The exact four-body equations of Alt, Grassberger, and Sandhas are solved for neutron-${}^3\mathrm{He}$ and proton-${}^3\mathrm{H}$ scattering in the energy regime above the four-nucleon breakup threshold. Cross sections and spin observables for elastic, transfer, charge-exchange, and breakup reactions are calculated using realistic nucleon-nucleon interaction models, including the one with effective many-nucleon forces due to explicit $\mathrm{\Delta }$-isobar excitation. The experimental data are described reasonably well with only few exceptions such as vector analyzing powers.

We determine the transverse system size of the initial nonequilibrium Glasma state and of the hydrodynamically evolving fireball as a function of produced charged particles in $p+p$, $p+\mathrm{Pb}$, and $\mathrm{Pb}+\mathrm{Pb}$ collisions at the Large Hadron Collider. Our results show features similar to those of recent measurements of Hanbury Brown–Twiss (HBT) radii by the ALICE Collaboration. Azimuthal anisotropy coefficients $v_n$ generated by combining the early time Glasma dynamics with viscous fluid dynamics in $\mathrm{Pb}+\mathrm{Pb}$ collisions are in excellent agreement with experimental data for a wide range of centralities. In particular, event-by-event distributions of the $v_n$ values agree with the experimental data out to fairly peripheral centrality bins. In striking contrast, our results for $p+\mathrm{Pb}$ collisions significantly underestimate the magnitude and do not reproduce the centrality dependence of data for $v_2$ and $v_3$ coefficients. We argue that the measured $v_n$ data and HBT radii strongly constrain the shapes of initial parton distributions across system sizes that would be compatible with a flow interpretation in $p+\mathrm{Pb}$ collisions. Alternately, additional sources of correlations may be required to describe the systematics of long-range rapidity correlations in $p+p$ and $p+\mathrm{Pb}$ collisions.

The direct $3\alpha$ decay branch from the $0_2^{+}$ state at $E_x=7.65\mathrm{MeV}$ in ${}^{12}\mathrm{C}$, which is known as the Hoyle state, is considered to affect the triple-$\alpha$ reaction rate strongly and to give crucial information on its structure. We have performed a high-precision measurement of the $3\alpha$ decay from this state using the ${}^{12}\mathrm{C}({}^{12}\mathrm{C},3\alpha ){}^{12}\mathrm{C}$ reaction at $E_{{}^{12}\mathrm{C}}=110\mathrm{MeV}$. The branching ratio of the direct $3\alpha$ decay was under the detection limit in the present experiment. By comparing with Monte Carlo simulations for three decay mechanisms as the sequential decay through the ground state of ${}^8\mathrm{Be}$, the direct decay with equal energies of three $\alpha$ particles, and the direct decay to the phase space uniformly, we have obtained the upper limit of 0.2% on the direct $3\alpha$ decay.

Search for a new kind of superfluidity built on collective proton-neutron pairs with aligned spin is performed studying the Gamow-Teller decay of the $T=1$, $J^{\pi }=0^{+}$ ground state of ${}^{62}\mathrm{Ge}$ into excited states of the odd-odd $N=Z$ nucleus ${}^{62}\mathrm{Ga}$. The experiment is performed at GSI Helmholtzzentrum für Shwerionenforshung with the ${}^{62}\mathrm{Ge}$ ions selected by the fragment separator and implanted in a stack of Si-strip detectors, surrounded by the RISING Ge array. A half-life of $T_{1/2}=82.9(14)\mathrm{ms}$ is measured for the ${}^{62}\mathrm{Ge}$ ground state. Six excited states of ${}^{62}\mathrm{Ga}$, populated below 2.5 MeV through Gamow-Teller transitions, are identified. Individual Gamow-Teller transition strengths agree well with theoretical predictions of the interacting shell model and the quasiparticle random phase approximation. The absence of any sizable low-lying Gamow-Teller strength in the reported beta-decay experiment supports the hypothesis of a negligible role of coherent $T=0$ proton-neutron correlations in ${}^{62}\mathrm{Ga}$.

We report the first measurements of the moments—mean ($M$), variance (${\sigma }^2$), skewness ($S$), and kurtosis ($\kappa$)—of the net-charge multiplicity distributions at midrapidity in $\mathrm{Au}+\mathrm{Au}$ collisions at seven energies, ranging from $\sqrt{s_{\mathit{\text{NN}}}}=7.7$ to 200 GeV, as a part of the Beam Energy Scan program at RHIC. The moments are related to the thermodynamic susceptibilities of net charge, and are sensitive to the location of the QCD critical point. We compare the products of the moments, ${\sigma }^2/M$, $S\sigma$, and $\kappa {\sigma }^2$, with the expectations from Poisson and negative binomial distributions (NBDs). The $S\sigma$ values deviate from the Poisson baseline and are close to the NBD baseline, while the $\kappa {\sigma }^2$ values tend to lie between the two. Within the present uncertainties, our data do not show nonmonotonic behavior as a function of collision energy. These measurements provide a valuable tool to extract the freeze-out parameters in heavy-ion collisions by comparing with theoretical models.

In this Letter, we introduce the concept of in-trap nuclear decay spectroscopy of highly charged radioactive ions and describe its successful application as a novel spectroscopic tool. This is demonstrated by a measurement of the decay properties of radioactive mass $A=124$ ions (here, ${}^{124}\mathrm{In}$ and ${}^{124}\mathrm{Cs}$) in the electron-beam ion trap of the TITAN facility at TRIUMF. By subjecting the trapped ions to an intense electron beam, the ions are charge bred to high charge states (i.e., equivalent to the removal of $N$-shell electrons), and an increase of storage times to the level of minutes without significant ion losses is achieved. The present technique opens the venue for precision spectroscopy of low branching ratios and is being developed in the context of measuring electron-capture branching ratios needed for determining the nuclear ground-state properties of the intermediate odd-odd nuclei in double-beta ($\beta \beta$) decay.

Using the Penning trap mass spectrometer TITAN, we performed the first direct mass measurements of ${}^{20,21}\mathrm{Mg}$, isotopes that are the most proton-rich members of the $A=20$ and $A=21$ isospin multiplets. These measurements were possible through the use of a unique ion-guide laser ion source, a development that suppressed isobaric contamination by 6 orders of magnitude. Compared to the latest atomic mass evaluation, we find that the mass of ${}^{21}\mathrm{Mg}$ is in good agreement but that the mass of ${}^{20}\mathrm{Mg}$ deviates by $3\sigma$. These measurements reduce the uncertainties in the masses of ${}^{20,21}\mathrm{Mg}$ by 15 and 22 times, respectively, resulting in a significant departure from the expected behavior of the isobaric multiplet mass equation in both the $A=20$ and $A=21$ multiplets. This presents a challenge to shell model calculations using either the isospin nonconserving universal $sd$ USDA and USDB Hamiltonians or isospin nonconserving interactions based on chiral two- and three-nucleon forces.

We report measurements of single- and double-spin asymmetries for $W^{\pm }$ and $Z/{\gamma }^{*}$ boson production in longitudinally polarized $p+p$ collisions at $\sqrt{s}=510\mathrm{GeV}$ by the STAR experiment at RHIC. The asymmetries for $W^{\pm }$ were measured as a function of the decay lepton pseudorapidity, which provides a theoretically clean probe of the proton’s polarized quark distributions at the scale of the $W$ mass. The results are compared to theoretical predictions, constrained by polarized deep inelastic scattering measurements, and show a preference for a sizable, positive up antiquark polarization in the range $0.05<x<0.2$.

Local parity-odd domains are theorized to form inside a quark-gluon plasma which has been produced in high-energy heavy-ion collisions. The local parity-odd domains manifest themselves as charge separation along the magnetic field axis via the chiral magnetic effect. The experimental observation of charge separation has previously been reported for heavy-ion collisions at the top RHIC energies. In this Letter, we present the results of the beam-energy dependence of the charge correlations in $\mathrm{Au}+\mathrm{Au}$ collisions at midrapidity for center-of-mass energies of 7.7, 11.5, 19.6, 27, 39, and 62.4 GeV from the STAR experiment. After background subtraction, the signal gradually reduces with decreased beam energy and tends to vanish by 7.7 GeV. This implies the dominance of hadronic interactions over partonic ones at lower collision energies.

A marked difference in the nuclear charge radius was observed between the $I^{\pi }=3^{+}$ ground state and the $I^{\pi }=0^{+}$ isomer of ${}^{38}\mathrm{K}$ and is qualitatively explained using an intuitive picture of proton-neutron pairing. In a high-precision measurement of the isomer shift using bunched-beam collinear laser spectroscopy at CERN-ISOLDE, a change in the mean-square charge radius of $⟨r_{\mathrm{c}}^2⟩{(}^{38}{\mathrm{K}}^m)-⟨r_{\mathrm{c}}^2⟩{(}^{38}{\mathrm{K}}^g)=0.100(6){\mathrm{fm}}^2$ was obtained. This is an order of magnitude more accurate than the result of a previous indirect measurement from which it was concluded that both long-lived states in ${}^{38}\mathrm{K}$ have similar charge radii. Our observation leads to a substantially different understanding since the difference in charge radius is, moreover, opposite in sign to previously reported theoretical predictions. It is demonstrated that the observed isomer shift can be reproduced by large-scale shell-model calculations including proton and neutron excitations across the $N,Z=20$ shell gaps, confirming the significance of cross-shell correlations in the region of ${}^{40}\mathrm{Ca}$.

Recent results for moments of multiplicity distributions of net protons and net-electric charge from the STAR Collaboration are compared to lattice QCD results for higher order fluctuations of baryon number and electric charge by the Wuppertal-Budapest Collaboration, with the purpose of extracting the freeze-out temperature and chemical potential. All lattice simulations are performed for a system of $2+1$ dynamical quark flavors, at the physical mass for light and strange quarks; all results are continuum extrapolated. We show that it is possible to extract an upper value for the freeze-out temperature, as well as precise baryochemical potential values corresponding to the four highest collision energies of the experimental beam energy scan. Consistency between the freeze-out parameters obtained from baryon number and electric charge fluctuations is found. The freeze-out chemical potentials are now in agreement with the statistical hadronization model.

An excitation function of one- and two-neutron transfer channels for the ${}^{60}\mathrm{Ni}+{}^{116}\mathrm{Sn}$ system has been measured with the magnetic spectrometer PRISMA in a wide energy range, from the Coulomb barrier to far below it. The experimental transfer probabilities are well reproduced, for the first time with heavy ions, in absolute values and in slope by microscopic calculations which incorporate nucleon-nucleon pairing correlations.

A new isomer with a half-life of 23.0(8) ms has been identified at 2406 keV in ${}^{126}\mathrm{Pd}$ and is proposed to have a spin and parity of ${10}^{+}$ with a maximally aligned configuration comprising two neutron holes in the $1h_{11/2}$ orbit. In addition to an internal-decay branch through a hindered electric octupole transition, $\beta$ decay from the long-lived isomer was observed to populate excited states at high spins in ${}^{126}\mathrm{Ag}$. The smaller energy difference between the ${10}^{+}$ and $7^{-}$ isomers in ${}^{126}\mathrm{Pd}$ than in the heavier $N=80$ isotones can be interpreted as being ascribed to the monopole shift of the $1h_{11/2}$ neutron orbit. The effects of the monopole interaction on the evolution of single-neutron energies below ${}^{132}\mathrm{Sn}$ are discussed in terms of the central and tensor forces.

Recent observations of ${}^6\mathrm{Li}$ in metal poor stars suggest a large production of this isotope during big bang nucleosynthesis (BBN). In standard BBN calculations, the ${}^2\mathrm{H}(\alpha ,\gamma ){}^6\mathrm{Li}$ reaction dominates ${}^6\mathrm{Li}$ production. This reaction has never been measured inside the BBN energy region because its cross section drops exponentially at low energy and because the electric dipole transition is strongly suppressed for the isoscalar particles ${}^2\mathrm{H}$ and $\alpha$ at energies below the Coulomb barrier. Indirect measurements using the Coulomb dissociation of ${}^6\mathrm{Li}$ only give upper limits owing to the dominance of nuclear breakup processes. Here, we report on the results of the first measurement of the ${}^2\mathrm{H}(\alpha ,\gamma ){}^6\mathrm{Li}$ cross section at big bang energies. The experiment was performed deep underground at the LUNA 400 kV accelerator in Gran Sasso, Italy. The primordial ${}^6\mathrm{Li}/{}^7\mathrm{Li}$ isotopic abundance ratio has been determined to be $(1.5\pm 0.3)\times {10}^{-5}$, from our experimental data and standard BBN theory. The much higher ${}^6\mathrm{Li}/{}^7\mathrm{Li}$ values reported for halo stars will likely require a nonstandard physics explanation, as discussed in the literature.

It is studied how the $\alpha$ cluster degrees of freedom, such as $\alpha$ clustering configurations close to the $\alpha$ decay threshold in ${}^{12}\mathrm{C}$ and ${}^{16}\mathrm{O}$, including the linear chain, triangle, square, kite, and tetrahedron, affect nuclear collective vibrations with a microscopic dynamical approach, which can describe properties of nuclear ground states well across the nuclide chart and reproduce the standard giant dipole resonance (GDR) of ${}^{16}\mathrm{O}$ quite nicely. It is found that the GDR spectrum is highly fragmented into several apparent peaks due to the $\alpha$ structure. The different $\alpha$ cluster configurations in ${}^{12}\mathrm{C}$ and ${}^{16}\mathrm{O}$ have corresponding characteristic spectra of GDR. The number and centroid energies of peaks in the GDR spectra can be reasonably explained by the geometrical and dynamical symmetries of $\alpha$ clustering configurations. Therefore, the GDR can be regarded as a very effective probe to diagnose the different $\alpha$ cluster configurations in light nuclei.

The low-lying continuum spectrum of the ${}^6\mathrm{He}$ nucleus is investigated for the first time within an ab initio framework that encompasses the ${}^4\mathrm{He}+n+n$ three-cluster dynamics characterizing its lowest decay channel. This is achieved through an extension of the no-core shell model combined with the resonating-group method, in which energy-independent nonlocal interactions among three nuclear fragments can be calculated microscopically, starting from realistic nucleon-nucleon interactions and consistent ab initio many-body wave functions of the clusters. The three-cluster Schrödinger equation is solved with three-body scattering boundary conditions by means of the hyperspherical-harmonics method on a Lagrange mesh. Using a soft similarity-renormalization-group evolved chiral nucleon-nucleon potential, we find the known $J^{\pi }=2^{+}$ resonance as well as a result consistent with a new low-lying second $2^{+}$ resonance recently observed at GANIL at 2.6 MeV above the ${}^6\mathrm{He}$ ground state. We also find resonances in the $2^{-}$, $1^{+}$, and $0^{-}$ channels, while no low-lying resonances are present in the $0^{+}$ and $1^{-}$ channels.

The isoscalar monopole response has been measured in the unstable nucleus ${}^{68}\mathrm{Ni}$ using inelastic alpha scattering at $50A\mathrm{MeV}$ in inverse kinematics with the active target MAYA at GANIL. The isoscalar giant monopole resonance (ISGMR) centroid was determined to be $21.1\pm 1.9\mathrm{MeV}$ and indications for a soft monopole mode are provided for the first time at $12.9\pm 1.0\mathrm{MeV}$. Analysis of the corresponding angular distributions using distorted-wave-born approximation with random-phase approximation transition densities indicates that the $L=0$ multipolarity dominates the cross section for the ISGMR and significantly contributes to the low-energy mode. The $L=0$ part of this low-energy mode, the soft monopole mode, is dominated by neutron excitations. This demonstrates the relevance of inelastic alpha scattering in inverse kinematics in order to probe both the ISGMR and isoscalar soft modes in neutron-rich nuclei.

The half-lives of 20 neutron-rich nuclei with $Z=27–30$ have been measured at the RIBF, including five new half-lives of ${}^{76}\mathrm{Co}(21.7_{-4.9}^{+6.5}\mathrm{ms})$, ${}^{77}\mathrm{Co}(13.0_{-4.3}^{+7.2}\mathrm{ms})$, ${}^{79}\mathrm{Ni}({43.0}_{-7.5}^{+8.6}\mathrm{ms})$, ${}^{80}\mathrm{Ni}(23.9_{-17.2}^{+26.0}\mathrm{ms})$, and ${}^{81}\mathrm{Cu}(73.2\pm 6.8\mathrm{ms})$. In addition, the half-lives of ${}^{73–75}\mathrm{Co}$, ${}^{74–78}\mathrm{Ni}$, ${}^{78–80}\mathrm{Cu}$, and ${}^{80–82}\mathrm{Zn}$ were determined with higher precision than previous works. Based on these new results, a systematic study of the $\beta$-decay half-lives has been carried out, which suggests a sizable magicity for both the proton number $Z=28$ and the neutron number $N=50$ in ${}^{78}\mathrm{Ni}$.

Three sets of chiral doublet band structures have been identified in the ${}^{103}\mathrm{Rh}$ nucleus. The properties of the observed chiral doublet bands are in good agreement with theoretical results obtained using constrained covariant density functional theory and particle rotor model calculations. Two of them belong to an identical configuration and provide the first experimental evidence for a novel type of multiple chiral doublets, where an “excited” chiral doublet of a configuration is seen together with the “yrast” one. This observation shows that the chiral geometry in nuclei can be robust against the increase of the intrinsic excitation energy.