0 Next - to - leading order QCD corrections to top quark spin correlations at hadron colliders : the reactions qq̄ → tt̄ ( g )

Next-to-leading order QCD corrections to top quark spin correlations at hadron colliders: the reactions q ¯ q → t ¯ t(g) Abstract: Future hadron collider experiments are expected to record large to huge samples of t ¯ t events. The analysis of these data with respect to t ¯ t spin-spin correlations requires precise predictions of the production of these quark pairs in a general spin configuration. Therefore we have computed, at next-to-leading order (NLO) in the QCD coupling, the spin density matrices describing t ¯ t production by quark antiquark annihilation, which is the dominant production process at the Tevatron. Moreover we have computed the strength of the t ¯ t spin correlation at NLO, using various spin quantization axes. Pairs of top and antitop quarks will be produced copiously with the upgraded Fer-milab Tevatron collider and in even larger numbers with the Large Hadron Collider (LHC) at CERN, allowing for detailed investigations of the properties of these quarks in the future. For this aim the study of top spin phenomena will play an important role. This is because the top quark, as compared with lighter quarks, is unique in that it is sufficiently short-lived to prevent hadronization effects from diluting the spin-polarisations and spin-spin correlations that were imprinted upon the t and ¯ t quarks by their production mechanism. Hence spin-polarization and spin-correlation phenomena will provide valuable information about the interactions of top quarks. An attempt to detect these spin correlations in a small t ¯ t dilepton sample collected at the Tevatron was recently reported by the D0 collaboration [1]. Needless to say, in order to interpret future data, the predictions of these spin phenomena should be as precise as possible. Within the Standard Model (SM) top antitop pair production at hadron colliders is determined by QCD. So far the next-to-leading order (NLO) QCD corrections are known for the spin-averaged differential t ¯ t cross section [2, 3, 4, 5], while spin correlations were analysed only to leading-order [6, 7, 8, 9, 10, 11] in α s. In this letter we report on progress in providing a complete description of these spin effects within QCD at NLO: We have computed, as a first step in this direction, the t ¯ t spin density matrices for the parton reactions q ¯ q → t ¯ t, t ¯ tg to order α 3 s. We have also calculated, …