The region of heavy calcium isotopes forms the frontier of experimental and theoretical nuclear structure research where the basic concepts of nuclear physics are put to stringent test. The recent discovery of the extremely neutron-rich nuclei around ${}^{60}\mathrm{Ca}$ O. B. Tarasov et al. [Phys. Rev. Lett. 121, 022501 (2018)] and the experimental determination of masses for ${}^{55–57}\mathrm{Ca}$ S. Michimasa et al. [Phys. Rev. Lett. 121, 022506 (2018)] provide unique information about the binding energy surface in this region. To assess the impact of these experimental discoveries on the nuclear landscape’s extent, we use global mass models and statistical machine learning to make predictions, with quantified levels of certainty, for bound nuclides between Si and Ti. Using a Bayesian model averaging analysis based on Gaussian-process-based extrapolations we introduce the posterior probability $p_{\mathrm{ex}}$ for each nucleus to be bound to neutron emission. We find that extrapolations for drip-line locations, at which the nuclear binding ends, are consistent across the global mass models used, in spite of significant variations between their raw predictions. In particular, considering the current experimental information and current global mass models, we predict that ${}^{68}\mathrm{Ca}$ has an average posterior probability $p_{\mathrm{ex}}\approx 76\%$ to be bound to two-neutron emission while the nucleus ${}^{61}\mathrm{Ca}$ is likely to decay by emitting a neutron ($p_{\mathrm{ex}}\approx 46\%$).

The ab initio understanding of hadronic three-body systems above threshold, such as exotic resonances or the baryon spectrum, requires the mapping of the finite-volume eigenvalue spectrum, produced in lattice QCD calculations, to the infinite volume. We present the first application of such a formalism to a physical system in form of three interacting positively charged pions. The results for the ground state energies agree with the available lattice QCD results by the NPLQCD collaboration at unphysical pion masses. Extrapolations to physical pion masses are performed using input from effective field theory. The excited energy spectrum is predicted. This demonstrates the feasibility to determine three-body amplitudes above threshold from lattice QCD, including resonance properties of axial mesons, exotics, and excited baryons.

New rotational bands built on the $\nu (h_{11/2})$ configuration have been identified in ${}^{105}\mathrm{Pd}$. Two bands built on this configuration show the characteristics of transverse wobbling: the $\mathrm{\Delta }I=1$ transitions between them have a predominant $E2$ component and the wobbling energy decreases with increasing spin. The properties of the observed wobbling bands are in good agreement with theoretical results obtained using constrained triaxial covariant density functional theory and quantum particle rotor model calculations. This provides the first experimental evidence for transverse wobbling bands based on a one-neutron configuration, and also represents the first observation of wobbling motion in the $A\sim 100$ mass region.

The kilonova emission observed following the binary neutron star merger event GW170817 provided the first direct evidence for the synthesis of heavy nuclei through the rapid neutron capture process ($r$ process). The late-time transition in the spectral energy distribution to near-infrared wavelengths was interpreted as indicating the production of lanthanide nuclei, with atomic mass number $A\gtrsim 140$. However, compelling evidence for the presence of even heavier third-peak ($A\approx 195$) $r$-process elements (e.g., gold, platinum) or translead nuclei remains elusive. At early times ($\sim \mathrm{days}$) most of the $r$-process heating arises from a large statistical ensemble of $\beta$ decays, which thermalize efficiently while the ejecta is still dense, generating a heating rate that is reasonably approximated by a single power law. However, at later times of weeks to months, the decay energy input can also possibly be dominated by a discrete number of $\alpha$ decays, ${}^{223}\mathrm{Ra}$ (half-life $t_{1/2}=11.43\mathrm{d}$), ${}^{225}\mathrm{Ac}$ ($t_{1/2}=10.0\mathrm{d}$, following the $\beta$ decay of ${}^{225}\mathrm{Ra}$ with $t_{1/2}=14.9\mathrm{d}$), and the fissioning isotope ${}^{254}\mathrm{Cf}$ ($t_{1/2}=60.5\mathrm{d}$), which liberate more energy per decay and thermalize with greater efficiency than $\beta$-decay products. Late-time nebular observations of kilonovae which constrain the radioactive power provide the potential to identify signatures of these individual isotopes, thus confirming the production of heavy nuclei. In order to constrain the bolometric light to the required accuracy, multiepoch and wideband observations are required with sensitive instruments like the James Webb Space Telescope. In addition, by comparing the nuclear heating rate obtained with an abundance distribution that follows the solar $r$ abundance pattern, to the bolometric lightcurve of AT2017gfo, we find that the yet-uncertain $r$ abundance of ${}^{72}\mathrm{Ge}$ plays a decisive role in powering the lightcurve, if one assumes that GW170817 has produced a full range of the solar $r$ abundances down to mass number $A\sim 70$.

The neutron-capture reaction plays a critical role in the synthesis of the elements in stars and is important for societal applications including nuclear power generation and stockpile-stewardship science. However, it is difficult—if not impossible—to directly measure neutron capture cross sections for the exotic, short-lived nuclei that participate in these processes. In this Letter we demonstrate a new technique which can be used to indirectly determine neutron-capture cross sections for exotic systems. This technique makes use of the $(d,p)$ transfer reaction, which has long been used as a tool to study the structure of nuclei. Recent advances in reaction theory, together with data collected using this reaction, enable the determination of neutron-capture cross sections for short-lived nuclei. A benchmark study of the ${}^{95}\mathrm{Mo}(d,p)$ reaction is presented, which illustrates the approach and provides guidance for future applications of the method with short-lived isotopes produced at rare isotope accelerators.

Detection of nuclear-decay $\gamma$ rays provides a sensitive thermometer of nova nucleosynthesis. The most intense $\gamma$-ray flux is thought to be annihilation radiation from the ${\beta }^{+}$ decay of ${}^{18}\mathrm{F}$, which is destroyed prior to decay by the ${}^{18}\mathrm{F}(p,\alpha ){}^{15}\mathrm{O}$ reaction. Estimates of ${}^{18}\mathrm{F}$ production had been uncertain, however, because key near-threshold levels in the compound nucleus, ${}^{19}\mathrm{Ne}$, had yet to be identified. We report the first measurement of the ${}^{19}\mathrm{F}({}^3\mathrm{He},t\gamma ){}^{19}\mathrm{Ne}$ reaction, in which the placement of two long-sought $3/2^{+}$ levels is suggested via triton-$\gamma \text{−}\gamma$ coincidences. The precise determination of their resonance energies reduces the upper limit of the rate by a factor of 1.5–17 at nova temperatures and reduces the average uncertainty on the nova detection probability by a factor of 2.1.

Experimental studies of nuclear collisions involving light weakly bound nuclei show a systematic suppression of the complete fusion cross section by $\sim 30\%$ with respect to the expectation for tightly bound nuclei, at energies above the Coulomb barrier. Although it is widely accepted that the phenomenon is related to the weak binding of these nuclei, the origin of this suppression is not fully understood. Here, we present a novel approach that provides the complete fusion for weakly bound nuclei and relates its suppression to the competition between the different mechanisms contributing to the reaction cross section. The method is applied to the ${}^{6,7}\mathrm{Li}+{}^{209}\mathrm{Bi}$ reactions, where we find that the suppression of complete fusion is mostly caused by the flux associated with nonelastic breakup modes, such as the partial capture of the projectile (incomplete fusion), whereas the elastic breakup mode is found to play a minor role. Finally, we demonstrate that the large $\alpha$ yields observed in these reactions can be naturally explained as a consequence of a Trojan Horse mechanism.

Even mass neutron-rich niobium isotopes are among the principal contributors to the reactor antineutrino energy spectrum. They are also among the most challenging to measure due to the refractory nature of niobium, and because they exhibit isomeric states lying very close in energy. The $\beta$-intensity distributions of ${}^{100\mathrm{gs},100m}\mathrm{Nb}$ and ${}^{102\mathrm{gs},102m}\mathrm{Nb}$ $\beta$ decays have been determined using the total absorption $\gamma$-ray spectroscopy technique. The measurements were performed at the upgraded Ion Guide Isotope Separator On-Line facility at the University of Jyväskylä. Here, the double Penning trap system JYFLTRAP was employed to disentangle the $\beta$ decay of the isomeric states. The new data obtained in this challenging measurement have a large impact in antineutrino summation calculations. For the first time the discrepancy between the summation model and the reactor antineutrino measurements in the region of the shape distortion has been reduced.

We present an efficient Monte Carlo framework for perturbative calculations of infinite nuclear matter based on chiral two-, three-, and four-nucleon interactions. The method enables the incorporation of all many-body contributions in a straightforward and transparent way, and makes it possible to extract systematic uncertainty estimates by performing order-by-order calculations in the chiral expansion as well as the many-body expansion. The versatility of this new framework is demonstrated by applying it to chiral low-momentum interactions, exhibiting a very good many-body convergence up to fourth order. Following these benchmarks, we explore new chiral interactions up to next-to-next-to-next-to-leading order (${\mathrm{N}}^3\mathrm{LO}$). Remarkably, simultaneous fits to the triton and to saturation properties can be achieved, while all three-nucleon low-energy couplings remain natural. The theoretical uncertainties of nuclear matter are significantly reduced when going from next-to-next-to-leading order to ${\mathrm{N}}^3\mathrm{LO}$.

An enhanced low-energy electric dipole ($E1$) strength is identified for the weakly bound excited states of the neutron-rich isotope ${}^{27}\mathrm{Ne}$. The Doppler-shift lifetime measurements employing a combination of the $\gamma$-ray tracking array GRETINA, the plunger device, and the S800 spectrograph determine the lower limit of $0.030e^2{\mathrm{fm}}^2$ or 0.052 W.u. for the $1/2^{+}\to 3/2^{-}E1$ transition in ${}^{27}\mathrm{Ne}$, representing one of the strongest $E1$ strengths observed among the bound discrete states in this mass region. This value is at least 30 times larger than that measured for the $3/2^{-}$ decay to the $3/2_{gs}^{+}$ ground state. A comparison of the present results to large-scale shell-model calculations points to an important role of core excitations and deformation in the observed $E1$ enhancement, suggesting a novel example of the electric dipole modes manifested in weakly bound deformed systems.

The most neutron-rich boron isotopes ${}^{20}\mathrm{B}$ and ${}^{21}\mathrm{B}$ have been observed for the first time following proton removal from ${}^{22}\mathrm{N}$ and ${}^{22}\mathrm{C}$ at energies around $230\mathrm{MeV}/\mathrm{nucleon}$. Both nuclei were found to exist as resonances which were detected through their decay into ${}^{19}\mathrm{B}$ and one or two neutrons. Two-proton removal from ${}^{22}\mathrm{N}$ populated a prominent resonancelike structure in ${}^{20}\mathrm{B}$ at around 2.5 MeV above the one-neutron decay threshold, which is interpreted as arising from the closely spaced $1^{-},2^{-}$ ground-state doublet predicted by the shell model. In the case of proton removal from ${}^{22}\mathrm{C}$, the ${}^{19}\mathrm{B}$ plus one- and two-neutron channels were consistent with the population of a resonance in ${}^{21}\mathrm{B}$ $2.47\pm 0.19\mathrm{MeV}$ above the two-neutron decay threshold, which is found to exhibit direct two-neutron decay. The ground-state mass excesses determined for ${}^{20,21}\mathrm{B}$ are found to be in agreement with mass surface extrapolations derived within the latest atomic-mass evaluations.

The first $2^{+}$ and $3^{-}$ states of the doubly magic nucleus ${}^{132}\mathrm{Sn}$ are populated via safe Coulomb excitation employing the recently commissioned HIE-ISOLDE accelerator at CERN in conjunction with the highly efficient MINIBALL array. The ${}^{132}\mathrm{Sn}$ ions are accelerated to an energy of $5.49\mathrm{MeV}/\mathrm{nucleon}$ and impinged on a ${}^{206}\mathrm{Pb}$ target. Deexciting $\gamma$ rays from the low-lying excited states of the target and the projectile are recorded in coincidence with scattered particles. The reduced transition strengths are determined for the transitions $0_{\mathrm{g}.\mathrm{s}.}^{+}\to 2_1^{+}$, $0_{\mathrm{g}.\mathrm{s}.}^{+}\to 3_1^{-}$, and $2_1^{+}\to 3_1^{-}$ in ${}^{132}\mathrm{Sn}$. The results on these states provide crucial information on cross-shell configurations which are determined within large-scale shell-model and Monte Carlo shell-model calculations as well as from random-phase approximation and relativistic random-phase approximation. The locally enhanced $B(E2;0_{\mathrm{g}.\mathrm{s}.}^{+}\to 2_1^{+})$ strength is consistent with the microscopic description of the structure of the respective states within all theoretical approaches. The presented results of experiment and theory can be considered to be the first direct verification of the sphericity and double magicity of ${}^{132}\mathrm{Sn}$.

Measurements of fragmentation functions for jets associated with an isolated photon are presented for the first time in $pp$ and Pb-Pb collisions. The analysis uses data collected with the CMS detector at the CERN LHC at a nucleon-nucleon center-of-mass energy of 5.02 TeV. Fragmentation functions are obtained for jets with $p_T^{\text{jet}}>30\mathrm{GeV}/c$ in events containing an isolated photon with $p_T^{\gamma }>60\mathrm{GeV}/c$, using charged tracks with transverse momentum $p_T^{\mathrm{trk}}>1\mathrm{GeV}/c$ in a cone around the jet axis. The association with an isolated photon constrains the initial $p_T$ and azimuthal angle of the parton whose shower produced the jet. For central Pb-Pb collisions, modifications of the jet fragmentation functions are observed when compared to those measured in $pp$ collisions, while no significant differences are found in the 50% most peripheral collisions. Jets in central Pb-Pb events show an excess (depletion) of low (high) $p_T$ particles, with a transition around $3\mathrm{GeV}/c$. This measurement shows for the first time the in-medium shower modifications of partons (quark dominated) with well-defined initial kinematics. It constitutes a new well-controlled reference for testing theoretical models of the parton passage through the quark-gluon plasma.

The isospin character of $p\text{−}n$ pairs at large relative momentum has been observed for the first time in the ${}^{16}\mathrm{O}$ ground state. A strong population of the $J,T=1,0$ state and a very weak population of the $J,T=0,1$ state were observed in the neutron pickup domain of ${}^{16}\mathrm{O}(p,pd)$ at 392 MeV. This strong isospin dependence at large momentum transfer is not reproduced by the distorted-wave impulse approximation calculations with known spectroscopic amplitudes. The results indicate the presence of high-momentum protons and neutrons induced by the tensor interactions in the ground state of ${}^{16}\mathrm{O}$.

We show that the measured intrinsic octupole moments of ${}^{220}\mathrm{Rn}$, ${}^{224}\mathrm{Ra}$, and ${}^{226}\mathrm{Ra}$ constrain the intrinsic Schiff moments of ${}^{225}\mathrm{Ra}$, ${}^{221}\mathrm{Rn}$, ${}^{223}\mathrm{Rn}$, ${}^{223}\mathrm{Fr}$, ${}^{225}\mathrm{Ra}$, and ${}^{229}\mathrm{Pa}$. The result is a dramatically reduced uncertainty in intrinsic Schiff moments. Direct measurements of octupole moments in odd nuclei will reduce the uncertainty even more. The only significant source of nuclear-physics error in the laboratory Schiff moments will then be the intrinsic matrix elements of the time-reversal noninvariant interaction produced by $CP$-violating fundamental physics. Those matrix elements are also correlated with octupole moments, but with a larger systematic uncertainty.

Asymmetric nuclear collisions of $p+\mathrm{Al}$, $p+\mathrm{Au}$, $d+\mathrm{Au}$, and ${}^3\mathrm{He}+\mathrm{Au}$ at $\sqrt{s_{NN}}=200\mathrm{GeV}$ provide an excellent laboratory for understanding particle production, as well as exploring interactions among these particles after their initial creation in the collision. We present measurements of charged hadron production $d{N}_{\text{ch}}/d\eta$ in all such collision systems over a broad pseudorapidity range and as a function of collision multiplicity. A simple wounded quark model is remarkably successful at describing the full data set. We also measure the elliptic flow $v_2$ over a similarly broad pseudorapidity range. These measurements provide key constraints on models of particle emission and their translation into flow.

This Letter presents a measurement of $\gamma \gamma \to {\mu }^{+}{\mu }^{-}$ production in $\mathrm{Pb}+\mathrm{Pb}$ collisions recorded by the ATLAS detector at the Large Hadron Collider at $\sqrt{s_{\mathrm{NN}}}=5.02\mathrm{TeV}$ with an integrated luminosity of $0.49{\mathrm{nb}}^{-1}$. The azimuthal angle and transverse momentum correlations between the muons are measured as a function of collision centrality. The muon pairs are produced from $\gamma \gamma$ through the interaction of the large electromagnetic fields of the nuclei. The contribution from background sources of muon pairs is removed using a template fit method. In peripheral collisions, the muons exhibit a strong back-to-back correlation consistent with previous measurements of muon pair production in ultraperipheral collisions. The angular correlations are observed to broaden significantly in central collisions. The modifications are qualitatively consistent with rescattering of the muons while passing through the hot matter produced in the collision.

Predictions are made for elliptic flow in collisions of polarized deuterons with a heavy nucleus. It is shown that the eccentricity of the initial fireball, evaluated with respect to the deuteron polarization axis perpendicular to the beam direction, has a substantial magnitude for collisions of highest multiplicity. Within the Glauber approach we obtain $\sim 7\%$ for the deuteron states with spin projection 0, and $\sim -3\%$ for spin projection $\pm 1$. We propose to measure the elliptic flow coefficient as the second order harmonic coefficient in the azimuthal distribution of produced charged hadrons with respect to the fixed polarization axis. Collective expansion yields a value of the order of 1% for this quantity, as compared to zero in the absence of polarization and/or collectivity. Such a vivid rotational symmetry breaking could be measured with the current experimental accuracy of the relativistic heavy-ion experiments. The effect has a fundamental significance for understanding the nature of dynamics in small systems, as its experimental confirmation would prove the presence of the shape-flow transmutation mechanism, typical of hydrodynamic expansion or rescattering in the later stages of the fireball evolution.