Hadron Multiplicity and Fragmentation in SIDIS

TL;DR

This paper presents COMPASS measurements of hadron multiplicities in SIDIS, comparing results with theoretical predictions and highlighting discrepancies in kaon data crucial for understanding strange quark polarization.

Contribution

It provides new experimental data on kaon multiplicities in SIDIS, challenging existing NLO and LO QCD models and emphasizing the need for refined fragmentation functions.

Findings

Good agreement of pion data with NLO QCD

Discrepancies in kaon multiplicities with existing models

Highlighting the importance of $K^-$/$K^+$ ratio at high z

Abstract

COMPASS final results on multiplicities of charged hadrons and of identified pions and kaons produced in the deep inelastic muon scattering off an isoscalar target are presented and compared to HERMES results. Measurements are done in bins of x, y and z in a wide kinematic range. The hadron and pion data show a good agreement with (N)LO QCD expectations. The kaon data are long awaited for since they are needed to extract kaon fragmentation functions, a crucial ingredient in solving the strange quark polarisation puzzle. COMPASS results for kaons differ from the expectations of the old NLO DSS fit and they cannot be well described by LO QCD either. In this context the importance of $K^-$/$K^+$ multiplicity ratio at high z is discussed.