gluon fusion

gluon fusion
Name	Gluon fusion
Caption	Leading-order Feynman diagram for Higgs boson production via gluon fusion.
Interaction	Strong interaction
Theorized	Early 1970s
Discovered	Observations consistent with process at the Tevatron and LHC

gluon fusion is a fundamental quantum chromodynamics process central to modern high-energy physics. It is the dominant production mechanism for the Higgs boson at hadron colliders like the LHC, proceeding through a quark loop involving primarily the top quark. The study of this process provides critical tests of the Standard Model and probes for physics beyond the Standard Model.

Overview

This process is a key scattering event at particle accelerators such as the LHC and the former Tevatron. It is instrumental in the discovery and ongoing study of the Higgs boson by the ATLAS experiment and CMS experiment collaborations. The theoretical framework for understanding its dynamics is provided by perturbative QCD, requiring sophisticated calculations that incorporate higher-order corrections.

Theoretical background

The mechanism was first studied in detail in the context of quantum chromodynamics following the development of the Standard Model. The foundational work involved calculations of parton distribution functions and the application of the Altarelli-Parisi equations. Key theoretical insights came from researchers like John Ellis, Mary K. Gaillard, and Dimitri Nanopoulos, who explored its implications for Higgs production. The process proceeds via a fermion loop, predominantly involving heavy quarks like the top quark and bottom quark, which couple to the gluon fields described by the QCD Lagrangian.

Experimental evidence

Indirect evidence accumulated through studies of jet production and transverse momentum spectra at the Tevatron at Fermilab. Conclusive confirmation came with the discovery of the Higgs boson in 2012 by the ATLAS experiment and CMS experiment at the LHC, with its production cross-section consistent with predictions. Further validation has been provided by precise measurements of Higgs properties, such as its couplings to top quarks and bottom quarks, conducted at CERN.

Role in Higgs boson production

It constitutes approximately 90% of the total Higgs boson production cross-section at the LHC at a center-of-mass energy of 13 TeV. This dominance makes it the primary channel for measuring Higgs properties, including its spin, CP properties, and interactions with Standard Model particles. Competing production modes include vector boson fusion, associated production with a vector boson or top quark, and Higgs strahlung.

Cross section and higher-order corrections

Calculating the production cross section requires complex higher-order corrections in quantum chromodynamics, including next-to-leading order and next-to-next-to-leading order contributions. These calculations involve intricate treatments of soft gluon emission and rely on advanced computational tools like SCET and collaborations such as the LHC Higgs Cross Section Working Group. Significant theoretical efforts have been led by groups at institutions like CERN, DESY, and the University of Zurich.

Related processes

Closely connected mechanisms include vector boson fusion, which involves the weak interaction and provides crucial complementary information on Higgs couplings. Other associated production processes, such as Higgs strahlung with a Z boson or top quark, are also studied at the LHC. Research into potential physics beyond the Standard Model often investigates modifications to this process through new particles like superpartners or through anomalous couplings studied at future colliders like the Future Circular Collider.

Category:Quantum chromodynamics Category:Higgs boson Category:Particle physics