- Guenther Dissertori: MC production ----------------------------------- G. Dissertori described the status of MC production. Generators are (almost) the same, KORALZ has the good Jetset tune, official latest versions of all software. Marie Noelle points out that there are serious data/MC discrepancies in electron reconstruction. (bhabhas are special because of their high energy, low angles and radiating properties) mu and tau pairs still missing, but despite Frederic volunteering, Guenther decided to do it himself.
- Ian Tomalin: A_FB(q-qbar) -------------------------- Ian Tomalin showed first results at 183 GeV. Standard p_L -weighting with kappa=0.3. Results consistent with S.M. There is almost exact cancellation of the different flavours and it was suggested to split the sample in b/non b events to enhance the effect.
- Elsa Merle : New e+e- selection -------------------------------- Elsa showed the result of her new selections. She noted problems with momentum scale and momentum resolution, which require fudge factors. Radiative background subtraction (in the case where s' is defined as inv mass of out going fermions only, i.e. from electron momenta) requires good understanding of the energy scale and resolution. She expressed preference for a s' definition from invariant mass of colliding electrons (i.e. propagator) that would reduce these corrections and associated systematics.
- Marc Swynghedauw: Dimuon analysis ---------------------------------- Marc swynghedauw presented a muon selection for all LEP2 energies (from 130 to 183 gev) with its cross section (sqrt(s'/s)>0.1,sqrt(s'/s)>0.9) and asymmetries. MUID is improved. Systematics on Particle ID and TPC calibration have to be included in the final numbers. Di-tau cross section/Asymmetries and Bhabhas cross section will follow as well. Marc's analysis on the limits on additional neutral gauge boson Z' will use these leptonic measurements. Asymmetries were presented with *again* a discussion on how to present the asymmetry results when close to 75%.
- Discussion : How to define s' ? --------------------------------- Ian Presented 3 possibilities A Difermion mass. This is possible for muon pairs and to a lesser extent for tau pairs. For electrons there are known experimental problems (see Elsa's talk) and for hadrons it it simply impossible to isolate photons from FSR from the jets, at least up to a certain angle, so one is reliant on the MC simulation. Furthermore, since FSR photon radiation often occurs after gluon emission, a definition based on the quark invariant mass is delicate. B propagator mass. For the moment this is effectively what is done for the hadronic cross-section, and would seem preferable for the bhabha analysis. There is an inherence ambiguity in this definition due to ISR/FSR interference, which can be solved by subtracting the contribution of the interference term to the cross sections and asymmetries. This is rather delicate. C follow Jadach's suggestion and make an experimental definition such as, include in the final state system all photons that are closer to the final state fermions than from the beam line. (some problems might remain for hadron jets!) It was concluded that one should stick to the present situation for publishing the 136-183 data and make sure that all ingredients are available in our Monte-Carlos to study the question more quantitatively before the next Winter conferences.
- Gerardo Ganis : Indirect leptoquark search ------------------------------------------- Gerardo Ganis emphasized that the Hera effect has now gone away and that their limits are now better than ours. The plot given for Jerusalem had the wrong sign for the interference term between s/t channel leptoquark diagrams. (true?) It was concluded that it will be best to 1.) recalculate the limits with the right sign. 2) Determine also the limits which can be applied to R parity violating squarks. 3) Include a paragraph in the paper to state what these limits are.
- Discussion: Plans for paper ---------------------------- Proposal that everyone writes their own section by the end of May at the latest. G. Dissertori volunteered to edit overall paper.
- Next meeting --->
To be arranged.
Alain Blondel