Heavy Neutral Leptons (HNLs)

Supervised by Dr. D. Samtleben (Nikhef) and Prof.dr. S. Pascoli (University of Bologna)

Heavy Neutral Leptons (HNLs)

Models introducing sterile neutrinos attempt to give a natural explanation for the existence and size of neutrinos masses, motivated by neutrino oscillation experiments. We considered the interactions in the Three Portal Model (Abdullahi et al. 2021) and studied its phenomenology. The model adds a new U'(1) symmetry which is broken under spontaneous symmetry braking, resulting in a low mass Dark photon Z' coupling to a Dark charge. The Z' mostly couples to a dark sector of dark neutrinos which obtain mass through a Dark Higgs.

Double bang signature

We focussed on studying how the HNLs could be observed through the double bang signature. In this process an atmospheric neutrino upscatters into a HNL through interaction with a nucleon in the detector. Due to the high energy of the incoming neutrino the nucleon is broken up producing a signal to be observed. The upscattered HNL subsequently decays after travelling some distance in the detector resulting in a second observable signal.

Artistic impression created by B.L.S Verkade

Deep Inelastic Scattering (DIS)

The energies involved in atmospheric neutrinos are so high that the dominant scattering process is DIS. To calculate the corresponding cross sections we used Parton Distribution Functions (PDFs) in combination with the coupling strength of the Dark photon for a set of benchmark parameters. Upscattering to three different HNLs (N4, N5, N6) mediated by the Dark photon Z' for a given benchmark are shown on the right. The resulting cross sections are ready to be implemented in event generator DarkNews (Abdullahi et al., 2022) to further allow studies of the constraining power of neutrino telescopes on sterile neutrino models.