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| HFAG | |
|---|---|
| Name | HFAG |
| Type | Scientific collaboration |
| Focus | Heavy flavour physics averages |
| Founded | circa 2002 |
| Headquarters | International |
HFAG HFAG is a collaborative particle physics forum that produced global averages of measurements in heavy-flavor physics, synthesizing results from multiple experiments to produce consensus values for parameters relevant to B meson, D meson, and tau lepton phenomenology. The group brought together experimental collaborations and theoretical communities to combine inputs from facilities such as KEK, CERN, SLAC National Accelerator Laboratory, and Fermilab to inform analyses related to the Cabibbo–Kobayashi–Maskawa matrix, CP violation, and rare-decay searches.
HFAG provided standardized averages, uncertainties, and correlations for quantities including branching fractions, lifetimes, oscillation frequencies, and mixing parameters for heavy-flavor hadrons and leptons. Its outputs were widely used by collaborations associated with experiments like Belle, BaBar, LHCb, CDF, D0, and CLEO and were cited in reviews such as those produced by the Particle Data Group and in theory articles addressing the Standard Model and beyond-Standard-Model scenarios including Supersymmetry, Leptoquark, and Z' boson hypotheses.
HFAG originated in the early 2000s as an ad hoc effort to coordinate averaging across disparate results emerging after major runs at KEKB, PEP-II, and the Tevatron. Founding participants included representatives from experimental collaborations such as Belle, BaBar, and CLEO together with theorists from institutions like CERN Theory Department, Massachusetts Institute of Technology, and INFN. Organizationally it formed topical working groups covering sectors aligned with experiments at SLAC, TRIUMF, DESY, and Brookhaven National Laboratory and adopted transparent procedures mirroring practices of the International Committee for Future Accelerators and standards promoted by the Institute of Physics.
HFAG developed averaging procedures that combined statistical and systematic uncertainties and handled correlations among measurements from Belle, BaBar, LHCb, CDF, and D0. Methods included weighted least squares fits, BLUE (Best Linear Unbiased Estimate) techniques akin to those used in LEP electroweak averages, and chi-squared minimization procedures comparable to fits performed by the CKMfitter Group and UTfit Collaboration. Treatment of systematic correlations required liaison with collaborations such as Belle II and ATLAS when comparing detector-specific effects. The group used covariance matrices, profile-likelihood inputs, and sometimes Bayesian methods paralleling approaches by Jeffreys and Gibbs in likelihood interpretation.
HFAG published global averages for parameters including the B0 mixing frequency, semileptonic branching fractions, tau lepton branching ratios, and D0–D0bar mixing parameters; these inputs influenced global fits of the CKM matrix and constraints on CP violation used by the Flavor Lattice Averaging Group and by phenomenologists studying rare B decays and flavor-changing neutral currents. HFAG averages were regularly cited in high-profile summaries such as Review of Particle Physics entries and in analyses testing Minimal Flavour Violation, Two-Higgs-Doublet Model, and Composite Higgs scenarios.
HFAG coordinated multiple topical subgroups that interfaced with collaborations including Belle, BaBar, CLEO, LHCb, CDF, D0, and later Belle II and ATLAS flavor analyses. Working groups often paralleled analyses carried out by the UTfit Collaboration and CKMfitter Group and consulted lattice groups like HPQCD and FNAL/MILC. Liaison with accelerator laboratories such as KEK, CERN, and Fermilab ensured timely incorporation of new datasets from runs like Run 1 (LHC), Run 2 (LHC), and the Tevatron Run II.
Primary inputs were peer-reviewed results and preliminary measurements from experiments at KEK, SLAC National Accelerator Laboratory, CERN, Fermilab, and DESY. HFAG incorporated published branching fractions from journals featuring work by collaborations such as BaBar and Belle, lifetime and mixing measurements from CDF and D0, and precision results from LHCb. The group also used theoretical inputs from lattice collaborations including HPQCD, ETM Collaboration, RBC/UKQCD, and perturbative calculations by authors affiliated with CERN Theory and MIT for radiative corrections and form-factor normalizations.
Critiques of HFAG centered on the handling of preliminary results, the treatment of correlated systematics across experiments, and the potential for averaging to obscure experiment-specific effects observed by collaborations like BaBar or Belle. Some commentators compared HFAG practices to alternative frameworks such as those used by CKMfitter Group and UTfit Collaboration and argued for more conservative error inflation in cases of tension among inputs. Debates occasionally referenced disputes in high-profile measurements involving B→K*μ+μ− angular observables and R(D) and R(D*) anomaly interpretations, where averaging choices influenced claims about new physics such as Lepton universality violation effects invoked by proponents of Z' boson or Leptoquark models.
HFAG’s conventions and public-average products influenced successor efforts and sustained community practices in flavor averaging, feeding into resources maintained by the Particle Data Group and guiding the formation of taskforces for Belle II and LHCb Upgrade eras. Legacy initiatives adopted HFAG-style covariance reporting, and successor collaborations including coordinated groups within LHCb and cross-experiment consortia at CERN and KEK carried forward averaging, validation, and data-preservation principles first popularized by HFAG.
Category:Particle physics organizations