期刊
PHYSICS LETTERS B
卷 541, 期 1-2, 页码 129-134出版社
ELSEVIER SCIENCE BV
DOI: 10.1016/S0370-2693(02)02192-5
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We consider the behaviour of the perturbative QCD corrections to the Re+e- ratio, in the limit that the c.m. energy roots vanishes. Writing Re+e-(s) = 3 Sigma(f) Q(f)(2) (1 + R(s)), with Q(f) denoting the electric charge of quark flavour f, we find that for N-f < 9 flavours of massless quarks, the perturbative correction R(s) to the parton model result smoothly approaches from below the infrared limit R(0) = 2/b, as s --> 0. Here b = (33 - 2N(f))/6 is the first QCD beta-function coefficient. This freezing holds to all-orders in perturbation theory. The s-dependence can be written analytically in closed form in terms of the Lambert W function. (C) 2002 Elsevier Science B.V. All rights reserved.
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