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Register a new userNew limits on heavy sterile neutrino mixing in ${^{8}rm{B}}$-decay obtained with the Borexino detector
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If heavy neutrinos with mass $m_{ u_{H}}geq$2$ m_e $ are produced in the Sun via the decay ${^8rm{B}} rightarrow {^8rm{Be}} + e^+ + u_H$ in a side branch of pp-chain, they would undergo the observable decay into an electron, a positron and a light neutrino $ u_{H}rightarrow u_{L}+e^++e^-$. In the present work Borexino data are used to set a bound on the existence of such decays. We constrain the mixing of a heavy neutrino with mass 1.5 MeV $leq m_{ u_{H}} le$ 14 MeV to be $|U_{eH}|^2leq (10^{-3}-4times10^{-6})$ respectively. These are tighter limits on the mixing parameters than obtained in previous experiments at nuclear reactors and accelerators.
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We present limits on sterile neutrino mixing using 4,438 live-days of atmospheric neutrino data from the Super-Kamiokande experiment. We search for fast oscillations driven by an eV$^2$-scale mass splitting and for oscillations into sterile neutrinos instead of tau neutrinos at the atmospheric mass splitting. When performing both these searches we assume that the sterile mass splitting is large, allowing $sin^2(Delta m^2 L/4E)$ to be approximated as $0.5$, and we assume that there is no mixing between electron neutrinos and sterile neutrinos ($|U_{e4}|^2 = 0$). No evidence of sterile oscillations is seen and we limit $|U_{mu4}|^2$ to less than 0.041 and $|U_{tau4}|^2$ to less than 0.18 for $Delta m^2 > 0.8$ eV$^2$ at the 90% C.L. in a 3+1 framework. The approximations that can be made with atmospheric neutrinos allow these limits to be easily applied to 3+N models, and we provide our results in a generic format to allow comparisons with other sterile neutrino models.
We study the effects induced by new neutral fermions below their mass threshold, due to their possible mixing with the standard neutrinos. We use as experimental constraints the recent results on lepton universality, together with the measurement of the $mu$ decay rate and the updated LEP data. In particular, the inclusion in our data set of the most recent determinations of the $tau$ branching fractions, mass and lifetime implies that a previous indication of a non-vanishing mixing for $ u_tau$ is no longer present. We obtain new stringent limits on the mixing parameters between $ u_e$, $ u_mu$, $ u_tau$ and heavy neutral states of different weak isospin. If no assumption on the type of neutrinos involved in the mixing is made, we find $snue^2<0.0071$, $snumu^2<0.0014$ and $snutau^2<0.033$.
The OPERA experiment, exposed to the CERN to Gran Sasso $ u_mu$ beam, collected data from 2008 to 2012. Four oscillated $ u_tau$ Charged Current interaction candidates have been detected in appearance mode, which are consistent with $ u_mu to u_tau$ oscillations at the atmospheric $Delta m^2$ within the standard three-neutrino framework. In this paper, the OPERA $ u_tau$ appearance results are used to derive limits on the mixing parameters of a massive sterile neutrino.
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.
A search for resonant absorption of solar axions by $^{169}$Tm nuclei was carried out. A newly developed approach involving low-background cryogenic bolometer based on Tm$_3$Al$_5$O$_{12}$ crystal was used that allowed for significant improvement of sensitivity in comparison with previous $^{169}$Tm based experiments. The measurements performed with $8.18$ g crystal during $6.6$ days exposure yielded the following limits on axion couplings: $|g_{Agamma} (g_{AN}^0 + g_{AN}^3) leq 1.44 times 10^{-14}$ GeV$^{-1}$ and $|g_{Ae} (g_{AN}^0 + g_{AN}^3) leq 2.81 times 10^{-16}$.
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