Theoretical Status of Higgs Production at Hadron Colliders in the Standard Model

The search for the Higgs boson, the last missing particle in the Standard Model (SM) responsible for the electroweak symmetry breaking, is a primary goal of the CERN Large Hadron Collider (LHC), and is a central part of Fermilab’s Tevatron program. In the Standard Model, mass generation is triggered by the Higgs mechanism, which predicts the existence of one scalar particle, the Higgs boson [1]. The coupling of the Higgs to fermions and gauge bosons is predicted by the model. The only unknown parameter is the Higgs boson mass. Direct searches at LEP restrict the Higgs boson mass to be greater than 114.4 GeV (at 95% CL) [2], while precision measurements point to a rather light Higgs, MH ≤ 157 GeV (95% CL) which increases to 186 GeV when including the LEPII direct search limit of 114 GeV (see [3] for regular updates). Recently, the Tevatron collaborations, CDF and D0, reported a 95% CL exclusion of a Standard Model Higgs boson mass in the range 160 < MH < 170 GeV [4]. The Standard Model Higgs coupling is strongest to the heaviest particles. Therefore, we distinguish three types of decays: into fermions, into massive gauge bosons and loop-induced decays through a massive loop of quarks or gauge bosons. Since the LHC will be able to find the Higgs, if it exists, and can provide a measurement of its couplings at the 10 − 30% level [5, 6], precise theoretical predictions of these decays are needed. Understanding the theoretical prediction is crucial to both the search for and exclusion of the Standard Model Higgs boson. Backgrounds to the Higgs signal are severe in many channels, particularly when a mass peak cannot be reconstructed such as in H → WW → lνlν, and knowledge of the signal shape and normalization is needed to optimize experimental searches. Signal and background cross sections must be, therefore, predicted as accurately as can be achieved. Higgs production at both hadron colliders, Tevatron and LHC, is dominated by gluon fusion, where two incoming gluons produce a Higgs boson via a virtual top quark loop. This is followed by vector boson fusion (VBF), where the incoming protons radiate a W or a Z boson, which subsequently interact weakly and fuse into a Higgs boson. The Higgs can also be produced in association with a pair of top quarks or through Higgs strahlung (associated WH or ZH production).