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

Chapter 4: Data Collection and Event Reconstruction 143
systematic on the tube hit efficiency.
Reconstruction efficiency of combined muon tracks
In principle, the efficiency with which objects are reconstructed in a particular
subdetector can be obtained from a Monte Carlo study. For example, the reconstruc-
tion efficiency for muons can be estimated from a simulated sample by comparing
the number of generated muons to the number of reconstructed muons. However, a
detector simulation will generally not be very accurate and, in particular, realistic
background conditions cannot be modeled with precision. Hence, it is preferable to
derive reconstruction efficiencies from real data with minimal reliance on simulation.
As stated in Section 4.2.3, we use combined muons from the Staco algorithm in our
analysis, so that we want to estimate the efficiency of this particular reconstruction
path. We derive the efficiency using two independent approaches, both of which
measure the combined muon reconstruction efficiency relative to the inner detector
track reconstruction efficiency. In the MS hit method, ID tracks are tagged as muon
tracks using hits in the muon spectrometer, while in the tag-probe method, ID tracks
are tagged as muon tracks by identifying them as coming from Z → µµ decays. Both
methods are described below.
The MS hit method
The selection criteria for events and for inner detector tracks used by this method
are summarized in Table 4.2. The event selection criteria maximize the probability
that the events are from collisions, while the kinematic and quality cuts on the tracks
select well-reconstructed tracks that have similar characteristics to tracks from Z