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

Section 2: W Mass 53
Number of tagged events
12
10
8
6
4
Events with SECVTX tags
SLT tags
data
Top
QCD
2
0
1 2 3 ≥4
Number of jets
Figure 27: Comparison of the observed and predicted rates of SLT tags in events with
SECVTX tags. The predictions are based on the W sample composition determined by the
measurement of the tt cross section with SECVTX.
seems to exclude a mistake in the predictions. On the other hand, since the tagging eciency
of JPB for c-jets is a factor of two smaller than the tagging eciency of SECVTX for b-jets,
it implies that the new W + c-jets production mechanism will have a cross section a factor
two larger than tt production.
For the SLT, it is useful to compare observed tags to expectations only in the sample
tagged by SECVTX since the sample without SECVTX tags has too much background. The
rates of observed and predicted SLT tags are shown in Fig. 27. In the W + 2 jet sample
tagged by SECVTX, there is an excess of 7:33:3events to be compared with an expectation
of 5.3 top events. So, in the SLT case, there is no sign of a discrepancy, within the large
statistical uncertainty. Still we are studying the kinematic features of these events and nd
some surprising features which cannot easily be explained by Standard Model processes.
More work is required before we fully unravel the mysteries behind these fascinating
anomalies. An article for Physical Review reporting the cross section measurements given
above is planned. These cross-sections have been recently blessed by the CDF Collaboration.