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Exploring Little Higgs Models with ATLAS at the LHC

G. Azuelos, K. Benslama, D. Costanzo, G. Couture J. E. Garcia, I. Hinchliffe, N. Kanaya, M. Lechowski, R. Mehdiyev, G. Polesello, E. Ros, D. Rousseau

TL;DR

The paper assesses ATLAS-level prospects for testing the Littlest Higgs model at the LHC by simulating detector responses to predictions including a vector-like $T$ quark, heavy gauge bosons ($W_H$, $Z_H$, $A_H$), and a triplet Higgs $\phi$. It analyzes distinct search channels for each new state—$T$ decays to $Wb$, $Zt$, and $ht$; dilepton and cascade decays of gauge bosons; and $\phi^{++}$ via WW fusion—quantifying discovery reach and mass ranges under plausible mixing and Higgs mass assumptions. Key findings show $T$ can be observed up to $m_T\approx 2.5$ TeV mainly through $T\to Wb$, while $Z_H$, $W_H$, and $A_H$ are discoverable across the model's parameter space, with several channels enabling coupling measurements such as $Z_H\to Zh$ and $W_H\to Wh$. The $\phi^{++}$ state remains challenging, requiring large $v'$ and favorable masses to achieve discovery within the analyzed luminosity; overall, ATLAS has robust potential to test the Littlest Higgs framework through multiple, complementary final states.

Abstract

We discuss possible searches for the new particles predicted by Little Higgs Models at the LHC. By using a simulation of the ATLAS detector, we demonstrate how the predicted quark, gauge bosons and additional Higgs bosons can be found and estimate the mass range over which their properties can be constrained.

Exploring Little Higgs Models with ATLAS at the LHC

TL;DR

The paper assesses ATLAS-level prospects for testing the Littlest Higgs model at the LHC by simulating detector responses to predictions including a vector-like quark, heavy gauge bosons (, , ), and a triplet Higgs . It analyzes distinct search channels for each new state— decays to , , and ; dilepton and cascade decays of gauge bosons; and via WW fusion—quantifying discovery reach and mass ranges under plausible mixing and Higgs mass assumptions. Key findings show can be observed up to TeV mainly through , while , , and are discoverable across the model's parameter space, with several channels enabling coupling measurements such as and . The state remains challenging, requiring large and favorable masses to achieve discovery within the analyzed luminosity; overall, ATLAS has robust potential to test the Littlest Higgs framework through multiple, complementary final states.

Abstract

We discuss possible searches for the new particles predicted by Little Higgs Models at the LHC. By using a simulation of the ATLAS detector, we demonstrate how the predicted quark, gauge bosons and additional Higgs bosons can be found and estimate the mass range over which their properties can be constrained.

Paper Structure

This paper contains 11 sections, 3 equations, 22 figures.

Table of Contents

  1. Introduction
  2. Search for $T$ and determination of its properties
  3. $T\to Zt$
  4. $T\to Wb$
  5. $T\to ht$
  6. Search for new gauge bosons
  7. Discovery of $Z_H$ and $A_H$
  8. Discovery of $W^{\pm}_H$
  9. Measurement of $Z_H\to Zh$, $A_H\to Zh$ and $W_H\to Wh$
  10. Search for $\phi^{++}$
  11. Model Constraints and Conclusions

Figures (22)

  • Figure 1: Figure showing the production rate of the $T$ quark at the LHC as a function of its mass Han:2003wu. The heavy dashed line shows the pair production and the solid and two dotted lines the single production rate for three value of $\lambda_2/\lambda_1$; from highest to lowest $\lambda_2/\lambda_1=2,1,0,5$. (We are grateful to T. Han for providing this figure.)
  • Figure 2: Reconstructed mass of the $Z$ and $t$ (inferred from the measured lepton, $\hbox{$E$} / _T$, and tagged $b-$jet). The signal $T \to Zt$ is shown for a mass of 1000 GeV. The background, shown as the filled histogram, is dominated by $WZ$ and $tbZ$ (the latter is larger) production. The signal event rates correspond to $\lambda_1/\lambda_2=1$ and a $BR(T\to ht)$ of 25%. More details can be found in Ref costanzo.
  • Figure 3: Reconstructed mass of the $W$ (inferred from the measured lepton and $\hbox{$E$} / _T$) and tagged $b-$jet. The signal arises from the decay $T \to Wb$ and is shown a for mass of 1000 GeV. The background, shown separately as the filled histogram, is dominated by $t\overline{t}$ and single top production (the former is larger). The signal event rates correspond to $\lambda_1/\lambda_2=1$ and a $BR(T\to Wb)$ of 50%. More details can be found in Ref costanzo.
  • Figure 4: Plot showing the dijet mass distribution arising from the decay $T \to ht$. All combinations of jets are shown.
  • Figure 5: Reconstructed mass of the $W$ (inferred from the isolated lepton and missing transverse energy) and three jets, two of which are required to have an invariant mass consistent with the Higgs mass. The signal arises from the decay $T \to ht$ and is shown for a mass of 1000 GeV. The background, shown in cross-hatching, is dominated by $t\overline{t}$ production. The signal event rates correspond to $\lambda_1/\lambda_2=1$ and a $BR(T\to ht)$ of 25%.
  • ...and 17 more figures