The limit of neutron-rich nuclei, the neutron drip line, evolves regularly from light to medium-mass nuclei except for a striking anomaly in the oxygen isotopes. This anomaly is not reproduced in shell-model calculations derived from microscopic two-nucleon forces. Here, we present the first microscopic explanation of the oxygen anomaly based on three-nucleon forces that have been established in few-body systems. This leads to repulsive contributions to the interactions among excess neutrons that change the location of the neutron drip line from ${}^{28}\mathrm{O}$ to the experimentally observed ${}^{24}\mathrm{O}$. Since the mechanism is robust and general, our findings impact the prediction of the most neutron-rich nuclei and the synthesis of heavy elements in neutron-rich environments.

We report the first measurements of the kurtosis ($\kappa$), skewness ($S$), and variance (${\sigma }^2$) of net-proton multiplicity ($N_p-N_{\overline{p}}$) distributions at midrapidity for $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=19.6$, 62.4, and 200 GeV corresponding to baryon chemical potentials (${\mu }_B$) between 200 and 20 MeV. Our measurements of the products $\kappa {\sigma }^2$ and $S\sigma$, which can be related to theoretical calculations sensitive to baryon number susceptibilities and long-range correlations, are constant as functions of collision centrality. We compare these products with results from lattice QCD and various models without a critical point and study the $\sqrt{s_{NN}}$ dependence of $\kappa {\sigma }^2$. From the measurements at the three beam energies, we find no evidence for a critical point in the QCD phase diagram for ${\mu }_B$ below 200 MeV.

The pair decay width of the first excited $0^{+}$ state in ${}^{12}\mathrm{C}$ (the Hoyle state) is deduced from a novel analysis of the world data on inelastic electron scattering covering a wide momentum transfer range, thereby resolving previous discrepancies. The extracted value ${\Gamma }_{\pi }=(62.3\pm 2.0)\mu \mathrm{eV}$ is independently confirmed by new data at low momentum transfers measured at the S-DALINAC and reduces the uncertainty of the literature values by more than a factor of 3. A precise knowledge of ${\Gamma }_{\pi }$ is mandatory for quantitative studies of some key issues in the modeling of supernovae and of asymptotic giant branch stars, the most likely site of the slow-neutron nucleosynthesis process.

A new class of many-body models, based on covariant density functional theory for excited states, is presented. It allows a parameter free description of the fragmentation of nuclear states induced by mode coupling of two-quasiparticle and two-phonon configurations. As compared to earlier methods it provides a consistent and parameter free theory of the fine structure of nuclear resonances. The method is applied very successfully to investigate the newly discovered low-lying dipole excitations in Sn and Ni isotopes with large neutron excess.

We report the first three-particle coincidence measurement in pseudorapidity ($\Delta \eta$) between a high transverse momentum ($p_{\perp }$) trigger particle and two lower $p_{\perp }$ associated particles within azimuth $|\Delta \varphi |<0.7$ in $\sqrt{s_{\mathrm{NN}}}=200\mathrm{GeV}$ $d+\mathrm{Au}$ and $\mathrm{Au}+\mathrm{Au}$ collisions. Charge ordering properties are exploited to separate the jetlike component and the ridge (long range $\Delta \eta$ correlation). The results indicate that the correlation of ridge particles are uniform not only with respect to the trigger particle but also between themselves event by event in our measured $\Delta \eta$. In addition, the production of the ridge appears to be uncorrelated to the presence of the narrow jetlike component.

Collisions induced by ${}^{9,10,11}\mathrm{Be}$ on a ${}^{64}\mathrm{Zn}$ target at the same c.m. energy were studied. For the first time, strong effects of the ${}^{11}\mathrm{Be}$ halo structure on elastic-scattering and reaction mechanisms at energies near the Coulomb barrier are evidenced experimentally. The elastic-scattering cross section of the ${}^{11}\mathrm{Be}$ halo nucleus shows unusual behavior in the Coulomb-nuclear interference peak angular region. The extracted total-reaction cross section for the ${}^{11}\mathrm{Be}$ collision is more than double the ones measured in the collisions induced by ${}^{9,10}\mathrm{Be}$. It is shown that such a strong enhancement of the total-reaction cross section with ${}^{11}\mathrm{Be}$ is due to transfer and breakup processes.

Collinear laser spectroscopy was performed on Ga ($Z=31$) isotopes at ISOLDE, CERN. A gas-filled linear Paul trap (ISCOOL) was used to extend measurements towards very neutron-rich isotopes ($N=36–50$). A ground state (g.s.) spin $I=1/2$ is measured for ${}^{73}\mathrm{Ga}$, being near degenerate with a $3/2^{-}$ isomer ($75\mathrm{eV}\lesssim E_{\mathrm{ex}}\lesssim 1\mathrm{keV}$). The ${}^{79}\mathrm{Ga}$ g.s., with $I=3/2$, is dominated by protons in the $\pi f_{5/2}$ orbital and in ${}^{81}\mathrm{Ga}$ the $5/2^{-}$ level becomes the g.s. The data are compared to shell-model calculations in the $f_{5/2}p{g}_{9/2}$ model space, calling for further theoretical developments and new experiments.

Hard-scattered parton probes produced in collisions of large nuclei indicate large partonic energy loss, possibly with collective produced-medium response to the lost energy. We present measurements of ${\pi }^0$ trigger particles at transverse momenta $p_T^t=4–12\mathrm{GeV}/c$ and associated charged hadrons ($p_T^a=0.5–7\mathrm{GeV}/c$) vs relative azimuthal angle $\Delta \varphi$ in $\mathrm{Au}+\mathrm{Au}$ and $p+p$ collisions at $\sqrt{s_{NN}}=200\mathrm{GeV}$. The $\mathrm{Au}+\mathrm{Au}$ distribution at low $p_T^a$, whose shape has been interpreted as a medium effect, is modified for $p_T^t<7\mathrm{GeV}/c$. At higher $p_T^t$, the data are consistent with unmodified or very weakly modified shapes, even for the lowest measured $p_T^a$, which quantitatively challenges some medium response models. The associated yield of hadrons opposing the trigger particle in $\mathrm{Au}+\mathrm{Au}$ relative to $p+p$ ($I_{AA}$) is suppressed at high $p_T$ ($I_{AA}\approx 0.35–0.5$), but less than for inclusive suppression ($R_{AA}\approx 0.2$).

Charge equilibration between two colliding nuclei can take place in the early stage of heavy-ion collisions. A basic mechanism of charge equilibration is presented in terms of the extension of single-particle motion from one nucleus to the other, from which the upper energy limit of the bombarding energy is introduced for significant charge equilibration. The formula for this limit is presented, and is compared to various experimental data. It is examined also by comparison to three-dimensional time-dependent density functional calculations. The suppression of charge equilibration, which appears in collisions at the energies beyond the upper energy limit, gives rise to remarkable effects on the synthesis of exotic nuclei with extreme proton-neutron asymmetry.

The fusion-evaporation reaction ${}^{244}\mathrm{Pu}({}^{48}\mathrm{Ca},3\mathrm{\text{−}}4n){}^{288,289}114$ was studied at the new gas-filled recoil separator TASCA. Thirteen correlated decay chains were observed and assigned to the production and decay of ${}^{288,289}114$. At a compound nucleus excitation energy of $E^{*}=39.8–43.9\mathrm{MeV}$, the $4n$ evaporation channel cross section was ${9.8}_{-3.1}^{+3.9}\mathrm{pb}$. At $E^{*}=36.1–39.5\mathrm{MeV}$, that of the $3n$ evaporation channel was ${8.0}_{-4.5}^{+7.4}\mathrm{pb}$. In one of the $3n$ evaporation channel decay chains, a previously unobserved $\alpha$ branch in ${}^{281}\mathrm{Ds}$ was observed (probability to be of random origin from background: 0.1%). This $\alpha$ decay populated the new nucleus ${}^{277}\mathrm{Hs}$, which decayed by spontaneous fission after a lifetime of 4.5 ms.

Among the most fundamental observables of nucleon structure, electromagnetic form factors are a crucial benchmark for modern calculations describing the strong interaction dynamics of the nucleon’s quark constituents; indeed, recent proton data have attracted intense theoretical interest. In this Letter, we report new measurements of the proton electromagnetic form factor ratio using the recoil polarization method, at momentum transfers $Q^2=5.2$, 6.7, and $8.5{\mathrm{GeV}}^2$. By extending the range of $Q^2$ for which $G_E^p$ is accurately determined by more than 50%, these measurements will provide significant constraints on models of nucleon structure in the nonperturbative regime.

Nuclear stopping has been investigated in central nuclear collisions at intermediate energies by analyzing kinematically complete events recorded with the help of the $4\pi$ multidetector INDRA for a large variety of symmetric systems. It is found that the mean isotropy ratio defined as the ratio of transverse to parallel momenta (energies) reaches a minimum near the Fermi energy, saturates or slowly increases depending on the mass of the system as the beam energy increases, and then stays lower than unity, showing that significant stopping is not achieved even for the heavier systems. Close to and above the Fermi energy, experimental data show no effect of the isospin content of the interacting system. A comparison with transport model calculations reveals that the latter overestimates the stopping power at low energies.

We argue that the presence of a very strong magnetic field in the chirally broken phase induces inhomogeneous expectation values, of a spiral nature along the magnetic field axis, for the currents of charge and chirality, when there is finite baryon density or an imbalance between left and right chiralities. This “chiral magnetic spiral” is a gapless excitation transporting the currents of (i) charge (at finite chirality), and (ii) chirality (at finite baryon density) along the direction of the magnetic field. In both cases it also induces in the transverse directions oscillating currents of charge and chirality. In heavy ion collisions, the chiral magnetic spiral possibly provides contributions both to the out-of-plane and the in-plane dynamical charge fluctuations recently observed at BNL RHIC.

Tetrahedral symmetry in strongly interacting systems would establish a new class of quantum effects at subatomic scale. Excited states in ${}^{156}\mathrm{Gd}$ that could carry the information about the tetrahedral symmetry were populated in the ${}^{155}\mathrm{Gd}(n,\gamma ){}^{156}\mathrm{Gd}$ reaction and studied using the GAMS4/5 Bragg spectrometers at the Institut Laue-Langevin. We have identified the $5_1^{-}\to 3_1^{-}$ transition of 131.983(12) keV in ${}^{156}\mathrm{Gd}$ and determined its intensity to be $1.9(3)x{10}^{-6}$ per neutron capture. The lifetime $\tau ={220}_{-30}^{+180}fs$ of the $5_1^{-}$ state in ${}^{156}\mathrm{Gd}$ has been measured using the GRID technique. The resulting $B(E2)={293}_{-134}^{+61}$Weisskopf unit rate of the 131.983 keV transition provides the intrinsic quadrupole moment of the $5_1^{-}$ state in ${}^{156}\mathrm{Gd}$ to be $Q_0={7.1}_{-1.6}^{+0.7}\mathrm{b}$. This large value, comparable to the quadrupole moment of the ground state in ${}^{156}\mathrm{Gd}$, gives strong evidence against tetrahedral symmetry in the lowest odd-spin, negative-parity band of ${}^{156}\mathrm{Gd}$.

An initially unpolarized beam of deuterons is found to acquire tensor polarization after traversing a foil of spin-zero target nuclei. The effect, called nuclear spin dichroism, has been predicted theoretically, albeit resulting in small values of $p_{zz}$ of the order of 0.01 for energies around 10 MeV. The experiment was carried out at the Köln tandem accelerator using carbon targets bombarded by deuterons. The observed polarization is as large as $p_{zz}=-0.28\pm 0.03$ for a beam of 14.8 MeV and a $129\mathrm{mg}/{\mathrm{cm}}^2$ target. The results allow one to produce tensor-polarized deuterons with $p_{zz}$ around $-0.30$ (or $+0.25$) from an initially unpolarized beam using a carbon target of appropriate thickness.

We report on the first successful extraction of a ${\beta }^{+}$ Gamow-Teller strength distribution from a radioactive isotope in an intermediate-energy charge-exchange experiment in inverse kinematics. The (${}^7\mathrm{Li},{}^7\mathrm{Be}+\gamma (429\mathrm{keV})$) reaction at $100A\mathrm{MeV}$ was used to measure Gamow-Teller transition strengths from ${}^{34}\mathrm{P}$ to states in ${}^{34}\mathrm{Si}$. The results show that little mixing occurs between $sd$ and $pf$ shell configurations for the low-lying $0^{+}$ and $2^{+}$ states even though ${}^{34}\mathrm{Si}$ neighbors the island of inversion and low-lying $2\hslash \omega$ intruder states exist. Shell-model calculations in the $sdpf$ model space are consistent with these findings.

We present a microscopic dynamical study of the reactions involving three ${}^4\mathrm{He}$ clusters. We show that the much discussed triple-$\alpha$ linear chain configuration of ${}^{12}\mathrm{C}$ is formed with a certain lifetime and subsequently makes a transition to a triangular configuration of ${}^{12}\mathrm{C}$ and then to a configuration near the ground state. Time-dependent Hartree-Fock theory coupled with a density constraint is used to study the properties of these configurations.

Energy levels of the double $\Lambda$ hypernucleus, ${}_{\Lambda \Lambda }{}^{11}\mathrm{Be}$ are calculated within the framework of a $\alpha \alpha n\Lambda \Lambda$ five-body model. Interactions between constituent particles are determined so as to reproduce reasonably the observed low-energy properties of the $\alpha \alpha$, $\alpha \alpha n$ nuclei and the existing data for $\Lambda$-binding energies of the $\alpha \Lambda$, $\alpha \alpha \Lambda$, $\alpha n\Lambda$, and $\alpha \alpha n\Lambda$ systems. An effective $\Lambda \Lambda$ interaction is constructed so as to reproduce, within the $\alpha \Lambda \Lambda$ three-body model, the $B_{\Lambda \Lambda }$ of ${}_{\Lambda \Lambda }{}^6\mathrm{He}$, which was extracted from the emulsion experiment, the NAGARA event. With no adjustable parameters for the $\alpha \alpha n\Lambda \Lambda$ system, $B_{\Lambda \Lambda }$ of the ground and bound excited states of ${}_{\Lambda \Lambda }{}^{11}\mathrm{Be}$ are calculated with the Gaussian expansion method. The Hida event, recently observed at KEK-E373 experiment, is interpreted as an observation of the ground state of the ${}_{\Lambda \Lambda }{}^{11}\mathrm{Be}$.

It is shown that the constant-temperature behavior of nuclei in the superfluid regime leads to an energy-sorting process if two nuclei are in thermal contact, as is the case in the fission process. This effect explains why an increase of the initial excitation energy leads an increase of the number of emitted neutrons from the heavy fission fragment, only. The observed essentially complete energy sorting may be seen as a new counterintuitive manifestation of quantum-mechanical properties of microscopic systems.

The symmetry energy of nuclear matter is a fundamental ingredient in the investigation of exotic nuclei, heavy-ion collisions, and astrophysical phenomena. New data from heavy-ion collisions can be used to extract the free symmetry energy and the internal symmetry energy at subsaturation densities and temperatures below 10 MeV. Conventional theoretical calculations of the symmetry energy based on mean-field approaches fail to give the correct low-temperature, low-density limit that is governed by correlations, in particular, by the appearance of bound states. A recently developed quantum-statistical approach that takes the formation of clusters into account predicts symmetry energies that are in very good agreement with the experimental data. A consistent description of the symmetry energy is given that joins the correct low-density limit with quasiparticle approaches valid near the saturation density.