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.
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.
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.
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.
122246859
The Effects of Standard Model Extensions on W-Boson Helicity Ratios in Top Quark Decay
In this letter, we investigate the contributions which W boson helicity fractions in top quark decay receive from a two-Higgs doublet model, a top-color assisted technicolor (TC2) and the noncommutative extension of the Standard Model. It is shown that the deviations coming from these models are much less than the experimental sensitivity in measurement of the helicity fractions.
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.
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
118539892
PROBING THE ANOMALOUS COUPLINGS OF THE TOP QUARK WITH GLUON AT THE LHC AND TEVATRON
In this paper, we study the sensitivity of the fraction of events arising from gluon–gluon fusion to the chromoelectric and chromomagnetic dipole moments (CEDM and CMDM) as well as the total and differential cross-sections at the LHC and Tevatron. The sensitivity of measured charged asymmetry at the LHC to CEDM and CMDM is also studied. We find that at the Tevatron and the LHC, nonzero values of CMDM could suppress the production rate. It is shown that the ratio of at the Tevatron is more sensitive to CEDM and CMDM than the LHC case. The presence of CEDM always increases the contribution of gluon–gluon fusion process in top pair rate at the Tevatron and LHC. Except for a small range of CMDM, the presence of CEDM and CMDM can increase the fraction of gluon–gluon fusion at the Tevatron and LHC. The measured ratio of at the Tevatron is used to derive bounds on the chromoelectric and chromomagnetic dipole moments as well as the total and differential cross-sections at the LHC and Tevatron, and the measured charged asymmetry at the LHC. The combination of and σLHC provides stringent limits on CMDM and CEDM.
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