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Impact of QED corrections to Higgs decay into four leptons at the LHC

C. M. Carloni Calame, M. Moretti, G. Montagna, O. Nicrosini, F. Piccinini, A. D. Polosa

TL;DR

This paper evaluates how QED radiative corrections affect the Higgs mass determination in $gg \to H \to 4l$ at the LHC. It implements exact ${\cal O}(\alpha)$ and higher-order QED corrections to Higgs decay using both a parton-shower leading-log approach and a full perturbative calculation, and treats infrared cancellations via a complex-mass scheme within the narrow-width approximation. Production and decay are coupled in a Monte Carlo framework (ALPGEN+H24F) with realistic lepton/photon cuts to mimic experimental conditions. The results show non-negligible Higgs mass shifts—up to several hundred MeV depending on the final state—emphasizing the need to include QED radiation effects for precision Higgs mass measurements at the LHC, with agreement between exact and leading-log approaches at the current accuracy level.

Abstract

At the LHC a precise measurement of the Higgs boson mass (if discovered), at the level of 0.1-1%, will be possible through the channel g g --> H --> 4l for a wide range of Higgs mass values. To match such an accuracy, the systematic effects induced by QED corrections need to be investigated. In the present study the calculation of O(alpha) and higher order QED corrections is illustrated as well as their impact on the Higgs mass determination, once realistic event selection criteria for charged leptons and photons are considered.

Impact of QED corrections to Higgs decay into four leptons at the LHC

TL;DR

This paper evaluates how QED radiative corrections affect the Higgs mass determination in at the LHC. It implements exact and higher-order QED corrections to Higgs decay using both a parton-shower leading-log approach and a full perturbative calculation, and treats infrared cancellations via a complex-mass scheme within the narrow-width approximation. Production and decay are coupled in a Monte Carlo framework (ALPGEN+H24F) with realistic lepton/photon cuts to mimic experimental conditions. The results show non-negligible Higgs mass shifts—up to several hundred MeV depending on the final state—emphasizing the need to include QED radiation effects for precision Higgs mass measurements at the LHC, with agreement between exact and leading-log approaches at the current accuracy level.

Abstract

At the LHC a precise measurement of the Higgs boson mass (if discovered), at the level of 0.1-1%, will be possible through the channel g g --> H --> 4l for a wide range of Higgs mass values. To match such an accuracy, the systematic effects induced by QED corrections need to be investigated. In the present study the calculation of O(alpha) and higher order QED corrections is illustrated as well as their impact on the Higgs mass determination, once realistic event selection criteria for charged leptons and photons are considered.

Paper Structure

This paper contains 3 sections, 4 equations, 5 figures, 1 table.

Table of Contents

  1. Introduction
  2. The calculation
  3. Numerical results

Figures (5)

  • Figure 1: Born diagrams for the decay $H\to 4e$.
  • Figure 2: The real-radiation diagrams are obtained attaching a real photon leg to every final state fermion.
  • Figure 3: Vertex (upper panel) and self-energy (lower panel) diagrams contribute to the factorizable corrections.
  • Figure 4: Example of pentagon diagram, which contributes to the non-factorizable corrections.
  • Figure 5: Higgs invariant mass in the laboratory frame for the decay $H \to e^+ e^- \mu^+ \mu^-$, after applying experimental cuts and momentum smearing, as obtained at tree level, with Parton Shower and with exact ${\cal O}(\alpha)$ corrections.