Singlet structure function g1 at small x and small Q2

Abstract

Explicit expressions for the singlet g1 at small x and small Q 2 are obtained with the total resummation of the leading logarithmic contributions. It is shown that g1 practically does not depend on x in this kinematic region. In contrast, it would be interesting to investigate its dependence on the invariant energy 2pq because, being g1 positive at small 2pq, it can turn negative at greater values of this variable. The position of the turning point is sensitive to the ratio between the initial quark and gluon densities, so its experimental detection would enable to estimate this ratio.

Comment on the recent COMPASS data on the spin structure function g 1

“…In Ref. [6] we have predicted that g 1 should not depend on x in the COMPASS kinematic region: indeed Eq. (4) shows that g 1 depends on z rather than x in the region G COMP ASS .…”

“…In Refs. [6,7] we have suggested an alternative approach for describing g 1 at small x and arbitrary Q 2 . Briefly, it combines the total resummation of the leading logarithms of x suggested in Refs.…”

“…(3,4) from the analysis of the Feynman graphs involved, and the value of µ is fixed from theoretical considerations (see Refs. [6,7] for detail). In Ref.…”

“…II we remind the expressions for g 1 obtained in Ref. [6]; in Sect. III we generalize them to the region of Eq.…”

“…According to Ref. [6], the LLA expression (≡ g LL 1 ) for the singlet g 1 at small x and arbitrary Q 2 is:…”