A new Collection by the Physical Review journals celebrates the 50th anniversary of the discovery of asymptotic freedom in quantum chromodynamics (QCD)—the theoretical basis for the strong force of nature that binds quarks and gluons into hadrons.

To mark the 243rd American Astronomical Society meeting, Physical Review Letters, Physical Review C, and Physical Review D highlighted several significant papers in astrophysics to illustrate the type of research these journals seek to publish.

The treatment of particle correlations and the description of clusters in the nuclear medium are important aspects that need to be better understood in the theoretical description of nuclear matter and the simulation of heavy-ion collisions. The authors propose a novel treatment of clustering for transport calculations based on a mechanism that suppresses cluster formation due to the Pauli principle via a medium-dependent cutoff in the momentum distribution of the clusters. The impact of clusters on the dynamics of unstable nuclear matter is clearly seen, and a `distillation’ mechanism is observed that affects the distribution of clusters between the low- and high-density regions. Although the approach has room for improvements, it captures the essential physics, and promises to have an impact on the further development of the field.

The nature of dark matter is one of the outstanding problems in particle physics and cosmology. To assist in the search for dark matter (DM), the authors examine the most general interactions between weakly interacting massive particles (WIMPs), assumed to be spin-1/2 fermions, and isotopes of the lightest nuclei, hydrogen and helium, using chiral effective field theory for a wide range of masses and coupling constants. The authors conclude that the scalar nuclear response functions are much greater than the others and severely constrained by the existing limits provided by experiments. The present study could be extended to other possible types of DM interactions, lighter DM candidates or heavier nuclei, such as lithium, argon, and xenon, currently widely used in dark matter detectors.

The proton dripline demarcates the nuclear landscape on the neutron-deficient side. A measurement at the SIS/FRS facility at GSI in Darmstadt, Germany of the anatomy of the immediate breakup of fragile 21Al into 20Mg + proton has now established that 21Al is unbound against proton emission in its ground state. The result thus places 21Al as the first Al isotope beyond the proton dripline. Its precise, negative proton separation energy will be a benchmark for nuclear structure models that treat nuclei as open quantum systems.

Lattice QCD calculations at finite temperature and zero or small baryon chemical potential have shown that there is no phase transition separating quasi-free quarks and those confined in baryons. Quarkyonic matter is a hypothetical state where quarks and baryons can coexist in a single Fermi sphere; quarks occupy the low momenta levels, hadrons the high momenta ones. This paper puts forward the idea that normal nuclear matter may, in fact, be quarkyonic and that the existence of this exotic phase may already have been seen in current electron-nucleus scattering data.

The American Physical Society (APS) is pleased to announce that it will begin sponsoring Astrobites, a daily astrophysical literature journal written by graduate students in astronomy. This mutually beneficial collaboration aims to enhance the dissemination of research, educational resources, and career insights in the field of astronomy and astrophysics.

The policy requires authors to explain where research data can be found starting Sept. 4.

Experiments at the Joint European Torus make the case for using gamma rays to determine the fusion reaction rate in a magnetically confined plasma.

Synopsis on:
A. Dal Molin et al.
Phys. Rev. Lett. 133, 055102 (2024)

Marica Rebai et al.
Phys. Rev. C 110, 014625 (2024)

Ab-initio calculations of atomic nuclei have revolutionized nuclear structure physics. Yet challenges remain, not least the reliable calculation of nuclear radii. In a concurrent development, modern machine-learning algorithms have excelled in a variety of computational tasks such as pattern recognition and interpolation. The authors have applied artificial neural networks (ANNs) to the extrapolation of no-core shell model calculations to infinite model spaces, effectively circumventing their computational limitations. In particular, the results show that min-max normalization, a common technique in machine learning, leads to the best results for radii. These advances offer hope that the ANN architecture is capable of handling other observables such as electromagnetic moments and transition strengths.

Atomic nuclei near mass 80 with approximately equal numbers of protons and neutrons are known to be strongly deformed while different shapes coexist in the same nucleus. These phenomena have challenged nuclear models but are also an opportunity to test the advances in theoretical approaches. The authors perform ab-initio coupled-cluster calculations for even-even nuclei near neutron-deficient 80Zr, including calculations of B(E2) transitions, using chiral NN and NNN forces. The results adequately describe shape coexistence even if they cannot unambiguously determine ground-state shapes. The calculations are a significant step forward in mass number for ab-initio computations of deformed nuclei.

Recent observations by the ATOMKI Collaboration of anomalies in electron-positron pair production following proton capture on light nuclides has led to the postulation of a new boson with mass around 17 MeV. Here a team of scientists from the United States, Canada, and France presents the most detailed microscopic calculations to date of the proton capture reactions, and is unable to find a conventional explanation for the anomalies. While these calculations do not confirm the existence of the so-called X17 boson, they provide strong motivation for continued and independent experiments to investigate the ATOMKI results. Further refinements of the calculations may provide theoretical constraints for future data.

Nucleosynthesis during the Big Bang (BBN) can produce the lightest elements, including lithium, but the observed abundance of lithium in old stellar populations is much less than that predicted from BBN. To solve this so-called “lithium puzzle”, it had been postulated that a previously unobserved resonance in 7Be could deplete lithium through resonant proton capture on 6Li and thus account for the deficit. The authors performed a detailed study using information from all possible reactions that could be influenced by such a state, utilizing the stringent constraint imposed by the unitarity of the scattering matrix. They conclude that the postulated 3/2+ state in 7Be is highly unlikely, but they also suggest that additional radiative capture data are required to solve lingering discrepancies.

When determining the authorship list for your next paper, be generous yet disciplined.

APS has selected 156 Outstanding Referees for 2024 who have demonstrated exceptional work in the assessment of manuscripts published in the Physical Review journals. A full list of the Outstanding Referees is available online.

APS has appointed Professor Joseph Kapusta, School of Physics and Astronomy, University of Minnesota as the Lead Editor of Physical Review C. Professor Kapusta takes the helm following the journal’s previous Lead Editor Benjamin F. Gibson.

A look back at Physical Review C’s first half century, and a salute to the talented authors and diligent referees who have made the journal a success.

Researchers look back at key contributions to the field of nuclear physics.

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