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  * Minutes of the EW meeting: 21-may-1996 *
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This was a general EW meeting.
 
1.  Monica gave  a brief summary of the  activities of the EW
    task force.
 
2.  Andrea reported on the measurement of the muon  cross-section.
    In particular he presented
      - very preliminary results on 93->95 data
      - an  evaluation of the acceptance with  the last version  of
        KORALZ (KORL07).
    Andrea uses the "official" selection, except for one change in the
    muon i.d. where he also demands that the number of expected planes
    be greater equal to 10. (This is a cut which is used by default
    by the HF group and which should allow to reduce the Bhabha
    background).
 
    New acceptances have been evaluated with KORL07, which allows the
    emission of two hard photons in the final state, using 90K
    muon MC events generated at peak energy (run 944).
    The difference in acceptance between the new and old KORALZ
    versions are close to what was expected and quoted as systematics
    in our previous papers (1.5 per mille).
 
    However if another  MC production is used  (run 1757) the
    acceptance is 4 per mille higher  than that obtained using
    run 944. What's the reason for this discrepancy?
    Is there something wrong with run 1757?
 
    40K (p+2) and 50K (p-2) muon events were also generated
    and the resulting acceptances do not agree very well with the
    estimation done in the past using a simple rescaling at
    Kingal level:
 
     eps_acc_p+-2 = (eps_acc_peak/eps_Kingal_peak) eps_Kingal_p+-2
 
     ===> to be understood
 
3.  Gerardo  gave a status report of the work done with Anna
    on sigma_tau.
 
    '95 data: the study of the background shows no significant
              discrepancies with previous years.
              For the efficiency, the '94 method has been applied
              to '95 data.
              Good agreement was found in  the  acceptance between
              the  93 estimates at Kingal level for the off-peak
              points and the present GALEPH+JULIA evaluations.
              For  the efficiencies the agreement is less good.
 
    '90-91  : the analysis has started
 
3.  Pere gave  a  brief status-report on the Bhabhas.
    Preliminary results for cross-sections and asymmetries
    are ready since a while, however checks are still going on.
 
    There is work going on to understand whether corrections
    to Afb due to s' cuts need to be applied.
 
    Separate efficiencies vs costheta were produced by Monica
    separately for the off-peak points. (Before peak efficiencies
    were used also off-peak due to the lack of off-peak MC).
    The impact of these separate efficiencies was however not
    yet available at the time of the meeting.
    From the efficiency  curves there was no obvious difference
    between s-channel and t-channel efficiencies. (This point
    is also being investigated by Henri).
 
    The preliminary asymm. at P-2 is slightly off w.r.t. the
    SM prediction (about  1.3 sigma).
    Henri and JC are providing an independent Bhabha selection
    to be cross-checked with the official one.