Zt and γt production via top flavour - changing neutral couplings at the Fermilab Tevatron

Associated single top production with a Z boson or a photon at large hadron colliders provides a precise determination of top flavour-changing neutral couplings. The best way to measure these couplings with the up quark at Tevatron is to search for events with three jets and missing energy or events with a pho-ton, a charged lepton, a jet and missing energy. The other significant decay channels are also studied. Large hadron colliders will be top factories, allowing to measure its properties very precisely. In contrast with its mass, which is the best known quark mass, top couplings are very poorly known [1]. In this Letter we point out that associated single top production with a Z boson or a photon is very sensitive to the flavour-changing neutral (FCN) couplings V tq, with V a Z boson, a photon or a gluon and q a light quark u or c. These vertices are very small in the Standard Model (SM), being then an obvious place to look for new physics. Although top pair production gives large top samples, the leptonic Zt and γt signals become cleaner and statistically more significant with increasing energy and luminosity. At any rate, the determination of top FCN couplings from Zt and γt production has a comparable, if not a higher precision than from top decays as we will show here for Tevatron. On the other hand, both measurements have not only to be consistent but they will improve their statistical significance when combined together. In the following we concentrate on Runs I and II with integrated luminosities of 109 pb −1 and 2 fb −1 , respectively. The charm contribution to associated top production with a Z boson or a photon is 1