1,619 research outputs found
Charm Production in -Collisions at the Charmonium Threshhold
We discuss the production of charmonium states in antiproton-nucleus
collisions at the threshold. It is explained that measurements in collisions will allow to get new information about the strengths of the
inelastic and interaction, on the production of
and in charmonium-nucleon interactions and for the first time about
the nondiagonal transitions . The inelastic
-nucleon cross section is extracted from the comparison of
hadron-nucleus collisions with hadron-nucleon collisions. Predictions for the
ratio of to yields in antiproton-nucleus scatterings close to
the threshold of 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 and the thresholds
We discuss the production of charmonium states in antiproton-nucleus
collisions at the threshold. It is explained that measurements in collisions will allow to get new information about the strengths of the
inelastic interaction, on the production of and
in charmonium-nucleon interactions and for the first time about
nondiagonal transitions . The inelastic -nucleon
cross section is extracted from the comparison of hadron-nucleus collisions
with hadron-nucleon collisions. We extract the total 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 -nucleon cross
section as well as the cross section for the nondiagonal transitions.
Predictions for the ratio of to yields in antiproton-nucleus
scatterings close to the threshold of 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 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
for large and the nearest-neighbor distribution
decreases exponentially when , with
, where is the inverse temperature of the gas
(1, 2 and 4 for the orthogonal, unitary and symplectic symmetry class
respectively). In the simplest case of , the model leads to the
so-called Semi-Poisson statistics characterized by particular simple
correlation functions e.g. . 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 dependence of
and suppression in collisions. We discuss two of the
effects found in that experiment with regard to color coherence effects: the
different suppression of the and the at and the
significant suppression of both at large . The small 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 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
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