Direct electromagnetic excitation N. --> delta. (1232), final-state interactions, and the multipoles M/sub 1//sub +//sup() 3/2/ and E/sub 1//sub +//sup() 3/2/ of photopion production off nucleons in the range 160< or approx. =E/sub. gamma. /< or approx. =800 MeV
In this paper one of the classics of particle theory in the resonance region is reexamined, namely the prediction of the amplitudes M/sub 1//sub +//sup() 3/2/ and E/sub 1//sub +//sup() 3/2/ of photopion production on nucleons around the resonance ..delta..(1232). The tool employed for this purpose is the final-state-interaction theory, and the principal aim of the study is to advocate for the appearance of two distinct dynamical mechanisms of photoexcitation in such an approach. Special emphasis is put then on the naturally emerging links between the present treatment and the isobaric approach and calculations based on the static quark model. It is argued that the dynamical meaning of the troublesome arbitrary constants (known to appear in most studies of the type presented in this paper) can be very convincingly explained when the resonances formed in the reaction (..delta..(1232) in this specific case) are treated as ''elementary'' objects represented in the T-matrix elements by singularities of the Castillejo-Dalitz-Dyson kind. In the case discussed here, ''direct'' magnetic-dipole excitation N..--> delta..(1232) seems to emerge very clearly as an independent dynamical mechanism of photoproduction in the p/sub 33/ state, parallel to the usual electromagnetic excitation of nonresonant ..pi..N systems, both followed by resonant pion-nucleon rescattering. It turns out that the magnitude of such direct ..gamma..N..delta.. coupling is completely determined by the related strong interactions. The necessity of allowing for both specified mechanisms in this and other similar calculations is emphasized.
- Research Organization:
- Istituto di Fisica ''G. Marconi'' Universita degli Studi, 00185 Roma, Italia and Institute of Nuclear Research, 00-681 Warsaw, Poland
- OSTI ID:
- 5309455
- Journal Information:
- Phys. Rev. D; (United States), Vol. 28:7
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
PIONS
PHOTOPRODUCTION
DELTA-1236 RESONANCES
ELECTROMAGNETIC INTERACTIONS
FINAL-STATE INTERACTIONS
M1-TRANSITIONS
MEV RANGE 100-1000
MULTIPOLES
NUCLEONS
PION-NUCLEON INTERACTIONS
QUARK MODEL
BARYON RESONANCES
BARYONS
BASIC INTERACTIONS
BOSONS
COMPOSITE MODELS
ELEMENTARY PARTICLES
ENERGY RANGE
ENERGY-LEVEL TRANSITIONS
FERMIONS
HADRON-HADRON INTERACTIONS
HADRONS
INTERACTIONS
MATHEMATICAL MODELS
MESON-BARYON INTERACTIONS
MESON-NUCLEON INTERACTIONS
MESONS
MEV RANGE
MULTIPOLE TRANSITIONS
N RESONANCES
PARTICLE INTERACTIONS
PARTICLE MODELS
PARTICLE PRODUCTION
PSEUDOSCALAR MESONS
RESONANCE PARTICLES
645202* - High Energy Physics- Particle Interactions & Properties-Theoretical- Electromagnetic Interactions & Properties