Single top observation analysis posterior probability density as a
function of the t-channel and s-channel cross sections in contours
of equal probability density. Also shown are the measured cross section,
SM expectation, and several representative new physics scenarios:
flavor-changing neutral currents with a Z boson coupling to the top and
up quark with a strength of 4% of the SM coupling, a 4-quark-generations
scenario with CKM matrix element Vts=0.2, a top-flavor model with new
heavy bosons at a scale m_x=1TeV, and a top-color model with a tb bound
state (Top Pion) with a mass of m_pi=250GeV [PRD 63, 014018 (2001); EPJ
C49, 791 (2007)].