Fermi motion and nuclear modification factor

It has been argued recently that the so-called nuclear modification factor ($R_{AA}$) is an observable useful for identifying the quark-gluon plasma. We discuss the effect of Fermi motion in nuclei on $R_{AA}$ at CERN SPS and BNL RHIC energies. Contrary to the simple intuition, rather large effects are found for CERN SPS. The Fermi motion in nuclei contributes significantly to the Cronin effect. The effect found is qualitatively similar to the one observed experimentally at CERN energies and similar to the one obtained in the models of multiple scattering of initial partons. We predict different size of the effect for different types of hadrons, especially at low energies.Comment: 16 pages + 6 figures, some calculations have been corrected, text has been modified accordingly, 1 figure has been added, in print Modern Physics Letters A19 (2004)

Pion-pion scattering above resonances

We model large angle intermediate energy pion-pion scattering by the pQCD two-gluon (2g) exchange contribution and discuss the onset of the dominance of the Glauber-Gribov-Landshoff (GGL) component. The pQCD 2g exchange contribution becomes substantial already at $|t|\sim$ 1 GeV^{2}, but the pQCD exchange dominance is deferred to $|t|\sim$ 3 GeV^{2} because of competing multiple soft rescattering effects. Based on the NN and $\pi N$ total cross section data and Regge factorization, we evaluate the dominant soft contribution to the $\pi \pi$ total cross section and find the results consistent with the ones deduced earlier from the absorption model analysis of the $\pi N \to X N, X \Delta$ data.Comment: A talk presented at the MESON2002, 7th International Workshop on Production, Properties and Interactions of Mesons; Cracow, Poland, 24-28 May 200

\bar u - \bar d asymmetry - a few remarks

We make a few remarks on possible sources of uncertainties of the $\bar d - \bar u$ asymmetry obtained by different methods and comment on its possible verification in the future. In addition we comment on its present understanding.Comment: 3 pages, a talk at the 7th International Workshop on Deep Inelastic Scattering and QCD (DIS99), Zeuthen, April 199