Hadron multiplicities in SIDID for an iso-scalar target measured in COMPASS

Multiplicities of hadrons in Semi-Inclusive DIS are related to the parton distribution functions of nucleon and fragmentation functions of hadrorons.

Multiplicities for charged pions and Kaons on iso-scalar target, 6LiD observed in COMPASS at CERN with a 160 GeV muon beam are reported in this talk.

The COMPASS data on the pion multiplicity sum show effectively independence of x as expected.
However, they  are not in agreement with HERMES data.

COMPASS collected as many as 620 data of Kaon multiplicity  according to x and z.

As for the Kaon multiplicity sum, a large difference was observed  between data of COMPASS and HERMES.

The COMPASS data at high z (0.8<z<0.95) show unexpectedly low Kaon multiplicity ratios(K-/K+).

Considering them at LO, assuming iso-spin and charge symmetry  for kaon fragmentation function,
neglecting the unfavored fragmentation functions, expecting the strange fragmentation functions
are larger than the favored fragmentations, the lowest limits for the ratio were given.

The observed ratios are well below the lowest limits.