Short-Range Correlations and Meson-Exchage Currents in Electron and Neutrino Scattering

TL;DR

The paper addresses the excess transverse strength observed in quasielastic electron scattering beyond single-particle models. It develops a correlated framework that combines meson-exchange currents with short-range correlations by solving the Bethe-Goldstone equation for nucleon pairs using a realistic Granada NN potential, implemented in the independent pair approximation. A key finding is that high-momentum components induced by SRC enable strong interference between one-body and two-body currents, particularly through the tensor-driven $^3S_1$-$^3D_1$ coupling, producing a pronounced enhancement of the transverse response that aligns with data without additional fitting. The work also discusses extending the formalism to neutrino scattering, where similar SRC-MEC effects are expected to influence oscillation experiments, underscoring the broad relevance for nuclear response modeling.

Abstract

We investigate meson-exchange currents (MEC) in the one-particle emission transverse response of nuclear matter, incorporating short-range correlations via the Bethe-Goldstone equation with a realistic nucleon-nucleon interaction. The interference between one-body and two-body currents, strengthened by the high-momentum components of correlated pairs, produces a marked enhancement of the transverse response. We also indicate how the formalism extends to neutrino scattering, where similar effects are expected to impact oscillation experiments.

Figures (7)

• Figure 1: Example of coupled radial wave functions $u_{ll'}^{SJ}(r)$ obtained from the Bethe--Goldstone equation. The relative momentum of the pair is $p=225$ MeV/c. We see the results for several values of the total momentum $P$.
• Figure 2: Example of momentum-space correlated wave functions $|\tilde{\Phi}_{ll'}^{SJ}(p')|^{2}$ in a coupled channel. The emergence of high-momentum components reflects the action of short-range correlations.
• Figure 3: Meson exchange currents contributing to the QE response: seagull, pion-in-flight, and $\Delta$ excitation diagrams.
• Figure 4: High-momentum MEC contributions induced by SRC in the two-body current.
• Figure 5: Scaling function $f_L(\psi')$ extracted from $^{12}$C data and the SuSA fit.