Jason gave a status of the WW Monte Carlo production.

• 1999 energies (4 energy points) detailed status can be found here. Available MC data sets :

• 2000 energies

Anne presented the status of version 1.0 of the common ntuple code. Details of the software can be found here. She then described the changes implemented in v1.1. Except bug fixes, the only main changes are : the implementation of the new tau reconstruction from Djamel and a lot of changes in the e/mu channel from A. Venturi to recover some of the features of the old code. All data and MC available should be processed with this new version.

Oliver gave a short status of the common fitting package that runs over the common ntuples to perform W mass fits. The code is not yet publicly available but is currently tested by several people (Djamel, Guillaume, etc…). It is promised to be delivered and documented! soon.

Stephane a status of Gauge Coupling analyses (NOT only TGCs) inside ALEPH.

• QGC : people are needed, ALEPH has still no study of the WWg and Zgg channels.
• ZZ : Aleph analysis has started, all energies should be looked at. Participation to the LEP working group needed to follow activities on generators (DELTGC) or coupling definitions (Gounaris et al. definition).
• Zg : Aleph analysis has stared, it is foreseen to include vvg channel. Some MC production at all energies with KK2f generator still missing. Same comment as for the ZZ channel for the participation to the LEP working group.
• Single-g : Analysis is going on.
• Single-W : Some improvements of the analysis understudy. MC events generated with GRACE (thanks to R. Tanaka!) have to be simulated.
• WW : A lot of tools are now in common with the W mass and WW cross section analyses. Aleph has two analyses (LL and OO). A lot of MC is missing to perform calibration curves.

Günther on gave a summary of the recent bug hunting inside Herwig from Gerald. The initial observations were that Herwig jets are thinner than Jetset jets (by Jason for e/mu and Eric for 4q) and even at parton level (by Ann). This is in contradiction to what is observed at the Z⁰. Gerald traced the problem to a feature/bug in Herwig. The HARDME option being active only on the case of Z/g->qqbar events. This option controls the kinematic of gluon emission from the qqbar system. The consequence is that too few soft gluons are emitted in HERWIG. The others 'features' discovered by Gerald are that HERWIG kinematic is not in general Lorentz invariant (the mean value of 1-Thrust in the W rest frame, weakly varies with Ö S). The Herwig authors have been contacted, to be followed up…

Ann introduced what covers the so called fragmentation error on the W mass measurement, which is in fact a convolution of several effects. It comes from difference between MC and data in : parton shower, particle composition and momentum spectra after hadronisation. It may have a detector component which is important to evaluate since this error is currently assumed to be 100% correlated between experiments. Ann looked, in the 4q channel, at the difference at kingal level between Jetset and HERWIG for distribution like q (rec.-gen.) vs q gen, jet energies vs q gen. She simulated the effect of the beam pipe by a simple cosq cut and found not mass shift between JT and HW (7± 8 MeV). She then removed undetectable particles (like neutrinos and soft momentum one) and still did not observe any significant mass shift (4± 7 MeV). She concluded that the detector response should be responsible for the mass shift observed after reconstruction (27± 9 MeV). Her work plan is to use fastsim to try to understand the effect of the detector response.

Eric, on a very similar subject looked at the JT, HW differences but at reconstruction level (after detector simulation). HW has a better q resolution than JT for every q gen. The difference between HW and JT on the opening angle of the two jets from a W does not depends upon the polar angle of the generated W. Reconstructed (before kinematical fit) jet masses are higher for JT (+130 MeV) than HW (independently of q ), jet energies are lower (187 MeV) for JT than for HW.

Benjamin summarized recent studies on Zg events. A bug was found in the weight computation, resulting in an underestimate of the LEP energy by 50 to 120 MeV (± ??) depending on the energy. The calibration curve, gets improved (slope : 1.036± 0.035, offset : 0.002± 0.02). New Monte Carlo data sets have also been produced for '99 energies with Galeph 309. It does not seem to change the results. The following table compares the previous and current results.

	Previous (MeV)	Current (MeV)
Hadronic channel (No ISR)	-421 ± 91 (stat.) ± 1001 (syst.)	-300 ± 92(stat.) ± 101 (syst.)
Hadronic channel with ISR	-462 ± 80 ± 100	-325 ± 79 ± 101
+ mm channel	-462 ± 77 ± 100	-342 ± 76 ± 101

Benjamin also studied the effect of the beam energy spread with the new KK2f generator. Within statistics no effect is observed (at the level of 20 MeV).

Fragmentation effects have also been studied by comparing, events fragmented with Jetset and Herwig (different events). Distributions of rapidity wrt to the jet axis, were compared for the different types of energy flow objects. Distributions are wider for type 0 and 5 objects. The kinagain facility should be used in future and a quantitative possible effect on LEP energy given.

Benjamin also presented the Delphi result (sent at Osaka). Di-muon events only have been used and a Breit Wigner fit performed. This method needs a calibration curve. The result is +158 ± 203 (stat.) ± 116 (syst.) MeV.

Patrice reported on recent studies performed by Adel on the possibility of measuring the mass difference between W⁺ and W^-. Those studies were triggered by recent theoretical papers on CPT. The only published result comes from CDF : M_W⁺-M_W^-=-0.19 ± 0.58 GeV. Preliminary studies indicate that a 50 MeV error could be obtained at the end of LEP by combining the results from the four experiments.

Franco presented the online WW cross section measurement and some comparison between MC and Data for some variables used in the selections. No discrepancies are observed.