A Strongly Coupled Fourth Generation at the LHC

TL;DR

This paper investigates the phenomenology of a strongly coupled fourth-generation quark sector at the LHC, focusing on production, decay signatures, and the potential to distinguish new strong interactions from standard QCD processes.

Contribution

It provides a detailed analysis of fourth-generation quark production and decay at the LHC, and explores methods to identify signatures of new strong interactions.

Findings

Heavy fourth-generation quarks (300-600 GeV) produce detectable multi-lepton signals at the LHC.

Distinguishing new strong interactions from QCD requires large data samples.

Early LHC runs can falsify these models, but confirmation needs high luminosity.

Abstract

We study extensions of the standard model with a strongly coupled fourth generation. This occurs in models where electroweak symmetry breaking is triggered by the condensation of at least some of the fourth-generation fermions. With focus on the phenomenology at the LHC, we study the pair production of fourth-generation down quarks, D4. We consider the typical masses that could be associated with a strongly coupled fermion sector, in the range (300--600) GeV. We show that the production and successive decay of these heavy quarks into final states with same-sign dileptons, trileptons and four leptons, can be easily seen above background with relatively low luminosity. On the other hand, in order to confirm the presence of a new strong interaction responsible for fourth-generation condensation, we study its contribution to D4 pair-production, and the potential to separate it from standard QCD-induced heavy quark production. We show that this separation might require large amounts of data. This is true even if it is assumed that the new interaction is mediated by a massive colored vector boson, since its strong coupling to the fourth generation renders its width of the order of its mass. We conclude that, although this class of models can be falsified at early stages of the LHC running, its confirmation would require high integrated luminosities.