Single hadron multiplicities in SIDIS @ COMPASS
Résumé
Single haron multiplicities in Semi-Inclusive Deep Inelastic Scattering (SIDIS) provide an important input for the understanding of the hadronisation process and its description in terms of Fragmentation Functions (FFs). COMPASS collaboration has undertaken a programme of measurements of these observables. I first give an overview of the results obtained in the range 0.20 < z < 0.85 for the fraction z of the virtual photon energy carried by the hadron. And I then focus on the multiplicity charge ratio, h −/h +, at large z, which results challenge the conventional picture of a factorisation between FFs and Parton Distribution Functions (PDFs).