On the migdal-watson approach to FSI effects in meson production in NN collisions
The influence of the nucleon-nucleon final-state interaction (FSI) on properties of the meson-production amplitude near threshold is discussed. For nucleon-nucleon interaction, a simple Yamaguchi potential and realistic potential models are considered. It is shown that FSI effects cannot be factorized from the production amplitude. The absolute magnitude of FSI effects depends on the momentum transfer (or on the mass of the produced meson) and hence is not universal. Only in the case of the production of rather heavy mesons like η′ or φ FSI do effects become universal. The Jost function approach to FSI effects is critically examined.
Threshold production cross section of the pp → ppη reaction in a nonrelativistic OBE model
Abstract The pp → ppη reaction at energies near threshold is studied in a nonrelativistic one-boson exchange model, where the S11 (1535 MeV) nucleon isobar is excited through the exchange of π, η and ϱ mesons. Providing NN and ηN final state interactions are taken into account, our predictions reproduce the energy dependence as well as the scale of the total production cross section near threshold, and thus enforce the validity of the S11 mechanism and perturbative approaches applied to η production in hadronic collisions.
CATARACT: A HISTORICAL PERSPECTIVE.
The earliest extant description of a surgical operation for the cure of cataract is that of Celsus, toho practiced medicine in Rome at the beginning of the Christian era. In his text De Meclicina he described in detail his method of couching, by which he inserted a bronze needle into the eye at the equator on the lateral side of ihe globe and depressed the cataract downward into the lower part of the vitreous where the surgeon hoped it would remain out of the way of vision. The same method had been employed by the Greeks and Hindus for at least several hundred years earlier and ivas to continue as the only operation available until the middle of the eighteenth century when Daviel of Paris described extraction of the lens through the cornea. The early couchers worked on the premise that the crystallin humor we know as the lens was the receptor for vision, and that in certain conditions of disease a suffusion flowed doivn in front of the crystallin humor where it solidified and formed a dense curtain. The purpose of couching was to press the hardened corrupt humor out of the way of the lens. That cataract was opaque material within the lens itself was not recognized until after the middle of ihe seventeenth century. Until then ihe surgeons were not even aware that it was the lens they were dislocating.