Gluon distributions and fits using dipole cross-sections.
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Authors
Thorne, Robert S
Publication Date
2005-01Series
Cavendish-HEP-05-01
Publisher
HEP, Cavendish Laboratory, University of Cambridge
Language
English
Type
Article
Metadata
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Thorne, R. S. (2005). Gluon distributions and fits using dipole cross-sections.. http://www.dspace.cam.ac.uk/handle/1810/224275
Abstract
I investigate the relationship between the gluon distribution obtained using a dipole
model fit to low-x data on F2(x,Q2) and standard gluons obtained from global fits with
the collinear factorization theorem at fixed order. I stress the necessity to do fits of
this type carefully, and in particular to include the contribution from heavy flavours
to the inclusive structure function. I find that the dipole cross-section must be rather
steeper than the gluon distribution, which at least partially explains why dipole model
fits produce dipole cross-sections growing quite strongly at small x, while DGLAP based
fits have valence-like, or even negative, small-x gluons as inputs. However, I also find that
the gluon distributions obtained from the dipole fits are much too small to match onto
the conventional DGLAP gluons at high Q2 ∼ 50GeV2, where the two approaches should
coincide. The main reason for this discrepancy is found to be the large approximations
made in converting the dipole cross-sections into structure functions using formulae which
are designed only for asymptotically small x. The shortcomings in this step affect the
accuracy of the extracted dipole cross-sections in terms of size and shape, and hence also
in terms of interpretation, at all scales.
Identifiers
This record's URL: http://www.dspace.cam.ac.uk/handle/1810/224275