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Minutes of the meeting of the Heavy Flavour Steering group  |
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 8 October 2001 (CERN)

The following topics have been covered:
   + b-quark fragmentation
   + final report
   + CKM Workshop
   + future of this activity

b-quark fragmentation:
======================
 In our averages we are using the result obtained by the Heavy Flavour
sub-group of the LEPEWWG which was based on rather old analyses (before 1995):
   <X_E> = E_B/E_beam = 0.702 +- 0.008

 More recent and more precise results have been obtained by ALEPH, DELPHI, 
SLD and OPAL. In the following we consider only the energy fraction taken
by a weakly decaying b-hadron:
  + ALEPH: (published)
     They analyze semileptonic decays into D(*) l nu and obtain:
      <X_E> = 0.7163 +-0.0061 +-0.0056

  + SLD: (published)
     They analyze inclusive weak decays of b-hadrons from 150K hadronic
Z decays:
     <X_E> = 0.714 +-0.005 +-0.007 +-0.002

  + SLD: (unpublished)
     They analyze more statistics (300K evts) and use better algorithms:
     <X_E> = 0.710 +-0.003 +-0.005 +-0.004 

  + DELPHI: (unpublished)
     They use also inclusive secondary vertices and obtain:
     <X_E> = 0.709 +-0.001 +-0.005

  + OPAL: (published)
   They analyze inclusive semileptonic decays:
     <X_E> = 0.709 +-0.003 +-0.003 +-0.013(models)

 Several remarks are in order:
   + there is a 3rd uncertainty quoted by SLD which corresponds
to systematic effects obtained when they use different shapes for the 
fragmentation function, in their simulation, during the unfolding procedure.
Such an uncertainty was found to be negligible in ALEPH and no provision
was made by DELPHI. In OPAL there is also a large uncertainty given to
models but they have not done an unfolding procedure to extract the 
fragmentation distribution.
  This point has to be clarified.

   + central values of all recent measurements are higher than the "old"
result

   + there is almost no correlation between systematic uncertainties 
contributing in the ALEPH result and in the SLD/DELPHI measurements.
Systematics between SLD and DELPHI are correlated.

 Using only these three measurements one gets:
  <X_E> = 0.711 +-0.004 +-0.004(models) (preliminary)
where the last error corresponds to the systematics quoted by SLD on models.


 The differential distribution:1/N dN/dX_E has been measured also.
The three results are in agreement.

 With these informations it is intended to:

   + finalize the average value for  <X_E> and conclude on the issue 
of model errors
   + produce an average differential distribution. For this we need
from DELPHI and SLD the values of this quantity at the different
chosen points in X_E and the complete covariance matrix (as points
are correlated after the unfolding procedure)
   + ask the lifetimes and oscillations groups to investigate the effects
of changing the central value and the shape, relative to what was
used up to now.
   + for b-baryons and Bs, the fragmentation distributions for a b-quark
into these particles can be different from the average b-hadron fragmentation
distribution. It has to be checked what was done exactly in the analyzes.


Final report:
=============

 We expect to produce, in 2002, a final report on our activities based
on the most recent results. These results have to be published (or accepted).

 We had a tour among the different collaborations to indicate possible 
problems:
   +ALEPH:
     -Bs oscillations will be ready
     -a paper on Dmd and inclusive b-lifetime measurement will be dropped

   +DELPHI:
     -Vcb with exclusive D* can be too late(?)

   +L3:
     - the B0d lifetime measurement using the D* l final state 
 is dropped 
    
   +OPAL:
     -new analyzes on b-frag. with inclusive vertices and on charm counting
in b-hadron decays cam be late.

   +SLD:
     -results on Bs oscillations will be ready
     -a measurement of Dmd can be too late

 Concerning the unpublished notes related to COMBOS and to the procedures 
used for lifetime averages it is intended to provide enough information in 
the paper inside the main text or in Appendices.

 A first version of the report, for internal distribution is expected by end
of 2001.

CKM Workshop(s):
================

 Achille gave a summary of the organization of the Workshops on the CKM 
unitarity triangle.
 Support has been given by the CERN authorities.
 The first Workshop will be in Febrtuary 2002 and the second by mid 2003.
Two yellow reports will be produced.

 A web page is being prepared and will be made accessible (also) 
from our different groups.

Future of averaging activities:
===============================
 A letter is being prepared, which will be sent to the different experiments
and PDG, in view of having these activities, which consist in preparing
world averages for parameters of interest in $b$-physics, pursued in
future. New version(s) will circulate within the steering group.

  Sincerely yours
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