2 The CDF Experiment at Fermilab Contents - Harvard University ...

82 Section 2: CDF Physics Analysis
of signal eciencies (based on Pythia Monte Carlo) and the background rates (based on \Jet
20" data).
In addition, in Run II every trigger has to have a full path (i.e., specied criteria at all
trigger levels), so we also place a cut on Level 1 P (L1) E T . While P (L2) E T is a sum of found
P calorimeter clusters, (L1) E T is just a sum over trigger towers above a threshold; the two are
physically dierent quantities, the latter being much more sensitive to underlying event and
pile-ups. The threshold for Level 1 sum is still under negotiations in the Trigger Working
Group (currently 1 GeV), with us favoring higher values.
P Fig. 40 shows the eciencies and the rates as a function of (L2) E T given the calorimeter
cuts at Levels 1 and 2, plus a requirement for two b-tags at Level 3.
The Use of Tracking
The lowering of the Level 2 calorimeter cuts necessarily increases the rate for the multijet
trigger. As outlined above, we cut the rate down by making use of the tracking devices
implemented in hardware: eXtremely Fast Tracker (XFT, operating on COT data at Level 1)
and Silicon Vertex Tracker (SVT, operating on SVXII data { seeded by XFT {atLevel 2).
The XFT-SVT combination provides measurements of p T , and d 0 for reconstructed tracks.
We assume that the set of \XFT tracks" (approximated by CTC tracks of Run I data)
that are reconstructed in the SVX', is a good approximation of an \SVT track" sample. We
studied the eciencies and the rates as a function of the number of XFT-SVT tracks, the
number of displaced tracks, and the displacement for a xed number of `displaced' tracks.
We found that a cut on d 0 > 150m ontwo or more tracks, or d 0 > 100m on three or more
is benecial.
Future Work
In order to complete this study in the near future, we plan to focus on
1. A combined simulation of XFT and SVT: A package consisting of XFTSIM and
SVTSIM is available, but awaits the SVX' alignment les from the SVTSIM experts for
Jet 20 data. Nonetheless, it is being claimed that the resolutions on p T and d 0 are
comparable to those of the Run I oine, so we expect the nal results to be similar to
our current estimates based on Run I data.
2. b-tagging in trigger using leptons: we will add lepton information as another basis