# (C) Other neutrino mixing results

The LSND collaboration reported in AGUILAR 2001 a signal which is consistent with ${{\overline{\mathit \nu}}_{{\mu}}}$ $\rightarrow$ ${{\overline{\mathit \nu}}_{{e}}}$ oscillations. In a three neutrino framework, this would be a measurement of $\theta _{12}$ and $\Delta \mathit m{}^{2}_{21}$. This does not appear to be consistent with most of the other neutrino data. The following listings include results from ${{\mathit \nu}_{{\mu}}}$ $\rightarrow$ ${{\mathit \nu}_{{e}}}$ , ${{\overline{\mathit \nu}}_{{\mu}}}$ $\rightarrow$ ${{\overline{\mathit \nu}}_{{e}}}$ appearance and ${{\mathit \nu}_{{\mu}}}$, ${{\overline{\mathit \nu}}_{{\mu}}}$, ${{\mathit \nu}_{{e}}}$, and ${{\overline{\mathit \nu}}_{{e}}}$ disappearance experiments, and searches for $\mathit CPT$ violation.

# Search for ${{\boldsymbol \nu}_{{\mu}}}$ or ${{\boldsymbol \nu}_{{e}}}$ $\rightarrow$ ${{\boldsymbol \nu}_{{s}}}$ INSPIRE search

VALUE CL% DOCUMENT ID TECN  COMMENT
• • • We do not use the following data for averages, fits, limits, etc. • • •
$<0.1$ 99 1
 2019
Neutrino-4
$<0.01$ 90 2
 2018
DANSS
$<0.06$ 90 3
 2018
STEREO
$<0.1$ 95 4
 2018
PROSPECT
$<0.1$ 95 5
 2018 A
Neutrino-4
$<0.4$ 90 6
 2017 B
ICCB IceCube-DeepCore
$<8 \times 10^{-3}$ 95 7
 2017
T $\beta$ decay
$<0.01$ 90 8
 2017
NEOS
$<0.02$ 90 9
 2016
ICCB IceCube
$<4.5 \times 10^{-4}$ 95 10
 2016 B
MINOS, DayaBay
$<0.086$ 95 11
 2016 C
MINS
$<0.011$ 95 12
 2016 B
DAYA
13
 2001
MCRO matter effects
14
 2000
SKAM neutral currents + matter effects
1  SEREBROV 2019 searches for ${{\overline{\mathit \nu}}_{{e}}}$ $\rightarrow$ ${{\overline{\mathit \nu}}_{{s}}}$ oscillations with baseline $6 - 12$ m with SM-3 research reactor that uses highly enriched ${}^{235}\mathrm {U}$ fuel. The spectrum is well described by the 1/$\mathit L{}^{2}$ dependence. However, the shape differs from the theoretical expectations, with the best fit corresponding to $\Delta$m${}^{2}_{41}$ = $7.34$ $\pm0.1$ eV${}^{2}$ and sin$^2(2\theta _{14})$ = $0.39$ $\pm0.12$ at 3$\sigma$ significance.
2  ALEKSEEV 2018 searches for ${{\overline{\mathit \nu}}_{{e}}}$ $\rightarrow$ ${{\overline{\mathit \nu}}_{{s}}}$ oscillations using the DANSS detector at 10.7, 11.2, and 12.7 m from the 3.1 GW$_{th}$ power reactor. The DANSS detector is highly segmented and moveable; the positions are changed usually 3 times a week. The analysis is based on the ratio of the events at top and bottom position; the middle position is used for checks of consistency. The best fit point is at $\Delta$m${}^{2}_{41}$ = 1.4 eV${}^{2}$ and sin$^2(2\theta _{14})$ = 0.05 with $\Delta \chi {}^{2}$ = 13.1 (statistical errors only) compared to the fit with 3 active neutrinos only. The quoted limit of 0.01 for sin$^2(2\theta _{14})$ corresponds to $\Delta$m${}^{2}_{41}$ $\sim{}$ 1.0 eV${}^{2}$.
3  ALMAZAN 2018 searches for the ${{\overline{\mathit \nu}}_{{e}}}$ $\rightarrow$ ${{\overline{\mathit \nu}}_{{s}}}$ oscillations with baseline from 9.4 to 11.1 m from the ILL research reactor with highly enriched ${}^{235}\mathrm {U}$ fuel. The STEREO detector consists of six separated cells with ${}^{}\mathrm {Gd}$ loaded scintillator, with 15 m water equivalent overburden. The detected rate is $396.3$ $\pm4.7$ ${{\overline{\mathit \nu}}_{{e}}}$/day with signal to background ratio of about 0.9. The reported results corresponds to 66 days of reactor-on. The analysis uses the relative rates normalized to the cell number 1. No indication of the oscillation to the sterile neutrinos is found, the stated limit on sin$^2(2\theta _{14})$ correspond to $\Delta$m${}^{2}_{41}$ $\sim{}$ 3.5 eV${}^{2}$ where the exclusion is maximal.
4  ASHENFELTER 2018 searches for the ${{\overline{\mathit \nu}}_{{e}}}$ $\rightarrow$ ${{\overline{\mathit \nu}}_{{s}}}$ oscillations at baseline from 6.7 to 9.2 m from the 85 MW research reactor with pure ${}^{235}\mathrm {U}$ core. The segmented 4 ton ${}^{6}\mathrm {Li}$-doped liquid scintillator is operated with about 1 m water equivalent overburden and recorded $25461$ $\pm283$ IBD events. No indication of oscillations into sterile neutrinos was observed. The stated limit for sin$^2(2\theta _{14})$ is for $\Delta$m${}^{2}_{41}$ $\sim{}$ 2 eV${}^{2}$ where the sensitivity is maximal.
5  SEREBROV 2018A searches for the ${{\overline{\mathit \nu}}_{{e}}}$ $\rightarrow$ ${{\overline{\mathit \nu}}_{{s}}}$ oscillation with baseline $6 - 12$ m from the core of the SM-3 research reactor that uses highly enriched ${}^{235}\mathrm {U}$. They find that oscillations with $\Delta$m${}^{2}_{41}$ $\sim{}$ $0.7 - 0.8$ eV${}^{2}$ and sin$^2(2{{\mathit \theta}_{{14}}})$ $\sim{}$ $0.10 - 0.15$ give better fit to the $\mathit L$ and $\mathit E$ dependence than the no oscillation scenario. The significance of this is about 2$\sigma$.
6  AARTSEN 2017B uses three years of upward-going atmospheric neutrino data in the energy range of 10-60 GeV to constrain their disappearance into light sterile neutrinos. The reported limit sin$^2\theta _{24}$ $<$ 0.11 at 90$\%$ C.L. is for $\Delta$m${}^{2}_{41}$ = 1.0 eV${}^{2}$. We convert the result to sin$^22\theta _{24}$ for the listing. AARTSEN 2017B also reports cos $^2\theta _{24}\cdot{}$sin$^2\theta _{34}$ $<$ 0.15 at 90$\%$ C.L. for $\Delta$m${}^{2}_{41}$ = 1.0 eV${}^{2}$.
7  ABDURASHITOV 2017 use the Troitsk nu-mass experiment to search for sterile neutrinos with mass 0.1 - 2 keV. We convert the reported limit from $\mathit U{}^{2}_{e4}<$0.002 to sin$^22\theta _{14}<$0.008 assume $\mathit U_{e4}\sim{}$ sin$\theta _{14}$. The stated limit corresponds to the smallest $\mathit U{}^{2}_{e4}$. The exclusion curve begins at $\mathit U{}^{2}_{e4}$ of 0.02 for m$_{4}$ = 0.1 keV.
8  KO 2017 reports on short baseline reactor oscillation search ( ${{\overline{\mathit \nu}}_{{e}}}$ $\rightarrow$ ${{\overline{\mathit \nu}}_{{s}}}$ ), motivated be the so-called "reactor antineutrino anomaly". The experiment is conducted at 23.7 m from the core of unit 5 of the Hanbit Nuclear Power Complex in Korea. the reported limited on sin$^2(2\theta _{41})$ for sterile neutrinos was determined using the reactor antineutrino spectrum determined by the Daya Bay experiment for $\Delta$m${}^{2}_{14}$ around 0.55 eV${}^{2}$ where the sensitivity is maximal. A fraction of the parameter space derived from the "reactor antineutrino anomaly" is excluded by this work. Compared to reactor models an event excess is observed at about 5 MeV, in agreement with other experiments.
9  AARTSEN 2016 use one year of upward-going atmospheric muon neutrino data in the energy range of 320 GeV to 20 TeV to constrain their disappearance into light sterile neutrinos. Sterile neutrinos are expected to produce distinctive zenith distribution for these energies for 0.01 ${}\leq{}\Delta$m${}^{2}{}\leq{}$10 eV${}^{2}$. The stated limit is for sin$^22\theta _{24}$ at $\Delta$m${}^{2}$ around 0.3 eV${}^{2}$.
10  ADAMSON 2016B combine the results of AN 2016B, ADAMSON 2016C, and Bugey-3 reactor experiments to constrain ${{\mathit \nu}_{{\mu}}}$ to ${{\mathit \nu}_{{e}}}$ mixing through oscillations into light sterile neutrinos. The stated limit for sin$^22\theta _{ {{\mathit \mu}} {{\mathit e}} }$ is at $\vert \Delta$m${}^{2}_{41}\vert$ = 1.2 eV${}^{2}$.
11  ADAMSON 2016C use the NuMI beam and exposure of $10.56 \times 10^{20}$ protons on target to search for the oscillation of ${{\mathit \nu}_{{\mu}}}$ dominated beam into light sterile neutrinos with detectors at 1.04 and 735 km. The reported limit sin$^2(\theta _{24})$ $<$ 0.022 at 95$\%$ C.L. is for $\vert \Delta$m${}^{2}_{41}\vert$ = 0.5 eV${}^{2}$. We convert the result to sin$^2(2\theta _{24})$ for the listing.
12  AN 2016B utilize 621 days of data to place limits on the ${{\overline{\mathit \nu}}_{{e}}}$ disappearance into a light sterile neutrino. The stated limit corresponds to the smallest sin$^2(2\theta _{14})$ at $\vert \Delta$m${}^{2}_{41}\vert$ $\sim{}$ $0.03$ eV${}^{2}$ (obtained from Figure 3 in AN 2016B). The exclusion curve begins at $\vert \Delta$m${}^{2}_{41}\vert \sim{}1.5 \times 10^{-4}$ eV${}^{2}$ and extends to $\sim{}0.25$ eV${}^{2}$. The analysis assumes sin$^2(2\theta _{12})$ = $0.846$ $\pm0.021$, $\Delta$m${}^{2}_{21}$ = ($7.53$ $\pm0.18$) $\times 10^{-5}$ eV${}^{2}$, and $\vert \Delta$m${}^{2}_{32}\vert$ = $0.00244$ $\pm0.00006$ eV${}^{2}$.
13  AMBROSIO 2001 tested the pure 2-flavor ${{\mathit \nu}_{{\mu}}}$ $\rightarrow$ ${{\mathit \nu}_{{s}}}$ hypothesis using matter effects which change the shape of the zenith-angle distribution of upward through-going muons. With maximum mixing and $\Delta$m${}^{2}$around $0.0024~$eV${}^{2}$, the ${{\mathit \nu}_{{\mu}}}$ $\rightarrow$ ${{\mathit \nu}_{{s}}}$ oscillation isdisfavored with 99$\%$ confidence level with respect to the ${{\mathit \nu}_{{\mu}}}$ $\rightarrow$ ${{\mathit \nu}_{{\tau}}}$ hypothesis.
14  FUKUDA 2000 tested the pure 2-flavor ${{\mathit \nu}_{{\mu}}}$ $\rightarrow$ ${{\mathit \nu}_{{s}}}$ hypothesis using three complementary atmospheric-neutrino data samples. With this hypothesis, zenith-angle distributions are expected to show characteristic behavior due to neutral currents and matter effects. In the $\Delta$m${}^{2}$ and sin$^22\theta$region preferred by the Super-Kamiokande data, the ${{\mathit \nu}_{{\mu}}}$ $\rightarrow$ ${{\mathit \nu}_{{s}}}$ hypothesis isrejected at the 99$\%$ confidence level, while the ${{\mathit \nu}_{{\mu}}}$ $\rightarrow$ ${{\mathit \nu}_{{\tau}}}$ hypothesis consistently fits all of the data sample.
References:
 SEREBROV 2019
JETPL 109 213 First Observation of the Oscillation Effect in the Neutrino-4 Experiment on the Search for the Sterile Neutrino
 ALEKSEEV 2018
PL B787 56 Search for sterile neutrinos at the DANSS experiment
 ALMAZAN 2018
PRL 121 161801 Sterile Neutrino Constraints from the STEREO Experiment with 66 Days of Reactor-On Data
 ASHENFELTER 2018
PRL 121 251802 First search for short-baseline neutrino oscillations at HFIR with PROSPECT
 SEREBROV 2018A
PPN 49 701 Sterile Neutrino Search in the Neutrino-4 Experiment at the SM-3 Reactor
 AARTSEN 2017B
PR D95 112002 Search for Sterile Neutrino Mixing using Three Years of IceCube DeepCore Data
 ABDURASHITOV 2017
JETPL 105 753 First Measeurements in Search for keV-Sterile Neutrino in Tritium beta-Decay by Troitsk nu-Mass Experiment
 KO 2017
PRL 118 121802 Sterile Neutrino Search at the NEOS Experiment
 AARTSEN 2016
PRL 117 071801 Searches for Sterile Neutrinos with the IceCube Detector
PRL 85 3999 ${{\mathit \tau}}$ Neutrinos Favored over Sterile Neutrinos in Atmospheric Muon Neutrino Oscillations