Damping of the continuum response from 2p-2h excitations

Abstract

The nuclear response function in the random-phase-approximation theory may be substantially altered at high excitation energy due to coupling of 1p-1h to 2p-2h or higher excitations. In the continuum region of quasi-elastic scattering, this coupling can be included by inserting into the random-phase-approximationGreen's function a complex self-energy for the p-h states, which depends only on their energy, spin (S), and isospin (X). This allows the full response to be expressed directly as an integral over the random-phase-approximation response. The self-energies, which can be determined from empirical single-particle spreading widths, are large in the spin and isospin channels, but small in the T,S =0,0 channel, giving rise to substantial damping in all channels except 0,0. We apply this method to calculate damping of the random-phase-approximation surface response, and discuss the consequences for cross sections and spin observables in quasi-elastic (p, p ) and (n, p) reactions.

Semirelativistic description of quasielastic neutrino reactions and superscaling in a continuum shell model

“…For example, it is well known from other work that final-state interactions can significantly modify the bare CSM or RPA responses, mainly through medium renormalization of the particle-hole excitations. This mechanism can be approximately taken into account by using an effective nucleon mass that produces a shift and by a folding of the bare responses, producing an asymmetric broadening which improves the agreement with the experimental data [62][63][64]. …”

Large-scale continuum random-phase approximation predictions of dipole strength for astrophysical applications

“…This empirical way of determining Γ(E) has the advantage of including, in principle, contributions from the excitation beyond 2p-2h [19]. The resulting resonance width can be compared with experimental data, such as photoabsorption cross sections.…”

“…These couplings can be taken into account in the framework of the relativistic or nonrelativistic timeblocking approximation [15][16][17]. However, such a method cannot be applied to large-scale calculations yet, essentially due to the numerical effort it represents, so that alternative phenomenological approximations need to be considered [18,19]. A similar approach is followed in the present work, as described in Sec.…”

Microscopic HFB + QRPA predictions of dipole strength for astrophysics applications

“…This empirical way of determining Γ(E) has the advantage of including, in principle, contributions from the excitation beyond 2p-2h [28]. The resulting resonance width can therefore be compared with experimental data, such as photoabsorption cross sections.…”

“…Formally, self-energy insertions on particle and hole lines spread the resonances and shift their centroids. In practice the ph QRPA strength is folded by a Lorentzian function representing the self-energy operator [13,28] f L (E ′ , E) = 1 2π…”