Study of perturbative QCD predictions at next-to-leading order and beyond for \pp -> H -> gamma gamma + X

TL;DR

This study assesses perturbative QCD predictions for $pp\rightarrow H\rightarrow \gamma\gamma+X$ at the LHC by comparing NNLO/NLO fully differential results (FEHIP) with MC@NLO plus a parton shower. It analyzes inclusive and accepted cross sections under varying Higgs mass, scales, and PDFs, and investigates differential observables such as $p_T^{m}$ and $Y^{*}$ to gauge signal discrimination against the irreducible diphoton background. The main finding is that acceptance corrections are stable across perturbative order and PDF choices, while absolute cross sections show notable order-dependent differences largely due to top-mass treatment, informing the reliability of higher-order predictions for Higgs-to-diphoton searches. The work provides benchmark predictions for phenomenology and helps guide future detector-level studies and more precise background modeling.

Abstract

We study predictions from perturbative Quantum Chromodynamics (QCD) for the process pp -> H -> gamma gamma + X. In particular, we compare fully differential calculations at next-to-leading (NLO) and next-to-next-to-leading order (NNLO) in the strong coupling constant to the results obtained with the MC@NLO Monte Carlo (MC) generator, which combines QCD matrix elements at NLO with a parton shower algorithm. Estimates for the systematic uncertainties in the various predictions due to the choice of the renormalization scale and the parton distribution functions are given for the inclusive and accepted cross sections and for the corresponding acceptance corrections, obtained after applying standard selection and acceptance cuts. Furthermore, we compare the distributions for the Higgs signal to those for the irreducible two-photon background, obtained with a NLO MC simulation.

Figures (7)

• Figure 1: Inclusive and accepted cross sections as a function of the Higgs mass, $m_\mathrm{H}$, obtained with MC@NLO and FEHIP (at NLO and NNLO).
• Figure 2: Inclusive and accepted cross sections at NNLO as a function of the Higgs mass, $m_\mathrm{H}$, for two different scale choices.
• Figure 3: The accepted cross section $\sigma_{\mathrm{acc}}$ predicted by MC@NLO and FEHIP (NLO and NNLO) as a function of the renormalization and factorization scale, $\mu$, for a Higgs mass of $m_\mathrm{H}=120 \;\mathrm{GeV}/c^2$.
• Figure 4: The distributions of the kinematic variables $p_{\mathrm{T}}^{\mathrm{m}}$ (left) and $Y^*$ (right), obtained with MC@NLO for the two pdf sets MRST01 NLO and CTEQ6M NLO. The standard cuts as indicated in the plots have been applied.
• Figure 5: The distributions of the kinematic variables $p_{\mathrm{T}}^{\mathrm{m}}$ (left) and $Y^*$ (right), obtained with MC@NLO for the two pdf sets MRST01 NLO and MRST01 NNLO. The standard cuts as indicated in the plots have been applied.