Longitudinal spin structure of the nucleon at COMPASS (SPS CERN)

We present new results on longitudinal inclusive double-spin asymmetry A _1,p (x) in deep-inelastic muon-proton scattering and proton spin-dependent structure function g ₁ ^p (x, Q ²). New COMPASS data on longitudinal polarised NH₃ target were collected during the year 2011 with beam of positive muons with energy E = 200 GeV. Kinematical threshold Q ² ≥ 1 (GeV/c)² and the fractional energy 0.1 < y < 0.9 allow us to cover low x region down to 0.025.