Resolvable heavy neutrino–antineutrino oscillations at colliders

Abstract

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 longlived 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.

Heavy neutrinos in displaced vertex searches at the LHC and HL-LHC

“…If the mass splitting is smaller than Γ N i , then the destructive interference between contributions from different N i to the diagram in Figure 3 leads to a suppression of processes that violate L [91]. In the intermediate regime where M i − M j ∼ Γ N i , Γ N j there can be non-trivial effects due to coherent oscillations amongst the heavy neutrinos [56,58,87,95,96]. Hence, a precise predicion of the number of events depends on parameters that may not be directly observable if the mass splitting is smaller than the kinematic resolution of the detector.…”

Common explanation to the RK(*) , RDMarzo1, Marzola2, Raidal3 2019Phys. Rev. D221110View full textAdd to dashboardCite

“…The proposed framework then connects the issue of flavour measurements to other open questions within neutrino physics and cosmology, such as the neutrino mass generation mechanism and the dynamics of baryogenesis via leptogenesis, extending the phenomenological reach of flavour experiments. We highlight that RHNs in the considered mass range can be discovered by the planned SHIP experiment at CERN [41], as well as in collider experiments through the implied lepton number violating effects [42].…”

Lepton-trijet and displaced vertex searches for heavy neutrinos at future electron-proton colliders

“…When the light neutrino masses are introduced via a small breaking of the protective symmetry, this can in principle (depending on the induced small mass splitting of the quasi-degenerate heavy neutrino pair) lead to observable lepton number violation via heavy neutrino-antineutrino oscillations. For displaced vertices the heavy neutrino-antineutrino oscillations might even be resolved via an oscillatory lifetime-dependence of Br(N → µ − + 2j)/Br(N → µ + + 2j), as discussed in [8].…”

“…Therefore our results should hold in more generality, unless unless |θ e | |θ µ |, |θ τ |, in which case the lepton flavor conserving signatures become most relevant. While in our model lepton number violation (LNV) is effectively absent for masses of O(100) GeV [8] it is interesting to consider the possibility of the LNV final states at lower masses. The lepton trijet signature with an anti-lepton is also free of background and can be detectable with a significance that is similar to the lepton number conserving lepton trijet.…”

“…When the symmetry is slightly broken (or only approximate), lepton number violation (LNV) is induced. A discussion for which parameter regions the LNV effects can be observable in the SPSS benchmark model with small symmetry breaking can be found in [8].…”