12th BEW meeting, Wednesday 25, February, 1998


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

Present: I.Tomalin, M.N.Minard, F.Teubert, C.Goy, M.Antonelli, 
         G.Sguazzoni, H.Videau, G.Dissertori, E.Simopoulou 

Minutes taken by G.Dissertori
_____________________________________________________________________

  Agenda : 


1.- BEW
    ---  
   o Single lepto-quark search (E.Simopoulou)

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






  
-  Single lepto-quark search (E.Simopoulou)
   ---------------------------------------


First a summary of the theory implemented in the MC generator
ERATO was given. The search is now updated to look for
leptoquarks in the full mass range 50GeV < Mlq < 170GeV.
In steps of 10GeV 1000 events have been generated for each step.
They have designed an analysis which is applied to the full
mass range. No optimized analyses for subranges have been applied
(such as for other searches). Basically one looks for one jet
plus an isolated lepton (electron).
Background studies have been performed, however, Bhabha and Tau 
backgrounds have not been studied yet.
They observe a number of events which is compatible with their
background calculations, the distribution of the Jet-Electron mass
is also compatible with background.
Therefore they compute limits in the plane Mlq vs. lambda (the coupling).

No error calculation has been performed yet, and the limits are
valid only for leptoquarks with electric charge -5/3 and
-1/3.   

Some discussion started about the limit calculation and the further steps 
to be taken. The decisions were the following:
The analysis will be shown at the Thursday meeting (26.2.), a
referee should be found which should take care that the missing
points are incorporated in the analysis. If this is done, a conference
note could be produced (a preliminary note already exists).
The major points to be considered are:

1) A full error analysis (statistical + systematic)
has to be carried out and propagated into the limit.

2) Backgrounds from Bhabhas and Tau-decays should be included

3) Limits should be given for each LQ charge state independently,
or otherwise the caption etc. in the paper should be made more
explicit

4) The calculation of the limit should be checked (background
subtraction etc.)

5) Eventually try to define optimized analsyes for various
mass regions and give a limit from the combination of the
individual analyses







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



1) Marie-Noelle reported that a lot of further checks on the
Tau x-section at 130GeV have been carried out. No evident
problem could be found, so some discrepancy (about 2.5 sigmas)
with the Standard Model remains.

2) The note will be available before the Thursday meeting.
The Bhabha x-section will not be changed for the moment (in
order to implement the new s' definition).





- Next meeting ---> to be announced 






Guenther Dissertori 

Mon, March 2, 14:30:38 MET DST 1998