Phys. Rev. C 110, 034002 (2024) – Published 6 September 2024
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.
Phys. Rev. C 110, L031301 (2024) – Published 3 September 2024
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 Al into Mg + proton has now established that Al is unbound against proton emission in its ground state. The result thus places Al 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.
Volker Koch, Larry McLerran, Gerald A. Miller, and Volodymyr Vovchenko
Phys. Rev. C 110, 025201 (2024) – Published 5 August 2024
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.
Marica Rebai, Davide Rigamonti, Andrea Dal Molin, Giulia Marcer, Angela Bracco, Franco Camera, Daniela Farina, Giuseppe Gorini, Evgeniy Khilkevitch, Massimo Nocente, Enrico Perelli Cippo, Oscar Putignano, Jimmy Scionti, Alexander Shevelev, Andrej Zohar, and Marco Tardocchi
Phys. Rev. C 110, 014625 (2024) – Published 30 July 2024
Phys. Rev. C 110, 014327 (2024) – Published 25 July 2024
- 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.
Phys. Rev. C 110, L011302 (2024) – Published 24 July 2024
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 - coupled-cluster calculations for even-even nuclei near neutron-deficient Zr, including calculations of transitions, using chiral and 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 - computations of deformed nuclei.
P. Gysbers, P. Navrátil, K. Kravvaris, G. Hupin, and S. Quaglioni
Phys. Rev. C 110, 015503 (2024) – Published 10 July 2024
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.
Phys. Rev. C 110, 015802 (2024) – Published 9 July 2024
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 Be could deplete lithium through resonant proton capture on Li 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 state in Be is highly unlikely, but they also suggest that additional radiative capture data are required to solve lingering discrepancies.
Phys. Rev. C 110, 014310 (2024) – Published 3 July 2024
Nuclear masses are among the most significant observables to elucidate nuclear structure and its evolution with proton and neutron number as well as nucleosynthesis in the cosmos. This is especially so in exotic nuclei where masses will be among the first observables measured for new nuclei. Yet, such measurements are extremely difficult due to the short lifetimes and low production yields at rare isotope beam facilities. The present work describes the Rare-RI Ring facility, an isochronous storage ring at RIKEN, and the first commissioning measurements to establish its capabilities. The full identification of each ion before injection into the storage ring and the measurement time of about 1 ms are excellently suited for measuring masses of the most exotic nuclei, promising a breakthrough in the precision mass spectrometry of extremely rare short-lived radionuclides.
Shahina, R. J. deBoer, J. Görres, R. Fang, M. Febbraro, R. Kelmar, M. Matney, K. Manukyan, J. T. Nattress, E. Robles, T. J. Ruland, T. T. King, A. Sanchez, R. S. Sidhu, E. Stech, and M. Wiescher
Phys. Rev. C 110, 015801 (2024) – Published 3 July 2024
The Ne + reaction has significant impact at the end of the core helium burning phase in red giant stars. Radiative capture, (,), heats the plasma while the (,) reaction provides neutrons for the weak process; their interplay determines the efficiency of the latter as a neutron source. The authors measure the strength of the resonance at keV in the Ne(,)Mg reaction. This resonance dominates the reaction rate for both the Ne(,)Mg reaction and the competing Ne(,)Mg radiative capture at temperatures larger than 0.25 GK. As a crucial step, the authors characterize the stilbene neutron detector, where relevant information on the neutron energy is retained, and evaluate the possible sources of neutron background in their measurement. The results significantly improve the characterization of the astrophysically impactful 830 keV resonance.
Phys. Rev. C 109, 064322 (2024) – Published 25 June 2024
Understanding nuclear properties away from the stability line and near the limits of the nuclear landscape relies heavily on theoretical calculations, because many unstable nuclei are difficult to reach in experiments. The authors apply two machine learning (ML) models to assess their performance in predicting nuclear mass excesses using available experimental data and a physics-based feature space. The models successfully reproduce known physical relationships and demonstrate a robust capability for extrapolation far beyond the training and test regions, offering results comparable to the model calculations. Incorporating techniques that enhance the interpretability of the ML models highlights their potential as powerful nuclear physics tools.
Matthew Heffernan, Charles Gale, Sangyong Jeon, and Jean-François Paquet
Phys. Rev. C 109, 065207 (2024) – Published 20 June 2024
The authors perform rigorous Bayesian inference on a variety of measurements in relativistic Pb-Pb collisions at the LHC using a comprehensive multistage model combining QCD-based initial states with viscous hydrodynamics and a hadronic afterburner. In particular, they extracted systematic constraints on the temperature dependence of shear and bulk viscosities of quark-gluon plasma that are significantly more precise due to improved physical models and statistical methods. For the range of plasma temperature probed in heavy-ion collisions, they find that the specific bulk viscosity demanded by the data is strongly non-zero and temperature-dependent, whereas the specific shear viscosity shows a much weaker temperature dependence that is indistinguishable from a constant value even with improved statistical analysis. Importantly, the authors showcase the application of transfer learning to efficiently explore a range of model uncertainties wider than had been considered previously. This work represents a substantial advancement in constraining the shear and bulk viscosities of strongly interacting matter.
Isak Svensson, Andreas Ekström, and Christian Forssén
Phys. Rev. C 109, 064003 (2024) – Published 18 June 2024
A chiral effective field theory (EFT) description of the nuclear interaction contains a power counting to organize the order-by-order contributions of the strong-interaction dynamics to nuclear observables. The truncation of the EFT expansion at finite order induces errors in predicted nucleon-nucleon scattering observables. These errors are correlated across scattering energies and angles, which robust uncertainty quantification needs to account for. This work reports a Bayesian analysis for neutron-proton scattering in a so-called -full version of chiral EFT. The authors employ Gaussian processes to learn about the correlation structure of the truncation errors and find that the effective number of neutron-proton scattering data is reduced by approximately a factor of 4 due to the correlation structure of the EFT truncation error (shown in the figure for differential cross sections). The results are important for analyzing the predictive capabilities in - nuclear theory.
Nanxi Yao, Agnieszka Sorensen, Veronica Dexheimer, and Jacquelyn Noronha-Hostler
Phys. Rev. C 109, 065803 (2024) – Published 17 June 2024
Properties of neutron stars such as their masses and radii arise from the characteristics of highly asymmetric nuclear matter (with many more neutrons than protons) which is not accessible in experiments. The authors consider a family of neutron-star equations of state characterized by a nontrivial behavior of nuclear matter at high densities, including a steep rise and then decline (i.e., a sharp peak) in the speed of sound with density, which is compatible with ultraheavy neutron stars up to 2.5 solar masses. The symmetry-energy expansion is then applied to obtain equations of state applicable to the almost symmetric nuclear matter created in heavy-ion collisions in the laboratory. The authors find that the description incorporating a sharp peak in the speed of sound profile aligns well with experimental data. The systematic approach opens promising perspectives for further investigations bridging the physics of neutron stars and heavy-ion collisions.
Phys. Rev. C 109, 065804 (2024) – Published 17 June 2024
This work studies the structure and dynamics of the inner crust of neutron stars where nuclear matter is expected to form slabs or so-called pasta phases. The authors report a first fully self-consistent calculation of the structure of the Coulomb lattice of nuclei immersed in a sea of dripped neutrons, taking fully into account, and on the same footing, both the band structure and superfluid effects. They employ a real-time method to extract the collective masses of a slab and of protons, which in turn quantify the conduction-neutron number density and the neutron effective mass, known as the entrainment effect. The results agree with recent self-consistent band calculations without superfluidity and demonstrate that the neutron effective mass is substantially reduced up to about 42% in the slab phase; superfluidity slightly enhances this anti-entrainment effect. The current one-dimensional formalism can be extended to two and three dimensions once the computational challenges of parallelization have been successfully addressed. This gives hope that the controversial situation concerning the entrainment effects in the inner crust of neutron stars can be resolved.
K. J. Kelly, M. Devlin, J. M. O'Donnell, D. Neudecker, C. Y. Wu, R. Henderson, A. E. Lovell, R. C. Haight, E. A. Bennett, J. L. Ullmann, N. Fotiades, and P. A. Copp
Phys. Rev. C 109, 064611 (2024) – Published 13 June 2024
Pianpian Qin, Sibo Wang, Hui Tong, Qiang Zhao, Chencan Wang, Z. P. Li, and Peter Ring
Phys. Rev. C 109, 064603 (2024) – Published 3 June 2024
Microscopic optical potentials based on realistic nucleon-nucleon interactions are important for describing the scattering phenomenology involving nuclei far away from the valley of nuclear stability. The authors construct a new optical potential by combining the relativistic Brueckner-Hartree-Fock theory with a microscopic description of the density profile of the target nucleus. The new model provides good reproduction of proton scattering data on five target nuclei, opening up interesting perspectives for applications to exotic nuclei, including setting up a reliable framework to investigate isospin effects in nuclear structure from a scattering perspective.
Phys. Rev. C 109, 054625 (2024) – Published 31 May 2024
At low temperatures (10–1000 K), negative muons injected into a mixture of deuterium (D) and tritium (T) can catalyze the fusion reaction into helium, which yields a neutron and 17.6 MeV energy. Following the catalyzed reaction, free muons can facilitate another fusion reaction, leading to a cyclic reaction known as muon-catalyzed fusion (CF), a potential candidate for energy production. CF has recently regained considerable research interest owing to several new developments and applications. For the nuclear reaction processes, the authors provide an elegant alternative to more complicated coupled-channels (CC) models (Kamimura , PRC 107, 034607) by replacing in the transition matrix the exact three-body wave function with a solution that uses a tailored - optical potential. The calculated results reproduce well those of the full CC calculations, and the proposed tractable transition-matrix model promises applications to other CF systems. The predicted low-energy negative muon spectrum will also be useful for the generation of an ultraslow negative muon beam by utilizing the CF for various applications, such as a scanning negative muon microscope and an injection source for the muon collider.
E. B. Norman, A. Drobizhev, N. Gharibyan, K. E. Gregorich, Yu. G. Kolomensky, B. N. Sammis, N. D. Scielzo, J. A. Shusterman, and K. J. Thomas
Phys. Rev. C 109, 055501 (2024) – Published 30 May 2024
Several past experiments such as SAGE, GALLEX, and BEST reported lower than expected neutrino capture rates on Ga. The origin of this so-called “gallium anomaly” could potentially indicate new neutrino physics, unless there was a more mundane explanation. Because the measured half-life of the electron-capture decay of Ge can be used to calculate the neutrino-capture cross section on Ga, the authors carried out three separate measurements to determine the half-life of Ge with high precision. Their new result of days for the Ge half-life is consistent with the currently accepted value, but significantly more precise. It rules out an unexpectedly long Ge half-life as a potential explanation of the puzzling anomaly, leaving the anomaly’s origin an open question.
Phys. Rev. C 109, 054913 (2024) – Published 28 May 2024
The modeling of relativistic collisions of nuclei is typically performed by numerically solving the equations of relativistic hydrodynamics. In a few rare cases, exact solutions to these equations exist. The authors derive two novel exact solutions which practitioners may use to verify their hydrodynamics algorithms. The work highlights the importance of an accurate description of the freeze-out configuration in systems characterized by large transverse and longitudinal flows and in collisions with large flow gradients, particularly in small systems.
B. Eriksson, S. Conroy, G. Ericsson, J. Eriksson, A. Hjalmarsson, C. R. Brune, M. Gatu Johnson, M. Nocente, S. Fugazza, and M. Rebai
Phys. Rev. C 109, 054620 (2024) – Published 23 May 2024
This work reports the first experimental measurements made at a magnetic confinement fusion device (JET) of the reaction, indicating the presence of an intermediate He state in the two-body resonant reaction . Such measurements, in which two tritium nuclei (H or T) fuse into helium (He or ), are relevant for modeling the neutron emission spectrum and estimating fuel content and confinement characteristics for magnetic confinement fusion. The results are also relevant for solar physics, as the mirror reaction plays a role in the proton-proton chain of solar fusion.
Phys. Rev. C 109, 055201 (2024) – Published 6 May 2024
The transition from the nucleon to the resonance is a sensitive test for models of the nucleon structure. A magnetic dipole () quark spin-flip transition essentially dominates photoexcitation of the , but smaller components in the nucleon and wave functions allow also electric quadrupole () contributions. The ratio then provides fundamental information on both the spatial deformation of the nucleon or , and on the corresponding states in their quark-model wave functions. The authors measured the ratio via single production from the proton with a circularly polarized photon beam and a longitudinally polarized proton target, exploiting the presence of interference terms between the measured amplitudes that enhance the effect of smaller contributions. This most precise experimental result to date for the ratio gives deep insight into the nucleon properties and provides a precision benchmark for all nonperturbative QCD models.
Phys. Rev. C 109, 045501 (2024) – Published 10 April 2024
Efforts toward a precise determination of and low-energy tests of the electroweak Standard Model have been ongoing for many years. The authors report a comprehensive re-evaluation of the values in superallowed nuclear decays based on a fully data-driven analysis of the nuclear -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.
Phys. Rev. C 109, L041602 (2024) – Published 10 April 2024
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 -wave resonance in La. By determining the spin-dependent nuclear structure factor that relates TRIV and PV cross sections, this work shows that a future search for -odd/-odd interactions in forward transmission of polarized neutrons on polarized La would possess high TRIV sensitivity.
Phys. Rev. C 109, 044314 (2024) – Published 8 April 2024
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 O spectral function from an - calculation with realistic two- and three-body interactions that is benchmarked against earlier 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 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.