Measurement of the fraction of t(t)over-bar production via gluon-gluon fusion in p(p)over-bar collisions at root s=1.96 Tev

We present a measurement of the ratio of the t (t) over bar production cross section via gluon-gluon fusion to the total t (t) over bar production cross section in p (p) over bar collisions at root s = 1.96 Tev at the Tevatron. Using a data sample with an integrated luminosity of 955 pb(-1) recorded by the CDF II detector at Fermilab, we select events based on the t (t) over bar decay to lepton + jets. Using an artificial neural network technique we discriminate between t (t) over bar events produced via q (q) over bar annihilation and gg fusion, and find G(f) = sigma(gg -> t (t) over bar/sigma(p (p) over bar -> t (t) over bar) < 0.33 at the 68% confidence level. This result is combined with a previous measurement to obtain the most stringent measurement of this quantity by CDF to date, G(f) = 0.07(-0.07)(+0.15).