The COMPASS experiment

The COMPASS Experiment at the CERN SPS has a broad physics program focused on the study of the spin structure of the nucleon and on hadron spectroscopy. Key measurements for the spin program are the gluon contribution to the spin of the nucleon, semi-inclusive measurements, and the first measurement of the transverse structure function $\Delta_{T}q(x)$. Its state-of-the-art apparatus consists of a two-stage large acceptance spectrometer designed for high data rates and equipped with high-resolution tracking, particle identification and electromagnetic and hadronic calorimetry. The first year of physics run (2002) was devoted to the spin programme, using a polarised $\mu^{+}$ beam at 160 GeV/c and a polarised $^{6}$LiD target.