Remarks on polarized quark distributions extracted from SIDIS experiments

Abstract

The results of SIDIS experiments concerning the first moments of the polarized quark distributions are considered. The possible reasons of the deviation from the fundamental restrictions such as the Bjorken sum rule and the ways to properly improve the analysis of measured SIDIS asymmetries are discussed. The possibility of broken polarized sea scenario is analysed. PACS number(s): 13.60.Hb, 12.38-t, 13.30-a, 13.88.+eThe extraction of the polarized quark and gluon densities is the main task of the SIDIS experiments with the polarized beam and target. Of a special importance for the modern SIDIS experiments are the questions of strange quark and gluon contributions to the nucleon spin, and, also the sea quark share as well as the possibility of broken sea scenario. Indeed, it is known [1] that the unpolarized sea of light quarks is essentially asymmetric, and, thus, the question arises: does the analogous situation occurs in the polarized case, i.e. whether the polarized density ∆ū is equal to ∆d or not.The crucial tests for the polarized quark distributions extracted from the SIDIS data are the sum rules dictated by SU f (2) and SU f (3) symmetries. While SU f (3) symmetry (and, as a consequence, the respective sum rule) is rather approximate (see, for example [2] and refs.

NLO QCD method of the polarized semiinclusive DIS data analysis

“…is the function reconstructed with application of MJEM (4), and N max + 1 is the number of the highest of moments used in Eq. (4).…”

“…[4]) that to obtain the reliable distributions at relatively low average Q 2 available to the modern SIDIS experiments 4 , the leading order (LO) analysis is not sufficient and NLO analysis is necessary. In Ref.…”

“…In Ref. [5] it was proposed the procedure allowing the direct extraction from the SIDIS data of the first moments (truncated to the accessible for measurement Bjorken x region) of the quark helicity 1 E-mail address: sisakian@jinr.ru 2 E-mail address: shev@mail.cern.ch 3 E-mail address: ivon@jinr.ru 4 For example, HERMES data [2] on semi-inclusive asymmetries is obtained at Q 2 mean = 2.5 GeV 2 distributions in NLO QCD. However, in spite of the special importance of the first moments 5 , it is certainly very desirable to have the procedure of reconstruction in NLO QCD of the polarized densities themselves.…”

NLO QCD procedure of the semi-inclusive deep inelastic scattering data analysis with respect to the light quark polarized sea

“…The obtained in this way estimations [3] 0.023 0 dx ∆u V ≃ 0.03, 0.023 0 dx ∆d V ≃ −0.03 seem to be rather underestimated (see discussion on this subject in ref. [2]). …”

“…At the same time, it was stressed in [2] that this is just a speculation, and, to get the reliable results on ∆q from the data obtained at the relatively small average Q 2 = 2.5 GeV 2 [3], one should apply NLO QCD analysis. The main goal of this paper is to present such a NLO QCD procedure allowing the direct extraction of the quantity ∆ 1ū − ∆ 1d from the SIDIS data.…”