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

Chapter 6: Event Selection 194
• ID tracks:
– the TRT event phase is non-zero, and lies in the interval [-25, 25] ns
– track fit χ 2 /DoF < 5
– the track has at least 20 hits in the TRT
– 2×SCT hits ≥ 8 (note that the Pixels were off in the run used for the
measurement)
– the transverse impact parameter d0 < 299 mm
– the longitudinal impact parameter z0 < 540 mm
– track p ≥ 2 GeV/c
For this study, we use events from the IDCosmic 5 stream of the run. Only those
events with exactly one ID track are used. The matching of an ID track with an MS
track requires:
• the difference in the polar angle θ between the two tracks, δθ < 50 mrad
• the difference in the azimuthal angle φ between the two tracks, δφ < 50 mrad
Figures 6.15 and 6.16 show the fitted distributions of Pdiff respectively for positive
and negative muons, in bins of p ID
T . The fit function is a Gaussian convoluted with
a Landau distribution. A second Gaussian is added to describe the tails due to
mismatched ID-MS pairs; its normalization is forced to be no more than 30% of the
total number of entries.
5 The IDCosmic stream contains events with a high probability of having at least one track
traversing the ID, as estimated from the pattern of hits in the ID subdetectors at Level-2.