We study the spin polarization generated by the hydrodynamic gradients. In addition to the widely studied thermal vorticity effects, we identify an undiscovered contribution from the fluid shear. This shear-induced polarization (SIP) can be viewed as the fluid analog of strain-induced polarization observed in elastic and nematic materials. We obtain the explicit expression for SIP using the quantum kinetic equation and linear response theory. Based on a realistic hydrodynamic model, we compute the differential spin polarization along both the beam direction $\widehat{z}$ and the out-plane direction $\widehat{y}$ in noncentral heavy-ion collisions at $\sqrt{s_{NN}}=200\mathrm{GeV}$, including both SIP and thermal vorticity effects. We find that SIP contribution always shows the same azimuthal angle dependence as experimental data and competes with thermal vorticity effects. In the scenario that $\mathrm{\Lambda }$ inherits and memorizes the spin polarization of a strange quark, SIP wins the competition, and the resulting azimuthal angle dependent spin polarization $P_y$ and $P_z$ agree qualitatively with the experimental data.

We explore the out-of-equilibrium dynamics of the quark-gluon plasma at zero and finite net-baryon density based on an effective kinetic theory of quantum chromodynamics (QCD). By investigating the isotropization of the longitudinal pressure, we determine the relevant time and temperature scales for the onset of viscous hydrodynamics and quantify the dependence on the chemical composition of the quark-gluon plasma. By extrapolating our results to realistic coupling strength, we discuss phenomenological consequences regarding the role of the preequilibrium phase at different collision energies.

High-accuracy mass measurements of neutron-deficient Yb isotopes have been performed at TRIUMF using TITAN’s multiple-reflection time-of-flight mass spectrometer (MR-TOF-MS). For the first time, an MR-TOF-MS was used on line simultaneously as an isobar separator and as a mass spectrometer, extending the measurements to two isotopes further away from stability than otherwise possible. The ground state masses of ${}^{150,153}\mathrm{Yb}$ and the excitation energy of ${}^{151}{\mathrm{Yb}}^m$ were measured for the first time. As a result, the persistence of the $N=82$ shell with almost unmodified shell gap energies is established up to the proton drip line. Furthermore, the puzzling systematics of the $h_{11/2}$-excited isomeric states of the $N=81$ isotones are unraveled using state-of-the-art mean field calculations.

We have performed the first direct measurement of the ${}^{83}\mathrm{Rb}(p,\gamma )$ radiative capture reaction cross section in inverse kinematics using a radioactive beam of ${}^{83}\mathrm{Rb}$ at incident energies of 2.4 and $2.7A\mathrm{MeV}$. The measured cross section at an effective relative kinetic energy of $E_{\mathrm{cm}}=2.393\mathrm{MeV}$, which lies within the relevant energy window for core collapse supernovae, is smaller than the prediction of statistical model calculations. This leads to the abundance of ${}^{84}\mathrm{Sr}$ produced in the astrophysical $p$ process being higher than previously calculated. Moreover, the discrepancy of the present data with theoretical predictions indicates that further experimental investigation of $p$-process reactions involving unstable projectiles is clearly warranted.

The event-by-event correlations between three flow amplitudes are measured for the first time in Pb-Pb collisions, using higher-order symmetric cumulants. We find that different three-harmonic correlations develop during the collective evolution of the medium when compared to correlations that exist in the initial state. These new results cannot be interpreted in terms of previous lower-order flow measurements since contributions from two-harmonic correlations are explicitly removed in the new observables. A comparison to Monte Carlo simulations provides new and independent constraints for the initial conditions and system properties of nuclear matter created in heavy-ion collisions.

We report on the first measurement of charm-strange meson $D_s^{\pm }$ production at midrapidity in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{\mathrm{NN}}}=200\mathrm{GeV}$ from the STAR experiment. The yield ratio between strange ($D_s^{\pm }$) and nonstrange ($D^0$) open-charm mesons is presented and compared to model calculations. A significant enhancement, relative to a pythia simulation of $p+p$ collisions, is observed in the $D_s^{\pm }/D^0$ yield ratio in $\mathrm{Au}+\mathrm{Au}$ collisions over a large range of collision centralities. Model calculations incorporating abundant strange-quark production in the quark-gluon plasma and coalescence hadronization qualitatively reproduce the data. The transverse-momentum integrated yield ratio of $D_s^{\pm }/D^0$ at midrapidity is consistent with a prediction from a statistical hadronization model with the parameters constrained by the yields of light and strange hadrons measured at the same collision energy. These results suggest that the coalescence of charm quarks with strange quarks in the quark-gluon plasma plays an important role in $D_s^{\pm }$-meson production in heavy-ion collisions.

We derive a set of nontrivial relations between second-order transport coefficients which follow from the second law of thermodynamics upon considering a regime close to uniform rotation of the fluid. We demonstrate that an extension of hydrodynamics by spin variable is equivalent to modifying conventional hydrodynamics by a set of second-order terms satisfying the relations we derived. We point out that a novel contribution to the heat current orthogonal to vorticity and temperature gradient reminiscent of the thermal Hall effect is constrained by the second law.

The COMPASS Collaboration experiment recently discovered a new isovector resonancelike signal with axial-vector quantum numbers, the $a_1(1420)$, decaying to $f_0(980)\pi$. With a mass too close to and a width smaller than the axial-vector ground state $a_1(1260)$, it was immediately interpreted as a new light exotic meson, similar to the $X$, $Y$, $Z$ states in the hidden-charm sector. We show that a resonancelike signal fully matching the experimental data is produced by the decay of the $a_1(1260)$ resonance into $K^{*}(\to K\pi )\overline{K}$ and subsequent rescattering through a triangle singularity into the coupled $f_0(980)\pi$ channel. The amplitude for this process is calculated using a new approach based on dispersion relations. The triangle-singularity model is fitted to the partial-wave data of the COMPASS experiment. Despite having fewer parameters, this fit shows a slightly better quality than the one using a resonance hypothesis and thus eliminates the need for an additional resonance in order to describe the data. We thereby demonstrate for the first time in the light-meson sector that a resonancelike structure in the experimental data can be described by rescattering through a triangle singularity, providing evidence for a genuine three-body effect.

Diffusion wake is an unambiguous part of the jet-induced medium response in high-energy heavy-ion collisions that leads to a depletion of soft hadrons in the opposite direction of the jet propagation. New experimental data on $Z$-hadron correlation in $\mathrm{Pb}+\mathrm{Pb}$ collisions at the Large Hadron Collider show, however, an enhancement of soft hadrons in the direction of both the $Z$ and the jet. Using a coupled linear Boltzmann transport and hydro model, we demonstrate that medium modification of partons from the initial multiple parton interaction (MPI) gives rise to a soft hadron enhancement that is uniform in azimuthal angle while jet-induced medium response and soft gluon radiation dominate the enhancement in the jet direction. After subtraction of the contributions from MPI with a mixed-event procedure, the diffusion wake becomes visible in the near-side $Z$-hadron correlation. We further employ the longitudinal and transverse gradient jet tomography for the first time to localize the initial jet production positions in $Z/\gamma$-jet events in which the effect of the diffusion wake is apparent in $Z/\gamma$-hadron correlation even without the subtraction of the MPI contribution.

In the context of the search for the QCD critical point using non-Gaussian fluctuations, we obtain the evolution equations for non-Gaussian cumulants to the leading order of the systematic expansion in the magnitude of thermal fluctuations. We develop a diagrammatic technique in which the leading order contributions are given by tree diagrams. We introduce a Wigner transform for multipoint correlators and derive the evolution equations for three- and four-point Wigner functions for the problem of nonlinear stochastic diffusion with multiplicative noise.

The cyclotron frequency ratio of ${{}^{187}\mathrm{Os}}^{29+}$ to ${{}^{187}\mathrm{Re}}^{29+}$ ions was measured with the Penning-trap mass spectrometer PENTATRAP. The achieved result of $R=1.000000013882(5)$ is to date the most precise such measurement performed on ions. Furthermore, the total binding-energy difference of the 29 missing electrons in Re and Os was calculated by relativistic multiconfiguration methods, yielding the value of $\mathrm{\Delta }E=53.5(10)\mathrm{eV}$. Finally, using the achieved results, the mass difference between neutral ${}^{187}\mathrm{Re}$ and ${}^{187}\mathrm{Os}$, i.e., the $Q$ value of the ${\beta }^{-}$ decay of ${}^{187}\mathrm{Re}$, is determined to be 2470.9(13) eV.

We present a consistent ab initio computation of the longitudinal response function $R_L$ in ${}^{40}\mathrm{Ca}$ using the coupled-cluster and Lorentz integral transform methods starting from chiral nucleon-nucleon and three-nucleon interactions. We validate our approach by comparing our results for $R_L$ in ${}^4\mathrm{He}$ and the Coulomb sum rule in ${}^{40}\mathrm{Ca}$ against experimental data and other calculations. For $R_L$ in ${}^{40}\mathrm{Ca}$ we obtain a very good agreement with experiment in the quasielastic peak up to intermediate momentum transfers, and we find that final state interactions are essential for an accurate description of the data. This work presents a milestone towards ab initio computations of neutrino-nucleus cross sections relevant for experimental long-baseline neutrino programs.

A recent analysis of experimental data [J. Wilson et al., Nature (London) 590, 566 (2021)] found that the angular momenta of nuclear fission fragments are uncorrelated. Based on this finding, the authors concluded that the spins are therefore determined only after scission has occurred. We show here that the nucleon-exchange mechanism, as implemented in the well-established event-by-event fission model freya, while agitating collective rotational modes in which the two spins are highly correlated, nevertheless leads to fragment spins that are largely uncorrelated. This counterexample invalidates the conclusion in [J. Wilson et al.] that uncorrelated spins must necessarily have been generated after scission (a potentious conclusion that would rule out all models that generate the fragment spins prior to scission). Furthermore, it was reported [J. Wilson et al.] that the mass dependence of the average fragment spin has a sawtooth structure. We demonstrate that such a behavior naturally emerges when shell and deformation effects are included in the moments of inertia of the fragments at scission.

Normalizing flows are a class of machine learning models used to construct a complex distribution through a bijective mapping of a simple base distribution. We demonstrate that normalizing flows are particularly well suited as a Monte Carlo integration framework for quantum many-body calculations that require the repeated evaluation of high-dimensional integrals across smoothly varying integrands and integration regions. As an example, we consider the finite-temperature nuclear equation of state. An important advantage of normalizing flows is the ability to build highly expressive models of the target integrand, which we demonstrate enables precise evaluations of the nuclear free energy and its derivatives. Furthermore, we show that a normalizing flow model trained on one target integrand can be used to efficiently calculate related integrals when the temperature, density, or nuclear force is varied. This work will support future efforts to build microscopic equations of state for numerical simulations of supernovae and neutron star mergers that employ state-of-the-art nuclear forces and many-body methods.

The strong interactions among nucleons have an approximate spin-isospin exchange symmetry that arises from the properties of quantum chromodynamics in the limit of many colors, $N_c$. However this large-$N_c$ symmetry is well hidden and reveals itself only when averaging over intrinsic spin orientations. Furthermore, the symmetry is obscured unless the momentum resolution scale is close to an optimal scale that we call ${\mathrm{\Lambda }}_{\mathrm{large}\text{−}{N}_c}$. We show that the large-$N_c$ derivation requires a momentum resolution scale of ${\mathrm{\Lambda }}_{\mathrm{large}-N_c}\sim 500\mathrm{MeV}$. We derive a set of spin-isospin exchange sum rules and discuss implications for the spectrum of ${}^{30}\mathrm{P}$ and applications to nuclear forces, nuclear structure calculations, and three-nucleon interactions.

It was recently proposed that there is a phase in thermal QCD (IR phase) at temperatures well above the chiral crossover, featuring elements of scale invariance in the infrared (IR). Here, we study the effective spatial dimensions $d_{\mathrm{IR}}$ of Dirac low-energy modes in this phase, in the context of pure-glue QCD. Our $d_{\mathrm{IR}}$ is based on the scaling of mode support toward thermodynamic limit, and hence is an IR probe. Ordinary extended modes, such as those at high energy, have $d_{\mathrm{IR}}=3$. We find $d_{\mathrm{IR}}<3$ in the spectral range whose lower edge coincides with ${\lambda }_{\mathrm{IR}}=0$, the singularity of spectral density defining the IR phase, and the upper edge with ${\lambda }_A$, the previously identified Anderson-like nonanalyticity. Details near ${\lambda }_{\mathrm{IR}}$ are unexpected in that only exact zero modes are $d_{\mathrm{IR}}=3$, while a thin spectral layer near zero is $d_{\mathrm{IR}}=2$, followed by an extended layer of $d_{\mathrm{IR}}=1$ modes. With only integer values appearing, $d_{\mathrm{IR}}$ may have a topological origin. We find similar structure at ${\lambda }_A$, and associate its adjacent thin layer ($d_{\mathrm{IR}}⪆2$) with Anderson-like criticality. Our analysis reveals the manner in which nonanalyticities at ${\lambda }_{\mathrm{IR}}$ and ${\lambda }_A$, originally identified in other quantities, appear in $d_{\mathrm{IR}}(\lambda )$. This dimension structure may be important for understanding the near-perfect fluidity of the quark-gluon medium seen in accelerator experiments. The role of ${\lambda }_A$ in previously conjectured decoupling of IR component is explained.

We derive the collision term in the Boltzmann equation using the equation of motion for the Wigner function of massive spin-$1/2$ particles. To next-to-lowest order in $\hslash$, it contains a nonlocal contribution, which is responsible for the conversion of orbital into spin angular momentum. In a proper choice of pseudogauge, the antisymmetric part of the energy-momentum tensor arises solely from this nonlocal contribution. We show that the collision term vanishes in global equilibrium and that the spin potential is, then, equal to the thermal vorticity. In the nonrelativistic limit, the equations of motion for the energy-momentum and spin tensors reduce to the well-known form for hydrodynamics for micropolar fluids.

The Breit-Wheeler process which produces matter and antimatter from photon collisions is experimentally investigated through the observation of 6085 exclusive electron-positron pairs in ultraperipheral $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=200\mathrm{GeV}$. The measurements reveal a large fourth-order angular modulation of $\cos 4\mathrm{\Delta }\varphi =(16.8\pm 2.5)\%$ and smooth invariant mass distribution absent of vector mesons ($\varphi$, $\omega$, and $\rho$) at the experimental limit of $\le 0.2\%$ of the observed yields. The differential cross section as a function of $e^{+}{e}^{-}$ pair transverse momentum $P_{\perp }$ peaks at low value with $\sqrt{⟨P_{\perp }^2⟩}=38.1\pm 0.9\mathrm{MeV}$ and displays a significant centrality dependence. These features are consistent with QED calculations for the collision of linearly polarized photons quantized from the extremely strong electromagnetic fields generated by the highly charged Au nuclei at ultrarelativistic speed. The experimental results have implications for vacuum birefringence and for mapping the magnetic field which is important for emergent QCD phenomena.

We propose a new approach to excite the isomeric ${}^{229}\mathrm{Th}$ nuclear state, which has attracted much attention recently as a potential “nuclear clock.” Our approach is based on a laser-driven electron recollision process, the core process of strong-field atomic physics. Bringing together knowledge of recollision physics and of the related nuclear physics, we calculate the isomeric excitation probability. This new approach does not require precise knowledge of the energy of the isomeric state. The excitation is well timed which may be exploited to control the coherence of the isomeric state. Experimental realization is within reach using tabletop laser systems.

We show that the widely used relaxation time approximation to the relativistic Boltzmann equation contains basic flaws, being incompatible with micro- and macroscopic conservation laws if the relaxation time depends on energy or general matching conditions are applied. We propose a new approximation that fixes such fundamental issues and maintains the basic properties of the linearized Boltzmann collision operator. We show how this correction affects transport coefficients, such as the bulk viscosity and particle diffusion.