Fixing theoretical ambiguities in the improved QCD fits to xF₃ Tevatron DIS data at NNLO and beyond

by Andrei KATAEV (CERN - TH & INR, Moscow)

Friday 18 May 2001, 14:00 → 15:00 Europe/Zurich

TH Auditorium (CERN)

Definite results of our collaborative work with G. Parente and A.V. Sidorov are presented. We perform the reanalysis of the 1997 Tevatron data for the xF₃ structure function of nN deep-inelastic scattering, using new theoretical information, which comes from calculations of the NNLO perturbative corrections to anomalous dimensions of xF₃ odd Mellin moments and of the N³LO corrections to the related coefficient functions. The improved fits were done with the help of the Jacobi polynomial method with and without twist-4 power-suppressed terms, fixed by application of the Infared Renormalon (IRR) model. Among the results to be presented are the values of the free parameter of the considered IRR model and the values of a_s(M_Z), obtained at the NLO, NNLO and estimated at the N³LO. The effects of interplay of higher-order perturbative QCD corrections to the Mellin moments with O(1/Q²) terms is discussed. The results are compared to the definite NLO and NNLO ones, obtained recently by van Neerven, Vogt (hep-ph/0103123) using their NNLO model of DGLAP kernel, and by Santiago, Yndurain (hep-ph/0102247) with the help of Bernstein polynomial technique. Theoretical questions of applicability of the renormalon-inspired large-b₀ approximation for estimating NNLO and N³LO terms of the coefficient functions of odd moments for xF₃ and even non-singlet moments for F₂ are also considered. The estimates are compared to the ones obtained by means of the Padé approximation technique. The importance of further improvement of perturbative theory approximations by getting new explicit information for the quantities related to even moments of xF₃, is discussed.