The analyzing power in inclusive charged pion production has been measured using the 200 GeV Fermilab polarized proton beam. A striking dependence in xF is observed in which AN increases from 0 to 0.42 with increasing xF for the π+ data and decreases from 0 to -0.38 with increasing xF for π- data. The kinematic range covered is 0.2≤xF≤0.9 and 0.2≤pT≤2.0 GeV/c. In a simple model our data indicate that at large xF the transverse spin of the proton is correlated with that of its quark constituents.
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