Impact of CP violation searches at MOMENT experiment with sterile neutrinos

TL;DR

This work evaluates the MOMENT experiment's capability to probe CP violation in the presence of a eV-scale sterile neutrino within a 3+1 framework. It derives the 4-flavor transition probabilities, develops bi-probability representations, and analyzes CP phases $δ_{13}$ (standard) and $δ_{14}$ (sterile) under effectively vacuum-like conditions at MOMENT's first oscillation maximum. Using GLoBES simulations with a 500 kton detector and a 150 km baseline, it finds that sterile mixing degrades the CP sensitivity to $δ_{13}$ due to degeneracies with $δ_{14}$, but MOMENT still retains substantial ability to measure $δ_{13}$ and to reconstruct $δ_{14}$. The study also provides δ_{13}-δ_{14} contour-based reconstruction ranges, demonstrating that MOMENT can contribute meaningful constraints to global CP-violation and sterile-neutrino investigations in the near future.

Abstract

We examine the scope of the MOMENT experiment in the context of CP violation searches with the presence of extra eV scale sterile neutrino. MOMENT is a proposed medium baseline neutrino oscillation experiment using muon beams for neutrinos production, making it advantageous over $π_0$ background and other technical difficulties. We work over the first oscillation maxima which matches the peak value of flux with a run time of 5 years for both neutrino and anti-neutrino modes. We perform the bi-probability studies for both 3 and 3+1 flavor mixing schemes. The CP violation sensitivities arising from the fundamental CP phase $δ_{13}$ and unknown CP phase $δ_{14}$ are explored at the firm footing. Slight deteriorations are observed in CP violations induced by $δ_{13}$ as the presence of sterile neutrino is considered. We also look at the reconstruction of CP violations phases $δ_{13}$ and $δ_{14}$ and the MOMENT experiment shows significant capabilities in the precise measurement of $δ_{13}$ phase.

Figures (6)

• Figure 1: Electron appearance probabilities for neutrinos and anti-neutrinos after averaging over the fast oscillations are plotted against energy(varying from 0.1 to 0.8 GeV) with matter density kept fixed at 2.7 g/cc. The oscillation probability for 3 flavor is shown by black curve while the colored curve represents the oscillation probability in 3+1 mixing scenario for four different values of $\delta_{14}$ i.e. $-90^\circ$,$0^\circ$,$90^\circ$, and $180^\circ$. The left column corresponds to the neutrino transition probabilities for two different values of $\delta_{13}$ whereas the right one is for anti-neutrino transition probabilities.
• Figure 2: Muon appearance probabilities for neutrinos and anti-neutrinos after averaging over the fast oscillations are plotted against energy(varying from 0.1 to 0.8 GeV) with matter density kept fixed at 2.7 g/cc. The oscillation probability for 3 flavor is shown by black curve while the colored curve represents the oscillation probability in 3+1 mixing scenario for four different values of $\delta_{14}$ i.e. $-90^\circ$,$0^\circ$,$90^\circ$, and $180^\circ$. The left column corresponds to the neutrino transition probabilities for two different values of $\delta_{13}$ whereas the right one is for anti-neutrino transition probabilities.
• Figure 3: Bi-probability plots under the normal hierarchy are shown for both 3 flavor and 3+1 flavor mixing scheme. The CP trajectory diagram for the 3-flavor is drawn by black color while the orange, magenta, blue and green closed curves corresponds to the fixed values of $\delta_{14}$ phase as mentioned in each legend. The neutrino energy is kept fixed at its first oscillation peak value of 0.3 GeV. The CP-phase $\delta_{13}$ is varied in the range $[-\pi,\pi]$. Four different values of $\delta_{13}$ phase (i.e. $0^\circ$, $180^\circ$, $-90^\circ$, and $90^\circ$) are marked by different symbols for comparing the orientation of ellipses.
• Figure 4: The expected number of signal events are plotted against the reconstructed neutrino energy. The black curve refers to 3 flavor case while the colored histograms are for (3+1) scheme with different values of $\delta_{14}$ as mentioned in the legend. The left panel corresponds to $\nu_e$ appearance events while the right one is for $\overline{\nu}_e$ appearance events.
• Figure 5: The figure indicated the potential of MOMENT experiment for the discovery of CP violation induced by the fundamental phase $\delta_{13}$. The black curve shows the behavior under 3 flavor scheme while the colored curves in each panel are of different values of $\delta_{14}$. The left figure $\Delta m^2_{31}$ is kept fixed for both 3 and 3+1 flavor mixing while we marginalize over $\theta_{23}$ value whereas in the right figure, we marginalised over both hierarchy $\Delta m^2_{31}$ and $\theta_{23}$.