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

Chapter 4: Data Collection and Event Reconstruction 147
tracks. The results are summarized in Table 4.4.
Standalone tracks Combined tracks Overall
Data efficiency 0.981 ± 0.003 0.991 ± 0.002 0.972 ± 0.003
MC efficiency 0.993 0.997 0.991
Table 4.4: Measured relative muon reconstruction efficiency in data and Monte Carlo
using a factorized method. Errors on the data measurement are statistical only.
Errors on the Monte Carlo numbers are negligibly small.
Since the samples used in this method contain decay-in-flight contamination, the
difference between these results and those from the template fit corrected method
is a measure of the uncertainty arising from the contamination. The overall data
efficiency in Table 4.4 differs from the decay-in-flight corrected efficiency by ≈ 2%.
We take this number as a conservative estimate of the systematic from this source.
Other sources of systematic error on the combined reconstruction efficiency include
the error on inner detector track reconstruction efficiency (1%), the error in MDT hit
efficiency (0.3%), selection bias due to the tagging criteria (0.4%) and cut stability
(0.5%) [62]. The various contributions are added in quadrature, leading to an overall
systematic error on the measured efficiency of 2.4% (Table 4.5).
Data efficiency 0.994 ± 0.006 (stat) ±0.024 (syst)
MC efficiency 0.986
Data/MC scale factor 1.008 ± 0.006 (stat) ±0.024 (syst)
Table 4.5: Final results, including the data/MC scale factor, for the MS hit method
of estimating combined track reconstruction efficiency.
The tag-probe method
The tag-probe method utilizes the correlation between the two muons in Z → µµ
decays. The first step is to define a sample of tagged events which contain at least