Doubly Charged Higgs Boson Production at Hadron Colliders II: A Zee-Babu Case Study

TL;DR

This paper investigates the phenomenology of the Zee-Babu model for neutrino masses at the LHC, finding it difficult to distinguish from the Type II Seesaw model due to similar production rates and discussing implications for current and future collider searches.

Contribution

It provides a detailed comparison of Zee-Babu and Type II Seesaw models, showing their collider signatures are nearly indistinguishable and introduces new computational tools for simulations.

Findings

Production rates for charged scalars are similar in both models.

Differences in cross sections are small and often hidden by unknown branching ratios.

Updated neutrino data can help discriminate models through lepton flavor-violating observables.

Abstract

Motivated by searches for so-called leptonic scalars at the LHC and the recent measurement of the $W$ boson's mass at the Tevatron, we revisit the phenomenology of the Zee-Babu model for neutrino masses and the ability to differentiate it from the Type II Seesaw model at the LHC. We conclude that this task is much more difficult than previously believed. All inputs equal in the two scenarios, we find that total and differential rates for producing pairs of doubly and singly charged scalars are identical in shape and only differ in normalization. The normalization is given by the ratio of hadronic cross sections and can be unity. Differences in cross sections are small and can be hidden by unknown branching rates. This holds for Drell-Yan, $\gamma\gamma$ fusion, and $gg$ fusion, as well as observables at LO and NLO in QCD. This likeness allows us to reinterpret Run II limits on the Type II Seesaw and estimate projections for the HL-LHC. Using updated neutrino oscillation data, we also find that some collider observables, e.g., lepton flavor-violating branching ratios, are now sufficiently precise to provide a path forward. Other means of discrimination are also discussed. As a byproduct of this work, we report the availability of new Universal \texttt{FeynRules} Object libraries, the \texttt{SM\_ZeeBabu} UFO, that enable fully differential simulations up to NLO+LL(PS) with tool chains employing \texttt{MadGraph5\_aMC@NLO}.