Two-photon annihilation into pion pairs

We discuss pion pair production in two-photon collisions in two different kinematical regimes. When both photons are real and at moderately large center-of-mass energy s we elaborate on partonic transverse momentum and Sudakov corrections within the hard scattering approach. We also point out the difference between our approach and that of other authors. When one of the photons is highly virtual the produced pion pair can be described in terms of a two-pion distribution amplitude, for which we derive the perturbative limit at large s.Comment: Latex, 7 pages, 6 Postscript figures, Talk given at "PHOTON2000", Ambleside, UK, August 2000; to appear in the proceedings. Eq. (2) and typo correcte

The Handbag Contribution to Two-Photon Annihilation Into Meson Pairs

We report on the handbag contribution to two-photon annihilation into pion and kaon pairs at large energy and momentum transfer. The underlying physics of the mechanism is outlined and characteristic features and predictions are presented.Comment: 6 pages, 4 figures, uses ws-procs9x6.cls. Talk presented at workshops QCD-N'02, Ferrara, Italy, April 3-6, and Exclusive Processes at High Momentum Transfer, Jefferson Lab, Newport News, VA, USA, May 15-18, 200

Graptemys pseudogeographica

Number of Pages: 6Integrative BiologyGeological Science

Graptemys oculifera

Number of Pages: 2Integrative BiologyGeological Science

Graptemys

Number of Pages: 3Integrative BiologyGeological Science

Pseudemys alabamensis

Number of Pages: 2Integrative BiologyGeological Science

Iterated Monoidal Categories

We develop a notion of iterated monoidal category and show that this notion corresponds in a precise way to the notion of iterated loop space. Specifically the group completion of the nerve of such a category is an iterated loop space and free iterated monoidal categories give rise to finite simplicial operads of the same homotopy type as the classical little cubes operads used to parametrize the higher H-space structure of iterated loop spaces. Iterated monoidal categories encompass, as a special case, the notion of braided tensor categories, as used in the theory of quantum groups.Comment: 55 pages, 3 PostScript figure

Shadowing and Absorption Effects on J/psi Production in dA Collisions

We study medium modifications of J/psi production in cold nuclear media in deuterium-nucleus collisions. We discuss several parameterizations of the modifications of the parton densities in the nucleus, known as shadowing, an initial-state effect. We also include absorption of the produced J/psi by nucleons, a final-state effect. Both spatially homogeneous and inhomogeneous shadowing and absorption are considered. We use the number of binary nucleon-nucleon collisions as a centrality measure. Results are presented for d+Au collisions at sqrt{S_{NN}} = 200 GeV and for d+Pb collisions at sqrt{S_{NN}} = 6.2 TeV. To contrast the centrality dependence in pA and dA collisions, we also present pPb results at sqrt{S_{NN}} = 8.8 TeV.Comment: 22 pages, 11 figures, uses revte