Interaction cross sections for ${}^{42–51}\mathrm{Ca}$ on a carbon target at $280\mathrm{MeV}/\mathrm{nucleon}$ have been measured for the first time. The neutron number dependence of derived root-mean-square matter radii shows a significant increase beyond the neutron magic number $N=28$. Furthermore, this enhancement of matter radii is much larger than that of the previously measured charge radii, indicating a novel growth in neutron skin thickness. A simple examination based on the Fermi-type distribution, and mean field calculations point out that this anomalous enhancement of the nuclear size beyond $N=28$ results from an enlargement of the core by a sudden increase in the surface diffuseness of the neutron density distribution, which implies the swelling of the bare ${}^{48}\mathrm{Ca}$ core in Ca isotopes beyond $N=28$.

Whether, how, and to what extent solutions of Bjorken-expanding systems become insensitive to aspects of their initial conditions is of importance for heavy-ion collisions. Here we study $1+1\mathrm{D}$ and phenomenologically relevant boost-invariant $3+1\mathrm{D}$ systems in which initial conditions approach a universal attractor. In Israel-Stewart theory (IS) and kinetic theory where the universal attractor extends to arbitrarily early times, we show that all initial conditions approach the attractor at early times by a power law while their approach is exponential at late times. In these theories, the physical mechanisms of hydrodynamization operational at late times do not drive the approach to the attractor at early times, and the early-time attractor is reached prior to hydrodynamization. In marked contrast, the attractor in strongly coupled systems is realized concurrent with hydrodynamization. This qualitative difference may offer a basis for discriminating weakly and strongly coupled scenarios of heavy-ion collisions.

The study of the strength and behavior of the antikaon-nucleon ($\overline{K}N$) interaction constitutes one of the key focuses of the strangeness sector in low-energy quantum chromodynamics (QCD). In this Letter a unique high-precision measurement of the strong interaction between kaons and protons, close and above the kinematic threshold, is presented. The femtoscopic measurements of the correlation function at low pair-frame relative momentum of ($K^{+}p\oplus K^{-}\overline{p}$) and ($K^{-}p\oplus K^{+}\overline{p}$) pairs measured in $pp$ collisions at $\sqrt{s}=5$, 7, and 13 TeV are reported. A structure observed around a relative momentum of $58\mathrm{MeV}/c$ in the measured correlation function of ($K^{-}p\oplus K^{+}\overline{p}$) with a significance of $4.4\sigma$ constitutes the first experimental evidence for the opening of the $({\overline{K}}^{0}n\oplus K^0\overline{n})$ isospin breaking channel due to the mass difference between charged and neutral kaons. The measured correlation functions have been compared to Jülich and Kyoto models in addition to the Coulomb potential. The high-precision data at low relative momenta presented in this work prove femtoscopy to be a powerful complementary tool to scattering experiments and provide new constraints above the $\overline{K}N$ threshold for low-energy QCD chiral models.

We investigate the impact of different properties of the nuclear equation of state in core-collapse supernovae, with a focus on the proto-neutron-star contraction and its impact on the shock evolution. To this end, we introduce a range of equations of state that vary the nucleon effective mass, incompressibility, symmetry energy, and nuclear saturation point. This allows us to point to the different effects in changing these properties from the Lattimer and Swesty to the Shen et al. equations of state, the two most commonly used equations of state in simulations. In particular, we trace the contraction behavior to the effective mass, which determines the thermal nucleonic contributions to the equation of state. Larger effective masses lead to lower pressures at nuclear densities and a lower thermal index. This results in a more rapid contraction of the proto-neutron star and consequently higher neutrino energies, which aids the shock evolution to a faster explosion.

We probe the $N=82$ nuclear shell closure by mass measurements of neutron-rich cadmium isotopes with the ISOLTRAP spectrometer at ISOLDE-CERN. The new mass of ${}^{132}\mathrm{Cd}$ offers the first value of the $N=82$, two-neutron shell gap below $Z=50$ and confirms the phenomenon of mutually enhanced magicity at ${}^{132}\mathrm{Sn}$. Using the recently implemented phase-imaging ion-cyclotron-resonance method, the ordering of the low-lying isomers in ${}^{129}\mathrm{Cd}$ and their energies are determined. The new experimental findings are used to test large-scale shell-model, mean-field, and beyond-mean-field calculations, as well as the ab initio valence-space in-medium similarity renormalization group.

Experimental evidence exists that the $\mathrm{\Xi }$-nucleus interaction is attractive. We search for $NN\mathrm{\Xi }$ and $NNN\mathrm{\Xi }$ bound systems on the basis of the AV8 $NN$ potential combined with either a phenomenological Nijmegen $\mathrm{\Xi }N$ potential or a first principles HAL QCD $\mathrm{\Xi }N$ potential. The binding energies of the three-body and four-body systems (below the $d+\mathrm{\Xi }$ and ${}^3\mathrm{H}/{}^3\mathrm{He}+\mathrm{\Xi }$ thresholds, respectively) are calculated by a high precision variational approach, the Gaussian expansion method. Although the two $\mathrm{\Xi }N$ potentials have significantly different isospin ($T$) and spin ($S$) dependence, the $NNN\mathrm{\Xi }$ system with quantum numbers ($T=0$, $J^{\pi }=1^{+}$) appears to be bound (one deep for Nijmegen and one shallow for HAL QCD) below the ${}^3\mathrm{H}/{}^3\mathrm{He}+\mathrm{\Xi }$ threshold. Experimental implications for such a state are discussed.

The elliptic flow of muons from the decay of charm and bottom hadrons is measured in $pp$ collisions at $\sqrt{s}=13\mathrm{TeV}$ using a data sample with an integrated luminosity of $150{\mathrm{pb}}^{-1}$ recorded by the ATLAS detector at the LHC. The muons from heavy-flavor decay are separated from light-hadron decay muons using momentum imbalance between the tracking and muon spectrometers. The heavy-flavor decay muons are further separated into those from charm decay and those from bottom decay using the distance-of-closest-approach to the collision vertex. The measurement is performed for muons in the transverse momentum range 4–7 GeV and pseudorapidity range $|\eta |<2.4$. A significant nonzero elliptic anisotropy coefficient $v_2$ is observed for muons from charm decays, while the $v_2$ value for muons from bottom decays is consistent with zero within uncertainties.

We present a high-accuracy calculation of the deuteron structure radius in chiral effective field theory. Our analysis employs the state-of-the-art semilocal two-nucleon potentials and takes into account two-body contributions to the charge density operators up to fifth order in the chiral expansion. The strength of the fifth-order short-range two-body contribution to the charge density operator is adjusted to the experimental data on the deuteron charge form factor. A detailed error analysis is performed by propagating the statistical uncertainties of the low-energy constants entering the two-nucleon potentials and by estimating errors from the truncation of the chiral expansion as well as from uncertainties in the nucleon form factors. Using the predicted value for the deuteron structure radius together with the very accurate atomic data for the difference of the deuteron and proton charge radii we, for the first time, extract the charge radius of the neutron from light nuclei. The extracted value reads $r_n^2=-{0.106}_{-0.005}^{+0.007}{\mathrm{fm}}^2$ and its magnitude is about $1.7\sigma$ smaller than the current value given by the Particle Data Group. In addition, given the high accuracy of the calculated deuteron charge form factor and its careful and systematic error analysis, our results open the way for an accurate determination of the nucleon form factors from elastic electron-deuteron scattering data measured at the Mainz Microtron and other experimental facilities.

The nuclei below lead but with more than 126 neutrons are crucial to an understanding of the astrophysical $r$ process in producing nuclei heavier than $A\sim 190$. Despite their importance, the structure and properties of these nuclei remain experimentally untested as they are difficult to produce in nuclear reactions with stable beams. In a first exploration of the shell structure of this region, neutron excitations in ${}^{207}\mathrm{Hg}$ have been probed using the neutron-adding ($d$,$p$) reaction in inverse kinematics. The radioactive beam of ${}^{206}\mathrm{Hg}$ was delivered to the new ISOLDE Solenoidal Spectrometer at an energy above the Coulomb barrier. The spectroscopy of ${}^{207}\mathrm{Hg}$ marks a first step in improving our understanding of the relevant structural properties of nuclei involved in a key part of the path of the $r$ process.

The low-lying energy spectrum of the extremely neutron-deficient self-conjugate ($N=Z$) nuclide ${{}_{44}{}^{88}\mathrm{Ru}}_{44}$ has been measured using the combination of the Advanced Gamma Tracking Array (AGATA) spectrometer, the NEDA and Neutron Wall neutron detector arrays, and the DIAMANT charged particle detector array. Excited states in ${}^{88}\mathrm{Ru}$ were populated via the ${}^{54}\mathrm{Fe}({}^{36}\mathrm{Ar},2n\gamma ){{}^{88}\mathrm{Ru}}^{*}$ fusion-evaporation reaction at the Grand Accélérateur National d’Ions Lourds (GANIL) accelerator complex. The observed $\gamma$-ray cascade is assigned to ${}^{88}\mathrm{Ru}$ using clean prompt $\gamma \text{−}\gamma$-2-neutron coincidences in anticoincidence with the detection of charged particles, confirming and extending the previously assigned sequence of low-lying excited states. It is consistent with a moderately deformed rotating system exhibiting a band crossing at a rotational frequency that is significantly higher than standard theoretical predictions with isovector pairing, as well as observations in neighboring $N>Z$ nuclides. The direct observation of such a “delayed” rotational alignment in a deformed $N=Z$ nucleus is in agreement with theoretical predictions related to the presence of strong isoscalar neutron-proton pair correlations.

The excitation functions for quasielastic scattering of ${}^{22}\mathrm{Ne}+{}^{248}\mathrm{Cm}$, ${}^{26}\mathrm{Mg}+{}^{248}\mathrm{Cm}$, and ${}^{48}\mathrm{Ca}+{}^{238}\mathrm{U}$ are measured using a gas-filled recoil ion separator. The quasielastic barrier distributions are extracted for these systems and are compared with coupled-channel calculations. The results indicate that the barrier distribution is affected dominantly by deformation of the actinide target nuclei, but also by vibrational or rotational excitations of the projectile nuclei, as well as neutron transfer processes before capture. From a comparison between the experimental barrier distributions and the evaporation residue cross sections for Sg ($Z=106$), Hs (108), Cn (112), and Lv (116), it is suggested that the hot fusion reactions take advantage of a compact collision, where the projectile approaches along the short axis of a prolately deformed nucleus. A new method is proposed to estimate the optimum incident energy to synthesize unknown superheavy nuclei using the barrier distribution.

We present predictions for jet suppression from small to intermediate to very large radius, for high energy jets created in heavy ion collisions at the LHC. We find that jet suppression is surprisingly independent of the anti-kT radius $R$, first slightly increasing as one increases $R$, then at larger values of $R$ very slowly decreasing. This behavior arises from two competing effects, namely the larger energy loss of the hard jet components, which tends to increase suppression, versus the partial recovery of the lost energy due to medium response, reducing suppression.

Understanding the hadronization of the quark-gluon plasma (QGP) remains a challenging problem in the study of strong-interaction matter as produced in ultrarelativistic heavy-ion collisions (URHICs). The large mass of heavy quarks renders them excellent tracers of the color neutralization process of the QGP when they convert into various heavy-flavor (HF) hadrons. We develop a 4-momentum conserving recombination model for HF mesons and baryons that recovers the thermal and chemical equilibrium limits and accounts for space-momentum correlations (SMCs) of heavy quarks with partons of the hydrodynamically expanding QGP, thereby resolving a long-standing problem in quark coalescence models. The SMCs enhance the recombination of fast-moving heavy quarks with high-flow thermal quarks in the outer regions of the fireball. We also improve the hadrochemistry with “missing” charm-baryon states, previously found to describe the large ${\mathrm{\Lambda }}_c/D^0$ ratio observed in proton-proton collisions. Both SMCs and hadrochemistry, as part of our HF hydro-Langevin-recombination model for the strongly coupled QGP, importantly figure in the description of recent data for the ${\mathrm{\Lambda }}_c/D^0$ ratio and $D$-meson elliptic flow in URHICs.

There is sparse direct experimental evidence that atomic nuclei can exhibit stable “pear” shapes arising from strong octupole correlations. In order to investigate the nature of octupole collectivity in radium isotopes, electric octupole ($E3$) matrix elements have been determined for transitions in ${}^{222,228}\mathrm{Ra}$ nuclei using the method of sub-barrier, multistep Coulomb excitation. Beams of the radioactive radium isotopes were provided by the HIE-ISOLDE facility at CERN. The observed pattern of $E3$ matrix elements for different nuclear transitions is explained by describing ${}^{222}\mathrm{Ra}$ as pear shaped with stable octupole deformation, while ${}^{228}\mathrm{Ra}$ behaves like an octupole vibrator.

The presence of clusterlike narrow resonances in the vicinity of reaction or decay thresholds is a ubiquitous phenomenon with profound consequences. We argue that the continuum coupling, present in the open quantum system description of the atomic nucleus, can profoundly impact the nature of near-threshold states. In this Letter, we discuss the structure of the recently observed near-threshold resonance in ${}^{11}\mathrm{B}$, whose very existence explains the puzzling beta-delayed proton emission of the neutron-rich ${}^{11}\mathrm{Be}$.

We show through first-principles nuclear structure calculations that the special nature of the strong nuclear force determines highly regular patterns heretofore unrecognized in nuclei that can be tied to an emergent approximate symmetry. This symmetry is ubiquitous and mathematically tracks with a symplectic symmetry group. This, in turn, has important implications for understanding the physics of nuclei: we find that nuclei are made of only a few equilibrium shapes, deformed or not, with associated vibrations and rotations. It also opens the path for ab initio large-scale modeling of open-shell intermediate-mass nuclei without the need for renormalized interactions and effective charges.

Radioactive ${}^{129}\mathrm{Sb}$, which can be treated as a proton plus semimagic ${}^{128}\mathrm{Sn}$ core within the particle-core coupling scheme, was studied by Coulomb excitation. Reduced electric quadrupole transition probabilities, $B(E2)$, for the $2^{+}\otimes \pi g_{7/2}$ multiplet members and candidate $\pi d_{5/2}$ state were measured. The results indicate that the total electric quadrupole strength of ${}^{129}\mathrm{Sb}$ is a factor of 1.39(11) larger than the ${}^{128}\mathrm{Sn}$ core, which is in stark contrast to the expectations of the empirically successful particle-core coupling scheme. Shell-model calculations performed with two different sets of nucleon-nucleon interactions suggest that this enhanced collectivity is due to constructive quadrupole coherence in the wave functions stemming from the proton-neutron residual interactions, where adding one nucleon to a core near a double-shell closure can have a pronounced effect. The enhanced electric quadrupole strength is an early signal of the emerging nuclear collectivity that becomes dominant away from the shell closure.

The ${}^7\mathrm{H}$ system was populated in the ${}^2\mathrm{H}({}^8\mathrm{He},{}^3\mathrm{He}){}^7\mathrm{H}$ reaction with a 26 AMeV ${}^8\mathrm{He}$ beam. The ${}^7\mathrm{H}$ missing mass energy spectrum, the ${}^3\mathrm{H}$ energy and angular distributions in the ${}^7\mathrm{H}$ decay frame were reconstructed. The ${}^7\mathrm{H}$ missing mass spectrum shows a peak, which can be interpreted either as unresolved $5/2^{+}$ and $3/2^{+}$ doublet or one of these states at 6.5(5) MeV. The data also provide indications of the $1/2^{+}$ ground state of ${}^7\mathrm{H}$ located at 1.8(5) MeV with quite a low population cross section of $\sim 25\mu \mathrm{b}/\mathrm{sr}$ within angular range ${\theta }_{\mathrm{c}.\mathrm{m}.}\simeq (17°–27°)$.