Measurement of the W boson mass with the DO detector and determination of the strong coupling constant with the ATLAS detector
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Abstract
A good theoretical description of electroweak boson production in hadronic
collisions at high center of mass energies is essential for the measurement of
the W boson mass. The DYRES computer program allows for the precise calculation
of the relevant production cross section, however, is limited in performance.
In this thesis, the DYRES program was significantly improved, leading to a new
tool named DYTURBO. In order to test the performance of the DYTURBO program,
the transverse momentum spectrum of Z bosons, pT(Z), produced in
proton-proton collisions at a center of mass energy of 13 TeV was
measured, using data collected by the ATLAS Experiment at the Large Hadron
Collider. Due to the large speed improvements of DYTURBO compared to
previous similar theoretical tools, it was possible for the first time to
extract the strong coupling constants by fitting the measured pT(Z)
distribution. This approach yields a value of αs(M²) = 0.1177 ± 0.0014
(syst+syst) ± 0.0086 (theo), in agreement with other measurements of the
ATLAS collaboration. The actual measurement of the W boson mass was
developed using data of proton--anti-proton collisions, recorded from 2009
to 2010 at √s = 1.96 TeV by the DØ experiment at Tevatron. The W boson mass
is extracted using the transverse energy distribution of decay electrons as
well as the transverse mass observable, using a novel, two-dimensional
fitting technique. The work focused on the estimation of uncertainties due
to the limited knowledge of parton density functions, which are the largest
theoretical uncertainties of the W boson mass measurement. Since the final
W boson mass analysis was not yet approved by the collaboration at the time
of the thesis submission, only the expected uncertainty can be made public
at this stage. The upcoming measurement of the DØ experiment is expected to
have a statistical and systematic uncertainty of 14 MeV and 19 MeV,
respectively.