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.
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.
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.
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.
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.
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.
117164527
Search for t-Channel Single Top Quark Production in Proton-Proton Collisions at 14 TeV and Single Photoelectron Spectra Analysis for the HF Calorimeter of the CMS detector
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.
118407947
Probing the Anomalous FCNC Interactions in Top-Higgs Final State and Charge Ratio Approach
We study the anomalous production of a single top quark in association with a Higgs boson at the LHC originating from flavor changing neutral current (FCNC) interactions in $tqg$ and $tqH$ vertices. We derive the discovery potentials and $68\%$ C.L. upper limits considering leptonic decay of the top quark and the Higgs boson decay into a $b\bar{b}$ pair with 10 fb$^{-1}$ integrated luminosity of data in proton-proton collisions at the center-of-mass energy of 14 TeV. We propose a charge ratio for the lepton in top quark decay in terms of lepton $p_{T}$ and $\eta$ as a strong tool to observe the signal. In particular, we show that the charge ratio increases significantly at large $p_{T}$ of the charged lepton. While the main background from $t\bar{t}$ is nearly charge symmetric and $W+jets$ background has much smaller charge ratio with respect to the signal. We show that this feature can also be used in the probe of anomalous single top production with a $Z-$boson or a photon which are under the attention of the experimental collaborations.
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.