A W boson mass measurement using the ratio of transverse masses of the W and Z bosons in pp collisions at 1.8 TeV with the DO detector.

摘要

This dissertation reports on the measurement of the W boson mass from a direct determination of the ratio of the transverse masses of W and Z bosons using the DO detector at the Tevatron collider at Fermilab. The analysis is based on the W → enu and Z → e+e- decay modes.;In the standard DO W boson mass measurement method the transverse mass distribution of the W → enu decay products is compared to Monte Carlo templates for a set of input W mass values, and a sample of Z events is used for the calibration of electron and hadronic energy. The ratio method compares the transverse mass of the W sample directly to the scaled transverse mass of the Z sample. The comparison is based on the assumption that the transverse mass of the two decay products is insensitive to the production and decay mechanism of the two bosons but depends on the mass of the parent boson. If the MT( Z) distribution is scaled down by a factor of M( W)/M(Z), the new distribution would be identical to that of MT(W) for ideally measured transverse momenta of the decay products. The W mass is given by the product of the Z mass measured precisely at the LEP collider at CERN and the scale factor that optimizes the Kolmogorov-Smirnov probability for the two transverse mass distributions corrected for the detector acceptance and energy resolution.;As compared to the standard DO W mass analysis, the ratio method is less sensitive to uncertainties in the W and Z production model but has a larger statistical error due to a limited sample of Z events. The overall performance of the ratio method is expected to be competitive with the that of the conventional method in Run II of the Tevatron collider.;This study corresponds to an integrated luminosity of 82 pb-1 acquired by the DO detector during the Tevatron collider Run Ib (1994--1995). The data samples have been collected in both central and forward region of the detector. The W boson mass is found to be: mW=80.115+/- 0.211stat.+/-0.050 syst.GeV. .