The Spin Structure Function $g_1^{\rm p}$ of the Proton and a Test of the Bjorken Sum Rule

Understand

New results for the double spin asymmetry $A_1^{\rm p}$ and the proton longitudinal spin structure function $g_1^{\rm p}$ are presented.

• They were obtained by the COMPASS collaboration using polarised 200 GeV muons scattered off a longitudinally polarised NH$_3$ target.
• The data were collected in 2011 and complement those recorded in 2007 at 160\,GeV, in particular at lower values of $x$.
• They improve the statistical precision of $g_1^{\rm p}(x)$ by about a factor of two in the region $x\lesssim 0.02$.