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Register a new userTop quark theory review for the Tevatron, LHC, and ILC
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Authors
D. Wackeroth
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I will briefly review the status of higher-order calculations for top-quark observables, comment on the need for improvements, discuss some of the recent theoretical advances, and present a few examples to highlight the role of top-quark observables in searches for signals of physics beyond the Standard Model.
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Spin correlations of top quarks produced in hadron collisions have not been observed experimentally with large significance. In this Letter, we propose a new variable that may enable demonstration of the existence of spin correlations with 3-4 sigma significance using just a few hundred dilepton events both at the Tevatron and the LHC. Such number of dilepton events has been observed at the Tevatron. At the LHC, it will become available once integrated luminosity of a few hundred inverse picobarns is collected.
This paper provides a review of the experimental studies of processes with a single top quark at the Tevatron proton-antiproton collider and the LHC proton-proton collider. Single top-quark production in the t-channel process has been measured at both colliders. The s-channel process has been observed at the Tevatron, and its rate has been also measured at the center-of-mass energy of 8 TeV at the LHC in spite of the comparatively harsher background contamination. LHC data also brought the observation of the associated production of a single top quark with a W boson as well as with a Z boson. The Cabibbo-Kobayashi-Maskawa matrix element |Vtb| is extracted from the single-top-quark production cross sections, and t-channel events are used to measure several properties of the top quark and set constraints on models of physics beyond the Standard Model. Rare final states with a single top quark are searched for, as enhancements in their production rates, if observed, would be clear signs of new physics.
We explore the possibility that the right-handed top quark is composite. We examine the consequences that compositeness would have on $t bar{t}$ production at the Tevatron, and derive a weak constraint on the scale of compositeness of order a few hundred GeV from the $t bar{t}$ inclusive cross section. More detailed studies of differential properties of $t bar{t}$ production could potentially improve this limit. We find that a composite top can result in an enhancement of the $t bar{t} t bar{t}$ production rate at the LHC (of as much as $10^3$ compared to the Standatd Model four top rate). We explore observables which allow us to extract the four top rate from the backgrounds, and show that the LHC can either discover or constrain top compositeness for wide ranges of parameter space.
The top quark and electroweak bosons (W and Z) represent the most massive fundamental particles yet discovered, and as such refer directly to the Standard Models greatest remaining mystery: the mechanism by which all particles gained mass. This report summarizes the work done within the top-ew group of the Tevatron-for-LHC workshop. It represents a collection of both Tevatron results, and LHC predictions. The hope is that by considering and comparing both machines, the LHC program can be improved and aided by knowledge from the Tevatron, and that particle physics as a whole can be enriched. The report includes measurements of the top quark mass, searches for single top quark production, and physics of the electroweak bosons at hadron colliders.
We carry out a comprehensive analysis of models for top A_{FB} at CDF in light of new top data arriving from the LHC. We begin with a careful Tevatron analysis, considering in general which sets of effective vertices give rise to a large forward-backward asymmetry while suppressing the contribution to the total t tbar cross-section. We show on general grounds that scalar models struggle to produce sufficient asymmetries consistent with CDF observations, while vector models can produce a large asymmetry with a less significant tension in the total cross-section and $tbar{t}$ invariant mass distribution at the Tevatron. We examine the essential observables of these models for top physics at LHC7 with 1 fb^{-1} of data, including the total cross-section, invariant mass distribution and number of additional jets in t tbar events. In the case of t-channel mediators, the LHC total cross-section places a strong constraint on light mediators, while the Tevatron invariant mass distributions place strong constraints on heavy mediators that are able to produce the asymmetry. Heavy axigluons are becoming increasingly squeezed by LHC7 t tbar and dijet resonance searches. We conclude that LHC7 top analyses are rapidly closing the window for viable models of the CDF top A_{FB}.
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