Charm Production in pˉA\bar pA-Collisions at the Charmonium Threshhold

We discuss the production of charmonium states in antiproton-nucleus collisions at the $\psi'$ threshold. It is explained that measurements in $\bar p A$ collisions will allow to get new information about the strengths of the inelastic $J/\psi N$ and $\psi'N$ interaction, on the production of $\Lambda_c$ and $\bar{D}$ in charmonium-nucleon interactions and for the first time about the nondiagonal transitions $\psi' N\to J/\psi N$. The inelastic $J/\psi$-nucleon cross section is extracted from the comparison of hadron-nucleus collisions with hadron-nucleon collisions. Predictions for the ratio of $J/\psi$ to $\psi'$ yields in antiproton-nucleus scatterings close to the threshold of $\psi'$ production for different nuclear targets are presented.Comment: Talk given at International Conference on Low Energy Antiproton Physics (LEAP'05), Bonn, Juelich, Germany, 16-22 May 200

Charm production in antiproton-nucleus collisions at the J/ψJ/\psi and the ψ′\psi' thresholds

We discuss the production of charmonium states in antiproton-nucleus collisions at the $\psi'$ threshold. It is explained that measurements in $\bar p A$ collisions will allow to get new information about the strengths of the inelastic $J/\psi N, \psi'N$ interaction, on the production of $\Lambda_c$ and $\bar{D}$ in charmonium-nucleon interactions and for the first time about nondiagonal transitions $\psi' N\to J/\psi N$. The inelastic $J/\psi$-nucleon cross section is extracted from the comparison of hadron-nucleus collisions with hadron-nucleon collisions. We extract the total $J/\psi$ nucleon cross section from photon-nucleon collisions by accounting for the color transparency phenomenon within the frame of the GVDM (Generalized Vector meson Dominance Model). We evaluate also within the GVDM the inelastic $\psi'$-nucleon cross section as well as the cross section for the nondiagonal transitions. Predictions for the ratio of $J/\psi$ to $\psi'$ yields in antiproton-nucleus scatterings close to the threshold of $\psi'$ production for different nuclear targets are presented.Comment: 13 pages, 10 figures, typos corrected, some discussion adde

Short-range plasma model for intermediate spectral statistics

We propose a plasma model for spectral statistics displaying level repulsion without long-range spectral rigidity, i.e. statistics intermediate between random matrix and Poisson statistics similar to the ones found numerically at the critical point of the Anderson metal-insulator transition in disordered systems and in certain dynamical systems. The model emerges from Dysons one-dimensional gas corresponding to the eigenvalue distribution of the classical random matrix ensembles by restricting the logarithmic pair interaction to a finite number $k$ of nearest neighbors. We calculate analytically the spacing distributions and the two-level statistics. In particular we show that the number variance has the asymptotic form $\Sigma^2(L)\sim\chi L$ for large $L$ and the nearest-neighbor distribution decreases exponentially when $s\to \infty$, $P(s)\sim\exp (-\Lambda s)$ with $\Lambda=1/\chi=k\beta+1$, where $\beta$ is the inverse temperature of the gas ($\beta=$1, 2 and 4 for the orthogonal, unitary and symplectic symmetry class respectively). In the simplest case of $k=\beta=1$, the model leads to the so-called Semi-Poisson statistics characterized by particular simple correlation functions e.g. $P(s)=4s\exp(-2s)$. Furthermore we investigate the spectral statistics of several pseudointegrable quantum billiards numerically and compare them to the Semi-Poisson statistics.Comment: 24 pages, 4 figure

Charmonium Suppression - Interplay of Hadronic and Partonic Degrees of Freedom

Last year the E866-group of the Fermilab measured the $x_F$ dependence of $J/\Psi$ and $\Psi'$ suppression in $pA$ collisions. We discuss two of the effects found in that experiment with regard to color coherence effects: the different suppression of the $J/\Psi$ and the $\Psi'$ at $x_F<0$ and the significant suppression of both at large $x_F$. The small $x_F$ regions is dominated by fully formed charmonium states and thus enables us to discuss the formation time and the cross section of the different charmonium states. In the large $x_F$ region the interaction of the charmonium states with nuclear matter has to be described by partonic degrees of freedom, because in that kinematic domain the formation time is much larger than the nuclear radii. The understanding of this region will be crucial for the interpretation of the data of the future heavy ion colliders RHIC and LHC.Comment: 4 pages, 1 table, 1 figure, Contribution to the Proceedings of the 15th Particles and Nuclei International Conference (PANIC 99), Uppsala, Sweden, June 10-16, 199