Prospects for a fourth generation of leptons in a 13 TeV p-p collider

TL;DR

This work investigates a sequential fourth generation of leptons ($\ell_4,\nu_4$) with a Dirac neutrino and analyzes collider signatures at $\sqrt{s}=13$ TeV. It implements the model with SARAH, assesses oblique constraints on mass splittings, and performs MC studies of $pp \to \ell_4\bar{\ell}_4$ with $m_{\ell_4}=190$ GeV and $m_{\nu_4}=100$ GeV, focusing on the dominant $\ell_4 \to W\nu_4$ decay and MET-based signatures. A CMS-like cut flow, jet-lepton kinematics, and mass reconstruction strategies are used to suppress backgrounds ($t\bar{t}$, $WW$, $ZZ$) and extract the signal, yielding a global significance of $1.46\pm0.068$ and a local significance of $3.33\pm0.241$ in the $180$–$300$ GeV window for $138\ \text{fb}^{-1}$, with discovery prospects improving at higher $\sqrt{s}$ and luminosity. The results indicate that HL-LHC and future colliders could probe the moderate-mass region, while very heavy leptons remain difficult to access within feasible run conditions. All relevant math is treated with proper notation, including oblique parameter expressions and decay kinematics.

Abstract

In the Standard Model, three discovered generations of leptons and quarks are known to date. However, speculations about existence of next generations have a strong foothold. In this study, we sequentially extrapolate the Standard Model to include a fourth generation of leptons (l4, nu4) with a massive Dirac neutrino. We perform MC simulated event generation of pp -> l4 l4(bar) scattering processes at an LHC-like p-p collider with sqrt(s) = 13 TeV by considering l4 mass of 190 GeV and nu4 mass of 100 GeV with PYTHIA. We demonstrate mass constraints of sequential leptons from oblique parameters and study important jet and lepton kinematics in our simulation with CMS like constraints. Fourth generation neutrino is stable in this scenario making l4 -> W nu4 the only dominant channel in collider searches. With the cut-flow, we achieve global excess of (1.46 +/- 0.068(stat.)) sigma and local excess of (3.33 +/- 0.241(stat.)) sigma in the 180-300 GeV signal window. Missing Transverse Energy (MET) provides clean signature of nu4. We assess discovery potential of the BSM lepton against lepton mass, center-of-mass energy (Ecom) and luminosities. Higher luminosities and Ecom are promising to probe BSM moderate mass lepton scenarios at present and future colliders.

Figures (19)

• Figure 1: W (Charged) vertex
• Figure 2: $Z$ (Neutral) vertex
• Figure 3: $\gamma$ (EM) vertex
• Figure 4: Higgs Yukawa coupling to $\ell_4$
• Figure 5: Decay $\ell_4 \to \ell_i A^0$ via pseudoscalar Yukawa coupling