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)

Multifragmentation and nuclear phase transitions (liquid-fog and liquid-gas)

Thermal multifragmentation of hot nuclei is interpreted as the nuclear liquid-fog phase transition. The charge distributions of the intermediate mass fragments produced in p(3.6 GeV) + Au and p(8.1 GeV) + Au collisions are analyzed within the statistical multifragmentation model with the critical temperature for the nuclear liquid-gas phase transition Tc as a free parameter. The analysis presented here provides strong support for a value of Tc > 15 MeV.Comment: 4 pages, 2 figures, Submittet to Proc. of NN2003 to be published in Nucl. Phys.

Multifragmentation in Collisions of 4.4gev-Deuterons with Gold Target

The relative velocity correlation function of pairs of intermediate mass fragments has been studied for d+Au collitions at 4.4 GeV. Experimental correlation functions are compared to that obtained by multibody Coulomb trajectory calculations under the assumption of various decay timees of the fragmenting system. The combined approach with the empirically modified intranuclear cascade code followed by the statistical multifragmentation model was used to generate the starting conditions for these calculations. The fragment emossion time is found to be less than 40 fm/c.Comment: Accepted for publication in Bulletin of the Russian Academy of Sciences. Physic

Investigation of large angle elastic and inelastic alpha particles scattering on Si isotopes

The distributions of differential cross sections for backward angles in case of three (28,20,3OSi) silicon isotopes were measured for five energies around 27 MeV. The comparison between existing data and measured data was done. Quantitative analysis of the data was made

Elastic scattering of 27.5 MeV alpha particles on 27^{27}Al, 28^{28}Si, 32^{32}S, Ti and 59^{59}Co nuclei and the r0r_{0} discrete ambiguity of the optical potential

Angular distributions for elastic scattering of alpha particles on $^{27}$Al, $^{28}$Si, $^{32}$S, Ti and $^{59}$Co nuclei have been measured in the angular range from about 20$^{\circ}$ to 179$^{\circ}$ (LAB). The experimental data were fitted with the optical model in full angular range. Many sets of four-parameter potentials, describing the elastic scattering, were found with the depths of the real part ranging from 40 to 450 MeV. A new discrete ambiguity in the optical model namely in $r_{0}$ was observed

On the SigmaN cusp in the pp -> pK+Lambda reaction

Measurements of the $pp \to pK^+\Lambda$ reaction at $T_p$ = 2.28 GeV have been carried out at COSY-TOF. In addition to the $\Lambda p$ FSI and $N^*$ resonance excitation effects a pronounced narrow structure is observed in the Dalitz plot and in its projection on the $p\Lambda$-invariant mass. The structure appears at the $pp \to$N$K^+\Sigma$ threshold and is interpreted as $\Sigma$N cusp effect. The observed width of 20 MeV/$c^2$ is substantially broader than anticipated from previous inclusive measurements. Angular distributions of this cusp structure are shown to be dissimilar to those in the residual $pK^+\Lambda$ channel, but similar to those observed in the $pK^+\Sigma^0$ channel

Cross section of the pp→K+Σ+npp\to K^+\Sigma^+n reaction close to threshold

We have measured inclusive data on $K^+$-meson production in $pp$ collisions at COSY J\"ulich close to the hyperon production threshold and determined the hyperon-nucleon invariant mass spectra. The spectra were decomposed into three parts: $\Lambda p$, $\Sigma^0p$ and $\Sigma^+n$. The cross section for the $\Sigma^+n$ channel was found to be much smaller than a previous measurement in that excess energy region. The data together with previous results at higher energies are compatible with a phase space dependence.Comment: accepted by Phys. lett. B some typos correcte