Measurement of the Z boson cross-section in - Harvard University ...

Chapter 4: Data Collection and Event Reconstruction 99
Number of Events
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Number of Seeds
Figure 4.2: Number of tracks seeds per event in data and simulation. The data is
not expected to agree with the simulation because, firstly, the track multiplicities are
different between the two and, secondly, the simulation did not include diffractive
events.
clusters removed and the tracks refitted again. Low-scoring tracks are then rejected
and the remaining candidates are extended into the TRT.
All TRT hits in a road around an extrapolated track candidate are associated
with the track. The track is then refitted and rescored. If the full track scores higher
than the original silicon-only track, the TRT extension is added to the silicon-only
track, forming a global inner detector track. Otherwise, only the silicon part of the
track is fitted; the TRT extension is kept as part of the track, but not used in the fit.
The final tracks are stored in a dedicated track collection 3 .
3 Note that, since the TRT extends only to |η| < 2.0, while the silicon extends to |η| < 2.5, some
inner detector tracks have no TRT extension.