The 2p–2h electromagnetic response in the quasielastic peak and beyond

Abstract

The contribution to the nuclear transverse response function R T arising from two particle-two hole (2p-2h) states excited through the action of electromagnetic meson exchange currents (MEC) is computed in a fully relativistic framework. The MEC considered are those carried by the pion and by ∆ degrees of freedom, the latter being viewed as a virtual nucleonic resonance. The calculation is performed in the relativistic Fermi gas model in which Lorentz covariance can be maintained.All 2p-2h many-body diagrams containing two pionic lines that contribute to R T are taken into account and the relative impact of the various components of the MEC on R T is addressed. The non-relativistic limit of the MEC contributions is also discussed and compared with the relativistic results to explore the role played by relativity in obtaining the 2p-2h nuclear response.

Density dependence of 2p-2h meson-exchange currents

“…Two-particle two-hole (2p-2h) excitations in electroweak nuclear reactions have been extensively explored in the past [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] in electron and neutrino scattering studies. These states, where two nucleons are promoted above the Fermi level leaving two holes inside the Fermi sea, are known to give a large contribution to the inclusive (e,e ) cross section in the so-called "dip region", corresponding to excitation energies lying between the quasielastic (QE) and (1232) excitation peaks.…”

Green’s Function Monte Carlo Calculations of the Electromagnetic and Neutral-Weak Response Functions in the Quasi-Elastic Sector

“…It is worth noting that the width of the quasi-elastic peak seems to be correctly reproduced-the nonrelativistic Fermi gas fails to predict this quantity at momentum transfers q ≃ 500 MeV. Thus, even at these relatively high momentum and energy transfers, the nonrelativistic dynamical framework may be more robust than comparisons between nonrelativistic and relativistic Fermi gas models would lead one to conclude [29].…”

Nuclear effects in (anti)neutrino charge-current quasielastic scattering at MINER νA kinematics

“…On the other hand, higher-energy data from the NOMAD experiment (E ν ∼ 3 − 100 GeV) [9] are well accounted for by IA models [10]. The MINERνA experiment is situated in between these two energy regions and its interpretation can therefore provide valuable information on the longstanding problem of assessing the role of correlations and meson exchange currents (MEC) in the nuclear dynamics [11][12][13].…”