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We present the O(alpha_s) corrections to the cross section for the reactione+e- --> gamma^* --> Q \bar Q in the energy region close to the threshold. Weassume that the energy of the reaction is such that both the perturbativeexpansion in the strong coupling constant and expansion in the relativevelocity of the heavy quarks can be used. We explicitly obtain termsO(alpha_s^2/beta^2, alpha_s^2/beta, alpha_s^2) in the relative correction tothe threshold cross section. Using the ideas of asymptotic expansions, wedemonstrate how an expansion of Feynman diagrams in the threshold region isconstructed. From this analysis we obtain a matching relation between thevector current in full QCD and the quark-antiquark current in NRQCD at leadingorder in 1/m and the second order in the strong coupling constant.Comment: 9 pages, revte

physical review letters

Two-Loop QCD Corrections to the Heavy Quark Pair Production Cross Section in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mi mathvariant="italic">e</mml:mi></mml:mrow><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:msup></mml:mrow><mml:mrow><mml:msup><mml:mrow><mml:mi mathvariant="italic">e</mml:mi></mml:mrow><mml:mrow><mml:mo>−</mml:mo></mml:mrow></mml:msup></mml:mrow></mml:math>Annihilation near Threshold

Two-Loop QCD Corrections to the Heavy Quark Pair Production Cross Section ine+e−Annihilation near Threshold