[Paper Review] Two-photon width of the Higgs boson

K. Moenig, A. Rosca|arXiv (Cornell University)|Jun 27, 2005

Particle physics theoretical and experimental studies1 references3 citations

TL;DR

This paper investigates the precision measurement of the Higgs boson's two-photon partial width times branching ratio into b-quarks at a future photon collider. Using 80 fb⁻¹ of integrated luminosity and advanced event reconstruction with b-tagging, the study achieves a 1.7% statistical uncertainty in measuring Γ(h→γγ) × BR(h→b̄b), demonstrating the feasibility of high-precision Higgs couplings extraction beyond the Standard Model.

ABSTRACT

This study investigates the potential of a photon collider for measuring the two photon partial width times the branching ratio of a light Higgs boson. The analysis is based on the reconstruction of the Higgs events produced in the gamma gamma -> h process, followed by Higgs decay into a b bbar pair. A statistical error of the measurement of the two-photon width times the b bbar branching ratio of the Higgs boson is found to be 1.7% with an integrated luminosity of 80 fb^-1 in the high energy part of the spectrum.

Motivation & Objective

• To assess the feasibility of measuring the Higgs boson's two-photon partial width times branching ratio using a photon collider.
• To evaluate the sensitivity of the measurement to physics beyond the Standard Model through deviations in the γγ coupling.
• To optimize event selection and background suppression techniques for Higgs boson signal reconstruction in γγ→h→b̄b processes.
• To quantify the statistical precision achievable with realistic detector simulation and background modeling.
• To validate the use of SHERPA and PYTHIA for background estimation with proper NLO corrections.

Proposed method

• Simulates high-energy photon beams via Compton backscattering of laser photons off electron beams, producing polarized γγ beams.
• Uses the CompAZ parameterization for photon energy spectra and SIMDET for detector response simulation, including energy-flow-object reconstruction.
• Applies the DURHAM jet clustering algorithm with y_cut = 0.02 to reconstruct jets from Higgs decays into b̄b pairs.
• Employs a neural network b-tagging algorithm combining impact parameter, vertex mass, and charm tagging to distinguish b-jets with 70% efficiency and 98% purity.
• Implements a multi-stage event selection: minimum visible energy >95 GeV, longitudinal momentum imbalance <10%, thrust angle cosθ < 0.7, and invariant mass window 114–126 GeV.
• Corrects SHERPA-generated background cross sections using NLO QCD calculations for γγ→q̄qg processes to avoid double-counting and ensure accuracy.

Experimental results

Research questions

• RQ1 Can the two-photon partial width of the Higgs boson be measured with sub-2% statistical precision at a photon collider?
• RQ2 How effective are b-tagging and event selection criteria in suppressing QCD continuum backgrounds in γγ→h→b̄b events?
• RQ3 To what extent do higher-order QCD corrections, particularly from gluon radiation, affect the background estimation?
• RQ4 Can the SHERPA generator accurately model γγ→q̄qg processes when combined with NLO cross sections?
• RQ5 What is the achievable statistical significance of the Higgs signal after optimizing the invariant mass window and selection cuts?

Key findings

• With 80 fb⁻¹ of integrated luminosity, the statistical uncertainty in measuring Γ(h→γγ) × BR(h→b̄b) is 1.7%.
• The signal efficiency after full event selection is 36%, with 4505 signal events and 1698 background events in the 114–126 GeV invariant mass window.
• The b-tagging neural network achieves 70% efficiency and 98% purity in identifying b-quark jets from Higgs decays.
• Background from γγ→b̄bg and γγ→c̄cg processes is significantly reduced by selecting events with equal photon helicities and applying stringent jet and mass cuts.
• The comparison between SHERPA and NLO cross sections shows good agreement, validating the use of SHERPA with NLO scaling for background estimation.
• The study confirms that the TESLA photon collider can achieve high-precision measurements of Higgs couplings, enabling sensitive tests of new physics beyond the Standard Model.