Dilepton Signals in the Inert Doublet Model

TL;DR

This paper assesses the LHC prospects for observing the Inert Doublet Model via dilepton plus missing-energy signatures, focusing on benchmark regions consistent with dark-matter relic density and electroweak constraints. Using detector-level simulations and a three-tier event-selection strategy, it shows that for $m_S\in[40,80]$ GeV and neutral-scalar mass splittings $\delta_1,\delta_2$ around $40$--$80$ GeV, signals can reach $S/\sqrt{B}$ of $\sim3$--$12$ with ${\cal L}=100\ \mathrm{fb}^{-1}$, including cases with $\delta_2> M_Z$ and $m_S\approx40$ GeV. The study highlights the importance of $M_{\ell\ell}$ windows and angular/topology cuts to suppress SM backgrounds, with notable discovery potential in several benchmarks (e.g., LH2, LH1, HH2). It also emphasizes complementary collider channels and noncollider signals to corroborate the IDM and distinguish it from other beyond-Standard-Model scenarios.

Abstract

The Inert Doublet Model is one of the simplest and most versatile scenarios for physics beyond the Standard Model. In this work, we examine the prospects for detecting the additional fields of this model at the LHC in the dilepton channel. We investigate a wide variety of theoretically- and phenomenologically-motivated benchmark scenarios, and show that within regions of model parameter space in which the dark-matter candidate is relatively light (between 40 and 80 GeV) and the mass splitting between the neutral scalars is also roughly 40 - 80 GeV, a signal at the 3 sigma to 12 sigma significance level can be observed with 100 fb^-1 of integrated luminosity. In addition, even if the mass splitting between the neutral scalars is larger than M_Z, a signal of more than 3 sigma can be observed as long as the mass of the dark matter candidate is around 40 GeV.

Figures (3)

• Figure 1: Diagrams corresponding to the contributions to the $pp\rightarrow \ell^+\ell^-{\not}E_T$ in the IDM discussed in the text.
• Figure 2: Dilepton-invariant-mass distributions for the benchmark points LH1 (left panel) and LH3 (right panel) both for the signal process and for the most relevant SM backgrounds.
• Figure 3: Distributions of the angular separation variables $\Delta R_{\ell \ell}$ (left panel) and $\cos\phi_{\ell \ell}$ (right panel) for benchmark point LH3, in which decays of the pseudoscalar $A$ occur via an off-shell $Z$. These distributions justify the imposition of the minimum $\cos\phi_{\ell\ell}$ and maximum $\Delta R_{\ell\ell}$ cuts described in the text.