Nuclear bound states of antikaons, or quantized multiskyrmions?

The spectrum of strange multibaryons is considered within the chiral soliton model using one of several possible SU(3$ quantization models (the bound state rigid oscillator version). The states with energy below that of antikaon and corresponding nucleus can be interpreted as antikaon-nucleus bound states. In the formal limit of small kaon mass the number of such states becomes large, for real value of this mass there are at least several states. For large values of binding energies interpretation of such states just as antikaon-nuclear bound states becomes more ambiguous.Comment: Corrections, amendments and additions made, references adde

Propagation of Fast Partons in the Nuclear Medium

The color dipole approach has been applied in the target rest frame to address the issues of transverse momentum broadening and energy loss of a fast quark propagating in the nuclear medium. A recent application of the theory to the FermiLab E772/E866 experimental data, determining the rate of energy loss of a quark propagating in the medium to be 2 to 3 GeV/fm, will be reviewed. Calculations for the transverse momentum distribution will be presented, and the results will be compared to the E866 data. The theory will be shown to compare favorably to the data, and these results will be shown to suggest that the momentum broadening of a quark is about twice the generally accepted size.Comment: 6 pages, 4 figures, Invited talk given at 4th International Conference on Perspectives in Hadronic Physic

Quenching of high-pT hadrons: Energy Loss vs Color Transparency

High-pT hadrons produced in hard collisions and detected inclusively bear peculiar features: (i) they originate from jets whose initial virtuality and energy are of the same order; (ii) such jets are rare and have a very biased energy sharing among the particles, namely, the detected hadron carries the main fraction of the jet energy. The former feature leads to an extremely intensive gluon radiation and energy dissipation at the early stage of hadronization, either in vacuum or in a medium. As a result, a leading hadron must be produced on a short length scale. Evaluation within a model of perturbative fragmentation confirms the shortness of the production length. This result is at variance with the unjustified assumption of long production length, made within the popular energy loss scenario. Thus we conclude that the main reason of suppression of high-pT hadrons in heavy ion collisions is the controlled by color transparency attenuation of a high-pT dipole propagating through the hot medium. Adjusting a single parameter, the transport coefficient, we describe quite well the data from LHC and RHIC for the suppression factor R_{AA} as function of pT, collision energy and centrality. We observe that the complementary effect of initial state interaction causes a flattening and even fall of R_{AA} at large pT. The azimuthal anisotropy of hadron production, calculated with no further adjustment, also agrees well with data at different energies and centralities.Comment: 17 pages, 19 figure

Heavy quarkonium production: Nontrivial transition from pA to AA collisions

Two novel QCD effects, double color filtering and mutual boosting of the saturation scales in colliding nuclei, affect the transparency of the nuclei for quark dipoles in comparison with proton-nucleus collisions. The former effect increases the survival probability of the dipoles, since color filtering in one nucleus makes the other one more transparent. The second effect acts in the opposite direction and is stronger, it makes the colliding nuclei more opaque than in the case of pA collisions. As a result of parton saturation in nuclei the effective scale is shifted upwards, what leads to an increase of the gluon density at small x. This in turn leads to a stronger transverse momentum broadening in AA compared with pA collisions, i.e. to an additional growth of the saturation momentum. Such a mutual boosting leads to a system of reciprocity equations, which result in a saturation scale, a few times higher in AA than in pA collisions at the energies of LHC. Since the dipole cross section is proportional to the saturation momentum squared, the nuclei become much more opaque for dipoles in AA than in pA collisions. For the same reason gluon shadowing turns out to be boosted to a larger magnitude compared with the product of the gluon shadowing factors in each of the colliding nuclei. All these effects make it more difficult to establish a baseline for anomalous J/Psi suppression in heavy ion collisions at high energies.Comment: 10 pages 8 figures. The accuracy of calculations is improve

Quantum-mechanical description of in-medium fragmentation

We present a quantum-mechanical description of quark-hadron fragmentation in a nuclear environment. It employs the path-integral formulation of quantum mechanics, which takes care of all phases and interferences, and which contains all relevant time scales, like production, coherence, formation, etc. The cross section includes the probability of pre-hadron (colorless dipole) production both inside and outside the medium. Moreover, it also includes inside-outside production, which is a typical quantum-mechanical interference effect (like twin-slit electron propagation). We observe a substantial suppression caused by the medium, even if the pre-hadron is produced outside the medium and no energy loss is involved. This important source of suppression is missed in the usual energy-loss scenario interpreting the effect of jet quenching observed in heavy ion collisions. This may be one of the reasons of a too large gluon density, reported by such analyzes.Comment: 20 pages, 7 figure

Breakdown of QCD factorization in hard diffraction

Factorization of short- and long-distance interactions is severely broken in hard diffractive hadronic collisions. Interaction with the spectator partons leads to an interplay between soft and hard scales, which results in a leading twist behavior of the cross section, on the contrary to the higher twist predicted by factorization. This feature is explicitly demonstrated for diffractive radiation of abelian (Drell-Yan, gauge bosons, Higgs) and non-abelian (heavy flavors) particlesComment: 6 pages, 9 figures. Invited talk at the XLV International Symposium on Multiparticle Dynamics, Wildbad Kreuth (Germany) 201

Small Angle Scattering of Polarized Protons

Experiment E950 at AGS, BNL has provided data with high statistics for the left-right asymmetry of proton-carbon elastic scattering in the Coulomb-nuclear interference region of momentum transfer. It allows to access information about spin properties of the Pomeron and has practical implications for polarimetry at high energies. Relying on Regge factorization the results for the parameter r_5, ratio of spin-flip to non-flip amplitudes, is compared with the same parameter measured earlier in pion-proton elastic and charge exchange scattering. While data for Im r_5 agree (within large systematic errors), there might be a problem for Re r_5. The \pi N data indicate at a rather small contribution of the f-Reggeon to the spin-flip part of the iso-scalar amplitude which is dominated by the Pomeron. This conclusion is supported by direct analysis of data for elastic and charge exchange pp and pn scattering which also indicate at a vanishing real part of the hadronic spin-flip amplitude at energies 20 GeV and higher. This is a good news for polarimetry, since the E950 results enhanced by forthcoming new measurements at AGS can be safely used for polarimetry at RHIC at higher energies.Comment: 11 pages. Prenary talk at 15th International Spin Physics Symposium "SPIN 2002", Brookhaven National Laborator