Parametrization of polarized parton distributions

We report the polarized parton distributions proposed by the Asymmetry Analysis Collaboration (AAC). Using parametrized distributions at Q 2 =1 GeV 2 and measured A1 data, we determine optimum polarized distributions in the leading order (LO) and next-to-leading order (NLO). We find that the polarized antiquark distribution is not well determined particularly at small x. It could lead to a rather small quark spin content in comparison with usually-quoted values of 10∼30%. In our analysis, it varies from 5% to 28% depending on the small-x extrapolation. It is necessary to have small x (< 10 −3) data for precise determination. In addition , the large-x region should be also studied for ∆¯ q, which cannot be determined solely by g1. We propose three sets of distributions as the longitudinally polarized parton distribution functions.