Wieslaw gave a status of the YFSWW program. Transparencies presented at the meeting can be found here, recent papers on KORALW and YFSWW are also available.

Wieslaw firstly recall the principle of Leading Pole Approximation (LPA), the 4f cross section is expended in power of (G_W/M_W) terms, the leading one being kept. In the WW context, the LPA is often called Double Pole Approximation (DPA) because of the two resonant Ws. The DPA based 4f cross section is estimated with a precision of the order of 2.5%, which is clearly not enough for our purpose. Corrections to the method have been developed by Beenakker, Berends and Chapovsky (BBC) who have computed the complete O(a) electroweak corrections for off shell W pair production. The precision on the 4f cross section improved to the 1% level. A precision of the order of 0.2% is claimed by Wieslaw on the 4f cross section by adding to the on-shell part computed by YFSWW3, including LL (a³L³) corrections to WW and NL LPA corrections (for on-shell case) the non resonant 4f part (up to a³L³) computed by KORALW. Similar precision is also achieved by the RACOONWW team. For comparison between those two programs, please refer to R. Pittau's talk at WW99 or to G. Passarino's one at the LEP2 MC workshop.

The net result is a decrease of the on-shell W-pair production cross-section by 1.5% at 200 GeV cm. energy. Comparison between the two programs is in progress.

The effect of FSR on the W mass has also been discussed by Wieslaw. As pointed out in the YFSWW3 and RACOONWW papers, a mass shift on the reconstructed W mass due to FSR is expected. However, since this effect is already implemented in the current version of the KORALW program that we are using in ALEPH, by calling PHOTOS, we should not worry any more!

However some remaining non-factorizable corrections to the 4f process need to be evaluated. In particular, as pointed out by in the paper by Chapovsky and Khoze, mass shift of the order of 5 MeV are expected due to higher order Coulomb effects.

Andrea summarised answers to a question from P. Janot about running at 161 GeV in 2000 during possible de-iceing.of LEP cryogenics.

Andrea gave a reminder of the W mass measurement at threshold. The statistical sensitivity per pb^-1 is similar to the one from direct reconstruction ( » 1100 MeV/Ö pb^-1). Systematic uncertainties are however uncorrelated between the two methods, making a run at threshold interesting for the W mass measurement.

The expected integrated luminosity could be anything between 0 and 20? pb^-1. No real conclusion was reached at the meeting, the general feeling was that a run at threshold in '00 would bring additional complexity to the W mass analysis. This point will be further discussed at a Thursday meeting next January.

Julian presented progresses on systematic studies for the 4q cross-section at 189 GeV. This study was initiated by the observed difference on the minimum and maximum jet energy distributions both for high energy (in the background region) and Z0 events.

For each of the NN14 variable, the NN output distribution has been reweighted according to the ratio of that given variable distribution at the Z between data and MC. The maximum effect +0.06 and +0.07 pb is observed for the maximum and minimum jet energy variables respectively.

The title of Andrea's talk is 'Increasing the entropy of the simulation systematics'. Andrea covered the following subjects :

1. Charged track acceptance in jets
2. Analytical DM_W given by Eugeni's angular bias
3. Brief status report of the calorimeter systematic evaluation prescription

The effective Pt threshold on charged tracks due to beam pipe and # of TPC hits has been looked at in qqbar events on data and MC. The threshold is around 150 MeV for central jets, increasing a bit for lower angle values, both shape and magnitude are nicely reproduced by the MC. Andrea has also checked by using central jets in data and in MC that simulating a fake beam pipe by applying a pt cut of 150 MeV w.r.t. the ALEPH y axis the change in jet energy and direction is in good agreement between data and MC.

Andrea has tested the so called Eugeni's angular bias formulae derived from Alain's suggestion (cosq '=0.99845 cosq ) using his analytical tool. On average the shift on the W mass (Mass(with bias)-Mass(wihtout bias)) is 7 MeV. There is however a strong q dependence, the shift is -9 MeV for |cosq _W|<0.7 and +29 MeV for |cosq _W |>0.7.

Andrea presented the data/MC ratio vs cosq for PECO and PHCO as measured on Z events. Those ratios have been used as input to the HCRESC and ECRESC routines which are going to be used for calorimeter systematics of the 189 GeV mass paper. Andrea presenter also the HCAL calibration stability as a function of time, in '99 the fluctuation is found to be 1.3%.

Roberto presented a study of jet angular reconstruction based on Z events the full presentation can be found here. The method is to use two jets '98 Z events and to decompose jets in three components : photons, charged tracks and hadron residuals (the famous type 5 objects). Two independent jet angle measurements can be performed : from charged tracks and from photons as the tracking devices and the em. calorimeter are not auto aligned. Difference between charged tracks and photons polar angle has been looked at for 40 q bins. MORE MC IS WELCOMED.

As a further step, hadrons residuals have been added to charged tracks (LCAL and SiCAL objects are not considered for the time being). No evidence for strong angular bias has been found, although some differences (of the order of several mrad) can be seen in the region 0.6<|cosq _W|<0.8 and in the last bin |cosq _W|>0.95. A parameterisation of these differences will be made available and tested on Zg and W events.

Barbara presented results of studies performed with W. Wiedenmann, A. Bonnissent and R. Tenchini. She looked at the difference between data and MC for polar and azimuthal angles and track momentum resolution as well.

She plotted the difference in polar angle vs polar angle for ITC-TPC only fitted tracks (FRFT 0) and VDET only for semileptonic events. No discrepancy above 0.3 mrad is observed between data and MC.

She concluded that angular resolution and bias (q and j ) differences between data and MC are below 1 mrad (a bit worst for q , due to possible angle between LEP beams or difference between beam energies).

The difference in momentum scale between data and MC is correctly taken into account by the sagitta correction, the difference in rms (pull : 1.4 for data, 1.1 for MC) has to be considered for systematic studies on the width measurement.

Baraba then announced that she discovered that the W production from RAL had no primary event vertex smearing.

Oliver has applied the famous Eugeni's angular correction (see above) to 189 GeV (both on jets and on leptons). He observe a shift (Mass(without bias)-Mass(with bias)) of -17 MeV on the eu qq channel (-11 MeV evt/evt mass shift), -19 MeV for the m u qq (evt/evt : -15) and -10 MeV on the 4q channel. In agreement with Andrea's expectation from his analytical tool.