14,884 research outputs found
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
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
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