Benchmarking neutrino-nucleus quasielastic scattering model predictions against a missing energy profile obtained using a monoenergetic neutrino beam

TL;DR

This work benchmarks three exclusive shell-based NEUT models (SF, SF*, ED-RMF) against the JSNS$^2$ missing-energy measurement from monoenergetic KDAR neutrinos on carbon to probe the neutron spectral function in $^{12}$C. Focusing on CCQE at $E_ u = 235.5$ MeV, it compares SF, SF*, and ED-RMF with and without NEUT intranuclear cascade and nuclear deexcitation (NucDeEx), including a single-nucleon knockout threshold $S_n$ as a cut. The results show that SF provides the best agreement to the full measurement, while SF* and ED-RMF fail to reproduce features near the $1p_{3/2}$ peak; when the $1NKO$ threshold is imposed, all three configurations become statistically acceptable. The study highlights how final-state interactions and deexcitation shape the extracted neutron-spectral-function interpretation and identifies areas for improvement in RMF-based approaches.

Abstract

We examine three exclusive nuclear ground state shell models implemented in the NEUT neutrino event generator and benchmark them against the recent JSNS$^2$ measurement of missing energy using a monoenergetic neutrino source. The nature of the measurement allows a detailed investigation of nuclear ground-state modeling using a neutrino source, and gives access to a direct measurement of the neutron spectral function in a $^{12}$C nucleus. The NEUT intranuclear cascade and nuclear deexcitation \textsc{NucDeEx} are used to simulate inelastic final-state interactions and nuclear deexcitations respectively. We find that the spectral function (SF) models perform better than relativistic mean field models in modeling both the ground state and the tail of the missing energy distribution when the NEUT cascade and nuclear excitation channels are turned on. We also find that taking into account the missing energy threshold for single nucleon knockout interactions results in all nuclear models being accepted based on the obtained $p$-values.

Figures (8)

• Figure 1: Area-normalised missing energy distributions for the ED-RMF, SF, and SF$^{*}$$\nu_\mu$ CCQE models in NEUT version 6.0.3. The SF$^{*}$ models the ground state of $^{11}$C with a Dirac delta function at 18.72 MeV.
• Figure 2: Shape-only missing energy differential cross section for the SF, SF$^{*}$, and ED-RMF models. The figures show cases where the NEUT FSI cascade and NucDeEx deexcitation are switched off (left), the NEUT FSI cascade is on and NucDeEx deexcitation is switched off (center) and both the NEUT FSI cascade and NucDeEx deexcitation are switched on (right). The data points are taken from JSNS$^2$ measurement KDAR:Marzec:2025.
• Figure 3: $\chi^{2}_{N-1}$ value without the single nucleon knockout threshold. The figures show cases where the NEUT FSI cascade and NucDeEx deexcitation are switched off (left), the NEUT FSI cascade is on and NucDeEx deexcitation is switched off (center) and both the NEUT FSI cascade and NucDeEx deexcitation are switched on (right). Dashed lines indicate the full $\chi^{2}$ value with all bins.
• Figure 4: The same as Fig. \ref{['fig:chi2_Nminus1_wo_1NKO']} but showing only bins above the single nucleon knockout threshold.
• Figure 5: The same as Figure \ref{['fig:MissE']} but showing the ED-RMF, RPWIA, EDAI and rEDAI nuclear potentials. The data points are taken from the JSNS$^{2}$ measurement KDAR:Marzec:2025.