CP Violation in Same-sign Dilepton Production at the LHC
Fatemeh Najafi, Jacky Kumar, David London, Richard MacKenzie
If the neutrino is a Majorana particle, low-energy lepton-number-violating (LNV) processes, such as neutrinoless double-beta (0νββ) decay, are possible. It may also be possible to observe high-energy 0νββ-like LNV processes at the LHC. These are distinguished by the presence of same-sign dileptons in the final state (e.g., u¯d→tb¯e−μ−). If such a process were observed, we would then want to know the nature of the underlying new physics (NP). In this paper, we show that CP-violating triple products (TPs) may be present in the process, and much information can be obtained by measuring them. If a nonzero TP were observed, we would know immediately that there are (at least) two interfering NP amplitudes, with different weak phases and different Lorentz structures. And if we had some knowledge of the NP, e.g., by direct production of NP particles, we could get information about the magnitudes and relative phases of its couplings by examining the angular distribution of the final-state particles. If the NP involves right-handed (RH) neutrinos, it may even be possible to probe the CP-violating Dirac and Majorana phases in the RH neutrino mixing matrix.