Probing new physics scenarios using high energy events at NOvA far detector

TL;DR

The paper investigates how sub-leading new physics—non-standard interactions and environmental decoherence—affect neutrino propagation in NOvA, with a focus on high-energy $4<E_ u<20$ GeV events. Using GLoBES-based simulations of NOvA data, it derives NSI-modified oscillation probabilities and analyzes their impact on $\nu_e$ appearance and related event rates, demonstrating that including high-energy tail data can remove degeneracies in $|\epsilon_{e\tau}|$ across $\delta_{CP}$ and $\delta_{e\tau}$. It separately analyzes $\epsilon_{e\mu}$ and shows that high-energy data tighten constraints on this NSI parameter as well. For decoherence, the study applies a Lindblad open-quantum-system framework with $\Gamma(E) = \Gamma_0 (E/E_0)^n$ and finds that HE data yield stronger upper bounds on $\Gamma_0$, particularly for $n=1,2$, and that decoherence can influence the preferred $\theta_{23}$ octant and $\delta_{CP}$ region, potentially alleviating some NOvA–T2K tensions. Overall, the work highlights the value of high-energy NOvA events for probing BSM neutrino physics with quantified degeneracy lifting and parameter constraints.

Abstract

NuMI Off-axis $ν_e$ Appearance (NOvA) experiment is an ongoing long baseline neutrino oscillation experiment. The primary channels of interest are the $ν_e$, $\barν_e$ appearance, $ν_μ$, $\barν_μ$ disappearance channels analyzed in the energy window $1< E_ν< 4$ GeV. However, NOvA far detector sees non-trivial high energy $ν_e$, $\barν_e$ events in the energy range $4 < E_ν< 20$ GeV. These high energy events provide us with an opportunity to investigate the subleading new physics scenarios. In this context, we study the sensitivity of the NOvA experiment to constrain the non-standard interaction (NSI) parameters and environmental decoherence. We observe that by including high energy events (signal + background) the degeneracy around $ε_{eτ} \sim 1.6$ can be removed throughout the $δ_{CP}$ and $δ_{eτ}$ range. Further, we examine the role of signal versus beam background events in removing this degeneracy. In addition, we constrain the decoherence parameter $Γ$ considering events from $1<E_ν<20$ GeV. Later, assuming the presence of decoherence in nature we obtain the allowed regions in $θ_{23}$ and $δ_{CP}$ plane.

Figures (10)

• Figure 1: Appearance probability versus neutrino energy and event rates versus reconstructed energy for $\nu_e$ ($\bar{\nu}_e$) in the upper (lower) row. We consider $|\epsilon_{e\tau}| = 0.4$ and corresponding phases to show modified probability and event rates in the presence of non-standard interaction.
• Figure 2: $\epsilon_{e\tau}$ (test) vs $\delta_{CP}$ (test) in the upper row and $\epsilon_{e\tau}$ (test) vs $\delta_{e\tau}$ (test) in the lower row. In the left panel 1 - 4 GeV and in the right panel 1 - 20 GeV. Marginalized over $\theta_{13}$, $\theta_{23}$, $\Delta m^2_{31}$, $\delta_{e\tau}$ ($\delta_{CP}$) in upper row (lower row).
• Figure 3: $\epsilon_{e \tau}$ vs $\delta_{CP}$ for fixed $\delta_{e\tau} = 0$ in left and $\delta_{e\tau} = 45\degree$ in right.
• Figure 4: $P_{ee}$ vs energy (left) and beam background events per bin with reconstructed energy (middle and right). In the middle $|\epsilon_{e\tau}| = 0.4$ and in the right $|\epsilon_{e\tau}| = 1.6$. We show the plots for different $\delta_{e\tau} = 0, 90\degree, 270\degree$ in both the figures.
• Figure 5: Appearance probability versus neutrino energy and event rates versus reconstructed energy for $\nu_e$ ($\bar{\nu}_e$) in the upper (lower) row. We consider $|\epsilon_{e\mu}| = 0.3$ and corresponding phases to show modified probability and event rates in the presence of non-standard interaction.