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Hi, here is the result of my investigation in the references of my thesis. The ssbar popping parameter is, in jetset, parj(2) and is also known as gamma_s. It has been measured by TASSO and JADE at center of mass energies between 12 and 36 GeV: A DETAILED STUDY OF STRANGE PARTICLE PRODUCTION IN E+ E- ANNIHILATION AT HIGH-ENERGY. By TASSO Collaboration (M. Althoff et al.). DESY-84-093, Sep 1984. 34pp. Published in Z.Phys.C27:27,1985 CHARGED PARTICLE AND NEUTRAL KAON PRODUCTION IN E+ E- ANNIHILATION AT PETRA. By JADE Collaboration (W. Bartel et al.). DESY 83/042, Jun 1983. 50pp. Published in Z.Phys.C20:187,1983 The paper from Jade has also a plot (18a) which shows the extrapolation of the jetset model down to sqrt(S)=3GeV (i.e. a jet energy -equivalent to Mx - down to 1.5 GeV) compared with the data from MARK I K0 PRODUCTION IN E+ E- ANNIHILATION. By V. Luth et al. SLAC-PUB-1947, LBL-6465, Jun 1977. 14pp. Published in Phys.Lett.B70:120,1977 The scaling seems to be ok down to our energies. The results of the two papers are gamma_s=0.35+/-0.05 Tasso gamma_s=0.27+/-0.06 Jade To account for extrapolation errors I would take as 1 sigma interval the sum of the two intervals, gamma_s=0.21-0.40, i.e. a 30% error on this parameter. So the suggestion is to do the systematic error on ss~ popping varying by 100% the resonant component and by 30% the non resonant one ciao ric