Pion and Kaon Multiplicities from muon-deuteron Deep Inelastic Scattering at COMPASS

The hadronization process, which turns partons into non-perturbative hadronic bound states in hard-scattering reactions, plays a fundamental role in our understanding of the proton structure. Currently, our knowledge of quark Fragmentation Functions into hadrons (FFs) originates mainly from existing global QCD analyzes which are mostly based on inclusive measurements in electron-positron annihilation process. While the latter, with current available data, mainly fixes the flavor singlet combinations of FFs, semi-inclusive DIS measurements give access to the flavor structure of FFs via hadron multiplicities. The COMPASS collaboration has recently measured charge separated pion and kaon multiplicities using 160 GeV/c muons off deuteron target. This measurement makes a fundamental experimental contribution towards a deeper understanding of the hadronization process.