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Searching for H --> tau tau in weak boson fusion at the LHC

D. Rainwater, D. Zeppenfeld, K. Hagiwara

TL;DR

This paper shows that the SM Higgs with mass in the intermediate range ($m_H$ ≈ 110–150 GeV) can be observed in the H → ττ decay channel via weak-boson fusion at the LHC, using two forward tagging jets and a central minijet veto to suppress backgrounds. A comprehensive parton-level Monte Carlo study, including both irreducible backgrounds (Z/γ → ττ and EW Zjj) and reducible backgrounds (Wj+jj and bb¯jj) along with detector effects and tau identification, demonstrates that a signal with a favorable S/B can emerge with around $L ightarrow 30$ fb$^{-1}$, allowing a direct measurement of the $Hττ$ coupling. The analysis emphasizes the role of minijet radiation patterns and a TSA-based central-jet veto to suppress QCD backgrounds, and shows that τ-pair mass reconstruction in the collinear limit, together with optimized kinematic cuts (e.g., $m_{jj} > 1$ TeV, $m_T(ℓ/ ot{p}_T) < 30$ GeV), yields a clean Higgs signal in a 20 GeV mass bin around $m_H$. The work also highlights practical calibration uses from the $Z o ττ$ peak and discusses potential improvements via multivariate techniques, while noting that full detector simulations would be needed for a final experimental assessment.

Abstract

Weak boson fusion is a copious source of intermediate mass Higgs bosons at the LHC. The additional very energetic forward jets in these events provide for powerful background suppression tools. We analyze the $H \to ττ$ decay mode for the Standard Model Higgs boson. A parton level analysis of the dominant physics backgrounds (mainly $Z \to ττ$ and Drell-Yan production of $τ$'s) and of reducible backgrounds (from $W+$ jet and $b\bar{b}$ production in association with two jets and subsequent leptonic decays) demonstrates that this channel allows the observation of $H \to ττ$ in a low background environment, yielding a significant Higgs signal with an integrated luminosity of about 30 fb$^{-1}$. The weak boson fusion process thus allows direct measurement of the $Hττ$ coupling.

Searching for H --> tau tau in weak boson fusion at the LHC

TL;DR

This paper shows that the SM Higgs with mass in the intermediate range ( ≈ 110–150 GeV) can be observed in the H → ττ decay channel via weak-boson fusion at the LHC, using two forward tagging jets and a central minijet veto to suppress backgrounds. A comprehensive parton-level Monte Carlo study, including both irreducible backgrounds (Z/γ → ττ and EW Zjj) and reducible backgrounds (Wj+jj and bb¯jj) along with detector effects and tau identification, demonstrates that a signal with a favorable S/B can emerge with around fb, allowing a direct measurement of the coupling. The analysis emphasizes the role of minijet radiation patterns and a TSA-based central-jet veto to suppress QCD backgrounds, and shows that τ-pair mass reconstruction in the collinear limit, together with optimized kinematic cuts (e.g., TeV, GeV), yields a clean Higgs signal in a 20 GeV mass bin around . The work also highlights practical calibration uses from the peak and discusses potential improvements via multivariate techniques, while noting that full detector simulations would be needed for a final experimental assessment.

Abstract

Weak boson fusion is a copious source of intermediate mass Higgs bosons at the LHC. The additional very energetic forward jets in these events provide for powerful background suppression tools. We analyze the decay mode for the Standard Model Higgs boson. A parton level analysis of the dominant physics backgrounds (mainly and Drell-Yan production of 's) and of reducible backgrounds (from jet and production in association with two jets and subsequent leptonic decays) demonstrates that this channel allows the observation of in a low background environment, yielding a significant Higgs signal with an integrated luminosity of about 30 fb. The weak boson fusion process thus allows direct measurement of the coupling.

Paper Structure

This paper contains 12 sections, 28 equations, 6 figures, 4 tables.

Table of Contents

  1. Introduction
  2. Calculational Tools
  3. The $qq\to qqH(g)$ signal process
  4. The QCD $\tau^{+}\tau^{-}+jj(j)$ physics background
  5. The EW $\tau^{+}\tau^{-}+jj(j)$ physics background
  6. The QCD $Wj+jj(j)$ reducible background
  7. The QCD $b\bar{b}jj$ reducible background
  8. Detector resolution
  9. Higgs signal and real $\tau^{+}\tau^{-}$ backgrounds
  10. Fake $\tau^{+}\tau^{-}$ events: reducible backgrounds
  11. Radiation patterns of minijets
  12. Discussion

Figures (6)

  • Figure 1: Invariant mass distribution of the two tagging jets for the $Hjj$ signal (solid line) and the QCD $Zjj$ background (dashed line), at the level of forward tagging cuts and $\tau$ reconstruction, Eqs. (\ref{['eq:basic']}-\ref{['eq:taumass2']},\ref{['eq:mTlnu']}).
  • Figure 2: Transverse mass distribution of the $\ell$-$/\!\!\!p_T$ system for the $Hjj$ signal (solid line) and the $Wj+jj$ reducible background (dashed line), at the level of far forward tagging cuts, $\tau$-reconstruction, and $m_{jj} > 1$ TeV (Eqs. \ref{['eq:basic']}-\ref{['eq:mjj']}).
  • Figure 3: Scatter plots of $x_{\tau_l}$ vs. $x_{\tau_h}$ with the cuts of Eqs.(\ref{['eq:basic']}-\ref{['eq:gap']},\ref{['eq:tauID']}, \ref{['eq:taumass2']}-\ref{['eq:mTlnu']}), for: (a) the 120 GeV $Hjj$ signal; (b) the combined QCD and EW $Zjj$ irreducible backgrounds; (c) the $Wj+jj$ and (d) the $b\bar{b}jj$ reducible backgrounds. The number of points in each plot is arbitrary and corresponds to significantly higher integrated luminosities than expected for the LHC. The solid lines indicate the cuts of Eq. (\ref{['eq:x1x2']}).
  • Figure 4: Reconstructed $\tau$ pair invariant mass distribution for the signal and backgrounds after the cuts of Eqs. (\ref{['eq:basic']}-\ref{['eq:x1x2']}) and multiplication of the Monte Carlo results by the expected survival probabilities. The solid line represents the sum of the signal and all backgrounds. Individual components are shown as histograms: the $Hjj$ signal (solid), the irreducible QCD $Zjj$ background (dashed), the irreducible EW $Zjj$ background (dotted), and the combined $Wj+jj$ and $b\bar{b}jj$ reducible backgrounds (dash-dotted).
  • Figure 5: (a) Transverse momentum and (b) pseudorapidity distributions of the charged "$\tau$" decay lepton after the cuts of Eqs. (\ref{['eq:basic']}-\ref{['eq:x1x2']}), for the $m_H = 120$ GeV signal (solid line), and backgrounds: QCD $Zjj$ production (dashed line), EW $Zjj$ events (dotted line), $Wj+jj$ events (dot-dashed line), and $b\bar{b}jj$ production (dash-double dotted line).
  • ...and 1 more figures