Constraining couplings of the top quarks to the Z boson in ttbar+Z production at the LHC

We study top quark pair production in association with a Z boson at the Large Hadron Collider (LHC) and investigate the prospects of measuring the couplings of top quarks to the Z boson. To date these couplings have not been constrained in direct measurements. Such a determination will be possible for the first time at the LHC. Our calculation improves previous coupling studies through the inclusion of next-to-leading order (NLO) QCD corrections in production and decays of all unstable particles. We treat top quarks in the narrow-width approximation and retain all NLO spin correlations. To determine the sensitivity of a coupling measurement we perform a binned log-likelihood ratio test based on normalization and shape information of the angle between the leptons from the Z boson decay. The obtained limits account for statistical uncertainties as well as leading theoretical systematics from residual scale dependence and parton distribution functions. We use current CMS data to place the first direct constraints on the ttbZ couplings. We also consider the upcoming high-energy LHC run and find that with 300 inverse fb of data at an energy of 13 TeV the vector and axial ttbZ couplings can be constrained at the 95% confidence level to C_V=0.24^{+0.39}_{-0.85} and C_A=-0.60^{+0.14}_{-0.18}, where the central values are the Standard Model predictions. This is a reduction of uncertainties by 25% and 42%, respectively, compared to an analysis based on leading-order predictions. We also translate these results into limits on dimension-six operators contributing to the ttbZ interactions beyond the Standard Model.Comment: JHEP version + error in Eq. 2.6 corrected and corresponding higher order operator limits modifie

Probing top-Z dipole moments at the LHC and ILC

We investigate the weak electric and magnetic dipole moments of top quark-Z boson interactions at the Large Hadron Collider (LHC) and the International Linear Collider (ILC). Their vanishingly small magnitude in the Standard Model makes these couplings ideal for probing New Physics interactions and for exploring the role of top quarks in electroweak symmetry breaking. In our analysis, we consider the production of two top quarks in association with a Z boson at the LHC, and top quark pairs mediated by neutral gauge bosons at the ILC. These processes yield direct sensitivity to top quark-Z boson interactions and complement indirect constraints from electroweak precision data. Our computation is accurate to next-to-leading order in QCD, we include the full decay chain of top quarks and the Z boson, and account for theoretical uncertainties in our constraints. We find that LHC experiments will soon be able to probe weak dipole moments for the first time.Comment: 17 pages, 6 figure

Cycles: exploring the intertextual relationships between Bheki Mseleku, Bokani Dyer and Thandi Ntuli

Bheki Mseleku was a South African-born jazz pianist, composer and improviser. During his life-time, Mseleku had a prominent career in London and since his death his compositions have been widely performed in South Africa. In the late 1970s he went into exile and moved to London, where he received greater recognition as a composer and performer than in his homeland. From 1991 to 2003 Mseleku recorded six original albums, displaying a lyrical and technical jazz pianism. As a composer, Mseleku was prolific, incorporating a cyclical style with extensive use of harmonic sequences, as is evident in his work Aja (1997). He also employs both Zulu and European musical aesthetics, such as in Celebration (1991), as well as an introspective spiritualism such as in Looking Within (1993) and Meditations (1992). In recent years, there has been renewed interest in Mseleku's music, both from jazz musicians as well as jazz scholars. This research discusses and considers the relationships between Mseleku's compositions and those of younger South African jazz pianists Bokani Dyer (b. 1986) and Thandi Ntuli (b. 1987). Through the use of intertextual theoretical frameworks and jazz analysis, this thesis explores the notion of influence and the dialogical relationships of these artists' compositions. These intertextual structures are paired with a close reading of selected works of Mseleku, Dyer and Ntuli, to critically discuss the posthumous influence that Mseleku has had on two members from a younger generation of South African jazz musicians. This research aims to consider Mseleku's role and influence within South African jazz music. This dissertation deconstructs the intertextual relationship between the music of Bheki Mseleku and Bokani Dyer and Thandi Ntuli. In doing so, this research questions how Mseleku's musical praxis informs that of Dyer's and Ntuli's, as well as how intertextual relationships can be explored through jazz musical analytical methodologies

Mixed scalar-pseudoscalar Higgs boson production through next-to-next-to-leading order at the LHC

We study the production of a mixed scalar-pseudoscalar Higgs boson in gluon fusion at the LHC, through next-to-next-to-leading order (NNLO) in QCD. We obtain fully differential results, including the decay of the Higgs boson to two charged lepton pairs. We discuss the impact of the interference between the scalar and pseudoscalar states. We also show differential distributions for several kinematic variables whose shape is sensitive to the parity of the Higgs boson, and assess the impact of the NNLO QCD corrections on these shapes

NNLO QCD corrections to weak boson fusion Higgs boson production in the H → bb‾\overline{b} and H → WW* → 4l decay channels

We compute the next-to-next-to-leading order QCD corrections to Higgs boson production in weak boson fusion followed by its decay to a b$\overline{b}$ pair or to a pair of leptonically-decaying W bosons. Our calculation allows us to compute realistic fiducial cross sections and assess the impact of fiducial cuts applied to the Higgs boson decay products on the magnitude of QCD radiative corrections in weak boson fusion

Analytic results for color-singlet production at NNLO QCD with the nested soft-collinear subtraction scheme

We present analytic formulas that describe the fully-differential production of color-singlet final states in qq̄ and gg annihilation, including all the relevant partonic channels, through NNLO QCD. We work within the nested soft-collinear scheme, which allows the fully local subtraction of infrared divergences.We demonstrate analytic cancellation of soft and collinear poles and present formulas for the finite parts of all integrated subtraction terms. These results provide an important building block for calculating NNLO QCD corrections to arbitrary processes at hadron colliders within the nested soft-collinear subtraction scheme