Flavour Lattice Averaging Group

Flavour Lattice Averaging Group
Name	Flavour Lattice Averaging Group
Abbreviation	FLAG
Formation	2006
Type	Research consortium
Headquarters	Europe
Fields	Particle physics, Theoretical physics, Computational physics

Contents

Flavour Lattice Averaging Group The Flavour Lattice Averaging Group provides community-wide averages of numerical results from lattice quantum chromodynamics collaborations to inform phenomenology in particle physics, electroweak studies, and flavour experiments. The group synthesizes lattice calculations from collaborations such as European Twisted Mass Collaboration, HPQCD Collaboration, RBC-UKQCD, MILC and ETM Collaboration to supply inputs used by experimental projects like Large Hadron Collider, Belle II, LHCb and theoretical programs at institutions including CERN, Fermilab, SLAC National Accelerator Laboratory and KEK.

Overview and mission

FLAG's mission is to produce reliable averages and assessments of lattice QCD quantities relevant to flavour physics for use by the Particle Data Group, CKMfitter Group, UTfit Collaboration, Heavy Flavor Averaging Group and experimental analyses from ATLAS, CMS and BaBar. The group evaluates results on decay constants, form factors, quark masses and hadronic matrix elements produced by research teams at DESY, Brookhaven National Laboratory, Lawrence Berkeley National Laboratory, INFN, Nikhef and Institute for Nuclear Theory to guide precision tests of the Standard Model, searches for Beyond the Standard Model effects, and inputs to global fits involving the Cabibbo–Kobayashi–Maskawa matrix.

FLAG originated from workshops linking lattice collaborations and phenomenologists following meetings at CERN and the Les Houches summer schools, with foundational contributions from researchers associated with University of Edinburgh, University of Cambridge, University of Glasgow, University of Regensburg and University of Rome La Sapienza. It organized into editorial boards and working groups drawing members from ETH Zurich, University of Bonn, University of Mainz, University of Valencia, University of Southampton, University of Washington and national laboratories such as Argonne National Laboratory and TRIUMF. FLAG issues periodic review reports and rating schemes in coordination with conferences like International Conference on High Energy Physics, Lattice Conference and workshops at Yukawa Institute.

FLAG develops criteria for quality assessment aligned with standards used by the Particle Data Group and methodologies applied in global fits by CKMfitter Group and UTFit Collaboration, incorporating statistical techniques from collaborations like HPQCD Collaboration and MILC》. The procedures account for systematic effects highlighted by studies at Jefferson Lab, RIKEN, CEA Saclay, Tokyo Institute of Technology and Max Planck Institute for Physics, including continuum extrapolation, chiral extrapolation, finite-volume effects, renormalization schemes used at RIKEN BNL Research Center and heavy-quark treatments championed by Fermilab Lattice and MILC collaborations. FLAG’s averaging uses recommendations informed by analyses at Princeton University, Yale University, Columbia University and statistical approaches discussed at Institut des Hautes Études Scientifiques.

FLAG provides recommended values for light and heavy meson decay constants, quark masses, kaon mixing parameters, and semileptonic form factors used in determinations of the CKM matrix elements |Vub| and |Vcb|, influencing interpretations of results from Belle, BaBar, LHCb and Belle II. FLAG averages feed into global fits performed by CKMfitter Group and UTfit Collaboration and into searches for new physics discussed at Moriond, EPS-HEP and Quark Matter. The group’s recommendations are cited by experiments at CERN, theoretical reviews at Annual Review of Nuclear and Particle Science and phenomenology papers from groups at MIT, Caltech, University of Chicago and Institute for Advanced Study.

FLAG coordinates working groups focused on light-quark physics, heavy-flavour physics, kaon physics and beyond-Standard-Model matrix elements with contributors from ETM Collaboration, RBC-UKQCD, JLQCD, CLS, Budapest-Marseille-Wuppertal Collaboration, HPQCD Collaboration, Fermilab Lattice and MILC collaborations and ALPHA Collaboration. It interacts with external bodies including the Particle Data Group, Heavy Flavor Averaging Group, CKMfitter Group, UTfit Collaboration and experimental collaborations at KEK, SLAC National Accelerator Laboratory and DESY to ensure consistency of inputs for analyses reported at venues like Vancouver Lattice Conference and Lattice 20XX meetings.

Critics have argued that FLAG’s averaging can obscure tensions between individual collaborations such as discrepancies noted between results from MILC and RBC-UKQCD or differing treatments used by HPQCD Collaboration and ETM Collaboration, which has sparked debate at workshops held at CERN and KITP. Discussions with members of CKMfitter Group, UTfit Collaboration and experimental teams at LHCb and Belle II emphasize transparency in error budgets and provoke methodological debates similar to those between proponents at Les Houches and critics from Princeton University and University of Oxford. FLAG has responded by refining grading criteria and increasing interaction with groups at INFN, Max Planck Institute for Physics and Institute for Nuclear Theory to address concerns about correlated uncertainties and publication selection.