Search

Heavy neutrino–antineutrino oscillations can appear in mechanisms of low-scale neutrino mass generation, where pairs of heavy neutrinos have almost degenerate masses. We discuss the case where the heavy neutrinos are sufficiently long-lived to decay displaced from the primary vertex, such that the oscillations of the heavy neutrinos into antineutrinos can potentially be observed at the (high-luminosity) LHC and at currently planned future collider experiments. The observation of these oscillations would allow to measure the mass splitting of the respective heavy neutrino pair, providing a deep insight into the nature of the neutrino mass generation mechanism. [ABSTRACT FROM AUTHOR]

We explore the sensitivity of displaced vertex searches at LHCb for testing sterile neutrino extensions of the Standard Model towards explaining the observed neutrino masses. We derive estimates for the constraints on sterile neutrino parameters from a recently published displaced vertex search at LHCb based on run 1 data. They yield the currently most stringent limit on active–sterile neutrino mixing in the sterile neutrino mass range between 4.5 GeV and 10 GeV. Furthermore, we present forecasts for the sensitivities that could be obtained from the run 2 data and also for the high-luminosity phase of the LHC. [ABSTRACT FROM AUTHOR]

Sterile neutrinos are among the most attractive extensions of the SM to generate the light neutrino masses observed in neutrino oscillation experiments. When the sterile neutrinos are subject to a protective symmetry, they can have masses around the electroweak scale and potentially large neutrino Yukawa couplings, which makes them testable at planned future particle colliders. We systematically discuss the production and decay channels at electron-positron, proton-proton and electron-proton colliders and provide a complete list of the leading order signatures for sterile neutrino searches. Among other things, we discuss several novel search channels, and present a first look at the possible sensitivities for the active-sterile mixings and the heavy neutrino masses. We compare the performance of the different collider types and discuss their complementarity. [ABSTRACT FROM AUTHOR]

We investigate the sensitivity of future lepton colliders to displaced vertices from the decays of long-lived heavy (almost sterile) neutrinos with electroweak scale masses and detectable time of flight. As future lepton colliders we consider the FCC-ee, the CEPC, and the ILC, searching at the Z-pole and at the center-of-mass energies of 240, 350 and 500 GeV. For a realistic discussion of the detector response to the displaced vertex signal and the Standard Model background we consider the ILC's Silicon Detector (SiD) as benchmark for the future lepton collider detectors. We find that displaced vertices constitute a powerful search channel for sterile neutrinos, sensitive to squared active-sterile mixing angles as small as 10-11. [ABSTRACT FROM AUTHOR]

In scenarios with sterile (right-handed) neutrinos with an approximate 'lepton-number-like' symmetry, the heavy neutrinos (the mass eigenstates) can have masses around the electroweak scale and couple to the Higgs boson with, in principle, unsuppressed Yukawa couplings, while the smallness of the light neutrinos' masses is guaranteed by the approximate symmetry. The on-shell production of the heavy neutrinos at lepton colliders, together with their subsequent decays into a light neutrino and a Higgs boson, constitutes a resonant contribution to the Higgs production mechanism. This resonant mono-Higgs production mechanism can contribute significantly to the mono-Higgs observables at future lepton colliders. A dedicated search for the heavy neutrinos in this channel exhibits sensitivities for the electron neutrino Yukawa coupling as small as . Furthermore, the sensitivity is enhanced for higher center-of-mass energies, when identical integrated luminosities are considered. [ABSTRACT FROM AUTHOR]

In this article we investigate the prospects of searching for sterile neutrinos in lowscale seesaw scenarios via the lepton flavour violating (but lepton number conserving) dilepton dijet signature. In our study, we focus on the final state e±μ∓jj at the HL-LHC and the FCC-hh (or the SppC). We perform a multivariate analysis at the detector level including the dominant SM backgrounds from di-top, di-boson, and tri-boson. Under the assumption of the active-sterile neutrino mixings |VlN|2 = |θe|2 = |θμ|2 and |VτN|2 = |θτ|2 = 0, the sensitivities on the signal production cross section times branching ratio σ(pp → l±N) × BR(N → l∓jj) and on |VlN|2 for sterile neutrino mass MN between 200 and 1000 GeV are derived. For the benchmark MN = 500 GeV, when ignoring systematic uncertainties at the HL-LHC (FCC-hh/SppC) with 3 (20) ab−1 luminosity, the resulting 2-σ limits on |VlN|2 are 4.9 × 10−3 (7.0 × 10−5), while the 2-σ limit on σ × BR are 4.4 × 10−2 (1.6 × 10−2) fb, respectively. The effect of the systematic uncertainty is also studied and found to be important for sterile neutrinos with smaller masses. We also comment on searches with τ±μ∓jj and τ±e∓jj final states. [ABSTRACT FROM AUTHOR]