Neutron-proton correlations in an exactly solvable model

Journal Article · Tue Apr 01 04:00:00 EST 1997 · Physical Review, C

DOI:https://doi.org/10.1103/PhysRevC.55.1781· OSTI ID:541980

Engel, J ^[1]; Pittel, S ^[2]; Stoitsov, M ^[3]; Vogel, P ^[4]; Dukelsky, J ^[5]

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1. Department of Physics and Astronomy, University of North Carolina, Chapel Hill, North Carolina 27599 (United States)
2. Bartol Research Institute, University of Delaware, Newark, Deleware 19716 (United States)
3. Institute of Nuclear Research and Nuclear Energy, Bulgarian Academy of Sciences, Sofia-1784 (Bulgaria)
4. Department of Physics, Caltech, 161-33, Pasadena, California 91125 (United States)
5. Instituto de Estructura de la Materia, Consejo Superior de Investigaciones Cientificas, Serrano 123, 28006 Madrid (Spain)

We examine isovector and isoscalar neutron-proton correlations in an exactly solvable model based on the algebra SO(8). We look particularly closely at Gamow-Teller strength and double {beta} decay, both to isolate the effects of the two kinds of pairing and to test two approximation schemes: the renormalized neutron-proton quasiparticle random phase approximation (QRPA) and generalized BCS theory. When isoscalar pairing correlations become strong enough a phase transition occurs and the dependence of the Gamow-Teller {beta}{sup +} strength on isospin changes in a dramatic and unfamiliar way, actually increasing as neutrons are added to an N=Z core. Renormalization eliminates the well-known instabilities that plague the QRPA as the phase transition is approached, but only by unnaturally suppressing the isoscalar correlations. Generalized BCS theory, on the other hand, reproduces the Gamow-Teller strength more accurately in the isoscalar phase than in the usual isovector phase, even though its predictions for energies are equally good everywhere. It also mixes T=0 and T=1 pairing, but only on the isoscalar side of the phase transition. {copyright} {ital 1997} {ital The American Physical Society}

• Research Organization: California Institute of Technology
• DOE Contract Number: FG03-88ER40397; FG05-94ER40827
• OSTI ID: 541980
• Journal Information: Physical Review, C, Journal Name: Physical Review, C Journal Issue: 4 Vol. 55; ISSN 0556-2813; ISSN PRVCAN
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
BCS THEORY
CORRELATIONS
DOUBLE BETA DECAY
GAMOW-TELLER RULES
INSTABILITY
ISOSPIN
NUCLEAR FORCES
NUCLEON-NUCLEON POTENTIAL
PAIRING INTERACTIONS
PHASE TRANSFORMATIONS
PROTON-NEUTRON INTERACTIONS
QUASI PARTICLES
RANDOM PHASE APPROXIMATION
RENORMALIZATION
SO-8 GROUPS