The E2/M1 mixing ratio in the excitation of the {Delta} from polarized photo-reactions

Conference · Wed Dec 01 00:00:00 EST 1993

OSTI ID:10108647

The LEGS Collaboration

In constituent quark models, a tensor interaction, mixing quark spins with their relative motion, is introduced to reproduce the observed baryon spectrum. This has a consequence completely analogous to the nuclear tensor force between the n and p in deuterium. A D state component is mixed into what would otherwise be a purely S-wave object. The D-wave component breaks spherical symmetry, resulting in a non-vanishing matrix element for the nucleon and a static quadrupole moment and deformation for its first excited state, the {Delta} resonance, at {approximately}325 MeV. The magnitude and sign of this D-state component are quite sensitive to the internal structure of the proton and have been of great interest in recent years. The intrinsic deformation of the spin 1/2 nucleon cannot be observed directly; it must be inferred from transition amplitudes such as N {yields} {Delta}. In a spherical bag model, the {Delta} is viewed as a pure quark-spin-flip transition proceeding only through M1 excitation. If there are D-state admixtures in the ground state of the nucleon and/or {Delta}, quadrupole excitation, in addition to spin-flip M1, is also allowed. The problem is to evaluate the relative magnitude of this E2 excitation in the presence of the dominant M1 transition. A variety of models predict this mixing ratio to be quite small, anywhere from {minus}0.9% to {minus}6%, so that a high degree of precision is demanded of experiment.

• Research Organization: Brookhaven National Lab., Upton, NY (United States)
• Sponsoring Organization: USDOE, Washington, DC (United States)
• DOE Contract Number: AC02-76CH00016
• OSTI ID: 10108647
• Report Number(s): BNL-49593; CONF-9308164-7; ON: DE94004235; TRN: 94:000161
• Resource Relation: Conference: 14. European conference on few-body problems in physics,Amsterdam (Netherlands),22-27 Aug 1993; Other Information: PBD: [1993]
• Country of Publication: United States
• Language: English

Related Subjects

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
PROTONS
PHOTONUCLEAR REACTIONS
DELTA BARYONS
EXCITATION
BAG MODEL
DEFORMATION
MIXING RATIO
SPIN FLIP
SYMMETRY
TRANSITION AMPLITUDES
M1-TRANSITIONS
E2-TRANSITIONS
POLARIZED BEAMS
662330
662410
PHOTON AND CHARGED-LEPTON INTERACTIONS WITH HADRONS
PROPERTIES OF BARYONS AND BARYON RESONANCES