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An Improved W Boson Mass Analysis with CDF Run II Data

 
Dan Beecher (c), Ilija Bizjak (c), Chris Hays (d), Bo Jayatilaka (b), Ashutosh Kotwal (b), Mark Lancaster (c), Sarah Malik (c), Emily Nurse (c), Larry Nodulman (a), Peter Renton (d), Tom Riddick (c), Ravi Shekar (b), Oliver Stelzer-Chilton (d), Dave Waters (c), Yu Zeng (b)
(a)Argonne National Laboratory, (b)Duke University, (c)University College London, (d)University of Oxford
 
 

The CDF collaboration has previously measured the mass of the W boson on 200 pb-1 of the Tevatron Run II data. The plots presented here are preliminary comparisons of the data and simulation using 2.3 fb-1 of the Tevatron Run II data for high pT muon and 2.4 fb-1 for high pT electron channels.

All the Z and W mass fits are blinded by a pre-selected unknown offset in the range of [-75MeV, 75MeV], which is different for Z and W bosons. The fit ranges are marked by arrows pointing to the lower and upper edges of the fit range. The fit plots quote the statistical uncertainty and the χ2 value of the fit.

 
 

Instantaneous luminosity

Instantaneous Luminosity profile

∑ET

Lumi Sum ET


Left: The comparison of the instantaneous luminosity distributions in Z→e+e+ decays for the sample used in the published result and the 2.4 fb-1 data. The average instantaneous luminosity in the 2.4 fb-1 data is 70 x 1030 s-1 cm-2.
Right: The comparison between the distributions of ∑ET, the sum of the ET deposits in the calorimeter, in data and simulation: the distributions are compared separately for events with instantaneous luminosity larger and lower than the average instantaneous luminosity, showing that the simulation captures the luminosity dependence of the distribution.
 
 

Z→μ+μ- invariant mass distribution


Left: The Z mass fit to the invariant mass of Z→μ+μ- decays.
Right: The comparison of the statistical uncertainties of the fitted Z mass: the statistical uncertainty for the published result (200 pb-1), the expected statistical uncertainty obtained by scaling the published result by the square root of the ratio of integrated luminosites, and the statistical uncertainty obtained from the presented preliminary fit. The fit uncertainties show that the muon momentum resolution in the 2.3 fb-1 dataset is comparable to that of the data used in the published result.
 
 

Z→e+e- invariant mass distribution


Left: The Z mass fit to the invariant mass of Z→e+e- decays.
Right: The comparison of the statistical uncertainties of the fitted Z mass: the statistical uncertainty for the published result (200 pb-1), the expected statistical uncertainty obtained by scaling the published result by the square root of the ratio of integrated luminosites, and the statistical uncertainty obtained from the presented preliminary fit. The fit uncertainties show that the electron energy resolution in the 2.4 fb-1 dataset is comparable to that of the data used in the published result.
 
 

Z→e+e- invariant mass plot using track information only


Left: The Z mass fit to the invariant mass of Z→e+e- decays, using track information of the electrons only.
Right: The comparison of the statistical uncertainties of the fitted Z mass: the statistical uncertainty for the published result (200 pb-1), the expected statistical uncertainty obtained by scaling the published result by the square root of the ratio of integrated luminosites, and the statistical uncertainty obtained from the presented preliminary fit. The fit uncertainties show that the electron tracking resolution in the 2.4 fb-1 dataset is comparable to that of the data used in the published result.
 
 

W→μν transverse mass distribution


Left: The W mass fit to the transverse mass of W→μν decays.
Right: The comparison of the statistical uncertainties of the fitted W mass: the statistical uncertainty for the published result (200 pb-1), the expected statistical uncertainty obtained by scaling the published result by the square root of the ratio of integrated luminosites, and the statistical uncertainty obtained from the presented preliminary fit. The fit uncertainties show that the degradation of the recoil resolution in the 2.3 fb-1 dataset has not significantly degraded the W transverse mass resolution.
 
 

W→eν transverse mass distribution


Left: The W mass fit to the transverse mass of W→ eν decays.
Right: The comparison of the statistical uncertainties of the fitted W mass: the statistical uncertainty for the published result (200 pb-1), the expected statistical uncertainty obtained by scaling the published result by the square root of the ratio of integrated luminosites, and the statistical uncertainty obtained from the presented preliminary fit. The fit uncertainties show that the degradation of the recoil resolution in the 2.4 fb-1 dataset has not significantly degraded the W transverse mass resolution.
 
 

W→eν E/pc distribution


Left: The fit to the E/pc distribution of W→ eν decays for the absolute scale of the energy measurement.
Right: The comparison of the W mass uncertainties due to the statistical uncertainty of the absolute energy scale fit : this uncertainty for the published result (200 pb-1), the expected uncertainty obtained by scaling the published result by the square root of the ratio of integrated luminosites, and the uncertainty obtained from the presented preliminary fit. The fit uncertainties show that the electron tracking and energy resolutions in the 2.4 fb-1 dataset are comparable to that of the data used in the published result.
 
 

J/ψ→μ+μ- invariant mass distribution


Left: The fit to the invariant mass distribution of J/ψ→μ+μ- decays for the absolute scale of the momentum measurement. The fit is performed in 8 bins of the average inverse muon momentum of the two muons, the example plot shown is for the highest momentum bin with significant statistics (0.1 < <1/pTμ> < 0.15 (GeV/c)-1, roughly corresponding to average muon momenta of 6.7 < <pTμ> < 10 GeV/c).
Right: The comparison of the W mass uncertainties due to the statistical uncertainty of the absolute momentum scale fit in the highest momentum bin: this uncertainty for the published result (200 pb-1), the expected uncertainty obtained by scaling the published result by the square root of the ratio of integrated luminosites, and the uncertainty obtained from the presented preliminary fit. The fit uncertainties show that the muon momentum resolution in the 2.3 fb-1 dataset is comparable to that of the data used in the published result.
 
 

Υ(1S)→μ+μ- invariant mass distribution


Left: The fit to the invariant mass distribution of Υ(1S)→μ+μ- decays for the absolute scale of the momentum measurement.
Right: The comparison of the W mass uncertainties due to the statistical uncertainty of the absolute momentum scale fit: this uncertainty for the published result (200 pb-1), the expected uncertainty obtained by scaling the published result by the square root of the ratio of integrated luminosites, and the uncertainty obtained from the presented preliminary fit. The fit uncertainties show that the muon momentum resolution in the 2.3 fb-1 dataset is comparable to that of the data used in the published result.