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

Appendix B
Comparison of muon curvature in
cosmic events
Figure B.1 shows the signed inverse momentum, i.e. , curvature of muon spec-
trometer tracks in bins of the momentum of inner detector tracks that have been
matched to the spectrometer tracks. The criteria used for track selection in the MS
and the ID as well as for the matching were described in Section 6.2.5.
If the ID and the MS measured exactly the same momentum for a track, each
histogram would have two peaks of identical shape symmetrically on each side of q/P
= 0. This is not seen to be not the case: events migrate to bins above and below
those that correspond to PID = PMS. Moreover, as the track momentum increases,
we see a corresponding increase in the fraction of tracks that migrate out of bin. In
particular, for PID > 120 GeV, a significant fraction of tracks migrate to higher
momentum (i.e. , lower curvature) bins. This effect is most pronounced in the [400,
1000] GeV bin (lower right plot in Figure B.1).
The observed migration is believed mainly to be due to misalignments in both
the ID and the MS, and in particular due to relative misalignment between the two
systems. It points to the need for more precise alignment within and between the
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