I show that particle collider experiments on relativistic nuclear collisions can serve as direct probes of the deformation of the colliding nuclear species. I argue that collision events presenting very large multiplicities of particles and very small values of the average transverse momentum of the emitted hadrons probe collision geometries in which the nuclear ellipsoids fully overlap along their longer side. By looking at these events one selects interaction regions whose elliptic anisotropy is determined by the deformed nuclear shape, which becomes accessible experimentally through the measurement of the elliptic flow of outgoing hadrons.

An inelastic excitation and cluster-decay experiment ${}^2\mathrm{H}({}^{16}\mathrm{C},{}^4\mathrm{He}+{}^{12}\mathrm{Be}\text{or}{}^6\mathrm{He}+{}^{10}\mathrm{Be}){}^2\mathrm{H}$ was carried out to investigate the linear-chain clustering structure in neutron-rich ${}^{16}\mathrm{C}$. For the first time, decay paths from the ${}^{16}\mathrm{C}$ resonances to various states of the final nuclei were determined, thanks to the well-resolved $Q$-value spectra obtained from the threefold coincident measurement. The close-threshold resonance at 16.5 MeV is assigned as the $J^{\pi }=0^{+}$ band head of the predicted positive-parity linear-chain molecular band with $(3/2_{\pi }^{-}{)}^2(1/2_{\sigma }^{-}{)}^2$ configuration, according to the associated angular correlation and decay analysis. Other members of this band were found at 17.3, 19.4, and 21.6 MeV based on their selective decay properties, being consistent with the theoretical predictions. Another intriguing high-lying state was observed at 27.2 MeV which decays almost exclusively to ${}^6\mathrm{He}+{}^{10}\mathrm{Be}(\sim 6\mathrm{MeV})$ final channel, corresponding well to another predicted linear-chain structure with the pure $\sigma$-bond configuration.

The excitation of the 8 eV ${}^{229m}\mathrm{Th}$ isomer through the electronic bridge mechanism in highly charged ions is investigated theoretically. By exploiting the rich level scheme of open $4f$ orbitals and the robustness of highly charged ions against photoionization, a pulsed high-intensity optical laser can be used to efficiently drive the nuclear transition by coupling it to the electronic shell. We show how to implement a promising electronic bridge scheme in an electron beam ion trap starting from a metastable electronic state. This setup would avoid the need for a tunable vacuum ultraviolet laser. Based on our theoretical predictions, determining the isomer energy with an uncertainty of ${10}^{-5}\mathrm{eV}$ could be achieved in one day of measurement time using realistic laser parameters.

The ${}^{12}\mathrm{C}+{}^{12}\mathrm{C}$ fusion reaction plays a critical role in the evolution of massive stars and also strongly impacts various explosive astrophysical scenarios. The presence of resonances in this reaction at energies around and below the Coulomb barrier makes it impossible to carry out a simple extrapolation down to the Gamow window—the energy regime relevant to carbon burning in massive stars. The ${}^{12}\mathrm{C}+{}^{12}\mathrm{C}$ system forms a unique laboratory for challenging the contemporary picture of deep sub-barrier fusion (possible sub-barrier hindrance) and its interplay with nuclear structure (sub-barrier resonances). Here, we show that direct measurements of the ${}^{12}\mathrm{C}+{}^{12}\mathrm{C}$ fusion cross section may be made into the Gamow window using an advanced particle-gamma coincidence technique. The sensitivity of this technique effectively removes ambiguities in existing measurements made with gamma ray or charged-particle detection alone. The present cross-section data span over 8 orders of magnitude and support the fusion-hindrance model at deep sub-barrier energies.

Carbon and oxygen burning reactions, in particular, ${}^{12}\mathrm{C}+{}^{12}\mathrm{C}$ fusion, are important for the understanding and interpretation of the late phases of stellar evolution as well as the ignition and nucleosynthesis in cataclysmic binary systems such as type Ia supernovae and x-ray superbursts. A new measurement of this reaction has been performed at the University of Notre Dame using particle-$\gamma$ coincidence techniques with SAND (a silicon detector array) at the high-intensity 5U Pelletron accelerator. New results for ${}^{12}\mathrm{C}+{}^{12}\mathrm{C}$ fusion at low energies relevant to nuclear astrophysics are reported. They show strong disagreement with a recent measurement using the indirect Trojan Horse method. The impact on the carbon burning process under astrophysical scenarios will be discussed.

We report on the first measurement of the charmed baryon ${\mathrm{\Lambda }}_c^{\pm }$ production at midrapidity ($|y|<1$) in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{\mathrm{NN}}}=200\mathrm{GeV}$ collected by the STAR experiment at the Relativistic Heavy Ion Collider. The ${\mathrm{\Lambda }}_c/D^0$ [denoting $({\mathrm{\Lambda }}_c^{+}+{\mathrm{\Lambda }}_c^{-})/(D^0+{\overline{D}}^0)$] yield ratio is measured to be $1.08\pm 0.16(\mathrm{stat})\pm 0.26(\mathrm{sys})$ in the 0%–20% most central $\mathrm{Au}+\mathrm{Au}$ collisions for the transverse momentum ($p_T$) range $3<p_T<6\mathrm{GeV}/c$. This is significantly larger than the pythia model calculations for $p+p$ collisions. The measured ${\mathrm{\Lambda }}_c/D^0$ ratio, as a function of $p_T$ and collision centrality, is comparable to the baryon-to-meson ratios for light and strange hadrons in $\mathrm{Au}+\mathrm{Au}$ collisions. Model calculations including coalescence hadronization for charmed baryon and meson formation reproduce the features of our measured ${\mathrm{\Lambda }}_c/D^0$ ratio.

It is commonly believed that the Sivers function has uniquely to do with processes involving a transversely polarized nucleon. In this Letter we show that this is not necessarily the case. We demonstrate that exclusive pion production in unpolarized electron-proton scattering in the forward region is a direct probe of the gluon Sivers function due to its connection to the QCD odderon.

The low-lying spectra of atomic nuclei display diverse behaviors, for example, rotational bands, which can be described phenomenologically by simple symmetry groups such as spatial SU(3). This leads to the idea of dynamical symmetry, where the Hamiltonian commutes with the Casimir operator(s) of a group, and is block diagonal in subspaces defined by the group’s irreducible representations or irreps. Detailed microscopic calculations, however, show these symmetries are in fact often strongly mixed and the wave function fragmented across many irreps. More commonly, the fragmentation across members of a band are similar, which is called a quasidynamical symmetry. In this Letter I explicitly, albeit numerically, construct unitary transformations from a quasidynamical symmetry to a dynamical symmetry, adapting the similarity renormalization group (SRG) in order to transform away the symmetry-mixing parts of the Hamiltonian. The standard SRG produces unsatisfactory results, forcing the induced dynamical symmetry to be dominated by high-weight irreps irrespective of the original decomposition. Using spectral distribution theory to rederive and diagnose standard SRG, I introduce a new form of SRG. The new SRG transforms a quasidynamical symmetry to a dynamical symmetry, that is, unmixes the mixed symmetries, with intuitively more appealing results.

The ${}^{12}\mathrm{C}(\alpha ,\gamma ){}^{16}\mathrm{O}$ reaction is one of the most crucial reactions in nuclear astrophysics. The $E2$ external capture to the ${}^{16}\mathrm{O}$ ground state (GS) has not been emphasized in previous analyses but may make a significant contribution to the ${}^{12}\mathrm{C}(\alpha ,\gamma ){}^{16}\mathrm{O}$ cross section depending on the value of the GS asymptotic normalization coefficient (ANC). In the present work, we determine this ANC to be $337\pm 45{\mathrm{fm}}^{-1/2}$ through the ${}^{12}\mathrm{C}({}^{11}\mathrm{B},{}^7\mathrm{Li}){}^{16}\mathrm{O}$ reaction using a high-precision magnetic spectrograph. This sheds light on the existing large discrepancy of more than 2 orders of magnitude between the previously reported ANC values. Based on the new ANC, we experimentally constrain the GS external capture and show that through interference with the high energy tail of the $2^{+}$ subthreshold state, a substantial enhancement in the GS $S_{E2}(300)$ factor can be obtained ($70\pm 7\mathrm{keV}\mathrm{b}$) compared to that of a recent review (45 keV b), resulting in an increase of the total $S$ factor from 140 to 162 keV b, which is now in good agreement with the value obtained by reproducing supernova nucleosynthesis calculations with the solar-system abundances. This work emphasizes that the external capture contribution for the ground state transition cannot be neglected in future analyses of the ${}^{12}\mathrm{C}(\alpha ,\gamma ){}^{16}\mathrm{O}$ reaction.

Elastic scattering of antiprotons off ${}^4\mathrm{He}$, ${}^{12}\mathrm{C}$, and ${}^{16,18}\mathrm{O}$ is described for the first time with a consistent microscopic approach based on the calculation of an optical potential (OP) describing the antiproton-target interaction. The OP is derived using the recent antiproton-nucleon ($\overline{p}N$) chiral interaction to calculate the $\overline{p}N$ $t$ matrix, while the target densities are computed with the ab initio no-core shell model using chiral interactions as well. Our results are in good agreement with the existing experimental data and the results computed at different chiral orders of the $\overline{p}N$ interaction display a well-defined convergence pattern.

The lifetimes of the first excited $2^{+}$ states in the $N=Z$ nuclei ${}^{80}\mathrm{Zr}$, ${}^{78}\mathrm{Y}$, and ${}^{76}\mathrm{Sr}$ have been measured using the $\gamma$-ray line shape method following population via nucleon-knockout reactions from intermediate-energy rare-isotope beams. The extracted reduced electromagnetic transition strengths yield new information on where the collectivity is maximized and provide evidence for a significant, and as yet unexplained, odd-odd vs even-even staggering in the observed values. The experimental results are analyzed in the context of state-of-the-art nuclear density-functional model calculations.

Detailed spectroscopy of the neutron-unbound nucleus ${}^{28}\mathrm{F}$ has been performed for the first time following proton/neutron removal from ${}^{29}\mathrm{Ne}/{}^{29}\mathrm{F}$ beams at energies around $230\mathrm{MeV}/\mathrm{nucleon}$. The invariant-mass spectra were reconstructed for both the ${}^{27}{\mathrm{F}}^{(*)}+n$ and ${}^{26}{\mathrm{F}}^{(*)}+2n$ coincidences and revealed a series of well-defined resonances. A near-threshold state was observed in both reactions and is identified as the ${}^{28}\mathrm{F}$ ground state, with $S_n({}^{28}\mathrm{F})=-199(6)\mathrm{keV}$, while analysis of the $2n$ decay channel allowed a considerably improved $S_n({}^{27}\mathrm{F})=1620(60)\mathrm{keV}$ to be deduced. Comparison with shell-model predictions and eikonal-model reaction calculations have allowed spin-parity assignments to be proposed for some of the lower-lying levels of ${}^{28}\mathrm{F}$. Importantly, in the case of the ground state, the reconstructed ${}^{27}\mathrm{F}+n$ momentum distribution following neutron removal from ${}^{29}\mathrm{F}$ indicates that it arises mainly from the $1p_{3/2}$ neutron intruder configuration. This demonstrates that the island of inversion around $N=20$ includes ${}^{28}\mathrm{F}$, and most probably ${}^{29}\mathrm{F}$, and suggests that ${}^{28}\mathrm{O}$ is not doubly magic.

We derive the general analytical solution of the viscous hydrodynamic equations for an ultrarelativistic gas of hard spheres undergoing Bjorken expansion, taking into account effects from particle number conservation, and use it to analytically determine its attractor at late times. Differently than all the cases considered before involving rapidly expanding fluids, in this example the gradient expansion converges. We exactly determine the hydrodynamic attractor of this system when its microscopic dynamics is modeled by the Boltzmann equation with a fully nonlinear collision kernel. The exact late time attractor of this system can be reasonably described by hydrodynamics even when the gradients are large.

Experimental studies of fission induced in relativistic nuclear collisions show a systematic enhancement of the excitation energy of the primary fragments by a factor of $\sim 2$, before their decay by fission and other secondary fragments. Although it is widely accepted that by doubling the energies of the single-particle states may yield a better agreement with fission data, it does not prove fully successful, since it is not able to explain yields for light and intermediate mass fragments. State-of-the-art calculations are successful to describe the overall shape of the mass distribution of fragments, but fail within a factor of 2–10 for a large number of individual yields. Here, we present a novel approach that provides an account of the additional excitation of primary fragments due to final state interaction with the target. Our method is applied to the ${}^{238}\mathrm{U}+{}^{208}\mathrm{Pb}$ reaction at $1\mathrm{GeV}/\mathrm{nucleon}$ (and is applicable to other energies), an archetype case of fission studies with relativistic heavy ions, where we find that the large probability of energy absorption through final state excitation of giant resonances in the fragments can substantially modify the isotopic distribution of final fragments in a better agreement with data. Finally, we demonstrate that large angular momentum transfers to the projectile and to the primary fragments via the same mechanism imply the need of more elaborate theoretical methods than the presently existing ones.

The two-particle momentum correlation function of a $K^{-}p$ pair from high-energy nuclear collisions is evaluated in the $\overline{K}N\text{−}\pi \mathrm{\Sigma }\text{−}\pi \mathrm{\Lambda }$ coupled-channel framework. The effects of all coupled channels together with the Coulomb potential and the threshold energy difference between $K^{-}p$ and ${\overline{K}}^{0}n$ are treated completely for the first time. Realistic potentials based on the chiral SU(3) dynamics are used which fit the available scattering data. The recently measured correlation function is found to be well reproduced by allowing variations of the source size and the relative weight of the source function of $\pi \mathrm{\Sigma }$ with respect to that of $\overline{K}N$. The predicted $K^{-}p$ correlation function from larger systems indicates that the investigation of its source size dependence is useful in providing further constraints in the study of the $\overline{K}N$ interaction.

We present the first laser spectroscopic measurement of the neutron-rich nucleus ${}^{68}\mathrm{Ni}$ at the $N=40$ subshell closure and extract its nuclear charge radius. Since this is the only short-lived isotope for which the dipole polarizability ${\alpha }_D$ has been measured, the combination of these observables provides a benchmark for nuclear structure theory. We compare them to novel coupled-cluster calculations based on different chiral two- and three-nucleon interactions, for which a strong correlation between the charge radius and dipole polarizability is observed, similar to the stable nucleus ${}^{48}\mathrm{Ca}$. Three-particle–three-hole correlations in coupled-cluster theory substantially improve the description of the experimental data, which allows to constrain the neutron radius and neutron skin of ${}^{68}\mathrm{Ni}$.

We study inclusive and diffractive dijet production in electron-proton and electron-nucleus collisions within the color glass condensate effective field theory. We compute dijet cross sections differentially in both mean dijet transverse momentum $\mathit{P}$ and recoil momentum $\mathbf{\Delta }$, as well as the anisotropy in the relative angle between $\mathit{P}$ and $\mathbf{\Delta }$. Our results cover a much larger kinematic range than accessible in previous computations performed in the correlation limit approximation, where it is assumed that $|\mathit{P}|\gg |\mathbf{\Delta }|$. We validate this approximation in its range of applicability and quantify its failure for $|\mathit{P}|\lesssim |\mathbf{\Delta }|$. We also predict significant target-dependent deviations from the correlation limit approximation for $|\mathit{P}|>|\mathbf{\Delta }|$ and $|\mathit{P}|\lesssim Q_s$, which offers a straightforward test of gluon saturation and access to multigluon distributions at a future Electron-Ion Collider.

The gyromagnetic factor of the low-lying $E=251.96(9)\mathrm{keV}$ isomeric state of the nucleus ${}^{99}\mathrm{Zr}$ was measured using the time-dependent perturbed angular distribution technique. This level is assigned a spin and parity of $J^{\pi }=7/2^{+}$, with a half-life of $T_{1/2}=336(5)\mathrm{ns}$. The isomer was produced and spin aligned via the abrasion-fission of a ${}^{238}\mathrm{U}$ primary beam at RIKEN RIBF. A magnetic moment $|\mu |=2.31(14){\mu }_N$ was deduced showing that this isomer is not single particle in nature. A comparison of the experimental values with interacting boson-fermion model IBFM-1 results shows that this state is strongly mixed with a main $\nu d_{5/2}$ composition. Furthermore, it was found that monopole single-particle evolution changes significantly with the appearance of collective modes, likely due to type-II shell evolution.