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80 Section 2: CDF Physics Analysis
We do not optimize on the basis of single number, such asS=B or S 2 =(S +B), since there is a
danger of being locked in a nonoptimal data point once new cuts are introduced a posteriori.
First Pass
Post-docs Petar Maksimovic and Werner Riegler were instrumental in carrying this study.
The initial changes to the Multijet trigger were suggested by the distributions of the Level 2
cluster quantities from both H + W=Z Monte Carlo and data. Since it was soon apparent
that the leading jet in H + W=Z events almost always has E T > 20 GeV, as a background
sample we perused the so-called \Jet 20" data, a Run I sample with at least one cluster with
E T
> 20 GeV required at Level 2. The signal sample is a Pythia Monte Carlo, simulated
through P the full Run I detector simulation. Fig. 39 shows the distributions the number of
jets, E T , and E T of the four highest-E T jets from W=Z +H Monte Carlo (solid) (generated
with m H = 110 GeV), and the Jet 20 data (dashed), normalized to the same area.
Motivated by the shapes of these distributions, we modied the old multijet trigger in
the following way:
1. We expect four jets in the WH or ZH event. Since not all jets are reconstructed, and
some are merged with others, we nd the requirement of four jets too restrictive, and
relax it to three.
2. We also relax the Level 2 P (L2) E T cut to 70 GeV.
3. To these kinematics cuts, we add the requirement of at least one displaced SVT track
at Level 2, and at least two SECVTX tags at Level 3.
Fig. 39 shows the comparison of the relevant distributions between the W=Z + H Monte
Carlo (solid) and the Jet 20 (dashed).
Run II trigger simulation of the calorimeter response
In order to study calorimeter requirements (which are fundamental for this trigger), we
utilized the Run II trigger simulation developed by the Run II Trigger Working Group.
The trigger simulation was applied to both signal Monte Carlo and to Jet 20 data (based
on the oine jet information). Given the importance of Level 2 criteria, we rst varied the
P
(L2) E T threshold, as well as the cuts on E T of individual jets, and examined the dependence