CP Violation in Rare Lepton-Number-Violating $W$ Decays at the LHC

Understand

Some models of leptogenesis involve a quasi-degenerate pair of heavy neutrinos $N_{1,2}$ whose masses can be small, $O({\rm GeV})$.

• Such neutrinos can contribute to the rare lepton-number-violating (LNV) decay $W^\pm \to \ell_1^\pm \ell_2^\pm (q'{\bar q})^\mp$.
• If both $N_1$ and $N_2$ contribute, there can be a CP-violating rate difference between the LNV decay of a $W^-$ and its CP-conjugate decay.
• In this paper, we examine the prospects for measuring such a CP asymmetry $A_{\rm CP}$ at the LHC.