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

Chapter 6: Event Selection 166
Entries
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-1
∫L
dt = 331 nb
Data 2010 (
Z → µ µ
bb
cc
W → µ ν
Z → τ
tt
s=7
TeV)
0
0 10 20 30 40 50
MDT hits/track
Figure 6.2: MDT hits per muon track for signal Monte Carlo, background Monte
Carlo and data after event preselection. The total Monte Carlo event number has
been normalized to the number of events in data.
segment must have at least 3 hits on it, in principle there should be no track with less
than 6 hits. We see a very small number of tracks with 3-5 hits, which are most likely
badly reconstructed tracks with two segments that share one or more MDT hits.
A track can have more than 20 MDT hits owing to two reasons:
• It traverses the overlap region between adjacent φ sectors. Such a track can
have a maximum of 40 hits, assuming that it does not have more than one hit
in any MDT tube layer.
• It traverses multiple tubes in the same tube layer. Because of the geometry of
the multilayers, there should be very few such tracks in collision events.
We see that a small number of tracks have more than 40 hits, which are tracks