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Paper   IPM / Particles / 12351
School of Particles and Accelerator
  Title:   Top Quark Forward-Backward Asymmetry and W -Boson with General Couplings
  Author(s): 
1.  Seyed Yaser Ayazi
2.  Sara Khatibi
3.  Mojtaba Mohammadi Najafabadi
  Status:   Published
  Journal: JHEP
  No.:  103
  Vol.:  1210
  Year:  2012
  Supported by:  IPM
  Abstract:
The measured forward-backward asymmetry in top pair events at the Fermilab Tevatron collider deviates significantly from the standard model expectation. Several models have been proposed to describe the observed asymmetry which grows with the rapidity difference of the top pairs and also with the tt? invariant mass. The presence of a heavy charged gauge boson W with the coupling W - t - d (left-handed, right-handed, and a mixture of left and right-handed couplings) could generate the desired top forward-backward asymmetry keeping the top pair cross section consistent with the standard model prediction. Such W -boson makes contribution to the electric dipole moment of the neutron through contribution to the d-quark electric dipole moment, recently measured charge asymmetry (AC) by the LHC experiments, and the total cross section of top pair at the LHC and Tevatron. We show that the upper bounds on neutron and top electric dipole moments exclude any W with a mass below 240 GeV which could explain the Tevatron forward-backward asymmetry. It is shown that the charge asymmetry provides an allowed region in the parameters space with no overlap with the allowed region where the asymmetry could be described. Therefore, the charge asymmetry excludes W model which could explain the observed top quark forward-backward asymmetry

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