Top quark forward-backward asymmetry in the little Higgs model

A sizable difference in top quark pair forward backward asymmetry (AFB) is observed at Tevatron. The discrepancy triggers many new physics beyond the standard model (SM) and then constrains the parameter spaces in them. In this article we calculate the AFB of the top-pair production at Tevatron up to next to leading order (NLO) in the little Higgs model (LHM). We find that the contribution of Z_H can be large enough to make up the gap between SM prediction and experimental data. Then, the parameter space for the couplings between Z_H and quarks are constrained. Thus, this model can fulfill the experimental data, both in AFB and in cross section.     

Forward-backward asymmetry in top quark semileptonic decay

The semileptonic decay of the top quark t → bW⁺ → bl⁺ν_l is analyzed in the rest system of the W. The forward-backward asymmetry of the lepton l⁺ with respect to the heavy quark direction is defined and computed. It is argued that this observable will be an ideal tool to study top quark properties at Tevatron and LHC. Higher order QCD corrections are calculated and their structure is elucidated in some detail.     

Lepton pairs as a signal for the top quark

Multipleton final states from the sequential decay of the top quark are studied. Lepton pairs with large invariant mass are proposed as a signal for the top quark. The background from different processes is estimated.     

Measurement of the strange quark forward-backward asymmetry around the Z^{0} peak

A precise measurement of the strange quark forward-backward asymmetry used 3.2M multihadronic events around the Z peak collected by the DELPHI experiment from 1992 to 1995. The ring imaging Cherenkov detectors in the barrel and end-cap regions identify high energy charged kaons which tag the s quark. The s quark asymmetry was measured at different centre-of-mass energies; in particular at the Z pole taking the expected d and u quark asymmetries from the Standard Model. The quark flavour fractions are assumed from the Standard Model and the fragmentation process is modelled by JETSET. From the s quark pole asymmetry the electroweak mixing angle was determined: The parity violating coupling of the s quark to the Z was determined to be: Received: 8 October 1999 / Revised version: 23 February 2000 / Published online: 18 May 2000     

Top quark asymmetry and Wjj excess at CDF from gauged flavor symmetry

We show that the scalar sector needed for fermion mass generation when the flavor symmetry of the standard model is maximally gauged can consistently explain two anomalies reported recently by the CDF Collaboration-the forward-backward asymmetry in tt pair production and the dijet invariant mass in the Wjj channel. A pair of nearly degenerate scalar doublets with masses in the range 150-200 GeV explain these anomalies, with additional scalars predicted in the mass range 100-400 GeV. Consistency of such low scale flavor physics with flavor-changing processes is shown, and expectations for the LHC are outlined.     

Top quark properties

Since the top quark was discovered at Tevatron in 1995, many top quark properties have been measured. However, the top quark is still interesting due to unique features which originate from the extremely heavy mass, and providing various test grounds on the Standard Model as well as searches for a new physics. Though the measurements of the top quark had been performed only at Tevatron so far, LHC is now ready for measurements with more top quarks than Tevatron. In this article, recent measurements of top quark properties from Tevatron (CDF and D?) as well as LHC (ATLAS and CMS) are presented.     

An effective approach to same sign top pair production at the LHC and the forward-backward asymmetry at the Tevatron

We study the phenomenology of same sign top pair production at the LHC in a model-independent way. The complete set of dimension six operators involving two top (or anti-top) quarks is introduced and the connection with all possible t- or s-channel heavy particle exchanges is established. Only in the former case, same and opposite sign top pair production can be related. We find that while current Tevatron data disfavor t-channel models, other production mechanisms are viable and can be tested at the LHC.     

Top and bottom quark condensates

It is possible that electroweak symmetry might be broken dynamically by a condensate of top quarks. We extend a previous study of top quark dynamics to include the bottom quark. The simultaneous gap equations in dressed ladder approximation for∑ _t (p),∑ _b (p) are studied numerically and analytically in various regions of parameter space, and the solutions are used to determine \(\langle \bar tt\rangle ,\langle \bar bb\rangle \) and the decay constantsF _±,F ₀, as well as the top and bottom masses. We discuss the question of fine-tuning, and show how our approach can be extended to other quark and lepton masses.