Search for single-top-quark production in proton-antiproton collisions at center of mass energy = 1.8 TeV.

Abstract

The observation of the top quark in <italic>pp&macr;</italic> collisions has relied on strong-interaction pair production, typically <italic> qq&macr;</italic> &rarr; <italic>g</italic> &rarr; <italic>tt&macr;</italic>. A top quark can also be produced singly, in conjunction with a <italic>b</italic> quark, through the electroweak interaction. The two dominant single-top production modes predicted by the Standard Model, W-gluon fusion (<italic>qg</italic> &rarr; <italic>tb&macr;q<super>'</super></italic>) and <italic>W</italic>* (<italic>qq&macr;<super>'</super></italic> &rarr; <italic> tb&macr;</italic>) have predicted cross sections 1.70 pb and 0.73 pb, respectively, compared to 5.1 pb for <italic>tt&macr;</italic> pair production. We present results of a search for electroweak single-top-quark production in 106 pb<super> -1</super> of data collected with the Collider Detector at Fermilab. We look for the signature of leptonic <italic>W</italic> decay plus one, two, or three jets, of which at least one jet is identified as likely to contain a <italic>b</italic> quark. We identify two additional kinematic variables, the reconstructed top-quark mass <italic>M</italic>&ell;nu<italic>b</italic> and the scalar sum of transverse energy <italic>H_T</italic>, which discriminate the single-top signal from <italic>tt&macr;</italic> and non-top backgrounds. We improve signal strength by requiring 140 < <italic>M</italic>&ell;nu<italic> b</italic> < 210 GeV/<italic>c</italic><super>2</super> and fit the <italic> H_T</italic> distribution of the remaining events to a linear superposition of Monte Carlo <italic>H_T</italic> distributions for signal and background. We set an upper limit on the single-top-production cross section of 14.3 pb, which is roughly six times larger than the Standard Model prediction.