Testing leptogenesis at the LHC and future muon colliders: a $Z'$ scenario

TL;DR

This paper explores the potential to test low-scale resonant leptogenesis through $Z'$ boson decays into right-handed neutrinos at the LHC and future muon colliders, focusing on signals with same-sign dileptons and CP violation indicators.

Contribution

It proposes a novel method to probe resonant leptogenesis at colliders via $Z'$ decays, extending the search reach to multi-TeV $Z'$ masses and highlighting the significance of CP violation signals.

Findings

Resonant leptogenesis can be tested at the HL-LHC for $Z'$ masses up to 12 TeV.

Future muon colliders at 10 and 30 TeV can probe $Z'$ masses up to 28 and 100 TeV.

Same-sign dilepton signals provide a nearly background-free signature for leptogenesis detection.

Abstract

If the masses of at least two generations of right-handed neutrinos (RHNs) are near-degenerate, the scale of leptogenesis can be as low as $\sim$ 100 GeV. In this work, we study probing such resonant leptogenesis in the $B-L$ model at the LHC and future multi-TeV muon colliders via the process $Z'\to NN\to\ell^\pm\ell^\pm+{\rm jets}$, with $Z'$ the $U(1)_{B-L}$ gauge boson and $N$ the RHN. The same-sign dilepton feature of the signal makes it almost background-free, while the event number difference between positive and negative leptons is a hint for $CP$ violation, which is a key ingredient of leptogenesis. We found that resonant leptogenesis can be tested at the HL-LHC for $M_{Z'}$ up to 12 TeV, while at a 10 (30) TeV muon collider the reach can be up to $M_{Z'}\sim28~(100)$ TeV via the off-shell production of $Z'$.