Observation of the Naive-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>T</mml:mi></mml:math>-Odd Sivers Effect in Deep-Inelastic Scattering

Abstract

Azimuthal single-spin asymmetries of leptoproduced pions and charged kaons were measured on a transversely polarized hydrogen target. Evidence for a naive-$T$-odd, transverse-momentum-dependent parton distribution function is deduced from nonvanishing Sivers effects for ${\ensuremath{\pi}}^{+}$, ${\ensuremath{\pi}}^{0}$, and ${K}^{\ifmmode\pm\else\textpm\fi{}}$, as well as in the difference of the ${\ensuremath{\pi}}^{+}$ and ${\ensuremath{\pi}}^{\ensuremath{-}}$ cross sections.