Narrow Results

A measurement of the production cross-section at with the DØ detector at the Fermilab Tevatron, based on the application of a multivariate topological method is presented. The integrated luminosity corresponds to 143.9 pb^-1 in the μ+jets and 141.2 pb^-1 in the e+jets channel. The preliminary cross-section is measured to be .

We have performed a search for the electroweak production of single top quarks in collisions at the Fermilab Tevatron at a center of mass energy of . The search was performed in the muon plus jets decay channel requiring at least one b-tagged jet. The data were collected using the DØ detector between August 2002 and September 2003 corresponding to an integrated luminosity of 158 pb^-1. The resulting 95% C.L. upper limits on the production cross sections are 27 pb in the s-channel, 41 pb in the t-channel, and 36 pb in the combined s + t channel using the secondary vertex tagger (SVT) algorithm. We also present results from the combined electron and muon channel search using the DØ detector.

In this paper we present new results from single-top-quark searches with the CDF II detector at the Fermilab Tevatron. In a data sample of 162 pb^-1 of proton-antiproton collisions accumulated at CDF, we find no significant evidence for signal and set an upper limit of 17.8 pb on the total single-top production rate, at 95% confidence level. Individual upper limits of 10.1 pb and 13.6 pb are set on the the individual rates of t–channel, and s–channel single-top, respectively.

We present a measurement of the top quark mass, using lepton+jets events collected in collisions at at the Fermilab Tevatron using the DØ detector. The dataset corresponds to an integrated luminosity of approximately 160 pb^-1 collected between April 2002 and November 2003. We use a template method for measuring the top quark mass using a kinematic fitting technique. We measure the top quark mass to be:

We present the results of a search for charged Higgs in the decay products of at the CDF II detector at the Tevatron. The search is based on the cross section measurements of production in three exclusive decay channels: dilepton, lepton + jets and lepton + hadronic tau. Assuming the charged Higgs decays only via , and , and , limits in the MSSM (m_Higgs, tan(β)) plane are obtained at tree level. A model-independent analysis is introduced in which the results are independent of Higgs branching ratios. This analysis results in BR(t→Hb)<0.7 at 95%CL for 80 GeV<m_Higgs<150 GeV.

We survey the flavor-changing neutral couplings (FCNC) of the top quark predicted by some extensions of the Standard Model: THDM, SUSY, Left–Right symmetric, TC2, 331, and models with extra quarks. Since the expected sensitivity of the LHC and ILC for the tcV (V = γ, g, Z) and tcH couplings is of order of a few percent, we emphasize the importance of any new physics effect that gives a prediction for these FCNC couplings within this limit. We also review the constraints imposed on these couplings from low-energy precision measurements.

As the heaviest known fundamental particle, the top quark has taken a central role in the study of fundamental interactions. Production of top quarks in pairs provides an important probe of strong interactions. The top quark mass is a key fundamental parameter which places a valuable constraint on the Higgs boson mass and electroweak symmetry breaking. Observations of the relative rates and kinematics of top quark final states constrain potential new physics. In many cases, the tests available with study of the top quark are both critical and unique. Large increases in data samples from the Fermilab Tevatron have been coupled with major improvements in experimental techniques to produce many new precision measurements of the top quark. The first direct evidence for electroweak production of top quarks has been obtained, with a resulting direct determination of V_tb. Several of the properties of the top quark have been measured. Progress has also been made in obtaining improved limits on potential anomalous production and decay mechanisms. This review presents an overview of recent theoretical and experimental developments in this field. We also provide a brief discussion of the implications for further efforts.

The existence of an exactly scale invariant sector possessing a nontrivial infrared fixed point at a higher energy scale and its possible communication with the Standard Model particles through a heavy messenger sector has been shown to lead to curious unparticle effects. We demonstrate that top physics at the Tevatron can already constrain such theories. We also consider possible improvements at the LHC and delineate some striking signatures.

Since the top quark FCNC processes are extremely supressed in the Standard Model (SM) but could be greatly enhanced in some new physics models, they could serve as a smoking gun for new physics hunting at the LHC. In this brief review we summarize the new physics predictions for various top quark FCNC processes at the LHC by focusing on two typical models: the minimal supersymmetric model (MSSM) and the topcolor-assisted technicolor (TC2) model. The conclusion is: (1) Both new physics models can greatly enhance the SM predictions by several orders; (2) The TC2 model allows for largest enhancement, and for each channel the maximal prediction is much larger than in the MSSM; (3) Compared with the 3σ sensitivity at the LHC, only a couple of channels are accessible for the MSSM while most channles are accesible for the TC2 model.

The LHC (Large Hadron Collider) will be a top-quark factory. With 80 million pairs of top quarks and an additional 34 million single tops produced annually at the designed high luminosity, the properties of this particle will be studied to a great accuracy. The fact that the top quark is the heaviest elementary particle in the Standard Model with a mass right at the electroweak scale makes it tempting to contemplate its role in electroweak symmetry breaking, as well as its potential as a window to unknown new physics at the TeV scale. We summarize the expectations for top-quark physics at the LHC, and outline new physics scenarios in which the top quark is crucially involved.

A review is presented of the current experimental status of the top quark sector of the Standard Model. The measurements summarized include searches for electroweak single top production, the latest results on the production cross-section, and searches for new physics in top quark production and decay. In addition, the recent measurement of the top quark mass to a precision of 0.7% is highlighted.

This review summarizes the program in the physics of the top quark being pursued at Fermilab's Tevatron proton–antiproton collider at a center-of-mass energy of 1.96 TeV. More than a decade after the discovery of the top quark at the two collider detectors CDF and D0, the Tevatron has been the only accelerator to produce top quarks and to study them directly.

The Tevatron's increased luminosity and center-of-mass energy offer the possibility to scrutinize the properties of this heaviest fundamental particle through new measurements that were not feasible before, such as the first evidence for electroweak production of top quarks and the resulting direct constraints on the involved couplings. Better measurements of top quark properties provide more stringent tests of predictions from the SM of elementary particle physics. In particular, the improvement in measurements of the mass of the top quark, with the latest uncertainty of 0.7% marking the most precisely measured quark mass to date, further constrains the prediction of the mass of the still to be discovered Higgs boson.

We study the impact of unparticle physics to the chromomagnetic dipole moment (CMDM) of the top quark. We compute the effect induced by unparticle operators of scalar and vector nature coupled to fermions on the CMDM. We find that this dipole moment is sensitive to the scale dimensions d_u of the unparticle and the new couplings of the respective effective operators. Using the bounds imposed on the CMDM by low-energy precision and Tevatron measurements we derive indirect limits on the unparticle parameter space. In particular, we find that the scalar-unparticle operator contribution fulfills both constraints for most of the unparticle parameter space, while the low-energy precision bound on the CMDM excludes a vector-unparticle contribution for low values of respective scale dimension d_u.

The present paper is based on the assumption that heavy quarks bound states exist in the Standard Model (SM). Considering New Bound States (NBS) of top–antitop quarks (named T-balls) we have shown that: (1) there exists the scalar 1S-bound state of ; (2) the forces which bind the top-quarks are very strong and almost completely compensate the mass of the twelve top–antitop-quarks in the scalar NBS; (3) such strong forces are produced by the Higgs–top-quarks interaction with a large value of the top-quark Yukawa coupling constant g_t≃1. Theory also predicts the existence of the NBS , which is a color triplet and a fermion similar to the t'-quark of the fourth generation. We have also considered the "b-quark-replaced" NBS, estimated the masses of the lightest fermionic NBS: M_NBS≳300 GeV, and discussed the larger masses of T-balls. We have developed a theory of the scalar T-ball's condensate and predicted the existence of three SM phases. Searching for heavy quark bound states at the Tevatron and LHC is discussed. We have constructed the possible form-factors of T-balls, and estimated the charge multiplicity coming from the T-ball's decays.

This review summarizes the highlights in the area of top quark physics obtained with the two general purpose detectors ATLAS and CMS during the first two years of operation of the Large Hadron Collider (LHC). It covers the 2010 and 2011 data taking periods, where the LHC provided pp collisions at a center-of-mass energy of . Measurements are presented of the total and differential top quark pair production cross-section in many different channels, the top quark mass and various other properties of the top quark and its interactions, for instance the charge asymmetry. Measurements of single top quark production and various searches for new physics involving top quarks are also discussed. The already very precise experimental data are in good agreement with the standard model (SM).

The single top quark production has an electroweak nature and provides an additional support to the top pair production source of the top quarks. The processes involving single top have unique properties and are very interesting from both theoretical and experimental viewpoints. Short review of the single top quark production processes is given in the paper.

The top quark pair production and decay are considered in the framework of the smeared-mass unstable particles model. The results for total and differential cross-sections in vicinity of threshold are in good agreement with the previous ones in the literature. The strategy of calculations of the higher order corrections in the framework of the model is discussed. Suggested approach significantly simplifies calculations compared to the standard perturbative one and can serve as a convenient tool for fast and precise preliminary analysis of processes involving intermediate timelike top quark exchanges in the near-threshold region.

The heaviest known elementary particle, the top quark, was discovered in 1995 by the CDF and D0 collaborations at the Tevatron proton–antiproton collider at Fermilab. Since its discovery, a large program was set in motion by the CDF and D0 collaborations to characterize the production and decay properties of top quarks, and investigate their potential for searches of new phenomena beyond the standard model. During the past 20 years, new methods were developed and implemented to improve the measurements and searches for new physics in the top quark sector. This paper reviews the achievements and results obtained through studies of the top quark at the Tevatron.

An experimental review of the current status of the top quark physics program at hadron colliders is presented. Since the discovery of the top quark at the Fermilab Tevatron collider in 1995, its production and the decay have been studied with an extraordinary level of sophistication both at the Tevatron and at the Large Hadron Collider. The top quark is the heaviest known elementary particle, with possible unique connections to the mechanism of electroweak symmetry breaking.

This review summarizes the recent results for top quark and Higgs boson measurements from experiments at Tevatron, a proton–antiproton collider at a center-of-mass energy of , and the Large Hadron Collider, a proton–proton collider at a center-of-mass energy of . These results include the discovery of a Higgs-like boson and measurement of its various properties, and measurements in the top quark sector, e.g. top quark mass, spin, charge asymmetry and production of single top quark.