Azimuthal asymmetry in meson productions in electron-nucleon deep inelastic scattering by HERMES Original Research Article

The spin structure of the nucleon is studied with deep inelastic scattering by HERMES. The electron (positron) beam at 27.6 GeV, polarized internal gas targets, and wide acceptance magnetic spectrometer with a ring imaging Cherenkov counter for the particle identification are the important ingredients of the experiment. The observation of significant azimuthal asymmetry in pion productions is reported. The measurement of the quark transverse spin distribution h1(x) which is underway is discussed.