Uncertainties of the CJK 5 flavour LO parton distributions in the real photon

Radiatively generated, LO quark (u,d,s,c,b) and gluon densities in the real,unpolarized photon, calculated in the CJK model being an improved realizationof the CJKL approach, have been recently presented. The results were obtainedthrough a global fit to the experimental F2^gamma data. In this paper wepresent, obtained for the very first time in the photon case, an estimate ofthe uncertainties of the CJK parton distributions due to the experimentalerrors. The analysis is based on the Hessian method which was recently appliedin the proton parton structure analysis. Sets of test parametrizations aregiven for the CJK model. They allow for calculation of its best fit partondistributions along with F2^gamma and for computation of uncertainties of anyphysical value depending on the real photon parton densities. We test theapplicability of the approach by comparing uncertainties of examplecross-sections calculated in the Hessian and Lagrange methods. Moreover, wepresent a detailed analysis of the chi^2 of the CJK fit and its relation to thedata. We show that large chi^2/DOF of the fit is due to only a few of theexperimental measurements. By excluding them chi^2/DOF approx 1 can beobtained.