Testing tree level TeV scale seesaw scenarios in $μ$TRISTAN

Abstract

We investigate TeV scale seesaw scenarios at $μ^+ e^-$ and $μ^+ μ^+$ colliders in the $μ$TRISTAN experiment. In minimal type-I seesaw scenario we consider two generations of Standard Model (SM) singlet heavy Majorana type Right Handed Neutrinos (RHNs) which couples with SM gauge bosons through light-heavy neutrino mixing. We discuss the prospects of probing heavy neutrinos via the processes such as $μ^+e^-\to νN_i\to e^+ j jν$ or $μ^- j jν$ for $\sqrt{s}=346$~GeV and $1\text{ ab}^{-1}$ luminosity. Studying these process, we estimate limits on the light-heavy neutrino mixing angles as a function of heavy neutrino mass, which could be two orders of magnitude stronger than electroweak precision data. Further, we study the effect of doubly charged scalar boson $(H^{++})$ from the type-II seesaw scenario in $μ^+ μ^+$ collision at $\sqrt{s}=2$ TeV. In this case we consider $μ^+ μ^+ \to \ell_i^+ \ell_j^+$ and $μ^+ μ^+ \to H^{++} Z/ γ$ processes followed by the same sign dilepton decay of $H^{++}$. We find that events involving $e^+ e^+$ among these final states can probe the neutrino mass ordering in $μ$TRISTAN experiment at 5$σ$ significance. In addition to that we study the production of positively charged triplet fermion in $μ$TRISTAN following $μ^+ μ^+ \to μ^+ Σ^+$ process where $Σ^+$ decays into $μ^+ jj$ mode through $Z$ boson exchange. Considering a triplet at 1 TeV and studying SM backgrounds we estimate the discovery potential of $μ^+ μ^+ jj$ signal at $μ$TRISTAN with respect to projected luminosity.