Crystalline Undulator with a Small Amplitude and a Short Period

The crystalline undulator is a single crystal with periodically bent crystallographic planes. If ultrarelativistic charged particles channel through such a crystal, they emit hard radiation of undulator type. A crystalline undulator with a bending amplitude smaller than the distance between the bent planes and a bending period shorter than the period of channeling oscillations is proposed. Heretofore, it was believed that such a range of bending parameters was unsuitable for a crystalline undulator. This point of view is refuted. In fact, the undulator with a small amplitude and a short period is far superior to what was proposed previously. It requires much lower beam energy for production of photons of the same frequency. Such an undulator allows for a larger effective number of undulator periods. It is predicted to emit intense undulator radiation in the forward direction with a narrow spectral distribution and a lower and softer background. The undulator effect is seen for both positron and electron beams. Using positrons is, however, preferable because they enable one to obtain higher intensity of the undulator radiation with lower background.Comment: 5 pages, 3 figures, 1 table, ReVTeX4. v3: misprints are corrected, the discussion on manufacturing the undulator is extende

Statistical hadronization of charmed quarks at SPS and RHIC

Production of open and hidden charm hadrons in heavy ion collisions is considered within the statistical coalescence model. The charmed quark-antiquark pairs are assumed to be created at the initial stage of the reaction in hard parton collisions. The number of these pairs is conserved during the evolution of the system. At the hadronization stage, the charmed (anti)quarks are distributed among open and hidden charm hadrons in accordance with the laws of statistical mechanics. The model is in agreement with the experimental data on J/psi to Drell-Yan ratio in Pb+Pb collisions at SPS. This agreement can be reached only if a rather strong enhancement of the open charm production in central Pb+Pb collisions is assumed. A possible mechanism of the charm enhancement is discussed. At the top RHIC energy, the model predicts an increase of J/psi to Drell-Yan ratio in more central nucleus-nucleus collisions with respect to less central ones.Comment: Presented at 16th International Conference "Quark Matter", Nantes (France), July 18-24, 2002; 4 pages, LaTeX, 2 PS-figure

Evidence for psi' regeneration in heavy ion collisions

The study of hidden charm production is an important part of the heavy ion program. The standard approach to this problem [1] assumes that c¯c bound states are created only at the initial stage of the reaction and then partially destroyed at later stages due to interactions with the medium [2, 3, 4]

The Breathing Modes of the B=2B=2 Skyrmion and the Spin-Orbit Interaction

The coupling of the breathing and rotational modes of the skyrmion-skyrmion system leads to a nucleon-nucleon spin-orbit interaction of short range, as well as to spin-orbit potentials for the transitions $NN \to N(1440)N$, $NN \to NN(1440)$ and $NN \to N(1440)N(1440)$. The longest range behaviour of these spin-orbit potentials is calculated in closed form.Comment: Latex, figures not include

Statistical J/psi production and open charm enhancement in Pb+Pb collisions at CERN SPS

Production of open and hidden charm hadrons in heavy ion collisions is considered within the statistical coalescence model. Charmed quarks and antiquarks are assumed to be created at the initial stage of the reaction and their number is conserved during the evolution of the system. They are distributed among open and hidden charm hadrons at the hadronization stage in accordance with laws of statistical mechanics. The model is in excellent agreement with the experimental data on J/psi production in lead-lead collisions at CERN SPS and predicts strong enhancement of the open charm multiplicity over the standard extrapolation from nucleon-nucleon to nucleus-nucleus collisions. A possible mechanism of the charm enhancement is proposed.Comment: Presented at 6th International Conference on Strange Quarks in Matter, Frankfurt am Main, 2001. 4 pages, LaTeX, 1 PS-figur