Experimental Program of the Future COMPASS-II Experiment at CERN

Abstract

Over the last decade the COMPASS experiment has successfully obtained precise results on nucleon structure and hadron spectroscopy, with statistical errors much lower than previously reported. Recently, the new COMPASS-II program, focused on the study of a more complete nucleon description, was approved by CERN. The goal of the program is to access the nucleon structure beyond the collinear approxi-mation, including the quark intrinsic transverse momentum distributions, which are described by the Transverse Momentum Dependent (TMD) Parton Distribution Functions (PDFs) and by Generalised Parton Distributions (GPDs). The COMPASS collaboration proposes to measure the TMD PDFs, for the first time, via the polarised Drell-Yan process. The results will be complementary to those already obtained in polarised Semi-Inclusive Deep Inelastic Scattering (SIDIS). The GPDs can be accessed using deeply virtual Compton scattering and hard exclusive meson production using an unpolarised hydrogen target in a kinematic region not yet covered by any existing experiment. Also unpolarised SIDIS will be studied, by improving the knowledge of the strange quark PDF and obtaining the kaon fragmentation functions. Another topic covered in this COMPASS-II program is the measurement of the pion and kaon polarisabilities using the Primakoff reaction, which corresponds to a test of the chiral perturbative theory.