CollectiveT- andP-Odd Electromagnetic Moments in Nuclei with Octupole Deformations

Abstract

Parity and time invariance violating forces produce collective P-and T-odd moments in nuclei with static octupole deformation. Collective Schiff moment, electric octupole and dipole and also magnetic quadrupole appear due to the mixing of rotational levels of opposite parity and can exceed singleparticle moments by more than a factor of 100. This enhancement is due to two factors, the collective nature of the intrinsic moments and the small energy separation between members of parity doublets. The above moments induce T-and P-odd effects in atoms and molecules. Experiments with such systems may improve substantially the limits on time reversal violation.Parity and time invariance nonconserving nuclear moments induced by P-, T-odd nuclear forces were discussed e.g. in Refs. [1][2][3][4][5][6]. These moments can be enhanced in nuclei which have close to the ground state (g.s.) levels of the same spin as the g.s. but opposite parity [3,4]. An interesting possibility to enhance the effect is to consider mechanisms producing collective T-, P-odd moments. In Ref. [7] it was shown that the "spin hedgehog" mechanism produces a collective magnetic quadrupole. In the present paper we want to consider a different mechanism: mixing of opposite parity rotational levels (parity doublets) by T-, Podd interaction in the nuclei with octupole deformation. This deformation was demonstrated to exist in nuclei from the Ra-Th and Ba-Sm region and produces such effects as parity doublets, large dipole and octupole moments in the intrinsic frame of reference and enhanced E1 and E3 transitions (see review [8]).Let us start our consideration from the expression for the electrostatic potential of a nucleus screened by the electrons of the atom. If we consider only the dipole T-, P-odd part of screening (Purcell-Ramsey-Schiff theorem [9]) one finds [4]: 1

Spin measurements forSm147+nresonances: Further evidence for nonstatistical effects

“…However, all ten measured asymmetries for resonances below 250 eV had the same sign. Models proposed to explain this sign effect are based on either distant [38,39,40,41,42,43,44,45,46] or nearby [47,48,49,50,51,52,53] (parity) doorway states. Perhaps the same type of model could be invoked to explain the observed deviations in the neutron width distributions from the expected PT shape, while at the same time these deviations might provide some clue to the physical origins of the doorway.…”

Effects of core polarization on the nuclear Schiff moment

“…The heavier isotopes of these elements (A=221-225) are found to have quadrupole plus octupole deformed shapes in the ground states [8,9]. It was suggested that in these heavier isotopes of Rn and Ra (as well as some other elements in this region ) the Schiff moments are strongly enhanced because of the quadrupole+octupole deformations [10,11]. It is therefore useful for the purpose of comparison to calculate accurately the Schiff moments in the neighboring, lighter isotopes where the onset of deformations has not yet occurred.…”

Do nuclei go pear-shaped? Coulomb excitation of220Rn and224Ra at REX-ISOLDE (CERN)

“…[2]) as well as cluster models [12]. The particular behaviour of the two radium isotopes ( 224 Ra and 226 Ra [4]) for which the B(E3) strength is known becomes more evident when the inverse sum rule B(E3)/E 3-is plotted (see Fig. 5.).…”

“…The reflection asymmetric pear-shape associated with strong octupole correlations leads to an asymmetric charge distribution in the nucleus. This asymmetric charge distribution would result in an enhancement of a CP-violating nuclear Schiff moment [4,5,6] in the neighbouring odd-mass nuclei, which would induce an electric-dipole moment (EDM) in the atomic system. Upper limits on EDMs have been measured to date constraining models, which propose physics beyond the standard model.…”