A Top Quark Mass Measurement Using the R32 Stabilized Variable with the ATLAS Detector

Guindon, Stefan

dc.contributor.advisor	Quadt, Arnulf Prof. Dr.	de
dc.contributor.author	Guindon, Stefan	de
dc.date.accessioned	2012-08-31T15:59:16Z	de
dc.date.accessioned	2013-01-18T13:42:14Z	de
dc.date.available	2013-01-30T23:51:13Z	de
dc.date.issued	2012-08-31	de
dc.identifier.uri	http://hdl.handle.net/11858/00-1735-0000-000D-F08C-4	de
dc.identifier.uri	http://dx.doi.org/10.53846/goediss-2928
dc.description.abstract	Die vorliegende Arbeit beschreibt die erste Messung der Masse des Top-Quarks mit dem ATLAS-Experiment, einem von vier gro	de
dc.format.mimetype	application/pdf	de
dc.language.iso	eng	de
dc.rights.uri	http://creativecommons.org/licenses/by-nc-nd/3.0/	de
dc.title	A Top Quark Mass Measurement Using the R32 Stabilized Variable with the ATLAS Detector	de
dc.type	doctoralThesis	de
dc.title.translated	Messung der Masse des Top-Quarks mit R32 mit dem ATLAS-Experiment	de
dc.contributor.referee	Brock, Ian Prof. Dr.	de
dc.date.examination	2012-06-25	de
dc.subject.dnb	530 Physik	de
dc.subject.gok	RDE400 Experimentalphysik	de
dc.description.abstracteng	This thesis presents one of the first measurements of the top quark mass at the ATLAS experiment, one of the four large experiments located along the LHC. First discovered in 1995 at the Tevatron experiments CDF and D0, the top quark is the heaviest of the known elementary particles. Due to its very large mass and large Yukawa coupling, it may yet play an unknown role in electroweak symmetry breaking. The large Yukawa coupling also means it has a strong connection to the Higgs field, and thus gives an indirect insight into the mass of the missing Higgs boson. To measure the top quark mass, a kinematic reconstruction is performed using the KLFitter to properly reconstruct the decay products in the lepton + jets channel of a ttbar pair decay. The lepton + jets channel has a significant branching ratio and a moderate background. Using the kinematic information of the event, along with the b-tagging efficiency and rejection, the kinematic likelihood fitter obtains a reconstruction efficiency of about 70 % for each of the separate mu + jets and e + jets channels. From the reconstructed event, a so-called R32 estimator is constructed, which is built from the hadronic hemisphere of the ttbar decay. The R32 is the ratio of the measured hadronic top mass and the reconstructed hadronic W mass. The ratio reduces the significant uncertainty due to the jet energy scale, the largest of the uncertainties on the top mass measurement. A further optimization of the estimator is performed to limit other systematics such as the bJES and initial and final state radiation effects. This is done with the use of the kinematic likelihood and larger pt cuts. A template fit is performed using a parametrization of the signal and background components of the R32 distribution. The method is cross-checked using ensemble tests. The resulting mass is determined using 1.04 fb^-1 of data collected during the 2011 ATLAS run. A large number of systematics are also quantified. The measurement is performed in both the e + jets and mu + jets channels separately and then combined into a single lepton + jets measurement using the best linear unbiased estimator (BLUE) method. The top mass is measured to be: m = 174.4 +/- 0.9 (stat.) +/- 2.5 (syst.) GeV/c^2, with only a 1.5 % relative uncertainty on the top mass, a significant achievement for the early ATLAS data taking.	de
dc.contributor.coReferee	Kollatschny, Wolfram Prof. Dr.	de
dc.contributor.thirdReferee	Frey, Ariane Prof. Dr.	de
dc.subject.topic	Physics	de
dc.subject.ger	Top Masse	de
dc.subject.ger	Quark	de
dc.subject.ger	Hochenergiephysik	de
dc.subject.ger	CERN	de
dc.subject.ger	LHC	de
dc.subject.ger	ATLAS	de
dc.subject.ger	Kernphysik	de
dc.subject.eng	Top Mass	de
dc.subject.eng	Quark	de
dc.subject.eng	High Energy Physics	de
dc.subject.eng	CERN	de
dc.subject.eng	LHC	de
dc.subject.eng	ATLAS	de
dc.subject.eng	Particle Physics	de
dc.subject.bk	33.46 Hochenergie-Kernphysik	de
dc.identifier.urn	urn:nbn:de:gbv:7-webdoc-3678-6	de
dc.identifier.purl	webdoc-3678	de
dc.affiliation.institute	Fakultät für Physik	de
dc.identifier.ppn	731660544	de

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