CP violating signal at DUNE in presence of nonstandard interactions and the role of second oscillation maxima

TL;DR

This study investigates leptonic CP violation in DUNE when nonstandard neutrino interactions (NSI) are present, emphasizing the role of the second oscillation maximum. It uses a perturbative expansion of the appearance probability P_{μe} into P0+P1+P2 and analyzes how NSI, via ε with phase φ, alters ΔP_{μe}^{CP} and entangles intrinsic δ with extrinsic matter effects. Through GLoBES simulations for SI and NSI (with NO) and a dual-beam strategy (120 GeV and 8 GeV), the authors show that the second maximum provides enhanced CP sensitivity and a path to disentangle intrinsic CP violation using observables like δ(ΔP^{CP}). They find that NSI can amplify CP signals, yielding >12σ discovery potential in the NSI case with the combined beams, while still enabling intrinsic δ extraction albeit with greater complexity, particularly away from CP-conserving values. Overall, the work highlights the importance of incorporating NSI and exploiting multiple oscillation maxima to maximize DUNE’s CP violation discovery potential.

Abstract

Neutrino oscillation among the three active neutrino flavors is well established and supported by experiments at diverse length scales and energy scales. It may be noted that five of the neutrino oscillation parameters in the three-flavor paradigm, namely the three mixing angles ($θ_{12}$, $θ_{13}$, $θ_{23}$) and the two mass-squared differences ($Δm^{2}_{21}$, $Δm^{2}_{31}$) are measured to a reasonable degree of precision. The three unknowns that are expected to be deciphered in the near future are the Dirac CP phase, $δ$, the neutrino mass ordering, and the octant of $θ_{23}$. The next generation of long baseline experiments, such as the Deep Underground Neutrino Experiment (DUNE), aims to resolve these unanswered questions. In the present work, by considering DUNE as an example, we assess the ability of long baseline experiments to extricate the intrinsic contribution from observables related to CP violation in scenarios considering SI and beyond. Additionally, we analyze the role of the second oscillation maximum in addressing the above mentioned questions. By carrying out event level and statistical analyses, we assess the potential of DUNE to probe CP violation effects both within and beyond the standard paradigm.

Figures (10)

• Figure 1: The oscillogram plot of variation of CP violation paramter $\Delta P^{CP}_{\mu e}$ with different NSI parameter. The left most panel depicts the dependency of $\Delta P^{CP}_{\mu e}$ with $\varepsilon_{ee}$ and $\varepsilon_{e\mu}$, middle panel represents the variation od the CP violation with $\varepsilon_{ee}$ and $\varepsilon_{e\tau}$ and the right panel depicts the same with the variation of $\varepsilon_{e\mu}$ and $\varepsilon_{e\tau}$.
• Figure 2: $\nu_{e}$ appearance probability in vacuum (solid lines), in presence of standard matter effect (dotted lines) and with non-standard interactions (dashed lines) with $\delta = 0, \pi/2, -\pi/2$.
• Figure 4: The figure illustrates the variation of the CP violation factor $\Delta P^{CP}_{\mu e}$ as a function of $\delta$ for different oscillation scenarios: vacuum (dotted line), standard matter effects (dashed line), and the presence of NSI (solid line). The red curves correspond to the first oscillation maximum at 2.68 GeV, while the blue curves represent the second oscillation maximum at 0.86 GeV. The shaded region highlights the excess contribution to CP violation arising from matter effects and NSI, beyond the intrinsic CP violation component. The plot demonstrates the amplification of CP violation effects due to matter interactions and NSI, with a stronger influence observed at the second oscillation maximum.
• Figure 5: The same plot as Fig. \ref{['fig:3']}, now presented with the parameter $\delta\left(\Delta P^{CP}_{\mu e}\right)=\Delta P^{CP}_{\mu e}\left(\delta\right)-\Delta P^{CP}_{\mu e}\left(\delta=0\right)$. This specific parameterization is employed to analyze the contribution of fake CP violation by considering the minimal value of the intrinsic CP phase. The approach allows for a more precise assessment of the impact of matter effects and NSI on CP violation, aiding in the disentanglement of intrinsic and extrinsic contributions Majhi:2022fed.
• Figure 6: Oscillogram plot for $\delta\left(\Delta P^{CP}_{\mu e}\right)=\Delta P^{CP}_{\mu e}\left(\delta\right)-\Delta P^{CP}_{\mu e}\left(\delta=0\right)$ in E(GeV)-$\delta\left(^\circ\right)$ plane for standard matter effect (left panel) and NSI (right panel)