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.

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.

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.

Neutron transmission experiments can realize a high-sensitivity search for time-reversal invariance violation (TRIV) in nucleon-nucleon interactions through the same enhancement mechanism observed for large parity violating (PV) effects in neutron-induced compound nuclear processes. A recent polarized beam/polarized target measurement has now quantified the sensitivity for the best-known case, the 0.75 eV $p$-wave resonance in ${}^{139}$La. By determining the spin-dependent nuclear structure factor that relates TRIV and PV cross sections, this work shows that a future search for $P$-odd/$T$-odd interactions in forward transmission of polarized neutrons on polarized ${}^{139}$La would possess high TRIV sensitivity.

Efforts toward a precise determination of $V_{ud}$ and low-energy tests of the electroweak Standard Model have been ongoing for many years. The authors report a comprehensive re-evaluation of the $ft$ values in superallowed nuclear $\beta$ decays based on a fully data-driven analysis of the nuclear $\beta$-decay form factor. They utilize isospin relations to connect the nuclear charged weak distribution to the measurable charge distributions. The approach supersedes previous shell-model estimations and allows for a rigorous quantification of theory uncertainties in the phase-space factor, using experimental input rather than nuclear models. The work identifies the need for specific future experimental research to drive further understanding toward a regime of precision that is relevant for weak-interaction physics and thus for physics beyond the Standard Model.

Neutrino experiments such as long-baseline oscillation measurements can determine properties of fundamental particles, but the present systematic uncertainties, e.g., in the neutrino-nucleus cross sections, must be significantly reduced. The authors determine the ${}^{16}$O spectral function from an $ab$-$initio$ calculation with realistic two- and three-body interactions that is benchmarked against earlier ${}^4$He results. They then obtain good results in the relativistic regime for quasi-elastic electron scattering as well as for neutrino scattering data from T2K. The predictions for both electron and neutrino scattering identify a particular need for low-energy electron-scattering data on ${}^{16}$O, for which a program is underway at MAMI in Germany. And being able to propagate the theoretical uncertainties to the final cross sections promises improved understanding of the anticipated more precise results from next-generation neutrino experiments.

The authors extend the proton-neutron finite-amplitude method, an iterative and efficient form of the Skyrme quasiparticle random-phase approximation that needs no diagonalization of the $pn$ QRPA matrix, for the coupling of quasiparticles to like-particle phonons. With this approach one can add beyond-QRPA correlations to computations of important nuclear properties such as Gamow-Teller strength and $\beta$-decay rates in deformed nuclei. The results show improved agreement with existing data for several deformed nuclei, a promising step toward a more reliable framework for large-scale $\beta$-decay calculations needed, e.g., for $r$-process modeling.

High-resolution experimental fusion excitation functions for ${}^{16,17,18}$O + ${}^{12}$C reveal a remarkable irregular behavior rooted in the structure of both the colliding nuclei and the quasimolecular composite system. Using a parameter-free time-dependent Hartree-Fock model, the authors assess the influence of the angular-momentum-dependent fusion barriers on fusion. They find that barrier penetrabilities taken directly from a density-constrained calculation provide a significantly improved description of the experimental data. The results expose the remaining deviations between the mean-field predictions and experimental fusion cross sections, and suggest this approach to garner insight into the impact of nuclear structure effects on fusion reactions.

A new theoretical analysis connects the results of high-energy particle experiments at the Large Hadron Collider with three-proton correlations inside nuclei.

Synopsis on:
A. Kievsky et al.
Phys. Rev. C 109, 034006 (2024)

The astrophysical origin for the chemical elements between the first and second $r$-process peaks is a matter of intense debate, with a number of nucleosynthesis processes at explosive stellar environments possibly contributing to their production. Modeling neutron-capture processes that would produce these elements requires reliable data on the trends of neutron separation energies of neutron-rich isotopes which are highly unstable and not readily accessible by experiment. This work describes the first application of an experimental technique, time-of-flight-magnetic-rigidity (ToF-B$\rho$), that is well-suited to measure masses of nuclei with very short half-lives in beams with relatively low intensities. The two-neutron separation energy deduced from the measured masses exhibits a smooth trend consistent with theoretical predictions within the range of experimental uncertainty, indicating that there is no sudden shape transition in these isotopes as hinted at by previous data. The successful application of the ToF-B$\rho$ technique to isotopes with $Z>28$ at the NSCL S800 spectrograph gives hope for a comprehensive program of mass measurements for isotopes relevant to $r$-process models with the same device at FRIB.

Neutrino mass is a key parameter in nuclear and particle physics and in cosmology. The Project 8 Collaboration developed an innovative method with potential to improve the current mass limits by more than an order of magnitude. Announced in a paper published last September (PRL 131, 102502; see also the Synopsis at https://physics.aps.org/articles/v16/s121), the method measures the frequency of radiation from tritium $\beta$-decay electrons spiraling in a magnetic field. In the current paper the authors provide the details of this unique measurement technique including the hardware and the role of simulations and precision spectroscopy that enabled their new direct mass measurement. This first, small-volume demonstration, along with the precision reached, shows a clear path to improve in future experiments on the conservative upper limit for the neutrino mass obtained here.

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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