CJK-improved 5 flavour LO parton distributions in the real photon
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Cornet, F.; Jankowski, P.; Krawczyk, M. CJK-improved 5 flavour LO parton distributions in the real photon. Acta Physica Polonica B, 35(9): 2215-2240 (2004). [http://hdl.handle.net/10481/32476]
PatrocinadorThis work was partly supported by the European Community's Human Potential Programme under contract HPRN-CT-2000-00149 Physics at Collider and HPRN-CT-2002-00311 EURIDICE. FC also acknowledges partial financial support by MCYT under contract FPA2000-1558 and Junta de Andalucía group FQM330. This work was partially supported by the Polish State Committee for Scientific Research (KBN), grant n. 1 P03B 040 26 and project n. 115/E-343/SPB/DESY/P-03/DWM517/2003-2005
Radiatively generated, LO quark (u,d,s,c,b) and gluon densities in the real, unpolarized photon, improved in respect to our previous paper F. Cornet, P. Jankowski, M. Krawczyk and A. Lorca, Phys. Rev. D68, 014010 (2003), are presented. We perform three global fits to the F2γ data, using the LO DGLAP evolution equation. We improve the treatment of the strong coupling running and use lower values of ΛQCD, as we have found that the too high values adopted in the previous work caused the high χ2 of the fits. In addition to the modified FFNSCJKL model, referred to as FFNSCJK1 we analyse a FFNSCJK2 model in which we take into account the resolved-photon heavy-quark contribution. New CJK model with an improved high-x behaviour of the F2γ( ) x,Q2 is proposed. Finally, in the case of the CJK model we abandon the valence sum rule imposed on the VMD input densities. New fits give χ2 per degree of freedom about 0.25 better than the old results. All features of the CJKL model, such as the realistic heavy-quark distributions, good description of the LEP data on the Q2 dependence of the F2γ and on F2,cγ are preserved. Moreover we present results of an analysis of the uncertainties of the CJK parton distributions due to the experimental errors. It is based on the Hessian method used for the proton and very recently applied for the photon by one of us. Parton and structure function parametrizations of the best fits in both FFNSCJK and CJK approaches are made accessible. For the CJK model we provide also sets of test parametrizations which allow for calculation of uncertainties of any physical value depending on the real photon parton densities.