Lepton number violation: From 0νββ decay to long-lived particle searches

We study the complementary tests of lepton number violation in 0νββ-decay experiments, long-lived particle (LLP) searches at the LHC main detectors ATLAS/CMS, and a proposed far detector MATHUSLA. In the context of a simplified model with a scalar doublet S and a Majorana fermion F, we show that while the 0νββ-decay experiments can probe a larger portion of parameter space, the LLP searches can uniquely probe the region of smaller couplings and masses if S is at TeV scale while F is at or below the electroweak scale. We also investigate constraints on the parameter space from the existing searches that are insensitive to lepton number violation.