Higgs Boson Production at Hadron Colliders with Soft Gluon Effects: I. Backgrounds

TL;DR

This work extends the Collins-Soper-Sterman soft-gluon resummation formalism to the production of Z^0Z^0 and diphoton backgrounds relevant to Higgs searches at hadron colliders. By resumming initial-state soft-gluon emissions and matching to fixed-order results, the authors obtain stable predictions for low transverse momenta and quantify the impact on key distributions and integrated rates at the LHC and upgraded Tevatron. The study finds that qq̄ and qg initiated backgrounds are consistent with NLO predictions while gg-induced diphoton production remains a substantial contributor, especially at low QT, underscoring the need for resummed calculations in background modeling. Overall, the results support using resummed predictions to accurately extract Higgs signals in H → γγ and H → ZZ decays by providing reliable background shapes and normalization across the full kinematic range.

Abstract

The gold-plated discovery mode of a Standard Model like Higgs boson at the CERN Large Hadron Collider (LHC) is the H -> Z^0 Z^0 decay mode. To find and then measure the properties of the Higgs, it is crucial to have the most precise theoretical prediction both for the signal and the QCD background in this mode. In this work we calculate the effects of the initial-state multiple soft-gluon emission on the kinematic distributions of photon and Z^0 pairs produced in hadron collisions. The Collins-Soper-Sterman formalism is extended to resum the large logarithmic terms due to soft-gluons. The resummed total rates, the invariant mass, transverse momentum, and rapidity distributions of the photon and Z^0 pairs, and the transverse momentum distributions of the individual vector bosons are presented and compared to the fixed order predictions in the whole kinematic range, for the LHC energies and for the upgraded Fermilab Tevatron. Our conclusion is that the resummed predictions should be used when extracting the Higgs signal at the LHC.

Figures (15)

• Figure 1: A representative set of Feynman diagrams included in the NLO calculation of $Z^0$ pair production.
• Figure 2: Transverse momentum distribution of $Z^0$ pairs from $q {\bar{q}} + q g$ partonic initial states at the LHC. The ${\cal O}(\alpha_s)$ (dotted) and the asymptotic (dash-dotted) pieces are coincide and diverge as $Q_T \to 0$. The resummed (solid) curve matches the ${\cal O}(\alpha_s)$ curve at about $Q_T = 320$ GeV. The resummed $q {\bar{q}}$ contribution (excluding the $qg$ contribution) is shown as dashed line.
• Figure 3: The integrated cross section for $Z^0$ boson pair production at the LHC. The resummed and the ${\cal O}(\alpha_s)$ distributions are shown in solid and dashed lines, respectively.
• Figure 4: Invariant mass and rapidity distributions of $Z^0$ boson pairs, and transverse momentum distributions of the individual $Z^0$ bosons at the LHC. The resummed contribution of the $q {\bar{q}} + q g \to Z^0 Z^0 X$ subprocess is shown by the solid curve, and of the $q \bar{q} \to Z^0 Z^0 X$ subprocess by the dashed curve. The leading order distribution of $q \bar{q} \to Z^0 Z^0$ is shown by the dash-dotted curve.
• Figure 5: Resummed and NLO transverse momentum distributions of $Z^0$ boson pairs at the LHC. The two resummed curves are calculated for $C_1 = b_0$ and $C_2 = 1$ (upper solid), and for $C_1= b_0/2$ and $C_2 = 1/2$ (lower solid), respectively. The NLO curves are the same as in Fig. \ref{['fig:ZZLHCQT']}.