Higgs boson pair production

Higgs boson pair production
Name	Higgs boson pair production
Participants	Higgs boson, Higgs boson
Theory	Standard Model, Beyond Standard Model
Experiment	Large Hadron Collider, ATLAS, CMS

Higgs boson pair production is the process by which two Higgs bosons are produced simultaneously in high-energy particle collisions. Predicted within the Standard Model and subject to enhancements in many Beyond Standard Model scenarios, the process probes the structure of the Higgs field and the self-interaction of the Higgs mechanism at colliders such as the Large Hadron Collider and proposed machines like the Future Circular Collider.

Overview

Higgs boson pair production arises primarily via gluon-gluon fusion mediated by heavy virtual particles such as the top quark in the LHC environment, with subleading contributions from vector-boson fusion studied in experiments by ATLAS and CMS. The small Standard Model rate and complex final states have motivated searches at the CERN accelerators and inspired theoretical work by groups at institutions including Fermilab, DESY, SLAC, and universities involved in collaborations such as the CMS Collaboration and the ATLAS Collaboration. Measurements are challenged by large backgrounds from processes like top quark pair production and multi-boson production observed in datasets collected during Run 2 and Run 3.

Theoretical predictions and mechanisms

The dominant production mechanism is loop-induced gluon-gluon fusion via top-quark loops, computed using perturbative Quantum Chromodynamics techniques developed by teams associated with Niels Bohr Institute, CERN Theory Group, and theoretical collaborations that include authors from Princeton University, Massachusetts Institute of Technology, University of Oxford, and University of Cambridge. Two interfering amplitudes—the "triangle" diagram involving the trilinear Higgs self-coupling (linked to the Higgs potential) and the "box" diagram involving top-quark loops—determine the cross section predicted by the Standard Model. Precision predictions incorporate higher-order corrections from next-to-leading order and next-to-next-to-leading order QCD, electroweak corrections studied by groups at Max Planck, INFN, and resummation techniques used by researchers at University of California, Berkeley and Yale University. Beyond the Standard Model effects—such as modified self-couplings in two-Higgs-doublet models, resonant production in supersymmetric extensions, or contributions from Composite Higgs models and extra dimensions—are computed in frameworks developed at Kavli Institute for Theoretical Physics and tested against global fits by collaborations including Particle Data Group.

Experimental searches and measurements

Search strategies at ATLAS and CMS target final states like bb̄γγ, bb̄τ+τ−, bb̄bb̄, and bb̄WW* leveraging detector subsystems designed by institutions such as Brookhaven and Lawrence Berkeley National Laboratory. Analyses use data from Run 1, Run 2, and Run 3 with combined results presented at conferences such as the ICHEP and EPS-HEP. Statistical interpretations employ tools developed in collaborations including CERN Open Data Portal and software from ROOT and RooFit, with combined ATLAS–CMS limits on the production cross section reported by working groups including members from IHEP (China), KEK, and TRIUMF. Dedicated searches for resonant di-Higgs production have been performed in contexts of models proposed at Caltech and Stanford University.

Backgrounds and analysis techniques

Major backgrounds include top quark pair production, single-top processes, and multijet events misidentified as heavy-flavor or photon signatures; these backgrounds are modeled using Monte Carlo generators maintained by collaborations at CERN, Fermilab, and SLAC. Advanced analysis techniques such as boosted-object tagging developed at Imperial College London, multivariate classifiers (including boosted decision trees and neural networks) pioneered by groups at University of Tokyo and Carnegie Mellon University and matrix-element methods from University of Chicago are crucial to improve signal sensitivity. Jet substructure algorithms and b-tagging calibrations are validated using control samples from Z boson and W boson measurements by detector teams at ATLAS and CMS. Systematic uncertainties are constrained through simultaneous fits and cross-calibrations with measurements from LHCb and heavy-flavor experiments at Belle II.

Implications for Higgs self-coupling and new physics

Higgs boson pair production directly probes the trilinear self-coupling parameter in the Higgs potential, a cornerstone of electroweak symmetry breaking first formulated in works by Peter Higgs, François Englert, and collaborators at institutions such as Imperial College London and University of Edinburgh. Deviations from the Standard Model rate could signal new dynamics from Supersymmetry, Composite Higgs models, or heavy resonances predicted in frameworks like Randall–Sundrum model and Little Higgs models. Global fits combining di-Higgs results with single-Higgs measurements by collaborations including ATLAS Collaboration and CMS Collaboration and precision electroweak data from LEP and SLAC constrain model parameter spaces explored by theorists at CERN Theory Group and Perimeter Institute.

Future prospects and collider projects

Improved sensitivity to Higgs pair production is a key goal for upgrades such as the HL-LHC and future machines including the Future Circular Collider, the International Linear Collider, and the Compact Linear Collider. Detector upgrades endorsed by consortia at CERN and funding agencies like European Commission and U.S. Department of Energy will enhance b-tagging and photon resolution, while theory improvements from collaborations at Princeton University and Stanford Linear Accelerator Center will reduce uncertainties. Proposed precision measurements at these projects are expected to either observe Standard Model di-Higgs production or reveal signatures of new physics advocated in proposals by research groups at MIT, Oxford University, and Tokyo Institute of Technology.

Category:Particle physics