  
|
    
|
The European Physical Journal C
ISSN: 1434-6044 (printed version)
ISSN: 1434-6052 (electronic version)
Abstract Volume 1 Issue 1/2 (1998) pp 301-320
theoretical physics:
Charm electroproduction viewed in the variable-flavour number scheme versus fixed-order perturbation theory
M. Buza (1) (a), Y. Matiounine (2), J. Smith (3) (b), W.L. van Neerven (4)
(1) NIKHEF/UVA, POB 41882, NL-1009 DB Amsterdam, The Netherlands
(2) Institute for Theoretical Physics, State University of New York at Stony Brook, New York 11794-3840, USA
(3) Deutsches Electronen-Synchrotron DESY Notkestrasse 85, D-22603, Hamburg, Germany
(4) Instituut-Lorentz, University of Leiden, PO Box 9506, NL-2300 RA Leiden, The Netherlands
Received: 9 April 1997
Abstract. Starting from fixed-order perturbation theory (FOPT) we derive expressions for the heavy-flavour components of the deep-inelastic structure functions $(F_{i,H}(x,Q^2,m_H^2), i = 2,L; H = c,b,t)$ in the variable-flavour number scheme (VFNS). These expressions are valid in all orders of perturbation theory. This derivation establishes a relation between the parton densities parametrized at $n_f$ and $n_f+1$ light flavours. One of the results is that the heavy quark parton density does not vanish when the factorization scale becomes equal to $m_H$ contrary to what is assumed in the literature. Further we observe that in charm electroproduction the exact and asymptotic expressions for the heavy-quark coefficient functions yield identical results for $F_{2,c}(x,Q^2,m_c^2)$ when $x<0.01$ and $Q^2 > 20$ (GeV$/c)^2$. From this observation and an analysis of the size of the higher order corrections we conclude that in this region the VFNS description of $F_{2,c}$ is better than the one given by FOPT. On the other hand in the charm threshold region i.e. $x>0.01$ and $Q^2 < 20$ (GeV$/c)^2$ it turns out that the reverse is true.
(a) supported by the Foundation for Fundamental Research on Matter (FOM)
(b) on leave from ITP, SUNY at Stony Brook, New York 11794-3840, USA
Article in PDF-Format
Article in (gzipped) PS-Format
Online publication: December 11, 1997
helpdesk@link.springer.de
© Springer-Verlag Berlin Heidelberg 1998