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Analysis of the $Wtb$ vertex from the measurement of triple differential angular decay rates of single top quarks produced in the $t$-channel at $\sqrt{s}=$8 Tev with ATLAS detector

Su, Jun (2017) Analysis of the $Wtb$ vertex from the measurement of triple differential angular decay rates of single top quarks produced in the $t$-channel at $\sqrt{s}=$8 Tev with ATLAS detector. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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The electroweak production and subsequent decay of single top quarks is determined by the properties of the Wtb vertex, which can be described by the complex parameters of an effective Lagrangian. An analysis of angular distributions of the decay products of single top quarks produced in the t-channel constrains these parameters simultaneously. The thesis presents this analysis which uses 20.2 fb−1 of proton–proton collision data at a centre-of-mass energy of 8 TeV collected with the ATLAS detector at the LHC. The fraction f1 of decays containing transversely polarised W bosons is measured to be f = 0.296+0.048 −0.051 (stat. + syst.). The phase δ_ between amplitudes for transversely and longitudinally polarised W bosons recoiling against left-handed b quarks, is measured to be δ_ = 0.002π+0.016π−0.017π (stat. + syst.), giving no indication of CP violation. The fraction of longitudinal to transverse W bosons accompanied by right-handed b-quarks are also constrained at 95% C.L. to f1+ < 0.118 and f0+ < 0.085. Based on these measurements limits are placed at 95% C.L. on the ratio of the complex coupling parameters gR and VL such that Re [gR /VL ] ∈ [−0.122, 0.168] and Im [gR /VL ] ∈ [−0.066, 0.059]. Constraints are also placed on the magnitudes of the ratios |VR/VL|, and |gL/VL|. Finally the polarisation of single top quarks in the t-channel is constrained to be P > 0.718 (95% C.L.). None of the above measurements make assumptions on the value of any of the other parameters or couplings and all of them are in agreement with the Standard Model.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairBoudreau,
Committee MemberMueller,
Committee MemberFreitas,
Committee MemberZentner,
Committee MemberPaulini,
Date: 1 July 2017
Date Type: Publication
Defense Date: 16 March 2017
Approval Date: 1 July 2017
Submission Date: 17 April 2017
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Number of Pages: 222
Institution: University of Pittsburgh
Schools and Programs: Dietrich School of Arts and Sciences > Physics
Degree: PhD - Doctor of Philosophy
Thesis Type: Doctoral Dissertation
Refereed: Yes
Uncontrolled Keywords: Top ; Single Top ; Anomalous Couplings ; EWEAK
Date Deposited: 02 Jul 2017 01:01
Last Modified: 02 Jul 2017 01:01


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