Abstract
The tau lepton plays important role in the correlation between the low-energy neutrino oscillation data and the lepton flavor structure in heavy neutrino decay. We investigate the lepton flavor signatures with tau lepton at hadron collider through lepton number violating (LNV) processes. In the Type I Seesaw with U$(1)_{\rm B-L}$ extension, we study the pair production of heavy neutrinos via a $Z'$ resonance. We present a detailed assessment of the search sensitivity to the channels with tau lepton in the subsequent decay of heavy neutrinos. For the benchmark model with $Z'$ only coupled to the third generation fermions, we find that the future circular collider (FCC-hh) can discover the LNV signal with tau lepton for $M_{Z'}$ up to 2.2 (3) TeV with the gauge coupling $g'=0.6$ and the integrated luminosity of 3 (30) ab$^{-1}$. The test on the flavor combinations of SM charged leptons would reveal the specific nature of different heavy neutrinos.
Highlights
It is well known that, in the context of the Standard Model (SM), the nonzero but small Majorana neutrino masses can be realized at leading order through a dimension-five operator [1]κ Λ lLlLHH; ð1Þ where lL and H stand for the SM lepton doublet and the Higgs doublet, respectively
For the benchmark model with Z0 only coupled to the third generation fermions, we find that the future circular collider can discover the lepton number violating signal with a tau lepton for MZ0 up to 2.2 (3) TeV with the gauge coupling g0 1⁄4 0.6 and the integrated luminosity of 3 ð30Þ ab−1
Low energy neutrino oscillation data lead to correlation with the flavor structure of the heavy neutrino decays and tau lepton plays manifest role in such correlation
Summary
It is well known that, in the context of the Standard Model (SM), the nonzero but small Majorana neutrino masses can be realized at leading order through a dimension-five operator [1]. In a flavored Uð1ÞB−L model [denoted by Uð1ÞðB−LÞ3] where only the third generation fermions couple to the new gauge boson Z0 [38,39], the constraint on the new gauge interaction is much weak and a single heavy neutrino preferably decays into the tau lepton. Pp → Z0 → NN; ð2Þ where Z0 is the new gauge boson of the Uð1ÞðB−LÞ3 symmetry and N denotes the heavy neutrino followed by the decay into tau lepton in LNV final states. Besides the gauge field B0μ, a new scalar field S ∼ ð1; 1; 0; 2x0Þ is introduced to break the local Uð1ÞB−L symmetry and generate the masses of right-handed neutrinos NR ∼ ð1; 1; 0; −x0Þ. We take the Uð1ÞðB−LÞ3 model for illustration, our result below is generic and applicable to any Uð1Þ0 model with heavy neutrinos
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