The role of meson retardation in deuteron photodisintegration above pion threshold

Abstract

Photodisintegration of the deuteron above π threshold is studied in a coupled channel approach including N ∆ and πd channels with consideration of pion retardation in potentials and exchange currents. A much improved description of total and differential cross sections in the energy region between π threshold and 400-450 MeV is achieved. With respect to polarization observables, the description of the linear photon asymmetry and the proton polarization remains problematic.

Meson retardation in deuteron electro-disintegration

“…As has been outlined in detail in [3], the e.m. coupling constant G ∆N M1 has been fixed for real photons by a fit of the M (3/2) 1+ -multipole of pion photoproduction on the nucleon. Due to nonresonant rescattering mechanisms, it becomes complex and dependent on the invariant mass W sub of the πN -subsystem for which we adopt the spectator-on-shell approach [3].…”

“…Due to nonresonant rescattering mechanisms, it becomes complex and dependent on the invariant mass W sub of the πN -subsystem for which we adopt the spectator-on-shell approach [3]. Moreover, when embedded into a nuclear medium, G ∆N M1 depends also on the photon momentum q and the photon energy ω.…”

“…The parameters in (6) have been fitted to the resulting coupling constant " G ∆N M1 (eff1)" discussed in [3] and are listed in Table I. In addition a contribution from the γN ∆-transtion charge density is included.…”

“…However, we restrict ourselves here to kinematics with Q 2 ≤ 4 fm −2 where the difference does not matter. With respect to the two-body currents, we consider, as in [3], meson retardation in the pure pion exchange contributions whereas retardation in γπρ/ω-MEC turned out to be unimportant in photodisintegration [12], but very CPU-time consuming. Therefore, in order to facilitate our numerical evaluation, we have neglected retardation in the latter contribution.…”

Few-nucleon systems (theory)

“…In order to keep the discussion as transparent as possible, technical aspects are mostly avoided. The interested reader is referred to [7,8,9,10] concerning further details. In order to treat a meson X as a dynamic degree of freedom, one has to work within a Hilbert space H where X is treated explicitly.…”