The novel technology of calorimetric low-temperature detectors (CLTDs) was applied to determine isotopic yields of fission fragments using the passive absorber method for thermal-neutron-induced fission reactions at the LOHENGRIN mass spectrometer at the Institut Laue-Langevin in Grenoble, France. Precise yields were determined for ${}^{92}\mathrm{Rb}$ and ${}^{96}\mathrm{Y}$. These fission products are the dominant contributors to the high-energy portion of the reactor antineutrino spectra. Our new measurements resolve inconsistencies between previous yield measurements and fission data libraries and reduce the nuclear data uncertainties in the computation of reactor antineutrino spectra by the summation method.

Experimental measurements indicate no suppression (e.g., $R_{\text{p}\text{Pb}}\approx 1$) but a surprisingly large $D$ meson $v_2$ was measured in $p+\mathrm{Pb}$ collisions. In order to understand these results, we use Trento $+\text{v-usp}\text{hydro}+dab-mod$ with event-by-event realistic hydrodynamic background to make predictions and propose a system size scan at the Large Hadron Collider (LHC) involving ${}^{208}\mathrm{PbPb}, {}^{129}\mathrm{XeXe}, {}^{40}\mathrm{ArAr}$, and ${}^{16}\mathrm{OO}$ collisions. We find that the nuclear modification factor approaches unity as the system size is decreased, but nonetheless, in the 0–10% most central collisions, $v_2\left\{2\right\}$ is roughly equivalent regardless of system size. These results arise from a rather nontrivial interplay between the shrinking path length and the enhancement of eccentricities in small systems at high multiplicity. Finally, we also find a surprising sensitivity of $D$ mesons $v_2\left\{2\right\}$ in 0–10% at $p_{\text{T}}=2–10\mathrm{GeV}$ to the slight deformation of ${}^{129}\mathrm{Xe}$ recently found at the LHC.

Background: The Fano factor is used to characterize statistical noises, in quantum optics to determine correlations and anticorrelations, in transport theory to characterize the limit of quantum chaos experienced by electrons in a mesoscopic cavity. However, to our knowledge, it has not been used in nuclear physics to study the spectral fluctuations.

Purpose: In the present contribution, we applied the square root of the Fano factor ($\widehat{f}$) to random matrix theory and to the energy level statistics of the nuclear excitation spectrum to determine if the Fano factor can be used to study nuclear energy spectra distributions.

Methods: We studied the fluctuation of the excited states of ${}^{48}\mathrm{Ca}, {}^{48}\mathrm{Ti}$, and ${}^{46}\mathrm{Ti}$ with symmetry $J^P=3^{+}$ as well as the Wigner distribution and the Fourier power spectrum of the energy level spacings for different quadrupole interactions so we can determine when we have a chaotic distribution. Later on we compared with the Fano factor of the same distributions.

Results: The Fano factor agrees with that obtained by the other methods. We show that $\widehat{f}=0.5$ corresponds to quantum chaos for the energy levels in the nuclear spectra.

Conclusions: The Fano factor can be used in nuclear physics (and other areas of science) to determine quantum chaos.

Purported signatures of collective dynamics in small systems like proton-proton ($pp$) or proton-nucleus ($p-A$) collisions still lack unambiguous understanding. Despite the qualitative and/or quantitative agreement of the data to hydrodynamic models, it has remained unclear whether the harmonic flows in small systems relate to the common physical picture of hydrodynamic collectivity driven by the initial geometry. In the present work, we aim to address this issue by invoking a novel concept of event shape engineering (ESE), which has been leveraged to get some control of the initial geometry in high-energy heavy-ion collisions. We utilize ESE by constructing a reference flow vector, $q_2$ that allows to characterize an event based on its ellipticity. Applying this technique on a data set, simulated from a $3+1$ dimensional viscous hydrodynamic model EPOS3, we study the event-shape dependent modifications to some of the bulk properties, such as inclusive transverse momentum ($p_T$) spectra and $p_T$-differential $v_2$ for $p$-Pb collisions at 5.02 TeV. Selecting events on the basis of different magnitudes of reference flow vector $q_2$, we observe a hint of event-shape induced modifications of $v_2$ as a function of $p_T$, but the inclusive $p_T$ spectra of charged particles seem to be insensitive to this event-shape selection.

The $n+{}^3\mathrm{H},$ $p+{}^3\mathrm{He},$ $p+{}^3\mathrm{H},$ and $n+{}^3\mathrm{He}$ elastic and charge exchange reactions at low energies are studied by means of the hyperspherical harmonic method. The considered nuclear Hamiltonians include modern two- and three-nucleon interactions, and in particular results are reported in case of chiral two-nucleon potentials, with and without the inclusion of chiral three-nucleon (3N) interactions. A detailed study of the convergence and numerical stability of the method is presented. We have found that the effect the 3N force is in general tiny except for $p+{}^3\mathrm{H}$ scattering below the opening of the $n+{}^3\mathrm{He}$ channel. In such a case, the effect of 3N forces is appreciable and a clear dependence on the cutoff used to regularize the high-momentum tail of the interactions is observed. Such a dependence is related to the presence of the poorly known sharp $0^{+}$ resonance, considered to be the first excited state of ${}^4\mathrm{He}$.

The neutron energy spectra in coincidence with both the correlated fission fragments in ${}^{32}\mathrm{S}+{}^{184}\mathrm{W}$ reaction forming the compound nucleus ${}^{216}\mathrm{Th}$ at an excitation energy of 71.31 MeV have been measured at various angles with respect to one of the fission fragments. Pre- and post-scission neutron multiplicities of $2.68\pm 0.48$ and $3.3\pm 0.20,$ respectively, have been extracted by analyzing angular correlation of the neutron energy spectra using moving source fitting procedure. The excess pre-scission neutron multiplicity in comparison to statistical model joanne2 code predictions have been converted into total fission delay. A comparative study of fission delay has been carried out for the ${}^{16}\mathrm{O}+{}^{208}\mathrm{Pb}$ reaction forming the compound nucleus ${}^{224}\mathrm{Th}$ at similar excitation energy as in ${}^{32}\mathrm{S}+{}^{184}\mathrm{W}$ reaction. Both the reactions have been analyzed within the frame work of joanne2 code including fission delay, deformation dependent level densities, particle binding energies, and transmission coefficients. The observed fission delay for both the reactions can be quantitatively understood if different formation time predicted by dynamical model hicol code are considered.

Background: The density of most nuclei is constant in the central region and is smoothly decreasing at the surface. A depletion in the central part of the nuclear density can have nuclear structure effects leading to the formation of “bubble” nuclei. However, probing the density profile of the nuclear interior is, in general, very challenging.

Purpose: The aim of this paper is to investigate the nuclear bubble structure, with nucleon-nucleus scattering, and quantify the effect that the bubble structure has on the nuclear surface profile.

Method: We employed high-energy nucleon-nucleus scattering, using the Glauber model to analyze various reaction observables, which helps in quantifying the nuclear bubble. The effectiveness of this method is tested on ${}^{28}\mathrm{Si}$ with harmonic-oscillator (HO) densities, before applying it on even-even $N=14$ isotones, in the $22\le A\le 34$ mass range, with realistic densities obtained from antisymmetrized molecular dynamics (AMD).

Results: Elastic scattering differential cross sections and reaction probability for the proton-${}^{28}\mathrm{Si}$ reaction are calculated using the HO density to design tests for signatures of the nuclear bubble structure. We then quantify the degree of bubble structure for $N=14$ isotones with the AMD densities by analyzing their elastic scattering at 325, 550, and 800 MeV incident energies. The present analyses suggest ${}^{22}\mathrm{O}$ as the most measurable candidate for a bubble nucleus, among even-even $N=14$ isotones, in the $22\le A\le 34$ mass range.

Conclusion: We have shown that the bubble structure information is imprinted on the nucleon-nucleus elastic scattering differential cross section, especially in the first diffraction peak. Bubble nuclei tend to have a sharper nuclear surface and deformation seems to be a hindrance in their emergence.

A recent study by Hoff and collaborators [Nature (London) 580, 52 (2020)] presented evidence that the ground-state spin of ${}^{73}\mathrm{Sr}$ is different from that of its mirror, ${}^{73}\mathrm{Br}$, likely due to an inversion of the ground- and first-excited states. Here, we assess the likelihood of such an inversion arising from normal isospin-symmetry breaking and, more broadly, whether such phenomena challenge our understanding of charge-symmetry-breaking forces in atomic nuclei. By placing the result within the context of previous experimental and theoretical work we demonstrate that this inversion lies entirely within the bounds of normal isospin-symmetry-breaking behavior. We further note that, in the context of isospin, neither level inversions nor the nuclear ground state hold any special significance.

We present the first measurement of the reaction $\gamma p\to a_2{\left(1320\right)}^{0}p$ in the photon energy range 3.5–$5.5\mathrm{Ge}\mathrm{V}$ and four-momentum transfer squared $0.2<-t<2.0{\mathrm{Ge}\mathrm{V}}^2$. Data were collected with the CEBAF Large Acceptance Spectrometer detector at the Thomas Jefferson National Accelerator Facility. The $a_2$ resonance was detected by measuring the reaction $\gamma p\to {\pi }^0\eta p$ and reconstructing the ${\pi }^0\eta$ invariant mass. The most prominent feature of the differential cross section is a dip at $-t\approx 0.55{\mathrm{Ge}\mathrm{V}}^2$. This can be described in the framework of Regge phenomenology, where the exchange degeneracy hypothesis predicts a zero in the reaction amplitude for this value of the four-momentum transfer.

Antiprotonic hydrogen and helium atoms are analyzed. Level shifts and width are expressed in terms of $\overline{p}$-nucleon subthreshold scattering lengths and volumes. Experimental data are compared to results obtained from the 2009 version of the Paris $N\overline{N}$ interaction potential. Comparison with the 1999 version is also made. Effects of $N\overline{N}$ quasibound states are discussed. Atomic $2P$ hyperfine structure is calculated for antiprotonic deuterium and the significance of new measurements is indicated.

Background: There is renewed interest in electric dipole strength distributions for a variety of reasons including the extraction of the dipole polarizability related to properties of the symmetry energy and a measure for the neutron skin thickness, understanding the structure of low-energy $E1$ strength in nuclei with neutron excess, and establishing the systematics of the isovector giant dipole resonance (IVGDR). Inelastic proton scattering at energies of a few hundred MeV and very forward angles including $0^{\circ }$ has been established as a tool for the study of electric and magnetic dipole strength distributions in nuclei.

Purpose: The present work aims at a systematic investigation of the electric and magnetic dipole strength distributions in the chain of stable even-mass tin isotopes.

Methods: Inelastic proton scattering experiments were performed at the Research Center for Nuclear Physics, Osaka, with a 295-MeV beam covering laboratory angles $0^{\circ }\text{–}{6}^{\circ }$ and excitation energies $6\text{–}22$ MeV. Cross sections due to $E1$ and $M1$ excitations were extracted with a multipole decomposition analysis (MDA) and then converted to reduced transition probabilities with the “virtual photon method” for $E1$ and the “unit cross section method” for $M1$ excitations, respectively. Including a theory-aided correction for the high-excitation-energy region not covered experimentally, the electric dipole polarizability was determined from the $E1$ strength distributions.

Results: Total photoabsorption cross sections derived from the $E1$ and $M1$ strength distributions show significant differences compared to those from previous $(\gamma ,xn)$ experiments in the energy region of the IVGDR. The widths of the IVGDR deduced from the present data with a Lorentz parametrization show an approximately constant value of about 4.5 MeV in contrast to the large variations between isotopes observed in previous work. The IVGDR centroid energies are in good correspondence to expectations from empirical systematics of their mass dependence. Furthermore, a study of the dependence of the IVGDR energies on bulk matter properties is presented. The $E1$ strengths below neutron threshold show fair agreement with results from $(\gamma ,{\gamma }^{\prime })$ experiments on ${}^{112,116,120,124}\mathrm{Sn}$ in the energy region between 6 and 7 MeV, where also isoscalar $E1$ strength was found for ${}^{124}\mathrm{Sn}$. At higher excitation energies, large differences are observed, pointing to a different nature of the excited states with small ground-state branching ratios. The isovector spin-$M1$ strengths exhibit a broad distribution between 6 and 12 MeV in all studied nuclei.

Conclusions: The present results contribute to the solution of a variety of nuclear structure problems including the systematics of the energy and width of the IVGDR, the structure of low-energy $E1$ strength in nuclei, new constraints to energy density functionals (EDFs) aiming at a systematic description of the dipole polarizability across the nuclear chart, from which properties of the symmetry energy can be derived, and the systematics of the isovector spin-$M1$ strength in heavy nuclei.

We present a measurement of the rate of correlated neutron captures in the WATCHBOY detector, deployed at a depth of approximately 390 meters water equivalent (m.w.e.) in the Kimballton Underground Research Facility (KURF). WATCHBOY consists of a cylindrical 2 ton water target doped with 0.1% gadolinium, surrounded by a 40 ton undoped water hermetic shield. We present a comparison of our results with the expected rate of correlated neutron captures arising from high-energy neutrons incident on the outside of the WATCHBOY shield, predicted by a hybrid fluka-geant4-based simulation. The incident neutron energy distribution used in the simulation was measured by a fast neutron spectrometer, the 1.8 ton Multiplicity and Recoil Spectrometer (MARS) detector, at the same depth. We find that the measured detection rate of two correlated neutrons is consistent with that predicted by simulation. The result lends additional confidence in the detection technique used by MARS, and therefore in the MARS spectra as measured at three different depths. Confirmation of the fast neutron flux and spectrum is important as it helps validate the scaling models used to predict the fast neutron fluxes at different overburdens.

We have used second-order relativistic hydrodynamics equipped with an equation of state which includes the critical point to study the propagation of a perturbation in a relativistic QCD fluid. The dispersion relation for the sound wave has been derived to ascertain the fate of the perturbation in the fluid near the QCD critical end point (CEP). We observe that the threshold value of the wavelength of the sound in the fluid diverges at the CEP, implying that all the modes of the perturbation are dissipated at this point. Some consequences of the suppression of sound near the critical point have been discussed.

Due to its importance as an astronomical observable in core-collapse supernovae (CCSNe), the reactions producing and destroying ${}^{44}\mathrm{Ti}$ must be well constrained. Generally, statistical model calculations such as Hauser-Feshbach are employed when experimental cross sections are not available, but the variation in such adopted rates can be large. Here, data from the literature is compared with statistical model calculations of the ${}^{44}\mathrm{Ti}(\alpha ,p){}^{47}\mathrm{V}$ reaction cross section and used to constrain the possible reaction rate variation over the temperatures relevant to CCSNe. Suggestions for targeted future measurements are given.

The single-particle structure of the $N=27$ isotones provides insights into the shell evolution of neutron-rich nuclei from the doubly magic ${}^{48}\mathrm{Ca}$ toward the drip line. ${}^{43}\mathrm{S}$ was studied employing the one-neutron knockout reaction from a radioactive ${}^{44}\mathrm{S}$ beam. Using a combination of prompt and delayed $\gamma$-ray spectroscopy the level structure of ${}^{43}\mathrm{S}$ was clarified. Momentum distributions were analyzed and allowed for spin and parity assignments. The deduced spectroscopic factors show that the ${}^{44}\mathrm{S}$ ground-state configuration has a strong intruder component. The results were confronted with shell-model calculations using two effective interactions. General agreement was found between the calculations, but strong population of states originating from the removal of neutrons from the $2p_{3/2}$ orbital in the experiment indicates that the breakdown of the $N=28$ magic number is more rapid than the theoretical calculations suggest.

We present results of barrier distribution measurements for ${}^{24}\mathrm{Mg}+{}^{90,92}\mathrm{Zr}$ systems by the backscattering method. The measurements were done at near-barrier beam energies of 68–88.5 MeV (in the laboratory frame) at six angles. A strong discrepancy between experimental results and the predictions of the standard coupled channels calculations was observed. To test the hypothesis that this discrepancy may be due to partial energy dissipation caused by coupling to many target noncollective levels, we performed calculations using the coupled channels plus random matrix theory ($\mathrm{CC}+\mathrm{RMT}$) model. The comparison of calculations with experimental results gives qualitative support of the hypothesis; however, quantitatively the agreement is not as good as in the case of the ${}^{20}\mathrm{Ne}$ projectile.