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: | PACS" target="_blank">PACS 12 38 Bx 13 60 Hb 13 88 +e |
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