Signal to background interference in $pp\to t H^-\to t W^- b\bar b$ at the LHC Run-II

TL;DR

This paper studies how interference effects between a heavy charged Higgs boson signal and background processes at the LHC can significantly alter search sensitivities, emphasizing the need to account for these effects in analyses.

Contribution

It demonstrates that interference effects are substantial and destructive, requiring rescaling of current LHC search limits for heavy charged Higgs bosons, and shows how these effects can be quantitatively incorporated.

Findings

Interference effects are large and destructive for heavy charged Higgs searches.

Current LHC limits need rescaling due to interference effects.

Interference impacts both inclusive and differential analysis levels.

Abstract

We investigate in the Large Hadron Collider (LHC) environment the possibility that sizeable interference effects between a {\sl heavy} charged Higgs boson signal produced via $bg\to tH^-$ (+ c.c.) scattering and decaying via $H^-\to W^- A\to W^- b\bar b$ (+ c.c.) and the irreducible background given by $bg\to t W^- b\bar b$ topologies could spoil current search approaches where the former and latter channels are treated separately. The rationale for this comes from the fact that a heavy charged Higgs state can have a large width, and so can happen for the CP-odd neutral Higgs state emerging in the ensuing decays well, which in turn enables such interferences. We conclude that effects are very significant, both at the inclusive and exclusive level (i.e., both before and after $H^\pm$ selection cuts are enforced, respectively) and typically of a destructive nature. This therefore implies that currently established LHC reaches for heavy charged Higgs bosons require some level of rescaling. However, this is possible a posteriori, as the aforementioned $H^\pm$ selection cuts shape the interference contributions at the differential level in a way similar to that of the isolated $H^\pm$ signal, so there is no need to reassess the efficiency of the individual cuts. We show such effects quantitatively by borrowing benchmarks points from different Yukawa types of a 2-Higgs Doublet Model parameter space for $H^\pm$ values starting from around 200 GeV.