What Can We Learn About the Origin Neutrino Masses at the Large Hadron Collider?

Sunday, 15 February 2015
Exhibit Hall (San Jose Convention Center)
Ajinkya S. Kamat, University of Virginia, Charlottesville, VA
Background. The origin of the neutrino masses is one of the most pressing problems in Particle Physics. A model of electroweak-scale right-handed neutrino (EWνR) was put forward a few years ago. In this model the Majorana masses of right-handed neutrinos are found to be naturally of the order of the electroweak scale. With the EWνRmodel it possible to directly produce the right handed neutrino and probe the origin of the neutrino masses at the LHC. This model does not violate the experimental constraints from the electroweak precision parameters. A minimal extension to this model can naturally give rise to a CP-even Higgs boson around 126 GeV mass, along with a rich spectrum of new scalar particles and mirror fermions. The objective of the present research is to determine the implications of this model in the light of the 126 GeV Higgs boson particle discovered in 2012 at the LHC. Method. The signal strengths associated with various decay channels of the 126 GeV Higgs boson have been measured by CMS and ATLAS. We scanned the parameter space of this model to obtain a 126 GeV Higgs boson, and compared the predictions of its decay signal strengths with the signal strengths of the 126 GeV Higgs boson at LHC. We also computed the decay signal strengths of heavier CP-even scalars in this model and compared them with results from the SM-like-heavy Higgs search at CMS and ATLAS. Results. We observed that the decay signal strengths of the 126 GeV Higgs boson candidate in the EWνR model agree with the experimental data at CMS and ATLAS. In an example case explored in detail, when a SM-like scalar is a dominant component in the 126 GeV Higgs boson at LHC, the signal strengths of its decays to 2 W and 2 Z bosons (0.71 to 0.84), bottom-anti-bottom quarks and tau-anti-tau leptons (1.00 to 1.18), and 2 photons (almost 0 to 2.5) agree with the experimental results for those decay channels. In this scenario, the heavier CP-even scalar can be ruled out in a mass region lower than about 410 GeV, but in the heavier-mass region it can strongly couple to the mirror fermions. Hence, the present heavy-Higgs-search data from CMS and ATLAS are not sufficient to make a conclusive statement about this scalar in the entire heavy-mass range. In addition to this scenario, we found a large part of the parameter space in the EWνRmodel, where the 126 GeV Higgs boson at LHC exhibits SM-like decay signal strengths, even if the SM-like scalar is a subdominant component in it. Thus, the Higgs boson at LHC appears to be an imposter with a dual-like nature within the regime of this model. Conclusions. Our analysis demonstrates that SM-like decay signal strengths are not sufficient to conclude whether or not the 126 GeV Higgs boson at LHC is really an SM-like Higgs or just an impostor. Thus, more experimental data and analysis is required to make a conclusive statement about the nature of this Higgs boson. Because our analysis reveals interconnection between neutrino masses and the Higgs sector, it shows that the study of EWνRmodel at LHC can provide deeper insights into the nature of the Higgs boson at LHC.