Isovector spin-singlet (T = 1, S = 0) and isoscalar spin-triplet (T = 0, S = 1) pairing interactions and spin-isospin response

Abstract

We review several experimental and theoretical advances that emphasize common aspects of the study of spin-singlet, T = 1, and spin-triplet, T = 0, pairing correlations in nuclei. We first discuss various empirical evidence of the special role played by the T = 1 pairing interaction. In particular, we show the peculiar features of the nuclear pairing interaction in the low-density regime, and possible outcomes such as the BCS–BEC crossover in nuclear matter and, in an analogous way, in loosely bound nuclei. We then move to the competition between T = 1 and T = 0 pairing correlations. The effect of such competition on the low-lying spectra is studied in N = Z odd-odd nuclei by using a three-body model; in this case, it is shown that the inversion of the and states near the ground state, and the strong magnetic dipole transitions between them, can be considered as a clear manifestation of strong T = 0 pairing correlations in these nuclei. The effect of T = 0 pairing correlations is also quite evident if one studies charge-changing transitions. The Gamow–Teller (GT) states in nuclei are studied here by using self-consistent Hartree–Fock–Bogoliubov (HFB) plus quasiparticle random-phase approximation calculations in which the T = 0 pairing interaction is taken into account. Strong GT states are found, near the ground state of daughter nuclei; these are compared with available experimental data from charge-exchange reactions, and such comparison can pinpoint the value of the strength of the T = 0 interaction. Pair transfer reactions are eventually discussed. While two-neutron transfer has long been proposed as a tool to measure the T = 1 superfluidity in the nuclear ground states, the study of deuteron transfer is still in its infancy, despite its potential interest for revealing effects coming from both T = 1 and T = 0 interactions. We also point out that the reaction mechanism may mask the strong pair transfer amplitudes predicted by the HFB calculations, because of the complexity arising from simultaneous and sequential pair transfer processes.

High-resolution study ofTz=+1→0Gamow-Teller transitions in theMg26(He

“…We find here that the present experimental result is in agreement with the choice of f ≈ 1 suggested in Ref. [48].…”

“…Such a fine structure of the GTR is reported in the heavier sd-shell nucleus 37 Ar (T z = +1/2) in the 37 Cl( 3 He,t) 37 Ar reaction [27]. Fine structures are also reported in pf -shell nuclei 50 Mn, 54 Co, and 58 Cu (T z = 0) [35][36][37][38], 47 V (T z = +1/2) [39], 48 V and 60 Cu (T z = +1) [5,40], 62 Cu (T z = +2) [5], and 64 Cu (T z = +3) [5,41]. However, the GTR structure was not found in 42 Sc (T z = 0) [26] and was not clear in 46 V (T z = 0) [38,42] as well as 44 Sc (T z = +1) [43].…”

Quasiparticle random-phase approximation with quasiparticle-vibration coupling: Application to the Gamow-Teller response of the superfluid nucleusSn120

“…Although the T = 0 pairing strength has not yet been very firmly constrained, several different types of analysis are consistent with values of the proportionality factor f which are close to 1, or slightly larger [35]. Accordingly, in this work we adopt the two values f = 0 and f = 1.…”

“…While the usual IV pairing determines the groundstate structure, the IS pairing is present in the QRPA residual interaction for Gamow-Teller transitions. In our previous works [18,34,35], we have shown the importance of the GT data to pin down the value of the IS pairing strength. Consequently, the role of such IS pairing in calculations beyond QRPA should also be assessed.…”

Pairing correlations and eigenvalues of two-body density matrix in atomic nuclei

“…at zero temperature) of various pairing Hamiltonians, commonly used to describe pairing in nuclei, and to assess the ability of Yang criterion for identifying the onset of pairing correlations in finite systems. In the first part of the paper we shall discuss, from the perspective of Yang criterion, the case of like-particle pairing and then we shall focus on the proton-neutron pairing correlations in self-conjugate nuclei, which is presently one of the most debated issues in nuclear structure [10,11].…”