The large values of the singlet and triplet two-nucleon scattering lengths locate the nuclear system close to the unitary limit. This particular position strongly constrains the low-energy observables in the three-nucleon system as depending on one parameter, the triton binding energy, and introduces correlations in the low-energy sector of light nuclei. Here we analyze the propagation of these correlations to infinite nuclear matter showing that its saturation properties, the equation of state of $\beta$-stable nuclear matter, and several properties of neutron stars, as their maximum mass, are well determined solely by a few number of low-energy quantities of the two- and three-nucleon systems. In this way we make a direct link between the universal behavior observed in the low-energy region of few-nucleon systems and fundamental properties of nuclear matter and neutron stars.

A novel shape evolution in the Sn isotopes by the state-of-the-art application of the Monte Carlo shell model calculations is presented in a unified way for the ${}^{100–138}\mathrm{Sn}$ isotopes. A large model space consisting of eight single-particle orbits for protons and neutrons is taken with the fixed Hamiltonian and effective charges, where protons in the $1g_{9/2}$ orbital are fully activated. While the significant increase of the $B(E2;0_1^{+}\to 2_1^{+})$ value, seen around ${}^{110}\mathrm{Sn}$ as a function of neutron number ($N$), has remained a major puzzle over decades, it is explained as a consequence of the shape evolution driven by proton excitations from the $1g_{9/2}$ orbital. A second-order quantum phase transition is found around $N=66$, connecting the phase of such deformed shapes to the spherical pairing phase. The shape and shell evolutions are thus described, covering topics from the Gamow-Teller decay of ${}^{100}\mathrm{Sn}$ to the enhanced double magicity of ${}^{132}\mathrm{Sn}$.

We confront observational data from gravitational wave event GW170817 with microscopic modeling of the cold neutron star equation of state. We develop and employ a Bayesian statistical framework that enables us to implement constraints on the equation of state from laboratory measurements of nuclei and state-of-the-art chiral effective field theory methods. The energy density functionals constructed from the posterior probability distributions are then used to compute consistently the neutron star equation of state from the outer crust to the inner core, assuming a composition consisting of protons, neutrons, electrons, and muons. In contrast to previous studies, we find that the 95% credibility range of predicted neutron star tidal deformabilities ($136<\mathrm{\Lambda }<519$) for a 1.4 solar-mass neutron star is already consistent with the upper bound deduced from observations of the GW170817 event. However, we find that lower bounds on the neutron star tidal deformability will very strongly constrain microscopic models of the dense matter equation of state. We also demonstrate a strong correlation between the neutron star tidal deformability and the pressure of beta-equilibrated matter at twice saturation density.

We demonstrate that the striking systematics of two-particle azimuthal Fourier harmonics $v_2$ and $v_3$ in ultrarelativistic collisions of protons, deuterons, and helium-3 ions off gold nuclei measured by the PHENIX Collaboration at the Relativistic Heavy Ion Collider (RHIC) is reproduced in the color glass condensate effective field theory. This contradicts the claim in C. Aidala et al. (PHENIX Collaboration), arXiv:1805.02973, that their data rule out initial state-based explanations. The underlying systematics of the effect, as discussed previously in K. Dusling, M. Mace, R. Venugopalan, Phys. Rev. D 97, 016014 (2018); Phys. Rev. Lett. 120, 042002 (2018); Proc. Sci., QCDEV2017 (2018) 039, arise from the differing structure of strong color correlations between gluon domains of size $1/Q_S$ at fine ($p_{\perp }⪆Q_S$) or coarser ($p_{\perp }⪅Q_S$) transverse momentum resolution. Further tests of the limits of validity of this framework can be carried out in light-heavy ion collisions at both RHIC and the Large Hadron Collider. Such measurements also offer novel opportunities for further exploration of the role of the surprisingly large short-range nuclear correlations measured at Jefferson Lab.

We compute the hydrodynamic relaxation times ${\tau }_{\pi }$ and ${\tau }_j$ for hot QCD at next-to-leading order in the coupling with kinetic theory. We show that certain dimensionless ratios of second-order to first-order transport coefficients obey bounds which apply whenever a kinetic theory description is possible; the computed values lie somewhat above these bounds. Strongly coupled theories with holographic duals strongly violate these bounds, highlighting their distance from a quasiparticle description.

Obtaining reliable data for nuclear reactions on unstable isotopes remains an extremely important task and a formidable challenge. Neutron capture cross sections—crucial ingredients for models of astrophysical processes, national security applications, and simulations of nuclear energy generation—are particularly elusive, as both projectile and target in the reaction are unstable. We demonstrate a new method for determining cross sections for neutron capture on unstable isotopes, using ${}^{87}\mathrm{Y}(n,\gamma )$ as a prototype. To validate the method, a benchmark experiment is carried out to obtain the known ${}^{90}\mathrm{Zr}(n,\gamma )$ cross section analogously. Our approach, which employs an indirect (“surrogate”) measurement combined with theory, can be generalized to a larger class of nuclear reactions. It can be used both with traditional stable-beam experiments and in inverse kinematics at rare-isotope facilities.

Full calculations of six-nucleon reactions with a three-body final state have been elusive and a long-standing issue. We present neutron spectra from the $T(t,2n)\alpha$ (TT) reaction measured in inertial confinement fusion experiments at the OMEGA laser facility at ion temperatures from 4 to 18 keV, corresponding to center-of-mass energies ($E_{\mathrm{c}.\mathrm{m}.}$) from 16 to 50 keV. A clear difference in the shape of the TT-neutron spectrum is observed between the two $E_{\mathrm{c}.\mathrm{m}.}$, with the ${}^5\mathrm{He}$ ground state resonant peak at 8.6 MeV being significantly stronger at the higher than at the lower energy. The data provide the first conclusive evidence of a variant TT-neutron spectrum in this $E_{\mathrm{c}.\mathrm{m}.}$ range. In contrast to earlier available data, this indicates a reaction mechanism that must involve resonances and/or higher angular momenta than $L=0$. This finding provides an important experimental constraint on theoretical efforts that explore this and complementary six-nucleon systems, such as the solar ${}^3\mathrm{He}({}^3\mathrm{He},2p)\alpha$ reaction.

We report on the measurement of the ${}^7\mathrm{Be}(n,p){}^7\mathrm{Li}$ cross section from thermal to approximately 325 keV neutron energy, performed in the high-flux experimental area (EAR2) of the n_TOF facility at CERN. This reaction plays a key role in the lithium yield of the big bang nucleosynthesis (BBN) for standard cosmology. The only two previous time-of-flight measurements performed on this reaction did not cover the energy window of interest for BBN, and they showed a large discrepancy between each other. The measurement was performed with a Si telescope and a high-purity sample produced by implantation of a ${}^7\mathrm{Be}$ ion beam at the ISOLDE facility at CERN. While a significantly higher cross section is found at low energy, relative to current evaluations, in the region of BBN interest, the present results are consistent with the values inferred from the time-reversal ${}^7\mathrm{Li}(p,n){}^7\mathrm{Be}$ reaction, thus yielding only a relatively minor improvement on the so-called cosmological lithium problem. The relevance of these results on the near-threshold neutron production in the $p+{}^7\mathrm{Li}$ reaction is also discussed.

We report measurements of the nuclear modification factor $R_{\mathrm{CP}}$ for charged hadrons as well as identified ${\pi }^{+(-)}$, $K^{+(-)}$, and $p(\overline{p})$ for $\mathrm{Au}+\mathrm{Au}$ collision energies of $\sqrt{s_{\mathrm{NN}}}=7.7$, 11.5, 14.5, 19.6, 27, 39, and 62.4 GeV. We observe a clear high-$p_T$ net suppression in central collisions at 62.4 GeV for charged hadrons which evolves smoothly to a large net enhancement at lower energies. This trend is driven by the evolution of the pion spectra but is also very similar for the kaon spectra. While the magnitude of the proton $R_{\mathrm{CP}}$ at high $p_T$ does depend on the collision energy, neither the proton nor the antiproton $R_{\mathrm{CP}}$ at high $p_T$ exhibit net suppression at any energy. A study of how the binary collision-scaled high-$p_T$ yield evolves with centrality reveals a nonmonotonic shape that is consistent with the idea that jet quenching is increasing faster than the combined phenomena that lead to enhancement.

Energy differences between analogue states in the $T=1/2$ ${}^{23}\mathrm{Mg}\text{−}{}^{23}\mathrm{Na}$ mirror nuclei have been measured along the rotational yrast bands. This allows us to search for effects arising from isospin-symmetry-breaking interactions (ISB) and/or shape changes. Data are interpreted in the shell model framework following the method successfully applied to nuclei in the $f_{7/2}$ shell. It is shown that the introduction of a schematic ISB interaction of the same type of that used in the $f_{7/2}$ shell is needed to reproduce the data. An alternative novel description, applied here for the first time, relies on the use of an effective interaction deduced from a realistic charge-dependent chiral nucleon-nucleon potential. This analysis provides two important results: (i) The mirror energy differences give direct insight into the nuclear skin; (ii) the skin changes along the rotational bands are strongly correlated with the difference between the neutron and proton occupations of the $s_{1/2}$ “halo” orbit.

Under the approximate chiral symmetry restoration, quark interactions with topological gluon fields in quantum chromodynamics can induce a chirality imbalance and parity violation in local domains. An electric charge separation (CS) could be generated along the direction of a strong magnetic field ($\mathbf{B}$), a phenomenon called the chiral magnetic effect (CME). CS measurements by azimuthal correlators are contaminated by major backgrounds from elliptic flow anisotropy ($v_2$). Isobaric ${}_{44}{}^{96}\mathrm{Ru}+{}_{44}{}^{96}\mathrm{Ru}$ and ${}_{40}{}^{96}\mathrm{Zr}+{}_{40}{}^{96}\mathrm{Zr}$ collisions have been proposed to identify the CME (expected to differ between the two systems) out of the backgrounds (to be almost the same). We show, by using the density functional theory calculations of the proton and neutron distributions, that these expectations may not hold as originally anticipated because the two systems may have sizable differences in eccentricity and $v_2$.

We report on the first $Q^2$-dependent measurement of the beam-normal single spin asymmetry $A_n$ in the elastic scattering of 570 MeV vertically polarized electrons off ${}^{12}\mathrm{C}$. We cover the $Q^2$ range between 0.02 and $0.05{\mathrm{GeV}}^2/c^2$ and determine $A_n$ at four different $Q^2$ values. The experimental results are compared to a theoretical calculation that relates $A_n$ to the imaginary part of the two-photon exchange amplitude. The result emphasizes that the $Q^2$ behavior of $A_n$ given by the ratio of the Compton to charge form factors cannot be treated independently of the target nucleus.

Final-state kinematic imbalances are measured in mesonless production of ${\nu }_{\mu }+A\to {\mu }^{-}+p+X$ in the MINERvA tracker. Initial- and final-state nuclear effects are probed using the direction of the ${\mu }^{-}\text{−}p$ transverse momentum imbalance and the initial-state momentum of the struck neutron. Differential cross sections are compared to predictions based on current approaches to medium modeling. These models underpredict the cross section at intermediate intranuclear momentum transfers that generally exceed the Fermi momenta. As neutrino interaction models need to correctly incorporate the effect of the nucleus in order to predict neutrino energy resolution in oscillation experiments, this result points to a region of phase space where additional cross section strength is needed in current models, and demonstrates a new technique that would be suitable for use in fine-grained liquid argon detectors where the effect of the nucleus may be even larger.

Fornal and Grinstein recently proposed that the discrepancy between two different methods of neutron lifetime measurements, the beam and bottle methods, can be explained by a previously unobserved dark matter decay mode, $n\to X+\gamma$. We perform a search for this decay mode over the allowed range of energies of the monoenergetic $\gamma$ ray for $X$ to be dark matter. A Compton-suppressed high-purity germanium detector is used to identify $\gamma$ rays from neutron decay in a nickel-phosphorous-coated stainless-steel bottle. A combination of Monte Carlo and radioactive source calibrations is used to determine the absolute efficiency for detecting $\gamma$ rays arising from the dark matter decay mode. We exclude the possibility of a sufficiently strong branch to explain the lifetime discrepancy with 97% confidence.

We perform the first direct mass measurements of neutron-rich calcium isotopes beyond neutron number 34 at the RIKEN Radioactive Isotope Beam Factory by using the time-of-flight magnetic-rigidity technique. The atomic mass excesses of ${}^{55–57}\mathrm{Ca}$ are determined for the first time to be $-18650(160)$, $-13510(250)$, and $-7370(990)\mathrm{keV}$, respectively. We examine the emergence of neutron magicity at $N=34$ based on the new atomic masses. The new masses provide experimental evidence for the appearance of a sizable energy gap between the neutron $2p_{1/2}$ and $1f_{5/2}$ orbitals in ${}^{54}\mathrm{Ca}$, comparable to the gap between the neutron $2p_{3/2}$ and $2p_{1/2}$ orbitals in ${}^{52}\mathrm{Ca}$. For the ${}^{56}\mathrm{Ca}$ nucleus, an open-shell property in neutrons is suggested.

Lifetimes of the first excited $2^{+}$ and $4^{+}$ states in the extremely neutron-deficient nuclide ${}^{172}\mathrm{Pt}$ have been measured for the first time using the recoil-distance Doppler shift and recoil-decay tagging techniques. An unusually low value of the ratio $B(E2:4_1^{+}\to 2_1^{+})/B(E2:2_1^{+}\to 0_{\mathrm{gs}}^{+})=0.55(19)$ was found, similar to a handful of other such anomalous cases observed in the entire Segré chart. The observation adds to a cluster of a few extremely neutron-deficient nuclides of the heavy transition metals with neutron numbers $N\approx 90–94$ featuring the effect. No theoretical model calculations reported to date have been able to explain the anomalously low $B(E2:4_1^{+}\to 2_1^{+})/B(E2:2_1^{+}\to 0_{\mathrm{gs}}^{+})$ ratios observed in these cases. Such low values cannot, e.g., be explained within the framework of the geometrical collective model or by algebraic approaches within the interacting boson model framework. It is proposed that the group of $B(E2:4_1^{+}\to 2_1^{+})/B(E2:2_1^{+}\to 0_{\mathrm{gs}}^{+}$) ratios in the extremely neutron-deficient even-even W, Os, and Pt nuclei around neutron numbers $N\approx 90–94$ reveal a quantum phase transition from a seniority-conserving structure to a collective regime as a function of neutron number. Although a system governed by seniority symmetry is the only theoretical framework for which such an effect may naturally occur, the phenomenon is highly unexpected for these nuclei that are not situated near closed shells.

Lifetime measurements of excited states in the neutron-rich nucleus ${}^{43}\mathrm{S}$ were performed by applying the recoil-distance method on fast rare-isotope beams in conjunction with the Gamma-Ray Energy Tracking In-beam Nuclear Array. The new data based on $\gamma \gamma$ coincidences and lifetime measurements resolve a doublet of $(3/2^{-})$ and $(5/2^{-})$ states at low excitation energies. Results were compared to the $\pi (sd)-\nu (pf)$ shell model and antisymmetrized molecular dynamics calculations. The consistency with the theoretical calculations identifies a possible appearance of three coexisting bands near the ground state of ${}^{43}\mathrm{S}$: the $K^{\pi }=1/2^{-}$ band built on a prolate-deformed ground state, a band built on an isomer with a $1f_{7/2}^{-1}$ character, and a suggested excited band built on a newly discovered doublet state. The latter further confirms the collapse of the $N=28$ shell closure in the neutron-rich region.

The rare-earth peak in the $r$-process abundance pattern depends sensitively on both the astrophysical conditions and subtle changes in nuclear structure in the region. This work takes an important step towards elucidating the nuclear structure and reducing the uncertainties in $r$-process calculations via precise atomic mass measurements at the JYFLTRAP double Penning trap. ${}^{158}\mathrm{Nd}$, ${}^{160}\mathrm{Pm}$, ${}^{162}\mathrm{Sm}$, and ${}^{164–166}\mathrm{Gd}$ have been measured for the first time, and the precisions for ${}^{156}\mathrm{Nd}$, ${}^{158}\mathrm{Pm}$, ${}^{162,163}\mathrm{Eu}$, ${}^{163}\mathrm{Gd}$, and ${}^{164}\mathrm{Tb}$ have been improved considerably. Nuclear structure has been probed via two-neutron separation energies $S_{2n}$ and neutron pairing energy metrics $D_n$. The data do not support the existence of a subshell closure at $N=100$. Neutron pairing has been found to be weaker than predicted by theoretical mass models. The impact on the calculated $r$-process abundances has been studied. Substantial changes resulting in a smoother abundance distribution and a better agreement with the solar $r$-process abundances are observed.