Longitudinal spin structure of the nucleon at COMPASS

For a large fraction of its already twenty year long existence, the COMPASS collaboration has studied the polarised structure of the nucleon via muon-nucleon scattering. This paper summa- rizes the final results obtained in longitudinally polarised DIS, either inclusive or semi-inclusive. For inclusive DIS, these cover the measurements of structure function g1 , and the information ex- tracted from them in terms of polarised PDFs (pPDFs) and Bjorken sum rule. From g1 measure- ments alone, combining COMPASS with world data, the quark spin contribution to the nucleon spin is determined to be 0.26 < ∆Σ < 0.36. And from COMPASS data alone, the Bjorken sum rule is verified to 9% accuracy. In semi-inclusive DIS, more information can be gained on the pPDFs of sea quarks and gluons. A selection of our achievements along this line are reported.