Place: 32-SC-22
 Time:  Thursday 5, April 2001; 11:00 hours

 Agenda
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(1) Gerrit Prange         Status of Double Tagged Analysis
(2) Armin Boehrer         Preview of eta-b talk
(3) Alex Finch            Status of new Pythia studies
(4) Klaus Affholderbach   Status of Photon structure function
(5) AOB

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Minutes, 5 April 2001, by RWL Jones

1)      Double-tagged dijet production – softer cuts than OPAL, partly because comparing to different models, partly because prepared to accept background. Neutral and charged psuedorapidity distributions agree with Monte Carlos better than for most gamma-gamma samples, partly because sample is more central. Systematics by variation of tag energy, theta and phi resolutions, also calorimeter resolutions for the hadronic system, and change to use PHOJET for corrections. However, arguments even from the authors that use of PHOJET is inappropriate. Invariant mass distributions and virtuality plot pretty good for NLO, PHOT02 and PYTHIA; PHOJET OK, but not as good. Also look at ln(W/(Q₁Q₂)²) – agrees well with Kwiecinski et al, QPM disfavoured, PHOJET OK but not great. BFKL calculations yield different results. Excess in high-Y region above QED not very significant. Conference note writing to begin almost immediately – abstract by the end of the month.

2)      Armin – h_b . Cross-section calculable, new predictions. Can compare with this based on some assumptions on decays. Expect from QCD 156 produced, 24 should be seen in 4 charged and 16 in the 6 charged. Low background or 0.3+-0.3 and 0.8+-0.4 events respectively. 95% upper limits set Br(h_b to 4 charged)<17%, Br(h_b to 6 charged)<38% (assume Gamma(h_b)=416eV+-25%) Really measure PBR<57,128eV respectively.

3)      Alex – playing with intrinsic pT in PYTHIA 6.146 – can now handle soft physics and jets separately after delving into code. Has now avoided the excess of high-pT tracks. Sphericity is also now down to acceptable levels. The jet-pT is a telling distribution, with a clear split between soft and hard physics on the two sides of the plot. This now looks better, bit a bit too much soft physics with respect to the hard physics. If this works, we will have two good models of the untagged data for the first time.

4)      Structure functions (verbal report). 189 data now done, but the x-distribution in PYTHIA bad – this is for test of the hadronisation model dependence. Could play tricks with reweighting to still do this systematic check. Unfolding is now almost packaged for general use (few weeks of real work for Johannes). The story so far can be written-up for a conference note.