

“…These seemingly many ingredients (coupling strengths, form factors and their cut-offs, see [8,9]) may cause the impression that the one-boson exchange approach to hadronic observables contains too many free parameters and does not have too much predictive power.…”

“…where s M is the square of the invariant mass of the produced off-mass shell meson with M = µ − iΓ tot /2 as its pole mass and total decay width Γ tot ; µ 2 f = 0, ξ = 2 in case of . For data quotation consult [8,9,18,19]. in [8,9,18,19]; the most recent results for η production in pn reactions [20] are depicted as squares (left).…”