We present a calculation of pion photo- and electroproduction in manifestly Lorentz-invariant baryon chiral perturbation theory up to and including order $q^4$. We fix the low-energy constants by fitting experimental data in all available reaction channels. Our results can be accessed via a Web interface, the so-called chiral MAID. We explain how our program works and how it can be used for further analysis.

When quenching jets deposit certain amounts of energy and momentum into ambient matter, part of it propagates in the form of shocks/sounds. The “sound surface”, separating disturbed and undisturbed parts of the fireball, makes what we call the sound edge of jets. In this work we semianalytically study its shape, in various geometries. We further argue that since hadrons with in the kinematical range of $p_{\perp }\sim 2\mathrm{GeV}$ originate mostly from the “rim” of the fireball, near the maximum of the radial flow at the freeze-out surface, only the intersection of the “sound surface” with this “rim” would be observable. The resulting “jet edge” has a form of extra matter at the elliptic curve, in $\Delta \varphi ,\Delta \eta$ coordinates, with radius $\left|\Delta \varphi \right|\sim \left|\Delta \eta \right|\sim 1$. In the case of large energy/momentum deposition $\sim 100\mathrm{GeV}$ we argue that the event should be considered as two subevents, with the interior of the “sound surface” having modified radial and directed flow. We further argue that in the kinematical range of $p_{\perp }\sim 3\mathrm{GeV}$ the effect of that can be large enough to be seen on an event-by-event basis. If so, this effect has the potential to become a valuable tool to address the geometry of jet production and quenching.

Since the start of the CERN Large Hadron Collider, a plethora of novel observables for jet tomography in heavy-ion collisions has appeared. Many of these studies initially found unexpectedly apparently unaltered jet properties, such as, for instance, the momentum distribution of hadrons in jets parallel to the jet axis. This has sparked (sometimes exotic) theoretical efforts to explain these findings. Subsequent results have then shown evidence for modifications when the data is considered in greater detail. However, it has to be realized that almost all current high-$P_T$ observables measure conditional probabilities of events, not probabilities. Thus, the correct starting point for their theoretical understanding is Bayes’ formula, and the biases introduced by the conditioning are crucial to understanding the outcome. Once this is introduced properly into the modeling process, the initially unexpected results are seen to find a natural explanation in terms of various biases and puzzles largely disappear. In this work, a conceptual framework to classify the various observables according to the types of bias to which they are sensitive is presented and illustrated with a large number of case studies ranging from simple jet finding to $2+1$ dihadron-triggered correlations.

We generalize the coupled-cluster (CC) approach with singles, doubles, and the noniterative treatment of triples termed $\Lambda$CCSD(T) to Hamiltonians containing three-body interactions. The resulting method and the underlying CC approach with singles and doubles only (CCSD) are applied to the medium-mass closed-shell nuclei ${}^{16}\text{O}$, ${}^{24}\text{O}$, and ${}^{40}\text{Ca}$. By comparing the results of CCSD and $\Lambda$CCSD(T) calculations with explicit treatment of three-nucleon interactions to those obtained using an approximate treatment in which they are included effectively via the zero-, one-, and two-body components of the Hamiltonian in normal-ordered form, we quantify the contributions of the residual three-body interactions neglected in the approximate treatment. We find these residual normal-ordered three-body contributions negligible for the $\Lambda$CCSD(T) method, although they can become significant in the lower-level CCSD approach, particularly when the nucleon-nucleon interactions are soft.

Recent theoretical work has renewed interest in radiochemically determined isotope distributions in reactions of ${}^{238}$U projectiles with heavy targets that had previously been published only in parts. These data are being reexamined. The cross sections σ($Z$) below the uranium target have been determined as a function of incident energy in thick-target bombardments. These are compared to predictions by a diffusion model whereby consistency with the experimental data is found in the energy intervals 7.65–8.30 MeV/u and 6.06–7.50 MeV/u. In the energy interval 6.06–6.49 MeV/u, the experimental data are lower by a factor of 5 compared to the diffusion model prediction indicating a threshold behavior for massive charge and mass transfer close to the barrier. For the intermediate energy interval, the missing mass between the primary fragment masses deduced from the generalized $Q_{\mathrm{gg}}$ systematics including neutron pair-breaking corrections and the centroid of the experimental isotope distributions as a function of $Z$ have been used to determine the average excitation energy as a function of $Z$. From this, the $Z$ dependence of the average total kinetic-energy loss ($\overline{\mathrm{TKEL}}$) has been determined. This is compared to that measured in a thin-target counter experiment at 7.42 MeV/u. For small charge transfers, the values of $\overline{\mathrm{TKEL}}$ of this work are typically about 30 MeV lower than in the thin-target experiment. This difference is decreasing with increasing charge transfer developing into even slightly larger values in the thick-target experiment for the largest charge transfers. This is the expected behavior which is also found in a comparison of the partial cross sections for quasielastic and deep-inelastic reactions in both experiments. The cross sections for surviving heavy actinides, e.g., ${}_{98}$Cf, ${}_{99}$Es, and ${}_{100}$Fm indicate that these are produced in the low-energy tails of the dissipated energy distributions, however, with a low-energy cutoff at about 35 MeV. Excitation functions show that identical isotope distributions are populated independent of the bombarding energy indicating that the same bins of excitation energy are responsible for the production of these fissile isotopes. A comparison of the survival probabilities of the residues of equal charge and neutron transfers in the reactions of ${}^{238}$U projectiles with either ${}^{238}$U or ${}^{248}$Cm targets is consistent with such a cutoff as evaporation calculations assign the surviving heavy actinides to the 3$n$ and/or 4$n$ evaporation channels.

This paper focuses on the scaling of the $S$ matrix for elastic nucleon-nucleon scattering at large $N_c$. It is argued that the logarithm of a typical $S$ matrix element is proportional to $N_c$ in the regime where the large $N_c$ limit is taken with momentum of the incident nucleons proportional $N_c$. The suggested scaling was previously derived within the framework of potential scattering models for purely elastic scattering in which the parameters scale the same way as in large $N_c$ QCD. A variety of heuristic arguments strongly suggest that the same scaling holds in the realistic case where both elastic and inelastic scattering are possible.

The neutron-rich, even-even ${}^{122,124,126}$Pd isotopes were studied via in-beam $\gamma$-ray spectroscopy at the RIKEN Radioactive Isotope Beam Factory. Excited states at 499(9), 590(11), and 686(17) keV were found in the three isotopes, which we assign to the respective $2_1^{+}\to 0_{gs}^{+}$ decays. In addition, candidates for the $4_1^{+}$ states at 1164(20) and 1300(22) keV were observed in ${}^{122}$Pd and ${}^{124}$Pd, respectively. The resulting $E_x\left(2_1^{+}\right)$ systematics are similar to the Xe ($Z=54$) isotopic chain and theoretical predictions by the proton-neutron interacting boson model (IBM-2), indicating the magic nature of $N=82$ in the Pd isotopes.

The 2040.7-keV $\gamma$ ray from the 69th excited state of ${}^{76}$Ge was investigated in the interest of Ge-based double-$\beta$-decay experiments like the Germanium Detector Array (GERDA) experiment. The predicted transition could interfere with valid $0\nu \beta \beta$ events at 2039.0 keV, creating false signals in large-volume ${}^{76}$Ge enriched detectors. The measurement was performed with the Gamma Array for Inelastic Neutron Scattering (GAINS) at the Geel Electron Linear Accelerator (GELINA) white neutron source, using the ($n$,$n^{\prime }$$\gamma$) technique and focusing on the strongest $\gamma$ rays originating from the level. Upper limits obtained for the production cross section of the 2040.7-keV $\gamma$ ray showed no possible influence on GERDA data. Additional analysis of the data yielded high-resolution cross sections for the low-lying states of ${}^{76}$Ge and related $\gamma$ rays, improving the accuracy and extending existing data for five transitions and five levels. The inelastic scattering cross section for ${}^{76}$Ge was determined for incident neutron energies up to 2.23 MeV, significantly increasing the energy range for which experimental data are available. Comparisons with model calculations using the talys code are presented indicating that accounting for the recently established asymmetric rotor structure should lead to an improved description of the data.

The potential energy surface plays a decisive role in nuclear fission. Together with inertia and viscosity, it influences the trajectory of the system, and the properties of the fission fragments result from the puzzling interplay between static and dynamical effects. A careful study on the influence of the parametrization of the potential energy landscape in heavy-ion-induced fission is performed. Dynamical calculations are done within the stochastic Langevin approach in a three-dimensional deformation space. Various prescriptions of the potential energy surface are considered, probing two different Liquid Drop models and the deformation dependence of the Wigner/congruence energy. A wide set of observables, including cross sections, particle multiplicities, and integral, as well as isotopic and isobaric, distributions of fission and evaporation products, is analyzed. Nuclei close to the Businaro-Gallone point are confirmed to be well suited for investigating the Liquid Drop parametrization, while the influence of the deformation-dependent Wigner/congruence energy is difficult to demonstrate unambiguously in fission at high excitation energies.

We comment on various issues in a recent paper on nonidentical protons as a resolution to the proton radius puzzle.

We reply to the Comment by Downie et al., which concerns the proton radius extracted from elastic electron-proton scattering data by using the assumption of nonidentical protons.

A study of excited states in ${}^{63}$Ni up to an excitation energy of 28 MeV and a probable spin of 57/2 was carried out with the ${}^{26}$Mg(${}^{48}$Ca,2$\alpha$3$n\gamma$)${}^{63}$Ni reaction at beam energies between 275 and 320 MeV. Three collective bands, built upon states of single-particle character, were identified. For two of the three bands, the transition quadrupole moments were extracted, herewith quantifying the deformation at high spin. The results have been compared with shell-model and cranked Nilsson-Strutinsky calculations. Despite the $Z=28$ shell closure and the approach to the purported $N=40$ subshell, the ${}^{63}$Ni isotope is able to sustain collective excitations at moderate and high spin.

We study pure neutron matter in the BEC-BCS crossover regime using renormalization-group-based low-momentum interactions within the Nozières-Schmitt-Rink framework. This is an attempt to go beyond the mean-field description for low-density matter. We work in the basis of so-called Weinberg eigenvectors where the operator $G_{0}V$ is diagonal, which proves to be an excellent choice that allows one to use nonlocal interactions in a very convenient way. We study the importance of correlations as a function of density. We notice that there is a significant reduction of the BCS critical temperature at low densities as the neutron matter approaches the unitary limit.

The low-lying dipole strength of the $N=28$ closed-shell nucleus ${}^{52}$Cr was studied with nuclear resonance fluorescence up to 9.9 MeV, using bremsstrahlung at the superconducting Darmstadt linear electron accelerator S-DALINAC. Twenty-eight spin-1 states were observed between 5.0 and 9.5 MeV excitation energy, 14 of which for the first time. Both electric dipole excitations ($E1$, around 8 MeV) and magnetic dipole excitations ($M1$, around 9 MeV) were detected. Microscopic calculations within the quasiparticle-phonon nuclear model were performed and show good agreement with experimental results. The structure of $E1$ and $M1$ excitations, respectively, is discussed.

The “island of inversion” around ${}^{32}$Mg is one of the most important paradigms for studying the disappearance of the stabilizing “magicity” of a shell closure. We present the first Penning-trap mass measurements of the exotic nuclides ${}^{29-31}$Na and ${}^{30-34}$Mg, which allow precise determination of the empirical shell gap for ${}^{32}$Mg. The new value of 1.10(3) MeV is the smallest observed shell gap for any nuclide with a canonical magic number.

Photonuclear reactions are shown to be used for studying neutrino (weak) nuclear responses involved in astroneutrino nuclear interactions and double beta decays. Charged current weak responses for ground and excited states are studied by using photonuclear reactions through isobaric analog states of those states, while neutral current weak responses for excited states are studied by using photonuclear reactions through the excited states. The weak interaction strengths are studied by measuring the cross sections of the photonuclear reactions, and the spin and parity of the states are studied by measuring angular correlations of particles emitted from the photonuclear reactions. Medium-energy polarized photons obtained from laser photons scattered off GeV electrons are very useful. Nuclear responses studied by photonuclear reactions are used to evaluate neutrino (weak) nuclear responses, i.e., nuclear beta and double beta matrix elements and neutrino-nuclear interactions, and to verify theoretical calculations for them.

Coherent photoproduction of ${\pi }^0\eta$ on the deuteron and ${}^3$He and ${}^4$He nuclei is considered in the energy region from threshold to a laboratory photon energy $E_{\gamma }=1.2$ GeV. The transition amplitude is derived in the impulse approximation. The effects of pion absorption are included by means of the Fernbach-Serber-Taylor model. For the reactions on $d$ and ${}^3$He the interaction of the produced $\eta$ meson with the recoiling nucleus is taken into account. The corresponding $\eta d$ and ${\eta }^3$He scattering amplitudes are obtained as solutions of the few-body equations for $\eta NN$ and $\eta -3N$ systems. The impact of this interaction on the differential cross section in the region of small relative $\eta$-nuclear momenta is discussed.

Neutron-induced fission cross sections for the plutonium isotopes from 236 to 244 are computed for neutrons of a few keV up to 5.5 MeV incident energy, using the Hauser-Feshbach statistical theory of nuclear reactions, modified to treat the fission decay channel in the $R$-matrix formalism. The fluctuations of the fission decay widths owing to the presence of intermediate structures in the second well and to the coupling of class I and class II states are simulated by Monte Carlo sampling of the underlying model parameter distributions. The accuracy of this approach is tested relative to the results of well-known analytical formulations for the average fission cross sections. Special attention is paid to the choice and consistency of the model input parameters, in part obtained from microscopic nuclear structure calculations. The predictive capabilities offered by our method are tested against the neutron-induced fission of the very short-lived ${}^{243}$Pu (${\tau }_{1/2}=4.95$ h) for which no measurement exist. Our calculations, consistent over all the Pu isotope series, demonstrate that ${}^{243}$Pu is fissile, in contrast to what is reported in the standard ENDF/B-VII.1 and JEFF-3.1.2 evaluated libraries. No recommendations are made in the JENDL-4.0 data library for this isotope.

We consider a hydrodynamic description of the spherically symmetric outward flow of nuclear matter, using a nuclear model that introduces a weakly dispersive effect in the flow. On the resulting stationary conditions of the flow, we apply an Eulerian scheme to derive a fully nonlinear equation of a time-dependent radial perturbation. In its linearized limit, with no dispersion, this equation implies the static acoustic horizon of an analog gravity model. This horizon also defines the minimum radius of the steady flow. We model the perturbation as a high-frequency traveling wave, in which the weak dispersion is taken iteratively. A WKB analysis shows that even arbitrarily small values of dispersion make the horizon fully opaque to any acoustic disturbance propagating against the bulk flow, with the amplitude and the energy flux of the radial perturbation decaying exponentially just outside the horizon. Nonlinear effects shift the horizon from its steady position.

We study the consequences of quark matter nucleation in cold hadronic matter employing three relativistic-mean-field models to describe the hadronic phase and the Nambu-Jona-Lasinio (NJL) model for the quark one. We explore the effect of a vector interaction in the NJL Lagrangian and of a phenomenological bag constant on neutron stars metastability. We delineate the region of parameters of the quark phase that allow for the formation of stable hybrid stars with mass compatible with the almost $2M_{\odot }$ pulsars PSR J1614-2230 ($1.97\pm 0.04M_{\odot }$) and PSR J0348+0432 ($2.01\pm 0.04M_{\odot }$). It is shown, however, that not all hybrid star configurations with $\sim$$2M_{\odot }$ are populated after nucleation.