Implementation of the Martini-Ericson-Chanfray-Marteau RPA-based neutrino and antineutrino cross-section model in the GENIE neutrino event generator

TL;DR

This work delivers the first GENIE implementation of the Martini-Ericson-Chanfray-Marteau RPA-based cross-section model for CC neutrino interactions, focusing on $1p1h$ and multinucleon $(2p2h,3p3h)$ excitations. It uses a Local Fermi Gas framework with separate NN, $ extDelta$-MEC, and $N extDelta$ interference contributions, and provides hadron-tensor lookup tables to enable direct comparison with the original calculations and with experimental data. Validation against $^{12}$C, $^{16}$O, and $^{40}$Ca shows overall reasonable agreement with T2K and MicroBooNE measurements, supporting the model as a viable component for reducing cross-section systematics in precision neutrino experiments. The study also details current limitations (tensor range, 3p3h treatment, removal-energy effects) and outlines clear avenues for future extensions to broaden applicability and accuracy.

Abstract

We discuss the first implementation of the Martini-Ericson-Chanfray-Marteau random phase approximation-based (anti)neutrino cross-section model for quasielastic (1p1h) and multinucleon (2p2h and 3p3h) excitations in the widely used GENIE neutrino event generator. Validation steps are presented, in particular, through direct comparisons of GENIE cross-section output with original calculations performed by the authors of the model. Predictions for $^{12}$C, $^{16}$O, and $^{40}$Ar are compared with some available T2K and MicroBooNE experimental measurements showing a reasonable agreement.

Figures (8)

• Figure 1: The total $\nu_\mu$ charged-current cross section on $^{12}$C as a function of neutrino energy predicted by the model of Martini et al. implemented in GENIE (red). For validation purposes, the results of calculations performed by the authors in Refs. Martini:2009ujMartini:2011wp are also shown (shaded band). The different contributions to the total cross section are highlighted: 1p1h (dashed), npnh (dotted) and their sum (solid). The predictions of other models available in GENIE [Nieves et al. (blue) and SuSAv2 (green)] are also shown for comparison.
• Figure 3: The T2K flux-integrated $\nu_\mu$ double differential cross section as a function of $q$ and $\omega$ for the 1p1h excitation channel, obtained from the GENIE implementation of the calculations in Ref. Martini:2011wp.
• Figure 5: Double differential cross sections $\frac{d^2\sigma}{d\omega\, d\Omega}$ for 1p1h (black) and npnh (blue) processes in muon neutrino (left) and muon antineutrino (right) interactions with oxygen, at a scattering angle of $60^\circ$ and incident (anti)neutrino energy of 0.75GeV. The cross section is plotted as a function of the energy transfer $\omega$ to the nucleus. Continuous lines: theoretical calculations of Refs. Martini:2009ujMartini:2011wpMartini:2013sha; histograms: the corresponding GENIE implementation.
• Figure 6: Double differential cross sections $\frac{d^2 \sigma}{dp_\mu \; d\!\cos\!\theta_\mu}$ per nucleon, as a function of outgoing muon momentum, for 1p1h and npnh processes in muon neutrino interactions with carbon, at an incident neutrino energy of 0.575GeV and for different scattering angle regions. The shaded bands correspond to theoretical calculations of Refs. Martini:2009ujMartini:2011wp; black continuous (1p1h) and blue dash-dotted (npnh) lines show the corresponding GENIE implementation.
• Figure 7: T2K flux-integrated $\nu_\mu$ charged-current double differential cross sections $\frac{d^2 \sigma}{d p_\mu \; d\!\cos \!\theta_\mu}$ without pions in the final state, measured per nucleon on (a) carbon and (b) oxygen targets T2K:2020jav. The measurements (points with error bars) are compared with the GENIE implementation of the Martini et al. model. The contributions shown are: 1p1h (thin solid black), npnh (dash-dotted), the pion absorption "$\pi$ abs" (dotted gray), and the total CC0$\pi$ (thick solid red), which is the sum of the previous ones. For all histograms, the last data point (which covers the energy range up to 30 GeV) is shifted to the middle of the presented energy bin. The total $\chi^2$ for the joint carbon and oxygen measurement is $\chi^2 = 76.6$ with 58 degrees of freedom.