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

Section 2: Z Decays to bb 63
2.3.4 Study of the decay Z ! bb
(Dr. Dorigo)
While decays of Z bosons to b-quark pairs have been studied for some years at LEP and
SLC, they have never been observed in pp collisions. The extraction of a signal in Run I data
is therefore interesting. The knowledge gained will prove invaluable for designing advanced
dedicated triggers for Run II. These events would help calibrate the absolute energy scale
for b-quark jets, substantially reducing one of the critical sources of systematic uncertainty
in the top quark mass measurement.
CDF PRELIMINARY
Events per 10 GeV/c 2
120
Selected Sample
100
— Unbinned Likelihood Fit
80
– – Background
60
… Z → bb Signal
40
20
0
0 20 40 60 80 100 120 140 160 180 200
Dijet Invariant Mass (GeV/c 2 )
Events per 10 GeV/c 2
5000
4000
3000
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1000
Background Sample
— Unbinned Likelihood Fit
0
0 20 40 60 80 100 120 140 160 180 200
Dijet Invariant Mass (GeV/c 2 )
Figure 32: Top: the Z peak in the signal sample; bottom: a signal-depleted sample is used to
extract the background shape.
Dorigo extracted a signal for Z ! b b signal using kinematic tools and b-quark tagging for
his Ph.D. thesis with Padova University (see Fig. 32). Starting from a dataset of about ve