Abstract
We calculate the ratio $R_{\ell\ell}$ of same sign (SS) to opposite sign (OS) dileptons in type I and generalized inverse seesaw models and show that it can be anywhere between 0 and 1 depending on the detailed texture of the right-handed neutrino mass matrix. Measurement of $R_{\ell\ell}$ in hadron colliders can therefore provide a way to probe the nature of seesaw mechanism and also to distinguish between the two types of seesaw mechanisms. We work within the framework of left-right symmetric model as an example. We emphasize that coherence of the final states in the $W_R$ decay is crucial for this discussion and it requires the right-handed neutrinos to be highly degenerate. We isolate the range of parameters in the model where this effect is observable at the LHC and future colliders.
Highlights
Different kinds of seesaw mechanism have been proposed as ultraviolet (UV)-complete theories that lead to the dimension-5 Weinberg operator [1] for understanding small neutrino masses
Seesaw model is that it leads to a spectacular lepton number violating (LNV) signal in hadron colliders in the form of two same-sign leptons and two jets with no missing energy [12]
This arises from the production and decay of heavy right-handed neutrino (RHN), both mediated by the WR gauge boson in the s-channel
Summary
Different kinds of seesaw mechanism have been proposed as ultraviolet (UV)-complete theories that lead to the dimension-5 Weinberg operator [1] for understanding small neutrino masses. A key predictions for the TeV-scale left-right type-I seesaw model is that it leads to a spectacular LNV signal in hadron colliders in the form of two same-sign leptons and two jets with no missing energy [12] This arises from the production and decay of heavy RHNs, both mediated by the WR gauge boson in the s-channel. In the inverse seesaw mechanism, lepton number breaking is very small, because the heavy singlet neutrino (N) is paired with another singlet fermion (S) to form a pseudo-Dirac pair and the Majorana nature of the neutrino emerges from a keV-scale Majorana mass μS of S fermion (for TeV-scale seesaw) This model when embedded into the TeV-scale left-right framework exhibits some interesting features. Some useful threebody decay widths for the RHN are listed in the Appendix
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