Expanding the reach of heavy neutrino searches at the LHC

• Main Authors: Andrés Flórez, Kaiwen Gui, Alfredo Gurrola, Carlos Patiño, Diego Restrepo
• Format: Article
• Language: English
• Published: Elsevier 2018-03-01
• Series: Physics Letters B
• Online Access: http://www.sciencedirect.com/science/article/pii/S0370269318300169

The observation of neutrino oscillations establishes that neutrinos have non-zero mass and provides one of the more compelling arguments for physics beyond the standard model (SM) of particle physics. We present a feasibility study to search for hypothetical Majorana neutrinos (N) with TeV scale masses, predicted by extensions of the SM to explain the small but non-zero SM neutrino mass, using vector boson fusion (VBF) processes at the 13 TeV LHC. In the context of the minimal Type-I seesaw mechanism (mTISM), the VBF production cross-section of a lepton (ℓ) and associated heavy Majorana neutrino (Nℓ) surpasses that of the Drell–Yan process at approximately mNℓ=1.4TeV. We consider second and third-generation heavy neutrino (Nμ or Nτ, where ℓ= muon (μ) or tau (τ) leptons) production through VBF processes, with subsequent Nμ and Nτ decays to a lepton and two jets, as benchmark cases to show the effectiveness of the VBF topology for Nℓ searches at the 13 TeV LHC. The requirement of a dilepton pair combined with four jets, two of which are identified as VBF jets with large separation in pseudorapidity and a TeV scale dijet mass, is effective at reducing the SM background. These criteria may provide expected exclusion bounds, at 95% confidence level, of mNℓ<1.7 (2.4) TeV, assuming 100 (1000) fb−1 of 13 TeV data from the LHC and mixing |VℓNℓ|2=1. The use of the VBF topology to search for mNℓ increases the discovery reach at the LHC, with expected significances greater than 5σ (3σ) for Nℓ masses up to 1.7 (2.05) TeV using 1000fb−1 of 13 TeV data from the LHC.