Physics – High Energy Physics – High Energy Physics - Phenomenology
Scientific paper
2003-12-09
Phys.Rev.D69:054021,2004
Physics
High Energy Physics
High Energy Physics - Phenomenology
9 pages, 15 eps figures, REVTeX, FORTRAN package is available at the web site http://www-hs.phys.saga-u.ac.jp/aac.html. Replac
Scientific paper
10.1103/PhysRevD.69.054021
We investigate the polarized parton distribution functions (PDFs) and their uncertainties by using the world data on the spin asymmetry A_1. The uncertainties of the polarized PDFs are estimated by the Hessian method. The up and down valence-quark distributions are determined well. However, the antiquark distributions have large uncertainties at this stage, and it is particularly difficult to fix the gluon distribution. The \chi^2 analysis produces a positively polarized gluon distribution, but even \Delta g(x)=0 could be allowed according to our uncertainty estimation. In comparison with the previous AAC (Asymmetry Analysis Collaboration) parameterization in 2000, accurate SLAC-E155 proton data are added to the analysis. We find that the E155 data improve the determination of the polarized PDFs, especially the polarized antiquark distributions. In addition, the gluon-distribution uncertainties are reduced due to the correlation with the antiquark distributions. We also show the global analysis results with the condition \Delta g(x)=0 at the initial scale, Q^2=1 GeV^2, for clarifying the error correlation effects with the gluon distribution.
Hirai Makoto
Kumano S.
Saito Naohito
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