Probing light sterile neutrino signatures at reactor and Spallation Neutron Source neutrino experiments

We investigate the impact of a fourth sterile neutrino at reactor and Spallation Neutron Source neutrino detectors. Specifically, we explore the discovery potential of the TEXONO and COHERENT experiments to subleading sterile neutrino effects through the measurement of the coherent elastic neutrino-nucleus scattering event rate. Our dedicated ${\chi }^2$-sensitivity analysis employs realistic nuclear structure calculations adequate for high purity sub-keV threshold Germanium detectors.

Figure 1

(Blue labeling): The quenching factor, $\mathcal{Q}u(T_N)$ for ${}^{76}\mathrm{Ge}$ and (Red labeling): the equivalent electron energy as a function of the nuclear recoil energy, $T_N$.

Figure 2

Top panel: $\mathrm{CE}\nu \mathrm{NS}$ events within the SM as a function of the detector threshold assuming different quenching factors and a 1 kg-day ${}^{76}\mathrm{Ge}$ target. A notable agreement is verified between the results obtained for the case of constant quenching factor in the range ${\mathcal{Q}}_f=0.20–0.25$ and the empirical quenching factor of Eq. (18). Bottom panel: Sensitivity of the TEXONO experiment to the quenching factor ${\mathcal{Q}}_f$ normalized to the empirical quenching factor of Eq. (18) for various systematic errors and a background of 1 cpd (see the text).

Figure 3

Ratio $\mathcal{R}=N_{\text{sterile}}^{\text{events}}/N_{\mathrm{SM}}^{\text{events}}$ for a detector threshold $T_{\text{thres}}=100{\mathrm{eV}}_{\mathrm{ee}}$ as a function of the baseline $L$, at the TEXONO experiment. The quenching effect is considered (neglected) in the thin (thick) lines. The vertical dotted line indicates the TEXONO baseline.

Figure 4

90% C.L. sensitivity regions in the $(|U_{\alpha 4}{|}^2,\mathrm{\Delta }{m}_{41}^2)$ planes with $\alpha =e$ (red region) and $\alpha =\mu$ (blue region) assuming a light sterile neutrino in the ($3+1$) scheme, at the TEXONO and COHERENT experiments respectively (for details see the text). In the left panel systematic uncertainties and background events are neglected, while in the right panel the calculation assumes a systematic error of ${\sigma }_{\mathrm{sys}}=10\%$ for the corresponding background events in each experiment.

Figure 5

Top panel: 90% C.L. sensitivity region in the $({\sin }^{2}2{\theta }_{ee},\mathrm{\Delta }{m}_{41}^2)$ plane for a light sterile neutrino in the ($3+1$) scheme, considering the current experimental setup at the TEXONO experiment for different values of systematic error for a background level of 1 cpd (solid lines) and 10 cpd (dashed lines). Bottom panel: 90% C.L. sensitivity region for different configurations of detector mass and operation threshold with neglected background and systematic uncertainties.

Figure 6

Top panel: 90% C.L. sensitivity region in the $({\sin }^{2}2{\theta }_{\mu \mu },\mathrm{\Delta }{m}_{41}^2)$ plane assuming a light sterile neutrino in the ($3+1$) scheme at the COHERENT experiment, for various nuclear targets. Different systematic uncertainties are considered while the assumed background events are 20% of the SM events. Only the delayed ${\overline{\nu }}_{\mu }$ beam is taken into account for the “current” and “future” experimental setup. Bottom panel: Same as above, but with zero systematic error and neglected backgrounds. The calculation refers to the case of a ${}^{76}\mathrm{Ge}$ target only.

Figure 7

90% C.L sensitivity regions in the $({\sin }^{2}2{\theta }_{e\mu },\mathrm{\Delta }{m}_{41}^2)$ plane from a combined analysis of COHERENT and TEXONO in the ($3+1$) scheme. Different experimental setups for the COHERENT experiment have been considered incorporating systematic uncertainties and backgrounds. For comparison the latest allowed regions from the LSND [20, 21] and MiniBooNE [23, 24] experiments are also shown.

Figure 8

Same as Fig. 7, considering different setups for TEXONO and COHERENT and neglecting systematic uncertainties and backgrounds. For COHERENT, we are assuming ${}^{76}\mathrm{Ge}$ as target material.