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

Section 2: Supersymmetry 41
multijet event. We developed a `tomographic' cleanup algorithm to reject the events with
the second most energetic jet pointing to a crack and being collinear with the missing energy
vector.
We refer to this procedure as \jet verication" and it is a a crucial element for
improving the reach of this analysis.
In the diagram of Fig. 20 a side view of quarter of the detector is drawn and the cracks
where the jets might escape detection are shown. One expects in the case of jets being lost
in the cracks the events to be distributed in the vs zvertex plane as shown in the bottom
diagram of Fig. 20.
Indeed in Fig. 21 we see this behavior in the data where the second jet falls in a detector
boundary and the 6E T is collinear with the second jet. We reject the events that fall in the
high density stripes on both the 2nd jet detector -event z vertex plane and the 6 E T
- 2nd jet
(in radians) plane.
The following requirements are designed to have good W/Z/top background rejection
eciency, they make use of the kinematic and topological characteristics of the SUSY signal
and eliminate residual QCD mismeasurements:
at least 3 jets
6E T 60 GeV
2nd jet
H T = ET
3rd jet
+ ET + 6E T : :200 GeV .
None of the two leading jets should be purely electromagnetic
No azimuthal correlation between the direction of the rst two jets and the 6E T .
After this selection the signal eciency for a high squark gluino mass point in the SUSY
parameter space is 15%. This signies an improvement over the Run Ia CDF seach (eciency
in the range of 1-5%) and over the Run Ib D0 search (in the range 1-10%).
W, Z Background Normalization
In order to get a precise estimate of the W/Z QCD associated background with a
neglidgable systematic dependance on the renormalization and factorization scale we normalize
the Monte Carlo prediction for Z ! + 3 jets and W ! + 2 jets rates
using the data rates of Z ! e + e , + 2 jets.