Heavy Flavor Averaging Group 1

Heavy Flavor Averaging Group
Revised February 2024 by U. Egede (Monash University) and A. Soffer (Tel AvivUniversity)
The Heavy Flavor Averaging Group (HFLAV) is an international collaboration ofphysicists from experiments measuring properties of heavy flavored particles, i.e., hadrons
containing b and c quarks, and τ leptons. HFLAV calculates and publishes [1] world
average values of quantities such as lifetimes, branching fractions, form factors, mixing
parameters, and CP -violating asymmetries. Most parameters concern decays of B and Dmesons, and many are related to elements of the Cabibbo-Kobayashi-Maskawa (CKM)
quark mixing matrix [2], [3].
HFLAV was originally formed in 2002 to continue the activities of the LEP Heavy
Flavor Steering group. Since its inception, a wide range of results have become available
from increasingly larger data sets. Consequently, HFLAV has expanded to include eightsubgroups:• b-hadron lifetimes and oscillations, including parameters of CP violation in b mixing;• decay-time-dependent CP violation in B decays, and angles of the CKM Unitarity
Triangle;• semileptonic decays of b-hadrons (B → Xℓν, ℓ = e, µ, τ ), including determinations of
the CKM matrix elements |Vcb | and |Vub |;• b-hadron decays to hadronic final states containing c-quarks (open charm andcharmonium);• (rarer) b-hadron decays to final states not containing c-quarks, including fully
hadronic, semileptonic (B → Xℓℓ, Xν ν̄), leptonic, and radiative decays;• CP - and T -violating asymmetries of D mesons and D0 –D̄0 mixing;• c-hadron decays (hadronic, semileptonic, leptonic), properties of excited D states
and charm baryons and determination of |Vcs | and |Vcd |;• τ -lepton physics including branching fractions, tests of lepton universality,determination of |Vus |, and searches for lepton flavor violation.
Each subgroup has one or two conveners and typically a half-dozen members representing
experiments that conduct measurements in that area. Most groups contain representatives
from the Belle II and LHCb experiments, and some groups have representatives fromthe ATLAS, BABAR, Belle, BESIII and CMS experiments. Members of HFLAV areappointed by their respective experimental collaborations. HFLAV has two co-leaders,
who are appointed by the managements of Belle II and LHCb.
The averaging procedures used by HFLAV are similar to those of the PDG [4].
When sufficient information is available in publications when calculating world averages,common parameters used for different input measurements are adjusted (rescaled) tocommon values. The p-value of the fit is provided to indicate the consistency of themeasurements included in the average. However, unlike the PDG, when obtaining aworld average with a low p-value (i.e., a large χ2 per degree of freedom), HFLAV
does not usually scale the resulting uncertainty. Rather, the systematic uncertainties
of the measurements are reviewed with experts from the experiments to understandthe discrepancy. Unless inconsistencies among measurements are found, no correction isS. Navas et al. (Particle Data Group), Phys. Rev. D 110, 030001 (2024)
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2Heavy Flavor Averaging Groupmade to the calculated uncertainty. Close communication between representatives of theexperiments and HFLAV members who perform averages helps ensure that measurement
uncertainties, known correlations, and systematic effects are properly accounted for.
If a special treatment is needed to calculate an average, or if an approximation usedin an average calculation might not be sufficiently accurate (e.g., assuming Gaussian
uncertainties when the likelihood function is non-Gaussian), a note is included in theHFLAV publication and online documentation to describe this.
In general, HFLAV uses all publicly available results that have written documentationsuch as a journal publication, preprint, or conference note. These include preliminary
results presented at conferences and workshops. However, preliminary results that remain
unpublished for an extended period of time, or for which no publication is planned, arenot included. A special subset of HFLAV averages are included in the PDG listings;
for these averages, only measurements that are published or accepted for publication
are used. The averages provided by HFLAV are listed by the PDG as “Produced by
HFLAV”.
All HFLAV averages and input measurements are documented in an approximatelybiennial journal paper or preprint; the most recent version is Ref. [1]. The latest results
and plots are posted on an extensive set of webpages that are updated several times peryear; these are available athttps://hflav.web.cern.ch.
References:
1. Y. S. Amhis et al. (Heavy Flavor Averaging Group), Phys. Rev. D107, 052008(2023), doi:10.1103/PhysRevD.107.052008 [arXiv:2206.07501], updated results andplots available at https://hflav.web.cern.ch/.
2. N. Cabibbo, Phys. Rev. Lett. 10, 531 (1963).
3. M. Kobayashi and T. Maskawa, Prog. Theor. Phys. 49, 652 (1973).
4. See Section 5 of the “Introduction” to this Review.

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