Improved spin basis for angular correlation studies in single top quark production at the Fermilab Tevatron

Abstract

We show in single top quark production that the spin of the top quark is correlated with the direction of the d-type quark in the event. For single top production in the W * channel, the d-type quark comes dominantly from the antiproton at the Tevatron, whereas for the W -gluon fusion channel the spectator jet is the d-type quark the majority of the time at this machine.Our results are that 98% of the top quarks from the W * process have their spins in the antiproton direction, and 96% of the top quarks in the W -gluon fusion process have their spins in the spectator jet direction. We also compare with the more traditional, but less effective, helicity basis. The direction of the top quark spin is reflected in angular correlations in its decay products.

Effective-field-theory approach to top-quark production and decay

“…In single top production, the top spin in its rest frame is always in the direction of the d ord quark [36]. Although this gets modified by the operator O tW in the production vertex as is shown in Eqs.…”

“…In the SM s− and t−channel single top production, the top quark is always polarized in the direction of d ord three-momentum in the top rest frame [36]. When O tW is present, the top quark spin devitates from its original direction, but is still in the production plane.…”

“…In the SM, the top spin in its rest frame is in the direction of thed three-momentum [36], therefore T = 0. When the CP-odd operator is added, the direction of the top quark spin can be computed.…”

Precision measurement of the top-quark mass from dilepton events at CDF II

“…[23,24] for the process qq → tt → bℓ + ν ℓ bℓ ′− ν ℓ ′ [25]. The term 1/N is defined such that the probability density satisfies the normalization condition, dx P s (x|M t ) = 1.…”

Spin effects in processes of single top quark production at hadron colliders

“…Mahlon and S. Parke have found that the direction of the spin of the single top quark in the production processes of W * and W-g fusion coincides with the momentum of the down-type quark. For the W * -process the down-type quark is thed-quark in the initial state [3], while in W-g fusion it is either the final spectator quark (in the majority of events), or the d-quark in the initial state [3], [4].…”