Spin structure function g1 at low x: status and plans

Abstract

A brief review of measurements and expectations concerning the spin structure function g1 of the nucleon at low values of the scaling variable x is given.

The spin structure of the proton at low x and low Q2 in two-dimensional grids from COMPASS

“…There are no significant differences between the datasets obtained with two diferent beam energies, and there is no significant trend in the data as function of Q 2 or x. There is a reasonable compatibility with the predictions of the model [1]. The same conclusions can be drawn for the other three sets of twodimensional bins studied, (ν, Q 2 ), (x, ν) and (Q 2 , x).…”

“…Superimposed are the predictions of the model from Ref. [1], based on GVMD ideas. We can see slightly positive asymmetries, as in the one-dimensional analyses.…”

“…However, in fixed target experiments, x and Q 2 are highly correlated, and probing the low x region implies also entering the non-perturbative region of Q 2 < 1 (GeV/c) 2 , which is poorly known experimentally and where perturbative QCD cannot be applied. Nevertheless, this region allows studies of the transition from the non-perturbative regime of photoproduction to the perturbative region of deep inelastic scattering where several predictions were formulated [1,2,3]. Previously, the Spin Muon Collaboration (SMC) has presented its results on A p 1 and g p 1 in this region [4].…”

Parton recombination effect in polarized parton distributions

“…The behavior of polarized parton distributions at small x is an important issue because the experimental determination of the first moment of polarized gluon distribution depending on it is rather strongly [1,6]. Moreover, the parton recombination can also influence the polarized parton distributions at a larger x region.…”

“…The parton recombination effect is generally considered as a phenomenon at the small x region, where the rapid increase of parton densities can be obviously suppressed, i.e., the saturation is predicted [5]. The behavior of polarized parton distributions at small x is an important issue because the experimental determination of the first moment of polarized gluon distribution depending on it is rather strongly [1,6]. Moreover, the parton recombination can also influence the polarized parton distributions at a larger x region.…”