Overview of Neutron-Proton Pairing

The role of neutron-proton pairing correlations on the structure of nuclei along the $N=Z$ line is reviewed. Particular emphasis is placed on the competition between isovector ($T=1$) and isoscalar $(T=0$) pair fields. The expected properties of these systems, in terms of pairing collective motion, are assessed by different theoretical frameworks including schematic models, realistic Shell Model and mean field approaches. The results are contrasted with experimental data with the goal of establishing clear signals for the existence of neutron-proton ($np$) condensates. We will show that there is clear evidence for an isovector $np$ condensate as expected from isospin invariance. However, and contrary to early expectations, a condensate of deuteron-like pairs appears quite elusive and pairing collectivity in the $T=0$ channel may only show in the form of a phonon. Arguments are presented for the use of direct reactions, adding or removing an $np$ pair, as the most promising tool to provide a definite answer to this intriguing question.Comment: 89 pages, 59 figures. Accepted for publication in Progress in Particle and Nuclear Physics (ELSEVIER

Partial-wave contributions to pairing in nuclei

We present a detailed study of partial-wave contributions of nuclear forces to pairing in nuclei. For T=1, J=0 pairing, partial waves beyond the standard 1S0 channel play an interesting role for the pair formation in nuclei. The additional contributions are dominated by the repulsive 3P1 partial wave. Their effects, and generally spin-triplet nuclear forces between paired nucleons, are influenced by the interplay of spin-orbit partners. We explore the impact of including partial waves beyond the 1S0 channel on neutron-neutron pairing gaps in semi-magic isotopic chains. In addition, we show that nuclear forces favor T=1, J=0 over T=0, J=1 pairing, except in low-j orbitals. This is in contrast to the free-space motivation that suggests the formation of deuteron-like T=0 pairs in N=Z nuclei. The suppression of T=0 pairing is because the 3S1 strength is distributed on spin-orbit partners and because of the effects of the repulsive 1P1 channel and of D waves.Comment: 10 pages, 16 figure

Competing particle–hole excitations in ³⁰Na: Constraining state-of-the-art effective interactions

The odd–odd nucleus ³⁰Na is studied via a one-proton, one-proton–one-neutron and one-neutron removal reaction using an intermediate-energy ³¹Mg, ³²Mg and ³¹Na radioactive ion beam, respectively. Combining high-resolution γ-ray spectroscopy with the selectivity of the three reaction mechanisms, we are able to distinguish multiple particle–hole configurations. Negative-parity states in ³⁰Na are observed for the first time, providing an important measure of the excitation of the 1p1h/3p3h configuration and hence the sd–pf shell gap. The extracted band structures and level energies serve as invaluable input for the theoretical refinement of the effective interactions used in this region

Partial-wave contributions to pairing in nuclei

We present a detailed study of partial-wave contributions of nuclear forces to pairing in nuclei. For T = 1, J = 0 pairing, partial waves beyond the standard ¹S₀ channel play an interesting role for the pair formation in nuclei. We explore the impact of including partial waves beyond the ¹S₀ channel on the odd-even mass staggering in semi-magic isotopic chains. The additional contributions are dominated by the repulsive ³P₁ partial wave

Motivations for early high-profile FRIB experiments

This white paper is the result of a collaboration by many of those that attended a workshop at the facility for rare isotope beams (FRIB), organized by the FRIB Theory Alliance (FRIB-TA), on ‘Theoretical Justifications and Motivations for Early High-Profile FRIB Experiments’. It covers a wide range of topics related to the science that will be explored at FRIB. After a brief introduction, the sections address: section 2: Overview of theoretical methods, section 3: Experimental capabilities, section 4: Structure, section 5: Near-threshold Physics, section 6: Reaction mechanisms, section 7: Nuclear equations of state, section 8: Nuclear astrophysics, section 9: Fundamental symmetries, and section 10: Experimental design and uncertainty quantification

A new Time-of-flight detector for the R 3 B setup

© 2022, The Author(s).We present the design, prototype developments and test results of the new time-of-flight detector (ToFD) which is part of the R3B experimental setup at GSI and FAIR, Darmstadt, Germany. The ToFD detector is able to detect heavy-ion residues of all charges at relativistic energies with a relative energy precision σΔE/ ΔE of up to 1% and a time precision of up to 14 ps (sigma). Together with an elaborate particle-tracking system, the full identification of relativistic ions from hydrogen up to uranium in mass and nuclear charge is possible.11Nsciescopu