Fine-tuning final state interactions model in NuWro Monte Carlo event generator

TL;DR

The paper tackles uncertainties in neutrino–nucleus cross sections by refining NuWro's nucleon-FSI modeling through an exact FSI reweighting framework. It leverages MINER${\nu}$A CC1$p$0$\pi$ data across four targets and tunes the cascade strength via a scale parameter $s$ that adjusts the nucleon mean free path, yielding a best-fit $s_0=0.76$ (with $1\sigma$ interval $[0.72,0.82]$). This corresponds to roughly a $24\%$ stronger FSI effect than previously assumed, consistently improving agreement across multiple observables while remaining within prior uncertainty. The results, validated against both LFG and SF initial-state models, provide a more realistic uncertainty band for NuWro predictions and will be incorporated into the next NuWro release, benefiting current and future oscillation analyses.

Abstract

Recent experimental data from MINERvA on transverse kinematics observables across four different nuclear targets - carbon, oxygen, iron, and lead - have been utilized to refine the modeling of final state interaction effects in the NuWro Monte Carlo neutrino event generator. For this purpose, we have developed an event reweighting tool for future applications to adjust the strength of final-state interactions. This study highlights the requirement for stronger nucleon reinteractions than previously assumed, but it still falls within the uncertainty range observed in a study comparing proton transparency measurements. This conclusion has significant implications for both experimental and theoretical work involving NuWro.

Figures (14)

• Figure 1: (Color online) Preservation of the overall normalization, as defined in Eq. (\ref{['eqn:scheme-performance']}), for the method summarized in Algorithm \ref{['alg:exact_reweighting_scheme']}. (Top) For different targets with $10^5$ events. (Bottom) For the lead target but with different statistics.
• Figure 2: (Top) Likelihood $\hat{L}(s)$ inferred using $\chi^2(s)$ for each observable. (Bottom) Overall likelihood $L_{T}(s)$ by summing over all observables. The red dashed line represents the peak. The red band represents the minimum length for which the enclosed area is $68.27\%$.
• Figure 3: (Color Online) Comparison of $|\mathbf{p}_{n}|$ with the MINER$\nu$A CC1$p$0$\pi$ data..
• Figure 4: (Color Online) Same as Fig. \ref{['fig:reconstructedNeutron_all_targets_cascde']} but for $|\mathbf{p}_{p_{T}}|$
• Figure 5: (Color Online) Same as Fig. \ref{['fig:reconstructedNeutron_all_targets_cascde']} but for the iron target, comparing LFG and SF models for the initial nucleon state using $s = s_{0}$.