Reconstructing a Heavy Neutral Lepton at the LHC

Heavy lepton singlets N slightly mixed with a standard neutrino ν_ are usually searched at the LHC in the trilepton plus pTᵐⁱˢˢ channel: pp → W⁺ → ⁺ N with N→ ⁻ W⁺ → ⁻ '⁺ ν. We show that for mN>mW the mass of the heavy lepton can be reconstructed. For mN≈ 90-$130$ GeV and the current luminosity (138 fb⁻¹ at 13 TeV), we estimate that this reconstruction would set the bound on |VN|² at 4× 10⁻⁴, versus the limit around 2× 10⁻³ obtained in a recent CMS analysis or |VN|²<10⁻³ from flavor and electroweak precision data.