***************************************** * MINUTES OF THE ELECTRO-WEAK MEETING * * ON 25TH JUNE * ***************************************** This was a general EW meeting. Alain Blondel: LEP energies 1993 to 1995 -------------- Alain presented the status of LEP energies from 1993 to 1995. In 1995 new NMRs were installed in the tunnel and a rise of energies during the fill has been observed. A new model has been used which takes into account the rise of energies as a function of day time (due to trains) and as a function of the time in fill (saturation). The results of the model are well consistent with data and within 20% with the resonant depolarization measurements. For 1993 data, the 95 model has been used and four long term experiments (only one really relevant: the temperature experiment) have been used to check. For 93 and 94 data, a test of consistency is being performed by two different groups (Arnaud and Eric for Aleph) analysing the Z mass at the beginning and at the end of the fill. It is not expected that the numbers for 93 will change sizeably, but we have to wait for the results of these tests. A new evaluation of the energy spread has been performed by Eric Lancon which allows to obtain an error on the Z width of the order of 0.3 MeV (to be compared with the old one of order 1 MeV). LEP will provide preliminary scan energies around 1st of July (no energies for prescan) and the covariance matrix will be calculates for LEP averages. Fow what concerns the prescan period, which consists of more than half of 95 data, there is no problem to use the nominal energy for R_l. For the asymmetries the situation is more delicate. It was decided to double the error used for the scan peak point (from 10 to 20 mev) and to use these data for asymmetries as well. Alain will look whether more precise info. can be obtained. Gigi would prefer to have LEP energies published before using them because the consistency checks are performed only by Aleph and our sensitivity alone could be not sufficient. Eric Lancon: 1995 preliminary luminosity ------------ The major change in 95 with respect to the 93 was the bunch train LEP running (A-B-C). Eric showed the distribution of the total energy of the cluster without any cuts on the fiducial region. In this plot the in-time Bhabha peak can be separated using a cut at the level of 70 GeV (in 94 it was 65 and in 93 was 55). In this way one looses the gain given by the cross-talk (which in principle could allow a gain of a factor ~63% for the previous bhabhas and a factor ~51% for the following bhabhas) but avoids the systematics introduced by the contaminations. A way to remove the remaining preceeding events is to use the radial width together with the energy: the off-time events can be well rejected requiring the width to be less than 0.4 and the energy greater than 37 GeV (box cut). The global systematics related to these cuts has been evaluated together for all the energy points. The systematics due to the total energy cut (which influences all the three bunches) has been evaluated using the 94 data and the first wagon of 95 data. The residual contamination from the other families is very small (of the order of ~10^-4) but further cross-checks are needed. The systematics due to the box cut (which influences only the previous B-C or the following A-B wagons) is fine. Despite the new LEP bunch train running, the global systematics (0.071%) is of the order of the one in 94 (0.069%). Some few things are still to be checked: the point to point error from bunch trains, the point to point correlation of the total energy cut and finally the year to year correlation. Everything should be ready in a few days. Lee Thompson: 1995 Bhabha cross section ------------- Lee presented the results on 1995 bhabha cross-section. He showed the stability plot (defined as the ratio between the selected events and the number of hadrons given by Marie-Noelle) as a function of the fill for events at peak and off peak: it is well flat in all the cases. The t-channel subtraction (including the interference term) has been performed as a function of cos_theta* bin by bin. The subtraction is more relevant for peak-2 events and it is peaked in the forward region. A great effort has been dedicated to generate new sets of Monte Carlo and for the first time also MC off peak has been used to measure the efficiencies. The MC efficiencies (peak and off peaks) are almost flat in the central cos_theta* region. The acceptance cuts (acollinearity and cos_theta*) as a function of the energy have been studied using simulated muons (korl07). The comparison of the final results on the cross-section with the Z-fitter prediction is good. As far as the asymmetry is concerned, a new small correction related to the acollinearity cut (for each bin in cos_theta* ) has been introduced. It has been calculated at the kingal level. The same correction has been evaluated by Henry Videau and Jean-Claude Briant using Z-fitter and it is slightly different. Investigations arew going on. The final asimmetries are well in agreement with the predictions. The question about the results to be sent to Warsaw was raised again by Monica. The two alternatives are to send only 95 preliminary results, or a complete set of new "preliminary" for 93-95. Henry remarked that the global analysis is almost finished, only small checks are needed and the final results should not change very much. Jean-Francois pointed out that this will be the last big conference for LEP 1 results and it will be better to have the updated set of data. Gigi agreed with that and it has been decided to send to Warsaw the updated set of results on lepton asymmetries (for 1993 to 1995). Andrea Venturi: 1995 muon cross section -------------- Andrea presented results from the "standard analysis" on 94 EA-EW and the global set of 95 data (four periods: prescan, peak, peak-2, peak+2). This selection is based on the single tracks characteristics and on the muon-identification of at least one of the two leading tracks. Andrea showed the improvements on the photon emission simulation with the new version of koralz (korl07) which allows the emission of more than one hard photon in the final state. The acceptance has been re-evaluated on this new MC and it is consistent with the old value. The cosmic background has been re-evaluated since the 95 ITC time window is larger than in previous years: the rejection cuts are not so effective as in the past but the situation has been improved rejecting events from the non-existing fourth bunch. The selection efficiency has been evaluated on data using single and double identified events. The stability plot (defined as the ratio between the selected events and the number of hadrons given by Marie-Noelle) as a function of the fill is well flat in all cases. Note: for the 95 prescan period and 94 EA-EW luminosities are not available and the numbers of hadrons have been used to normalize. The final results can be found in the copies of the transparencies. Monica pointed out that there is also another analysis performed by Imma Riu, the so called "single arm analysis", which is also ready. Comparisons between the two analyses are going on. Gerardo Ganis: 1995 tau cross section -------------- Gerardo presented the preliminary results for the tau cross-section to be sent to Warsaw. The major background sources have been re-evaluated and several cross-checks with previous year data performed. The cosmic background has been measured and found slightly larger than for previous years owing to the larger opening window. Stability plots was also shown and looks fine. Efficiencies were measured on data with the usual technique. The final values for the cross-sections are in good agreement with Z-fitter predictions. M.Noelle Minard: 1995 hadronic cross section ---------------- The calorimeter and TPC selection is unchanged, the background and the systematics have been re-evaluated on 1995 data. The ratio between the calorimeter and the TPC selection is constant over the run and fill number. In the TPC selection the gamma-gamma background has been evaluated using the non-resonant part of the cross-section. In the calorimeter selection the two non-resonant contaminations, the gamma-gamma and the bhabha, have been treated as in the past. The tau contamination and the error on the efficiency have been re-estimated on 95 data. note: ----- The luminosity on 95 prescan period is not evaluated by SICAL but using the number of hadrons. Different values of luminosity appeared during the talks due to different values of the hadronic cross-section used. The sample of events used in all the analyses presented at this meeting is exactly the same. Conclusions: +++++++++++++++ The luminosity and the correlations will be ready next week, the energy from LEP should be ready around the first of July. The global EW fit will be presented to the collaboration before the Warsaw conference, possibly at the Thursday meeting in about two weeks. In the meanwhile the results will be put on the Web. The LEP 2 electro-weak analyses (cross-sections and asymm. at high energy) will be performed by Marie-Noelle and a new student of hers.