Tuesday 15th June 1999
                                                Ian Tomalin

                MINUTES OF THE 32st BEW MEETING
               =================================

Agenda
------
 Two talks preparing for the next Thursday meeting -

  1)  Single Top Production at 189 GeV: M.Pepe-Altarelli 

  2)  R_c at 189 GeV: C. Goy
      
 plus two other topics -

  3)  Discussion: Shall we publish final 189 GeV BEW paper ? 

  4)  Update on 192 GeV dilepton results: M.-N. Minard 

Single Top Production at 189 GeV: M.Pepe-Altarelli 
--------------------------------------------------
  Search for e+e- -> t u/c, with t -> Wb.
=> 4 jets or 2 jets + lepton - reconstructed with kine. fit.

  b jet is most favoured QIPBTAG one, unless it's energy is too low.
Several cuts applied for each of the two topologies, optimized
bason on expected limit.

  Number of observed events:
                       4 jet           2 jet + lepton
   ----------------------------------------------------
    Data                16                   2
    MC Background        8.6                 1.0

Background dominated by bb events in 4 jet = 6.4, and WW events
in 2 jet + lepton = 0.95.
  C.L. for consistency with SM = 1% !

Systematics:
  i) After preselection, apply additional cuts one by one and
compare efficiency in data and MC => Main effect is b jet selection.
 ii) Study b tag efficiency at LEP1 => Similar conclusion.
iii) Vary b tag cut => Confidence level is lowest at cut used in 
                       analysis.
 iv) Depedence of signal efficiency on top mass.

 Measured single top cross section = 0.28 +- 0.14 pb, which is within
CDF limit. 95% upper limit is 0.67 pb. Much worse than expected
limit of 0.27 pb !

To do:
  a) Check b tag efficiency at LEP1 in 4 jet events.
  b) Take into account that some top quarks may decay to c Z0. 

R_c at 189 GeV: C. Goy
----------------------
  Old 183 GeV analysis simplified:
    i) bb rejection now relies only on QIPBTAG.
   ii) Neural network cc selection now uses 9 variables, not 12.

R_c = 0.266 +- 0.018 +- 0.022  (SM = 0.256)
  
  efficiency = 52%, purity = 43%.

Systematics:
  Semileptonic WW events used both to verify udsc efficiency
of QIPBTAG bb rejection and of NN cc selection. Latter done
for c enriched and uds enriched samples, derived applying NN
to other jet in W->qq system. Unfortunately c enriched sample
not very pure. 
  => Major systematic is cc efficiency.

To do:
  i) Use latest qq selection from M.-N. Minard
 ii) Do R_c measurement at Z0 for check.
iii) Understand better c enriched WW sample.

Discussion: Shall we publish final 189 GeV BEW paper ? 
------------------------------------------------------
  Wish to produce paper. Requires MC study of radiative 
pair events (to be shown by M.-N. Minard during ALEPH
week), plus use of final 1998 luminosities. Should also
include R_c measurement from C. Goy and d(sigma)/d(cos(theta))
measurements for dileptons and d(sigma)/d(abs(cos(theta))) ones
for hadronic events.
  Should prepare draft 1 before Tampere and send it to conference
if possible.

Update on 192 GeV dilepton results: M.-N. Minard 
------------------------------------------------
  No real surprises. Results seem consistent with SM.
Bhabha cross section is low (1.5 sigma) as last year.
More details to be shown in ALEPH week.