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

Chapter 6: Event Selection 197
Parameter µ + µ −
Energy loss [ GeV/c] 0.28 ± 0.09 0.43 ± 0.16
Multiple scattering [%] 3.60 ± 0.21 2.95 ± 0.66
Intrinsic resolution [10 −4 /( GeV/c)] 3.07 ± 0.61 4.19 ± 0.87
Table 6.13: Result of the pT resolution fits using MS-ID matched tracks, shown
separately for positive and negative muons.
The pT scale in each p ID
T bin is taken to be the fitted mean of the first Gaussian.
This choice corresponds to selecting the most probable value of the Landau distri-
bution. The scale thus derived is shown in Figure 6.17 separately for positive and
negative muons as a function of the muon pT. As can be seen, in the pT range of
interest for Z → µµ events (20-50 GeV), the scale is ≈ 1-2% for muons of both signs,
which approximately agrees with the measurement using fits to the Z peak.
The pT resolution is taken to be the fitted width of the first Gaussian. The
resolution thus derived is shown in Figures 6.18 separately for positive and negative
muons. The resolution vs. pT graphs are fitted with the following function:
F(p) =a/p ⊕ b ⊕ c · p, (6.13)
where the coefficients a, b, and c respectively describe the contribution to the overall
pT resolution from energy loss, multiple scattering, and intrinsic detector resolution.
The three components are added in quadrature. The results of the resolution fits are
summarized in Table 6.13.
We see that the resolution thus derived is ≈ 4% for both positive and negative
muons in the pT range of interest for Z → µµ events, which again agrees within error
with the values obtained from fits to the Z peak.
A comparison of the curvature (reciprocal of the momentum) between matched
MS and ID tracks can be found in Appendix B, together with a brief discussion of