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.
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
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.
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.
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.
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.
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.
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.
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.
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.
13934618
Constraints on the masses of fourth generation quarks
We study the one-loop contribution of the down-type quark of the standard model-like fourth generation (b') on the top quark electric dipole moment. Using the known limits on the top quark electric dipole moments, we place limits on the b' mass. Then, from the estimated ratio for the masses of the fourth generation of quarks from other studies and the achieved bound from top quark electric dipole moments on m b ', we obtain a limit for the up-type quark of fourth generation (t') mass.