The High W Challenge: Robust Neutrino Energy Estimators for LArTPCs

TL;DR

This work introduces a $W_{ m vis}^2$-based neutrino energy estimator for LArTPCs operating with broadband beams and benchmarks it against four established methods. By evaluating bias, variance, generator dependence, and sensitivity to final-state interactions and secondary variables, the study demonstrates that the $W_{ m vis}^2$ estimator offers the smallest energy-bias and strong robustness in inclusive channels, while calorimetric and other estimators retain value in different analysis regimes. The authors quantify the impact of estimator choice on oscillation parameters, showing that the $W^2$ and calorimetric methods provide strong discrimination power, with SF offering robustness at the cost of statistics. The work argues for a judicious combination of estimators to maximize precision and resilience in future LArTPC oscillation analyses, particularly for resolving $ heta_{CP}$ and the mass-splitting $ Delta m^2_{23}$.

Abstract

Accurate determination of the neutrino energy is central to precision oscillation measurements. In this work, we introduce the W$^2$-based estimator, a new neutrino energy estimator based on the measurement of the final-state hadronic invatiant mass. This estimator is particularly designed to be employed in liquid-argon time-projection chambers exposed to broadband beams that span the challenging transition region between shallow inelastic scattering and deep inelastic scattering. The performance of the W$^2$-based estimator is compared against four other commonly used estimators. The impact of the estimator choice is evaluated by performing measurements of $δ_{CP}$ and $Δm^2_{23}$ in a toy long-baseline oscillation analysis. We find that the W$^2$-based estimator shows the smallest bias as a funciton of true neutrino energy and it is particularly stable against the mismodelling of lepton scattering angle, missing energy, hadronic invariant mass and final state interactions. Such an inclusive channel complements well the strength of more exclusive methods that optimizes the energy resolution. By providing a detailed analysis of strengths, weaknesses and domain of applicability of each estimator, this work informs the combined used of energy estimators in any future LArTPC-based oscillation analysis.

Figures (18)

• Figure 1: Fractions of $\nu_{\mu}$ interactions on argon that produce final states with at least one proton (Np), at least one proton and no pions (Np0$\pi$), and exactly one proton and no pions (1p0$\pi$). The latter two categories reflect the subsets of events the proton based and SF methods target.
• Figure 2: Confusion matrices describing the smearing from true neutrino energy to estimated neutrino energy using each energy estimation.
• Figure 3: The distribution of fractional error in neutrino energy using the different estimation methods, calculated using events simulated with the GENIE neutrino event generator. All distributions are normalized to 1. The pink dashed line is the calculation assuming overall 20% smearing on the energy calculated with the calorimetric method.
• Figure 4: Fractional bias and variance as a function of true neutrino energy. The dashed lines in panels (b) and (c) indicate the performance of the calorimetric method when applying the full 20% smearing to the energy estimation.
• Figure 5: Comparison of the biases in neutrino energy when calculated using different event generators, for each method of neutrino energy estimation.