12635873
Single Top production at LHC
The Production of single top quarks at LHC provides an ideal framework to investigate the properties of electroweak interaction, in particular of the {\it tWb} coupling. Moreover, single top is a powerful mean to identify physics beyond the standard model. All three different production mechanisms of single top are expected to be observed at LHC. Recent studies from ATLAS and CMS are presented.
118595546
Top quark asymmetries and unparticle physics at the Tevatron and LHC
Among different measured observables of top-antitop quark pairs at hadron colliders, the forward-backward asymmetry ($A_{\text{FB}}$) measured by the CDF and D0 collaborations has inconsistency with the Standard Model prediction. The measured forward-backward asymmetry grows with $t\bar{t}$ invariant mass. Several new physics models have been proposed to explain this deviation. We consider the consistency of the parameter space of vector unparticle (in Flavor-Conserving scenario) with the existing $t\bar{t}$ production measurements. In particular, we look at the total cross sections at the LHC and Tevatron, differential cross section with $t\bar{t}$ invariant mass, and the LHC charge asymmetry to identify the regions in parameter space that can give the desired top $A_{\text{FB}}$ observed by the Tevatron. We show that in spite of the intrinsic tension between the LHC charge asymmetry and $A_{\text{FB}}$, there exists a region in the unparticle parameters space where the top $A_{\text{FB}}$ and the LHC charge asymmetry are satisfied simultaneously. Finally, we show that the consistent region with $t\bar{t}$ observables is consistent with the constraints coming from the dijet resonance searches.
118525591
Constraints on Randall-Sundrum model from top-antitop production at the LHC
A bstractWe study the top pair production cross section at the LHC in the context of Randall-Sundrum model including the Kaluza-Klein (KK) excited gravitons. It is shown that the recent measurement of the cross section of this process at the LHC restricts the parameter space in Randall-Sundrum (RS) model considerably. We show that the coupling parameter $ \left( {\frac{k}{{{{\bar{M}}_{{Pl}}}}}} \right) $ isexcludedbythismeasurementabove 0.03to0.23dependingonthemass of first KK excited graviton (m1). We also study the effect of KK excitations on the spin correlation of the top pairs. It is shown that the spin asymmetry in $ t\bar{t} $ events is sensitive to the RS model parameters with a reasonable choice of model parameters.
12405410
Semileptonic decay of a polarized top quark in the noncommutative standard model
In this paper we study the noncommutative effects to the lepton spectrum from the decay of a polarized top quark. It is shown that the lowest contribution comes from the quadratic terms of the noncommutative parameter. The deviations from the standard model are significant for small values of the noncommutative characteristic scale. However, the charged lepton spin correlation coefficient has a remarkable deviation from the standard model from very low values of the noncommutative characteristic scale to 1 TeV.
121010784
Angular correlations in top quark decays in standard model extensions
The CMS Collaboration at the CERN LHC has searched for the t-channel single top quark production using the spin correlation of the t-channel. The signal extraction and cross section measurement rely on the angular distribution of the charged lepton in the top quark decays, the angle between the charged lepton momentum and top spin in the top rest frame. The behavior of the angular distribution is a distinct slope for the t-channel single top (signal) while it is flat for the backgrounds. In this Brief Report, we investigate the contributions which this spin correlation may receive from a two-Higgs doublet model, a top-color assisted technicolor (TC2) and the noncommutative extension of the standard model.
118609768
Single top quark production in t-channel at the LHC in noncommutative space–time
Abstract We study the production cross section of the t -channel single top quark at the LHC in the noncommutative space–time. It is shown that the deviation of the t -channel single top cross section from the Standard Model value because of noncommutativity is significant when | θ → | ≳ 10 − 4 GeV − 2 . Using the present experimental precision in measurement of the t -channel cross section, we apply upper limit on the noncommutative parameter. When a single top quark decays, there is a significant amount of angular correlation, in the top quark rest frame between the top spin direction and the direction of the charged lepton momentum from its decay. We study the effect of noncommutativity on the spin correlation and we find that depending on the noncommutative scale, the angular correlation can enhance considerably. Then, we provide limits on the noncommutative scale for various possible relative uncertainties on the spin correlation measurement.
15185261
Noncommutative standard model in the top quark sector
In this article we aim to estimate the bounds on the noncommutative scale {lambda}{sub NC} and to extract the 95% exclusion contours for some {theta}{sub {mu}}{sub {nu}} components using the recent measurements of the top quark width and the W boson polarization in top pair events from CDF experiments at Tevatron.
119235505
The impact of the Kaluza–Klein excited W boson on the single top at the LHC and comparison with other models
We study the s-channel single top quark production at the Large Hadron Collider (LHC) in the context of extra dimension theories, including the Kaluza–Klein (KK) decomposition. It is shown that the presence of the first KK excitation of the W gauge boson can reduce the total cross section of the s-channel single top production considerably if (3.5 TeV) for 7 TeV (14 TeV) in proton–proton collisions. Then the results will be compared with the impacts of other beyond standard model (SM) theories on the cross section of a single top s-channel. The possibility of distinguishing different models via their effects on the production cross section of the s-channel is discussed.
119300457
Angular Correlations in Associated Production of Single Top and Higgs with and without Anomalous Wtb Couplings
We study the angular correlation and the amount of top quark polarization in the production of a higgs boson in association with a single top quark in the t−channel at the LHC. We also study the effect of anomalous Wtb couplings on the angular correlation and on the production cross section of the process. The cross section and angular correlation is almost insensitive to the variation of the Higgs boson mass within 3 GeV. The robustness of the angular correlation against the center-of-mass energy of the proton-proton collision, the variation of parton distribution functions, and the change of factorization scale is investigated. The sensitivity of this process to the anomalous couplings is examined.
119119331
Probing of Wtb anomalous couplings via the tW channel of single top production
The potential of LHC for investigation of the W-t-b vertex through the tW channel of single top quark production is studied. Unlike the other two single top quark production processes (t-channel and s-channel), the tW channel provides the possibility to study the Wtb vertex without receiving contamination from FCNC. This study has been done at parton level but is involved the separation of signal from backgrounds when both W-bosons decay to leptons. In this study is assumed to be conserved. The 68% C.L. bounds on the non-Standard Model couplings are estimated.
119158715
Probing the top quark chromoelectric and chromomagnetic dipole moments in single top $tW$-channel at the LHC
Abstract We study the effects of chromoelectric and chromomagnetic dipole moments (CEDM and CMDM) on the production cross section of single top tW -channel at the LHC based on the effective Lagrangian approach. We show that the impact of CEDM and CMDM could be large. Using the experimental measurement of the tW -channel cross section, constraints on CEDM and CMDM are extracted. These constraints are comparable with the ones obtained from the top pair analysis.