First Measurement of the Fraction of Top Quark Pair Production Through Gluon-Gluon Fusion

We present the first measurement of { sigma}(gG {yields} t{bar t})/{ sigma}(p{bar p} {yields} t{bar t}). We use 0.96 fb{sup -1} of {radical}s = 1.96 TeV p{bar p} collision data recorded with the CDF II detector at Fermilab. We identify the candidate t{bar t} events with a high- energy chargedlepton, a neutrino candidate, and four or more jets with at least one identified as originating from a b quark. Using charged particles with low transverse momentum in t{bar t} events, we find { sigma}(gg {yields} t{bar t})/{ sigma}(p{bar p} {yields} t{bar t}) = 0.07 {+-} 0.14(stat) {+-} 0.07(syst), in agreement with the standard model NLO prediction of 0.15 {+-} 0.05.