On the perturbative stability of the QCD predictions for the ratio R=FL/FT in heavy-quark leptoproduction |
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Authors: | N. Ya. Ivanov and B. A. Kniehl |
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Affiliation: | (1) Yerevan Physics Institute, Alikhanian Br. 2, 375036 Yerevan, Armenia;(2) II. Institut für Theoretische Physik, Universit?t Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany |
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Abstract: | We analyze the perturbative and parametric stability of the QCD predictions for the Callan–Gross ratio, R(x,Q 2)=F L /F T , in heavy-quark leptoproduction. We consider the radiative corrections to the dominant photon–gluon fusion mechanism. In various kinematic regions, the following contributions are investigated: exact NLO results at low and moderate Q 2≲m 2, asymptotic NLO predictions at high Q 2≫m 2, and both NLO and NNLO soft-gluon (or threshold) corrections at large Bjorken variable x. Our analysis shows that large radiative corrections to the structure functions F T (x,Q 2) and F L (x,Q 2) cancel each other in their ratio R(x,Q 2) with good accuracy. As a result, the NLO contributions to the Callan–Gross ratio are less than 10% in a wide region of the variables x and Q 2. We provide compact LO predictions for R(x,Q 2) in the case of low x ≪1. A simple formula connecting the high-energy behavior of the Callan–Gross ratio and low-x asymptotics of the gluon density is derived. It is shown that the obtained hadron-level predictions for R(x→0,Q 2) are stable under the DGLAP evolution of the gluon distribution function. Our analytic results simplify the extraction of the structure functions F 2 c (x,Q 2) and F 2 b (x,Q 2) from measurements of the corresponding reduced cross sections, in particular at DESY HERA. |
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Keywords: | KeywordHeading" >PACS 12.38.Bx 13.60.Hb 13.88.+e |
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