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Gluon distributions and fits using dipole cross-sections.

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Publication Date: 2005-01

Series: Cavendish-HEP-05-01

Publisher: HEP, Cavendish Laboratory, University of Cambridge

Language: English

Type: Article

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Citation: Thorne, R. S. (2005). Gluon distributions and fits using dipole cross-sections

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.


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Autor: Thorne, Robert S.



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