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.
119292661
Impact of torsion space?time on $t\bar{t}$ observables at hadron colliders
Starting from the effective torsion space-time model, we study its effects on the top pair production cross section at hadron colliders. We also study the effect of this model on top pair asymmetries at the Tevatron and the LHC. We find that torsion space-time can explain forward-backward asymmetry according to measured anomaly at Tevatron. We find an allowed region in the parameters space which
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.
18095986
On the Charged Higgs Bosons Effects in the Top Quark Decays
The collider experiments at the Tevatron and the LHC provide us the possibility of probing the existence of a light charged Higgs boson. In this paper we study semi-leptonic decay of a polarized top quark via the charged Higgs boson ($t(\uparrow)\to H^{+}b \to l^{+}\nu_{l}b$). It is shown that the asymmetry or spin correlation coefficient of the charged lepton depends on the $\tan\beta$ and $M_{H^{\pm}}$ and is quite different from the Standard Model. This sensitivity of asymmetry to $\tan\beta$ and $M_{H^{\pm}}$ could be utilized in the experimental searches for the light charged Higgs for separation of the signal from backgrounds in the $t\bar{t}\to H^{+}W^{-}b\bar{b}\to\tau^{+}\nu_{\tau}\l^{-}\bar{\nu_{\l}}b\bar{b}$ (and vice versa). It might be useful for obtaining better bounds in the ($\tan\beta,M_{H^{\pm}}$) plane too.
14038525
Heavy Charged Gauge Bosons with General CP Violating Couplings
Heavy gauge bosons such as W' are expected to exist in many extensions of the Standard Model. In this paper, the most general Lagrangian for the interaction of W' with top and bottom quarks is considered. This Lagrangian consists of V–A and V+A structure with in general complex couplings. Such interactions produce an Electric Dipole Moment (EDM) for the top quark at one loop level. We predict the allowed ranges for the mass and couplings of W' by using the upper limit on the top quark EDM.
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.
118541614
Study of anomalous top quark FCNC interactions via $tW$-channel of single top
The potential of the LHC for investigation of anomalous top quark interactions with gluon ($tug,tcg$) through the production of $tW$-channel of single top quark is studied. In the Standard Model, the single top quarks in the $tW$-channel mode are charge symmetric meaning that $\sigma(pp\to t+W^{-}) = \sigma(pp\to \bar{t}+W^{+})$. However, the presence of anomalous FCNC couplings leads to charge asymmetry. In this paper a method is proposed in which this charge asymmetry may be used to constrain anomalous FCNC couplings. The strength of resulting constraints is estimated for the LHC for the center of mass energies of 7 and 14 TeV.
8481784
Top Production from Black Holes at the LHC
In theories with large extra dimension and with low quantum gravity scale near a TeV, it is expected that TeV-scale black holes to be produced in proton-proton collisions at the LHC with the center of mass energy of 14 TeV. Since the black holes temperature can be around 1 TeV, top quark production is expected from them via Hawking radiation. Within the Standard Model of particle physics top quarks are produced via strong interaction in t pairs or via electroweak interaction singly. Therefore, black holes can be the new source of top quark production. In this article we present the total cross sections and transverse momentum distributions of top quark production from black holes at the LHC. We find that the top quarks from black holes tend to reside at very high transverse momentum region so it can be a very useful signature for the black holes at the LHC.
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.
119845469
Expectations for first single-top studies in CMS in proton-proton collisions
The first long physics run of LHC is taking place at a center-of-mass energy of 7 TeV, and is expected to continue until an integrated luminosity of 1 inverse femtobarn will have been collected. We present an analysis technique to measure the t-channel cross section for single top-quark production in CMS, that can confirm the recent observation of single-top quark production by the Tevatron experiments. Events leading to a signature of exactly one muon and two jets are selected and specific data-driven methods have been developed to reduce the sensitivity to the unknown level of background contamination. Single top quarks provide the possibility to study the polarization of an "isolated quark". This feature is exploited in the presented analysis for the measurement of SM-like single top; with more statistics, the chiral structure of the W-t-b vertex could be probed via the study of the top polarization and any sizable deviation from the Standard Model expectation would be a hint to new physics beyond the Standard Model.