Minutes of the EW Group meeting held on 22-Feb-97
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Present: A. Venturi (AV), A. Lucotte (AL), B. Bloch (BB), M. Girone (MG),  
          MN. Minard (MNM), M. Pepe-Altarelli (MP)

Main Topics: Class-24 problem / status of cm energy / t-channel subt. 

TAUS:       The problem raised inside the EW group by Gerardo 
            is discussed. This problem concerns the selection 
            of events without charged track above 2 GeV but  
            with at least one 2 GeV photons. This corresponds to
            2 per mille of the taus events. 
            For the leptons cross-section and asymmetries the need 
            for a reprocessing was not clearly demonstrated. In addition 
            the trigger conditions fullfilled by this class of 
            events are not clear, in particular for 2-gamma background.
            The discussion on this question still has to go on with
            people involved in these analyses.
            MG reports on the status of the taus selection: data
            have been re-run with sagitta correction (affecting 
            selection at the level of 3.10^{-5} as for muons) and 
            discovered a bug in the Energy Flow package, now corrected.
            Background estimations are not very sensitive to these 
            modifications. Although new selection efficiencies are not
            yet completed, a part of the note is now available on 
            the Web.
            
LUMINOSITY: BB pointed out that she could not provide a note including
            final numbers on luminosity since no FINAL energy numbers 
            are available at that time for 93-94 and 1995. The SiCAL 
            note concerning this period of data taking is therefore 
            freezed. AL will contact Guy Wilkinson / M. Koratzino to 
            have the lastest news from the LEP energy Group and reports
            asap.
 
ELECTRONS:  For Bolek Pietrzyk, MP reported about the estimation of 
            the THEORETICAL uncertainties affecting the t-channel 
            subtraction. 
            --> In the previous ALEPH EW paper published, the error 
                was 2% at the Peak as well as off-peak. 
            --> Now, new estimations from Wim Beenakker (including large 
                factor of security) lead to :
                     0.6% ... for E_cm = 88.45, 89.45, 90.20  GeV
                     0.7% ... for E_cm = 91.19 GeV
                     2.5% ... for E_cm = 91.95  "
                     4.5% ... for E_cm = 93.00  "
                     3.5% ... for E_cm = 93.70  "

EW PAPER:  An introduction has been written by MP. The section including 
           trigger definition is also available. It should include now the 
           way to estimate trigger efficiency in the different selections.

           Next meeting on thursday 6 at 10h. Location still 
           to be defined.

 Submitted by A Lucotte.