10th BEW meeting, Wednesday 11, February, 1998


Copies of the transparencies from this meeting can be found in the ALEPH secretariat.

Present: E.Merle, I.Tomalin, M.N.Minard, D.Schlatter, M.Kelly,
         F.Teubert, C.Goy, M.Antonelli, G.Dissertori, P.Dornan

Minutes taken by I. Tomalin 
_____________________________________________________________________

  Agenda : 


1.- BEW
    ---  
   o Status of hadronic x-section (Marie-Noelle Minard)
   o Status of leptonic x-sections (Elsa Merle)
   o Dimuon checks (Ian Tomalin)

2.- A.O.B 
    ----- 
   o Discussion






  
-  Status of hadronic x-section (Marie-Noelle Minard)
   --------------------------------------------------


Update using Guenther's new KORALZ MC. It looks better in calorimeters.
Analysis now uses cut on thrust to kill W+W- events and requires 
M_vis > 110 GeV to reduce Z return events.

Result at 183 GeV for sqrt(s'/s) > 0.9: 23.56 +- 0.75 +- 0.2      (SM = 22.98)

Frederic Teubert gets higher cross-section. Cause: he doesn't reject
gammas which are reconstructed in the detector, and these are badly simulated.







  
-  Status of leptonic x-sections (Elsa Merle)
   ---------------------------------------


  Comments: dimuons - want to tighten d0/z0 cuts to kill cosmics.
            Bhabha  - bhwide MC seems better than unibab MC, so would be
                      nice if Guenther could make some at 130-172 GeV.
                      Still excess of events in data at cos(theta*) = -0.9

  Results at 183 GeV for sqrt(s'/s) > 0.9
                     Sigma (pb)                                            A_FB
   e+  e- : 106.2 +- 1.4  +- 2.5  (SM=108.4)     
  mu+ mu- :  3.19 +- 0.24 +- 0.07 (SM=3.36)     0.561 +- 0.063 (SM=0.592)
 tau+tau- :  3.12 +- 0.29 +- 0.12 (SM=3.36)     0.563 +- 0.084 (SM=0.592)







  
-  Dimuon checks (Ian Tomalin)
   ------------------------


  Similar results to Elsa except:
    1) Asymmetry higher by about 0.5*sigma. 
    2) Much larger background from ISR.

Elsa computes s'/s from angles with respect to the photon (if found),
Ian with respect to the beam axis.









  
-  Discussion 
   ----------



1) There will be another BEW meeting next Wednesday at 14:30.
A draft version of the note containing BEW results for the conference
will be available beforehand.

2) Our Thursday meeting talk is arranged for 26th Febuary.

3) We decide to use a cut on sqrt(s'/s) > 0.9 for the exclusive channel.
The signal efficiency is defined as the fraction of events in which the true
difermion mass exceeds 0.9*sqrt(s) which pass the selection and have
reconstructed sqrt(s'/s) > 0.9. Events with a true difermion mass of 
less than 0.9*sqrt(s) are defined as background.







- Next meeting ---> 18.2.98 






Guenther Dissertori 

Wed February, 17:30:38 MET DST 1998