Measurements of the Mass and Width of the W Boson From e+e- → W+W- → (e/mu)nuqq¯ Events With the ALEPH Detector

Raeven, Barbara Maartje (2000) Measurements of the Mass and Width of the W Boson From e+e- → W+W- → (e/mu)nuqq¯ Events With the ALEPH Detector. PhD thesis, University of Glasgow.

Abstract

In 1998 at CERN (Geneva), 174 pb-1 of data was collected with the ALEPH detector, at an e+e- centre-of-mass energy of 188.6 GeV. For this dataset, the selection of semi-leptonic decays of W boson pairs (WW→(e/mu)nuqq¯) is improved. The resulting efficiencies for selecting enuqq¯ and muvqq¯ events are 82.0% and 88.1% respectively, with purities of 92.4% and 93.3%. For the first time in ALEPH, the width of the W boson is measured using a two parameter (mass Mw and width Gammaw) fit to the reconstructed W mass distribution, yielding: Mw = 80.313 +/- 0.119(stat.) +/- 0.052(syst.) GeV/c2 and Gammaw = 2.17+0.29-0.26(stat.)+0.11(syst.) GeV/c2, for enuqq¯ and muvqq¯ decays combined. The mass value is in good agreement with the world average mass and the width value is in good agreement with Standard Model calculations. The systematic error includes detector uncertainties as well as uncertainties in the background, the beam energy and the theoretical model. Additional studies are done with respect to previous years to take into account errors in the angular and energy resolutions of the ALEPH detector. The stability of the data fit results is checked as a function of various selection cuts. A preliminary measurement is performed at centre-of-mass energies ranging from 191.6 to 201.6 GeV. These results are combined with the result above to obtain the preliminary result for a total integrated luminosity of 411 pb-1: MW = 80.537 +/- 0.079 + 0.052 GeV/c2 and Gammaw = 2.11+0.20-0.18+/- 0.11 GeV/c2.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Adviser: D Saxon
• Keywords: High energy physics, Theoretical physics
• Date of Award: 2000
• Depositing User: Enlighten Team
• Unique ID: glathesis:2000-76277
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 19 Nov 2019 16:11
• Last Modified: 19 Nov 2019 16:11
• URI: https://theses.gla.ac.uk/id/eprint/76277