Thursday 5 November 1998
                                                     Ian Tomalin


                MINUTES OF THE 23RD BEW MEETING
               =================================

Agenda
========

  Two talks in preparation for the LEPC -

    M.-N. Minard: Hadronic cross section at 189 GeV.         
    E. Merle    : Dilepton results at 189 GeV.              

  Plus two updates -

    T. Medcalf    : Update on direct search for Excited Leptons.  
    M. Swynghedauw: Z' limits.

M.-N. Minard: Hadronic cross section at 189 GeV         
================================================

Using 172.8 pb**-1 of data (EF.GA.TR.MI.LX.LV).

  i) Reconstructed Z0 mass measured using jet angles is 1% lower in MC than 
     data. (Bad jet angle reconstruction in forward direction).
 ii) Reconstructed visible mass is 1% too high in MC for non-radiative events.
iii) HCAL calibration scale varies by 3.4%. Shows time dependence in year.
     Will be fixed during reprocessing.
 iv) For enriched WW sample (thrust < 0.75), DATA/KORALW MC = 81 +- 4%,
     whilst DATA/EXCALIBUR = 95%. Cause unknown (W polarization, ZZ events ?)
  v) Pythia gets ratio of up quark to down quark cross sections badly wrong
     at 189 GeV.

     Result:
       For sqrt(s'/s) > 0.1, sigma(qq) = 95.6  +- 0.77 +- 1.29 pb
       For sqrt(s'/s) > 0.9, sigma(qq) = 19.51 +- 0.42 +- 0.57 pb

     Agree with S.M. Systematic dominated by WW problems.
 
E. Merle: Dilepton results at 189 GeV
======================================

Dimuon Results: 
    For sqrt(s'/s) > 0.1, sigma = 7.56 +- 0.24 +- 0.21 pb
    For sqrt(s'/s) > 0.9, sigma = 2.65 +- 0.13 +- 0.06 pb
                            Afb = 0.59 +- 0.04

Ditau Results: 
    For sqrt(s'/s) > 0.1, sigma = 7.26 +- 0.31 +- 0.22 pb
    For sqrt(s'/s) > 0.9, sigma = 2.38 +- 0.15 +- 0.10 pb
                            Afb = 0.58 +- 0.07

Bhabha Results: 
    For -0.9 < cos(theta*) < 0.9, sigma = 84.6  +- 0.8  +- 1.5 pb   (SM=88.55)
    For -0.9 < cos(theta*) < 0.7, sigma = 17.05 +- 0.34 +- 0.26 pb  (SM=17.66)

All agree with S.M. except Bhabha which are 2 standard deviations too low.
However theoretical error for Bhabhas is about 4%.

Strong dependence of Ebeam/P seen on phi, expecially for |cos(theta)| > 0.95.
However, doesn't seem to affect selection efficiency.

T. Medcalf : Update on direct search for Excited Leptons
=========================================================
  Minor corrections result in two new e*e* candidates, which don't affect
previous limits, plus small change in singly produced nu* limits.
Also, now have better choice of difermion mass cut around Z0 peak (used to 
reject radiative returns to the Z0), since this background wasn't well 
contained in old cut.

M. Swynghedauw: Z' limits
==========================
  a) Now uses ALEPH LEP1 data, as decribed in ALEPH's 98 EW paper. This
     allows Z-Z' mixing angle to be constrained. 
  b) Takes into account theoretical error on difermion cross sections.
  c) Takes into account that luminosity error is correlated between data
     points.
  d) Proposes adding figure of Z' mass limit vs. mixing angle in paper.

Final limits will be available when jobs finish running on shift50. 
It was queried if these could be optimized to use less CPU.