An enhanced electric octupole (E3) strength of 45(5) W.u. has been measured for the $3^{-}\to 0^{+}$ transition in ${}^{150}\mathrm{Gd}$, providing direct evidence for large octupole collectivity in this nucleus. The value was determined following two sensitive experiments, to measure the mean lifetime of the $J^{\pi }=3^{-}$ level and the weak $E3$ decay branch direct to the ground state. The systematics of the $E3$ strength across the Gd isotopic chain reveals that enhanced octupole collectivity is obtained for ${}^{150}\mathrm{Gd}$. The increasing low-lying octupole strength in the Gd isotopes is analyzed with five state-of-the-art theoretical models. It is found to be best reproduced by quasiparticle random phase approximation calculations, providing a good understanding of octupole collectivity in the rare-earth region.

We propose a Bayesian inference estimation of in-medium modification of the cluster self-energies from light nuclei multiplicities measured in selected samples of central ${}^{136,124}\mathrm{Xe}+{}^{124,112}\mathrm{Sn}$ collisions with the INDRA apparatus. The data are interpreted with a relativistic quasiparticle cluster approach in the mean-field approximation without any prior assumption on the thermal parameters of the model. An excellent reproduction is obtained for H and He isotope multiplicities, and compatible posterior distributions are found for the unknown thermal parameters. We conclude that the cluster-$\sigma$-meson coupling is temperature dependent, becoming weaker when the temperature increases, in agreement with microscopic quantum statistical calculations. This implies a faster decrease of the light cluster abundances with temperature than previously estimated.

The low-energy enhancement (LEE) in $\gamma$-ray strength functions has been experimentally identified in a large number of nuclei during the past two decades; however, the origin of the enhancement is not fully understood. Building on previous theoretical work, we investigate the LEE and its relation to the scissors mode (SM) with an independent theoretical approach. We apply a novel angular-momentum-projected shell-model method that explicitly endows degrees of freedom to describe the scissors motion. Taking the recently measured $\gamma$-ray strength functions in Neodymium isotopes as examples, we find that the LEE arises from a quasi-free scissors motion appearing only in weakly-deformed nuclei, which can be viewed as an approximate free-rotation of neutrons with respect to protons. This leads us to propose a new type of collective motion, scissors rotation, to contrast the scissors vibration widely known in well-deformed nuclei. The observed LEE is naturally interpreted as the first evidence for this collective excitation mode.

We report the application of the new elimination of Rutherford elastic scattering technique for the measurement of proton-induced reaction cross sections utilizing stored ions decelerated to astrophysical energies. This approach results in a background reduction factor of about 1 order of magnitude, enabling the first measurement of a ($p$, $n$) cross section in a storage ring. Here, the reaction channels ${}^{124}\mathrm{Xe}(p,n)$ and ${}^{124}\mathrm{Xe}(p,\gamma )$ have been studied just above the neutron threshold energy. The new data provide valuable constraints for Hauser-Feshbach theory and extrapolation of the $(p,\gamma )$ cross section to lower energies. Most importantly, for nuclei of limited availability, the method represents a powerful improvement to efficiently study proton-induced reactions at energies within or close to the astrophysical Gamow window, bringing many reaction measurements within reach that were previously inaccessible in the laboratory.

The first-ever measurement of energy correlators within inclusive jets produced in heavy-ion collisions, revealed by the CMS Collaboration, shows a clear enhancement at large angles relative to the proton-proton (p-p) baseline. However, interpreting this enhancement is complicated due to selection bias from energy loss, which also distorts the energy correlator heavy-ion to p-p ratio in the hadronization region, hindering our understanding of parton/hadron dynamics in a colored medium. In this Letter, we introduce a new ratio of energy correlator observables that removes the leading effects of selection bias from the two-point energy correlator spectrum (E2C). pythia and herwig simulations show that the impact of selection bias in the E2C is reduced by an order of magnitude, while sensitivity to any other medium modifications is retained. This quantity can be obtained directly from the experimental measurements presented by CMS, as illustrated in an accompanying note [C. Andres and J. Holguin, arXiv:2409.07526].

The System for Measuring Overlap with Gas (SMOG2) at the LHCb detector enables the study of fixed-target ion-ion collisions at relativistic energies ($\sqrt{s_{\mathrm{NN}}}\sim 100\mathrm{GeV}$ in the center of mass). With input from ab initio calculations of the structure of ${}^{16}\mathrm{O}$ and ${}^{20}\mathrm{Ne}$, we compute $3+1\mathrm{D}$ hydrodynamic predictions for the anisotropic flow of $\mathrm{Pb}+\mathrm{Ne}$ and $\mathrm{Pb}+\mathrm{O}$ collisions to be tested with upcoming LHCb data. This will allow the detailed study of quark-gluon plasma formation as well as experimental tests of the predicted nuclear shapes. Elliptic flow ($v_2$) in $\mathrm{Pb}+\mathrm{Ne}$ collisions is greatly enhanced compared to the $\mathrm{Pb}+\mathrm{O}$ baseline due to the shape of ${}^{20}\mathrm{Ne}$, which is deformed in a bowling-pin geometry. Owing to the large ${}^{208}\mathrm{Pb}$ radius, this effect is seen in a broad centrality range, a unique feature of this collision configuration. Larger elliptic flow further enhances the quadrangular flow ($v_4$) of $\mathrm{Pb}+\mathrm{Ne}$ collisions via nonlinear coupling, and impacts the sign of the kurtosis of the elliptic flow vector distribution ($c_2\{4\}$). Exploiting the shape of ${}^{20}\mathrm{Ne}$ proves thus an ideal method to investigate the formation of quark-gluon plasma in fixed-target experiments at LHCb, and demonstrates the power of System for Measuring Overlap with Gas as a tool to image nuclear ground states.

Generalized thermodynamic relations are introduced into the framework of a relativistic perfect spin hydrodynamics. They allow for consistent treatment of spin degrees of freedom, including the use of spin tensors whose structure follows from microscopic calculations. The obtained results are important for establishing consistency between different formulations of spin hydrodynamics and form the basis for introducing dissipative corrections.

A study of light $\mathrm{\Lambda }$ hypernuclei in chiral effective field theory is presented. For the first time, chiral $\mathrm{\Lambda }\text{NN}$ and $\mathrm{\Sigma }\mathrm{NN}$ three-body forces are included consistently. The calculations are performed within the no-core shell model. Results for the separation energies of the hypernuclei ${}_{\mathrm{\Lambda }}{}^3\mathrm{H}$, ${}_{\mathrm{\Lambda }}{}^4\mathrm{H}/{}_{\mathrm{\Lambda }}{}^4\mathrm{He}$, ${}_{\mathrm{\Lambda }}{}^5\mathrm{He}$, and ${}_{\mathrm{\Lambda }}{}^7\mathrm{Li}$ are given. It is found that the experimental values can be fairly well reproduced once hyperon-nucleon-nucleon three-body forces are taken into account.

Neutron-induced reaction cross sections of short-lived nuclei are imperative to understand the origin of heavy elements in stellar nucleosynthesis and for societal applications, but their measurement is extremely complicated due to the radioactivity of the targets involved. One way of overcoming this issue is to combine surrogate reactions with the unique possibilities offered by heavy-ion storage rings. In this work, we describe the first surrogate-reaction experiment in inverse kinematics, which we successfully conducted at the Experimental Storage Ring (ESR) of the GSI/FAIR facility, using the ${}^{208}\mathrm{Pb}(p,p^{\prime })$ reaction as a surrogate for neutron capture on ${}^{207}\mathrm{Pb}$. Thanks to the outstanding detection efficiencies possible at the ESR, we were able to measure for the first time the neutron-emission probability as a function of the excitation energy of ${}^{208}\mathrm{Pb}$. We have used this probability to select different descriptions of the $\gamma$-ray strength function and nuclear level density, and provide reliable results for the neutron-induced radiative capture cross section of ${}^{207}\mathrm{Pb}$ at energies for which no experimental data exist.

We present a theoretical framework for treating the full excitation spectrum of $J^{\pi }=0^{+}$ pair addition modes, including the well-known low-lying and bound pairing vibrations on par with the predicted high-lying pairing vibrations, often called giant pairing vibrations. Our formalism includes the coupling to low-energy collective quadrupolar modes of the core, in such a way that both single-particle self-energy effects and the pairing interaction induced by phonon exchange are accounted for. The coupling with the continuum plays an important role and is also taken into account. The theory is applied to the case of the excitation spectrum of ${}^{14}\mathrm{C}$, recently populated by two-neutron transfer reactions.

Lead-208 is the heaviest known doubly magic nucleus and its structure is therefore of special interest. Despite this magicity, which acts to provide a strong restorative force toward sphericity, it is known to exhibit both strong octupole correlations and some of the strongest quadrupole collectivity observed in doubly magic systems. In this Letter, we employ state-of-the-art experimental equipment to conclusively demonstrate, through four Coulomb-excitation measurements, the presence of a large, negative, spectroscopic quadrupole moment for both the vibrational octupole $3_1^{-}$ and quadrupole $2_1^{+}$ state, indicative of a preference for prolate deformation of the states. The observed quadrupole moment is discussed in the context of the expected splitting of the $3^{-}\otimes 3^{-}$ two-phonon states, due to the coupling of the quadrupole and octupole motion. These results are compared with theoretical values from three different methods, which are unable to reproduce both the sign and magnitude of this deformation. Thus, in spite of its well-studied nature, ${}^{208}\mathrm{Pb}$ remains a puzzle for our understanding of nuclear structure.

The prediction of isotopic abundances resulting from the rapid neutron capture process ($r$ process) requires high-precision mass measurements. Using TITAN’s on-line time-of-flight spectrometer, first time mass measurements are performed for ${}^{83}\mathrm{Zn}$ and ${}^{86}\mathrm{Ga}$. These measurements reduced uncertainties, and are used to calculate isotopic abundances near the first $r$-process abundance peak using astrophysical conditions present during a binary neutron star (BNS) merger. Good agreement in abundance across a range of trajectories is found when comparing to several metal-poor stars while also strongly deviating from the solar $r$-process pattern. These findings point to a high degree of sensitivity to the electron fraction of a BNS merger on the final elemental abundance pattern for certain elements near the first $r$-process peak while others display universality. We find that small changes in electron fraction can produce distinct abundance patterns that match those of metal-poor stars with different classifications.

Mass measurements of ${}^{31–33}\mathrm{Na}$ and ${}^{31–35}\mathrm{Mg}$ using the TITAN MR-TOF-MS at TRIUMF’s ISAC facility are presented, with the uncertainty of the ${}^{33}\mathrm{Na}$ mass reduced by over 2 orders of magnitude. The excellent performance of the MR-TOF-MS has also allowed the discovery of a millisecond isomer in ${}^{32}\mathrm{Na}$. The precision obtained shows that the binding energy of the normally closed $N=20$ neutron shell reaches a minimum for ${}^{32}\mathrm{Mg}$ but increases significantly for ${}^{31}\mathrm{Na}$, hinting at the possibility of enhanced shell strength toward the unbound ${}^{28}\mathrm{O}$. We compare the results with new ab initio predictions that raise intriguing questions of nuclear structure beyond the dripline.

Excitation of long-lived states in bromine nuclei using a tabletop laser-plasma accelerator providing pulsed ($<100\mathrm{fs}$) electron beams provided a sensitive probe of $\gamma$ strength and level densities in the nuclear quasicontinuum and may indicate angular momentum coupling through electron-nuclear interactions. Solid-density active ${\mathrm{LaBr}}_3$ targets absorb real and virtual photons up to $35\pm 2.5\mathrm{MeV}$ and deexcite through $\gamma$ cascade into different states. A factor of $4.354\pm 0.932$ enhancement of the ${}^{80}{\mathrm{Br}}^m{/}^{80}{\mathrm{Br}}^g$ isomeric ratio was observed following electron irradiation, as compared to bremsstrahlung. Additional angular momentum transfer could possibly occur through nuclear-plasma or electron-nuclear interactions enabled by the ultrashort electron beam. Further investigation of these mechanisms could have far-reaching impact including decreased storage of long-term nuclear waste and an improved understanding of heavy element formation in astrophysical settings.

Heavy flavor jets provide ideal tools to probe the mass effect on jet substructure in both vacuum and quark-gluon plasma. An energy-energy correlator (EEC) is an excellent jet substructure observable owning to its strong sensitivity to jet physics at different scales. We perform a complete realistic simulation on medium modification of heavy and light flavor jet EECs in heavy-ion collisions. A clear flavor hierarchy is observed for jet EECs in both vacuum and quark-gluon plasma due to the mass effect. The medium modification of inclusive jet EECs at different angular scales exhibits a very rich structure: suppression at intermediate angles, and enhancement at small and large angles, which can be well explained by the interplay of mass effect, energy loss, medium-induced radiation, and medium response. These unique features of jet EECs are shown to probe the physics of jet-medium interaction at different scales, and can be readily validated by upcoming experiments.

Polonium isotopes having two protons above the shell closure at $Z=82$ show a wide variety of low-lying, high-spin isomeric states across the whole chain. The structure of neutron-deficient isotopes up to ${}^{210}\mathrm{Po}$ ($N=126$) is well established as they are easily produced through various methods. However, there is not much information available for the neutron-rich counterparts for which only selective techniques can be used for their production. We report on the first fast-timing measurements of yrast states up to the $8^{+}$ level in ${}^{214,216,218}\mathrm{Po}$ isotopes produced in the ${\beta }^{-}$ decay of ${}^{214,216,218}\mathrm{Bi}$ at ISOLDE, CERN. In particular, our new half-life value of 607(14) ps for the $8_1^{+}$ state in ${}^{214}\mathrm{Po}$ is nearly 20 times shorter than the value available in the literature and comparable with the newly measured half-lives of 409(16) and 628(25) ps for the corresponding $8_1^{+}$ states in ${}^{216,218}\mathrm{Po}$, respectively. The measured $B(E2;8_1^{+}\to 6_1^{+})$ transition probability values follow an increasing trend relative to isotope mass, reaching a maximum for ${}^{216}\mathrm{Po}$. The increase contradicts the previous claims of isomerism for the $8^{+}$ yrast states in neutron-rich ${}^{214}\mathrm{Po}$ and beyond. Together with the other measured yrast transitions, the $B(E2)$ values provide a crucial test of the different theoretical approaches describing the underlying configurations of the yrast band. The new experimental results are compared to shell-model calculations using the KHPE and H208 effective interactions and their pairing-modified versions, showing an increase in configuration mixing when moving toward the heavier isotopes.