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We report on the light sterile neutrino search from the first four-week science run of the KATRIN experiment in~2019. Beta-decay electrons from a high-purity gaseous molecular tritium source are analyzed by a high-resolution MAC-E filter down to 40 eV below the endpoint at 18.57 keV. We consider the framework with three active neutrinos and one sterile neutrino of mass $m_{4}$. The analysis is sensitive to a fourth mass state $m^2_{4} lesssim$ 1000 eV$^2$ and to active-to-sterile neutrino mixing down to $|U_{e4}|^2 gtrsim 2cdot10^{-2}$. No significant spectral distortion is observed and exclusion bounds on the sterile mass and mixing are reported. These new limits supersede the Mainz results and improve the Troitsk bound for $m^2_{4} <$ 30 eV$^2$. The reactor and gallium anomalies are constrained for $ 100 < Delta{m}^2_{41} < 1000$ eV$^2$.
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The recent analysis of the normalization of reactor antineutrino data, the calibration data of solar neutrino experiments using gallium targets, and the results from the neutrino oscillation experiment MiniBooNE suggest the existence of a fourth light neutrino mass state with a mass of O(eV), which contributes to the electron neutrino with a sizable mixing angle. Since we know from measurements of the width of the Z0 resonance that there are only three active neutrinos, a fourth neutrino should be sterile (i.e., interact only via gravity). The corresponding fourth neutrino mass state should be visible as an additional kink in beta-decay spectra. In this work the phase II data of the Mainz Neutrino Mass Experiment have been analyzed searching for a possible contribution of a fourth light neutrino mass state. No signature of such a fourth mass state has been found and limits on the mass and the mixing of this fourth mass states are derived.
In this work, we present an analysis of the sensitivity to the active-sterile neutrino mixing with the Indian Scintillator Matrix for Reactor Anti-Neutrino (ISMRAN) experimental set-up at very short baseline. In this article, we have considered the measurement of electron antineutrino induced events employing a single detector which can be placed either at a single position or moved between near and far positions from the given reactor core. Results extracted in the later case are independent of the theoretical prediction of the reactor anti-neutrino spectrum and detector related systematic uncertainties. Our analysis shows that the results obtained from the measurement carried out at a combination of the near and far detector positions are improved significantly at higher $Delta m^{2}_{41}$ compared to the ones obtained with the measurement at a single detector position only. It is found that the best possible combination of near and far detector positions from a 100 MW$_{th}$ power DHRUVA research reactor core are 7 m and 9 m, respectively, for which ISMRAN set-up can exclude in the range 1.4 $eV^{2} leq Delta m^{2}_{41} leq$ 4.0 $eV^{2}$ of reactor antineutrino anomaly region along with the present best-fit point of active-sterile neutrino oscillation parameters. At those combinations of detector positions, the ISMRAN set-up can observe the active sterile neutrino oscillation with a 95$%$ confidence level provided that $sin^{2}2theta_{14}geq 0.09$ at $Delta m^{2}_{41}$ = 1 eV$^{2}$ for an exposure of 1 ton-yr. The active-sterile neutrino mixing sensitivity can be improved by about 22% at the same exposure by placing the detector at near and far distances of 15 m and 17 m, respectively, from the compact proto-type fast breeder reactor (PFBR) facility which has a higher thermal power of 1250 MW$_{th}$.
Results are reported from a search for active to sterile neutrino oscillations in the MINOS long-baseline experiment, based on the observation of neutral-current neutrino interactions, from an exposure to the NuMI neutrino beam of $7.07times10^{20}$ protons on target. A total of 802 neutral-current event candidates is observed in the Far Detector, compared to an expected number of $754pm28rm{(stat.)}pm{37}rm{(syst.)}$ for oscillations among three active flavors. The fraction $f_s$ of disappearing umu that may transition to $ u_s$ is found to be less than 22% at the 90% C.L.
We construct a multiscalar and nonrenormalizable $B-L$ model with $A_4times Z_3times Z_4$ flavor symmetry which successfully explains the recent $3+1$ active-sterile neutrino data. The tiny neutrino mass the mass hierarchy are obtained by the type-I seesaw mechanism. The hierarchy of the lepton masses is satisfied by a factor of $v_H left(frac{v_l}{Lambda}right)^2 sim 10^{-4}, mathrm{GeV}$ of the electron mass compared to the muon and tau masses of the order of $frac{v_H v_l}{Lambda} sim 10^{-1}, mathrm{GeV}$. The recent $3+1$ active-sterile neutrino mixings are predicted to be $0.015 leq|U_{e 4}|^2leq 0.045$, $0.004 leq|U_{mu 4}|^2leq 0.012$, $0.004 leq|U_{tau 4}|^2leq 0.014$ for normal hierarchy and $0.020leq|U_{e 4}|^2leq 0.045$, $0.008 leq|U_{mu 4}|^2leq 0.018$, $0.008leq|U_{tau 4}|^2leq 0.022$ for inverted hierarchy. Sterile neutrino masses are predicted to be $0.7 lesssim m_s , (mathrm{eV}) lesssim 3.16$ for normal hierarchy and $2.6 lesssim m_s , (mathrm{eV}) lesssim 7.1$ for inverted hierarchy. For three neutrino scheme the model predicts $0.3401 leq sin^2theta_{12}leq 0.3415, , 0.460 leq sin^2theta_{23}leq 0.540,, -0.60 leq sindelta_{CP}leq -0.20$ for normal hierarchy and $0.3402 leq sin^2theta_{12}leq 0.3416,, 0.434leqsin^2theta_{23}leq 0.610,, -0.95 leq sindelta_{CP}leq -0.60$ for inverted hierarchy. The effective neutrino masses are predicted to be $35.70 leq langle m_{ee}rangle [mbox{meV}] leq 36.50$ in 3+1 scheme and $3.65 leq langle m^{(3)}_{ee}rangle [mbox{meV}] leq 4.10$ in three neutrino scheme for NH while $160.0 leq langle m_{ee}rangle [mbox{meV}] leq 168.0$ in 3+1 scheme and $47.80 leq langle m^{(3)}_{ee}rangle [mbox{meV}] leq 48.70$ in three neutrino scheme for for IH which are all in agreement with the recent experimental data.
The reactor antineutrinos are used for the precise measurement of oscillation parameters in the 3-neutrino model, and also used to investigate active-sterile neutrino mixing sensitivity in the 3$+$1 neutrino framework. In the present work, we study the feasibility of sterile neutrino search with the Indian Scintillator Matrix for Reactor Anti-Neutrino (ISMRAN) experimental set-up using electron antineutrinos ($overline{ u}_e$) produced from reactor as a source. The so-called 3$+$1 scenario is considered for active-sterile neutrino mixing, which leads to projected exclusion curves in the sterile neutrino mass and mixing angle plane. The analysis is performed considering both the reactor and detector related parameters. It is found that, the ISMRAN set-up can observe the active-sterile neutrino mixing sensitivity for $sin^{2}2theta_{14} geq$ 0.064 and $Delta m^{2}_{41}$ = 1.0 eV$^2$ at 90$%$ confidence level for an exposure of 1 ton-year by using neutrinos produced from the DHRUVA reactor with thermal power of 100 MW$_{th}$. It is also observed that, there is a significant improvement of the active-sterile neutrino mixing parameter $sin^{2}2theta_{14}$ to $sim$ 0.03 at the same $Delta m^{2}_{41}$ by putting the ISMRAN detector set-up at a distance of 20 m from the compact proto-type fast breeder reactor (PFBR) facility with thermal power of 1250 MW$_{th}$.
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