Abstract
Heavy neutral leptons are predicted in many extensions of the Standard Model with massive neutrinos. If kinematically accessible, they can be copiously produced from kaon and pion decays in atmospheric showers, and subsequently decay inside large neutrino detectors. We perform a search for these long-lived particles using Super-Kamiokande multi-GeV neutrino data and derive stringent limits on the mixing with electron, muon and tau neutrinos as a function of the long-lived particle mass. We also present the limits on the branching ratio versus lifetime plane, which are helpful in determining the constraints in non-minimal models where the heavy neutral leptons have new interactions with the Standard Model.
Highlights
We present the limits on the branching ratio versus lifetime plane, which are helpful in determining the constraints in non-minimal models where the heavy neutral leptons have new interactions with the Standard Model
There are compelling reasons to believe that neutrino masses are the first manifestation of a new physics (NP) scale, which can be identified with the mass of the heavy mediator(s) that generates neutrino masses
A Poissonian χ 2 function has been used: χ 2 = 2 Niα + Biα − niα + niα log i,α niα Niα + Biα where the sum runs over the angular bins, and α = {elbiikne,wμh-illiekeN}i.α Hiserteh,enpiαresdtaicntdesd fnour mthbeerdaotfa observed in each signal events and
Summary
There are compelling reasons to believe that neutrino masses are the first manifestation of a new physics (NP) scale, which can be identified with the mass of the heavy mediator(s) that generates neutrino masses. For masses below the kaon and pion mass the HNL becomes very long-lived: the value of its lifetime in the rest frame (τ ) depends strongly on its mass and on its mixing with the light states, in the minimal model described above it ranges between cτ ∼ (10−4−50)× |Uα|−2 (km), for m N between 40 MeV and 400 MeV. This makes atmospheric neutrino detectors a well-suited setup to search for their decay products. This can be useful in order to constrain non-minimal scenarios with uncorrelated production and decay, such as for example the dipole extension of Ref. [42]
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