vector boson fusion

vector boson fusion
Interaction	Electroweak interaction
Status	Experimentally observed
Theorized	1970s
Discovered	2010s
Experiment	ATLAS, CMS
Facility	Large Hadron Collider

vector boson fusion. It is a fundamental scattering process in high-energy particle physics where two vector bosons, typically W and Z bosons, radiated from initial quarks within colliding hadrons, fuse to produce a new particle. This mechanism is a crucial production mode for the Higgs boson and is extensively studied at facilities like the Large Hadron Collider at CERN. The process provides a unique experimental signature characterized by two forward jets with large separation in pseudorapidity.

Overview

This process is a type of electroweak scattering that becomes significant at the multi-TeV energy scales probed by modern colliders like the Large Hadron Collider. It is distinguished from other production mechanisms, such as gluon fusion, by its clear experimental signatures involving the remnant jets of the initial partons. The study of this channel is vital for testing the Standard Model and probing for physics beyond the Standard Model, as its rate and kinematics are sensitive to anomalous couplings. Research into this area is a primary focus of the ATLAS experiment and CMS experiment collaborations.

Theoretical basis

The theoretical framework originates from the Electroweak theory developed by Sheldon Glashow, Abdus Salam, and Steven Weinberg. In the process, two incoming quarks, often within protons at the Large Hadron Collider, radiate W or Z bosons which then interact via the Yukawa coupling or other gauge couplings. Key calculations for the cross-section were advanced through the work of theorists like Gordon Kane and contributions to the Les Houches Accords. The process is inherently sensitive to the structure of the Electroweak symmetry breaking sector and is calculated using tools like the Monte Carlo method for event generation.

Experimental signatures

The primary signature consists of two high-energy forward jets with a large gap in pseudorapidity and low hadronic activity in the central detector region, a pattern often called a "rapidity gap". The decay products of the central massive particle, such as Higgs decays to photon pairs or tau pairs, are measured with high precision by the ATLAS experiment and CMS experiment calorimeters and trackers. Additional discriminating variables include the dijet invariant mass and the transverse momentum of the central system, which are used to suppress backgrounds from QCD multijet production and top quark events.

Discovery and evidence

Definitive evidence for this production mode for the Higgs boson was established by the ATLAS experiment and CMS experiment collaborations in the mid-2010s following the initial Higgs discovery announcement in 2012. Analyses of data from Run 1 of the Large Hadron Collider and subsequent Run 2 of the Large Hadron Collider provided statistically significant measurements of the production cross-section, consistent with Standard Model predictions. The combined results were formally presented at major conferences like the International Conference on High Energy Physics and published in journals such as Physical Review Letters.

Role in Higgs boson studies

This channel is indispensable for directly measuring the Higgs boson couplings to W and Z bosons, providing a clean probe of the Electroweak symmetry breaking mechanism without interference from QCD effects dominant in gluon fusion. It enables precise studies of the CP properties of the Higgs boson and searches for physics beyond the Standard Model through deviations in measured rates or kinematic distributions. The HL-LHC upgrade is specifically designed to enhance the precision of these measurements.

Future prospects

Increased statistical precision is expected from the high-luminosity phase of the Large Hadron Collider (HL-LHC), and future colliders like the Future Circular Collider or the International Linear Collider will provide even cleaner experimental environments. These facilities will allow for detailed measurements of the triple gauge coupling and searches for new resonances produced via this mechanism, such as predicted by models like the Two-Higgs-Doublet Model. The continued study of this process remains a cornerstone of the experimental programs at CERN and other global high-energy physics laboratories.

Category:Particle physics Category:Scattering Category:Electroweak theory Category:Higgs boson