Testing the Standard Model with Top-Quark Production

Abstract

Now that the existence of the top quark is firmly established, attention turns to measuring its properties. Because of its large mass, the top quark may be sensitive to physics beyond the standard model. A promising candidate for this new physics is supersymmetry. Hence, we calculate the supersymmetric QCD correction to top-quark production at the Fermilab Tevatron, allowing for arbitrary left-right mixing of the squarks. We find that the correction is significant for several combinations of gluino and squark masses, e.g. +33% for m8= 200 GeV, m;-= mq= 75 GeV. Single-top-quark production at hadron colliders provides an opportunity to directly probe the charged-current weak interaction of the top quark. We calculate the next-to-leading-order corrections to single-top-quark production via W -gluon fusion at the Fermilab Tevatron, the CERN Large Hadron Collider, and DESY HERA. Using a b-quark distribution function to sum collinear logarithms, we show that there are two independent corrections, of order 1/ ln(m? /m~) and as. This observation is generic to processes involving a perturbatively derived heavy-quark distribution function at an energy scale large compared with the heavy-quark mass. Using the next-to-leading-order results for theW -gluon fusion cross section, we analyze the possibilities for studying single-top-quark production at the Tevatron and LHC. We find that there may be evidence for single-top-quark production in Run I data. Run II at the Tevatron should allow the W-gluon fusion cross section to be measured to ±22% with 2 fb- 1 of data. The LHC will have a statistical resolution of ±2% with the first 1 fb- 1 of data. The implications of these results for measuring Vrb and top-quark spin polarization are discussed.