Abstract
We perform a comparative study of the reach of future e^+e^- collider options for the scale of non-resonant new physics effects in the top quark sector, phrased in the language of higher-dimensional operators. Our focus is on the electroweak top quark pair production process e^+e^- rightarrow Z^*/gamma rightarrow tbar{t} , and we study benchmark scenarios at the ILC and CLIC. We find that both are able to constrain mass scales up to the few text {TeV} range in the most sensitive cases, improving by orders of magnitude on the forecast capabilities of the LHC. We discuss the role played by observables such as forward–backward asymmetries, and making use of different beam polarisation settings, and highlight the possibility of lifting a degeneracy in the allowed parameter space by combining top observables with precision Z-pole measurements from LEP1.
Highlights
Studies of the couplings of the top quark form one of the cornerstones of the analysis program pursued at the LHC, where top quark related processes, most notably ttproduction, are ubiquitous
Since we are most interested in the International Linear Collider (ILC) mass reach for new physics, in this study we focus on the 500 GeV ILC running
Given the unsatisfactory precision of current probes of top quark electroweak couplings from hadron collider measurements, they must be a key priority in the physics agenda of any future linear e+e− collider
Summary
Studies of the couplings of the top quark form one of the cornerstones of the analysis program pursued at the LHC, where top quark related processes, most notably ttproduction, are ubiquitous. [6–12] for a representative sample as well as [13] for a discussion of electroweak precision effects), and a similar effort is well under way in Higgs physics, where the associated limits on Wilson coefficients are typically statistics limited. The principal motivation is to perform a detailed precision study of the couplings of the Higgs boson in the much cleaner environment that a lepton collider affords, which will bring Higgs coupling measurements to an accuracy that will not be challenged by the LHC, even after it collects 3 ab−1 of data [18,19]. The only handle on top quark electroweak couplings from the LHC is through the associated production pp → ttV where V ∈ {Z , W, γ } Whilst measurements of these processes are approaching the 5σ level, the pull that they have on a global fit is small [7].
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