Testing leptogenesis at the LHC and future muon colliders: A <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msup><mml:mi>Z</mml:mi><mml:mo>′</mml:mo></mml:msup></mml:math> scenario
Wei Liu, Ke-Pan Xie, Zihan Yi
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 $\ensuremath{\sim}100\text{ }\text{ }\mathrm{GeV}$. In this work, we study probing such resonant leptogenesis in the $B\ensuremath{-}L$ model at the LHC and future multi-TeV muon colliders via the process ${Z}^{\ensuremath{'}}\ensuremath{\rightarrow}NN\ensuremath{\rightarrow}{\ensuremath{\ell}}^{\ifmmode\pm\else\textpm\fi{}}{\ensuremath{\ell}}^{\ifmmode\pm\else\textpm\fi{}}+\text{jets}$, with ${Z}^{\ensuremath{'}}$ the $U(1{)}_{B\ensuremath{-}L}$ 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 ${M}_{{Z}^{\ensuremath{'}}}$ up to 12 TeV, while at a 10 (30) TeV muon collider the reach can be up to ${M}_{{Z}^{\ensuremath{'}}}\ensuremath{\sim}30(100)\text{ }\text{ }\mathrm{TeV}$ via the off-shell production of ${Z}^{\ensuremath{'}}$.