Talks

• 3D vertexing status: Chris Barnes
  A lot of progress has been made towards achieving a high performance 3D primary vertexing tool for L3. Performance and consistency checks on ttbar, QCD and B_s Monte Carlo samples give following results:
  • Primary vertex does significantly better than beam spot constraint alone.
  • Pull distributions on reconstructed vertex position look reasonable. They have slight non-gaussian tails.
  • The width of the x and y distributions of the reconstructed vertex positions reproduce pretty well the generated MC beam spot widths, but are a bit narrower than they naively should be. For example, the width in x is found to be about 30 microns. However, it should be the quadrature sum of the generated width (30) and the width of the residual distribution (22) = 37 microns.
  • With some residual worries about this bias, it looks like the actual beam width in real data is of order 40 microns in x and 45 microns in y. This is a lot narrower than that obtained with offline vertexing. The suspicion is that the L3 vertexer is doing much better than the offline vertexer, but some more work needs to be done on this.
  Outstanding issues:
  • It would good to take the input beam tilts into account together with the reconstructed z of the primary vertex to get a better estimate of the xy beam spot position.
  • It would be good to take a look at the efficiency of the vertex finder as well as resolution in the optimization of the cut on Chisquared per degree of freedom. Good also to check that optimising on other MC samples gives approximately the same value of the cut.
  • As a test, it would be good to repeat the data and MC studies with the beam-spot uncertainty set to a large value, say 150 microns (in order to eliminate the possibility that the selection of tracks or the beam spot constraint is causing the width of the reconstructed primary vertex positions to be biassed towards too low values).
  • There is some concern that the cut at 0.2 on contribution of tracks to the chisquared per degree of freedom may be rather tight for low multiplicity vertices.
  Conclusion is that we already have a high performance 3D primary vertexing tool for L3 in p15.
• Status of comparator: Han Do
  
  • l3fanalyze-based comparator is making progress. Taus, electrons, jets and tracks have a few variables each checked.
  • .html files produced which summarize the results for each tool.
  • Ignoring events that are M&P either online or offline is an important part of this infrastructure. Han Do has created a new package "l3anasys" which makes it possible to know the M&P information both for online and offline within the rootuple. l3anasys also stores information on the on-/off-line values of the l3bits and l3 triggernames on the rootuple.
  • Some disquiet was expressed that time is being invested in a completely separate infrastructure based on TMB, before the l3fanalyze-based comparator has been finished. This will be discussed offline by Dan, Han and Terry.
• Informal update on status of L3Muon investigations: Martin Wegner
  Comparison between old and new data, on- and off-line results is continuing to try and understand the rejections obtained with the L3L15 filter.

Scribe: Terry Wyatt.