The chiral magnetic effect (CME) refers to charge separation along a strong magnetic field due to imbalanced chirality of quarks in local parity and charge-parity violating domains in quantum chromodynamics. The experimental measurement of the charge separation is made difficult by the presence of a major background from elliptic azimuthal anisotropy. This background and the CME signal have different sensitivities to the spectator and participant planes, and could thus be determined by measurements with respect to these planes. We report such measurements in $\mathrm{Au}+\mathrm{Au}$ collisions at a nucleon-nucleon center-of-mass energy of 200 GeV at the Relativistic Heavy-Ion Collider. It is found that the charge separation, with the flow background removed, is consistent with zero in peripheral (large impact parameter) collisions. Some indication of finite CME signals is seen in midcentral (intermediate impact parameter) collisions. Significant residual background effects may, however, still be present.

The interpretation of the emergent collective behavior of atomic nuclei in terms of deformed intrinsic shapes is at the heart of our understanding of the rich phenomenology of their structure, ranging from nuclear energy to astrophysical applications across a vast spectrum of energy scales. A new window into the deformation of nuclei has been recently opened with the realization that nuclear collision experiments performed at high-energy colliders, such as the CERN Large Hadron Collider (LHC), enable experimenters to identify the relative orientation of the colliding ions in a way that magnifies the manifestations of their intrinsic deformation. Here we apply this technique to LHC data on collisions of ${}^{129}\mathrm{Xe}$ nuclei to exhibit the first evidence of nonaxiality in the ground state of ions collided at high energy. We predict that the low-energy structure of ${}^{129}\mathrm{Xe}$ is triaxial (a spheroid with three unequal axes) and show that such deformation can be determined from high-energy data. This result demonstrates the unique capabilities of precision collider machines such as the LHC as new means to perform imaging of the collective structure of atomic nuclei.

We present converged ab initio calculations of structure factors for elastic spin-dependent WIMP scattering off all nuclei used in dark matter direct-detection searches: ${}^{19}\mathrm{F}$, ${}^{23}\mathrm{Na}$, ${}^{27}\mathrm{Al}$, ${}^{29}\mathrm{Si}$, ${}^{73}\mathrm{Ge}$, ${}^{127}\mathrm{I}$, and ${}^{129,131}\mathrm{Xe}$. From a set of established two- and three-nucleon interactions derived within chiral effective field theory, we construct consistent WIMP-nucleon currents at the one-body level, including effects from axial-vector two-body currents. We then apply the in-medium similarity renormalization group to construct effective valence-space Hamiltonians and consistently transformed operators of nuclear responses. Combining the recent advances of natural orbitals with three-nucleon forces expressed in large spaces, we obtain basis-space converged structure factors even in heavy nuclei. Generally results are consistent with previous calculations but large uncertainties in ${}^{127}\mathrm{I}$ highlight the need for further study.

The differential cross sections of the ${\mathrm{\Sigma }}^{-}p\to \mathrm{\Lambda }n$ reaction were measured accurately for the ${\mathrm{\Sigma }}^{-}$ momentum ($p_{\mathrm{\Sigma }}$) ranging from 470 to $650\mathrm{MeV}/c$ at the J-PARC Hadron Experimental Facility. Precise angular information about the ${\mathrm{\Sigma }}^{-}p\to \mathrm{\Lambda }n$ reaction was obtained for the first time by detecting approximately 100 reaction events at each angular step of $\mathrm{\Delta }\cos \theta =0.1$. The obtained differential cross sections show a slightly forward-peaking structure in the measured momentum regions. The cross sections integrated for $-0.7\le \cos \theta \le 1.0$ were obtained as $22.5\pm 0.68$ [statistical error(stat.)] $\pm 0.65$ [systematic error(syst.)] mb and $15.8\pm 0.83(\mathrm{stat})\pm 0.52(\mathrm{syst})\mathrm{mb}$ for $470<p_{\mathrm{\Sigma }}(\mathrm{MeV}/c)<550$ and $550<p_{\mathrm{\Sigma }}(\mathrm{MeV}/c)<650$, respectively. These results show a drastic improvement compared with past measurements of the hyperon-proton scattering experiments. They will play essential roles in updating the theoretical models of the baryon-baryon interactions.

Efficient production of nuclear isomers is critical for pioneering applications, like nuclear clocks, nuclear batteries, clean nuclear energy, and nuclear $\gamma$-ray lasers. However, due to small production cross sections and quick decays, it is extremely difficult to acquire a significant amount of isomers with short lifetimes via traditional accelerators or reactors because of low beam intensity. Here, for the first time, we experimentally present femtosecond pumping of nuclear isomeric states by the Coulomb excitation of ions with the quivering electrons induced by laser fields. Nuclei populated on the third excited state of ${}^{83}\mathrm{Kr}$ are generated with a peak efficiency of $2.34\times {10}^{15}\text{particles}/\mathrm{s}$ from a tabletop hundred-TW laser system. It can be explained by the Coulomb excitation of ions with the quivering electrons during the interaction between laser pulses and clusters at nearly solid densities. This efficient and universal production method can be widely used for pumping isotopes with excited state lifetimes down to picoseconds, and could be a benefit for fields like nuclear transition mechanisms and nuclear $\gamma$-ray lasers.

The notion of the “size” of nucleons and their constituents plays a pivotal role in the current paradigm of the formation and the fluctuations of the quark-gluon plasma produced in high-energy nuclear collision experiments. We report on state-of-the-art hydrodynamic results showing that the correlation between anisotropic flow $v_n^2$ and the mean transverse momentum of hadrons $[p_t]$ possesses a unique sensitivity to the nucleon size in off-central heavy-ion collisions. We argue that existing experimental measurements of this observable support a picture where the relevant length scale characterizing the colliding nucleons is of order 0.5 fm or smaller, and we discuss the broad implications of this finding for future global Bayesian analyses aimed at extracting initial-state and medium properties from nucleus-nucleus collision data, including $v_n^2\text{−}[p_t]$ correlations. Determinations of the nucleon size in heavy-ion collisions will provide a solid independent constraint on the initial state of small system collisions and will establish a deep connection between collective flow data in nucleus-nucleus experiments and data on deep inelastic scattering on protons and nuclei.

We present the first direct measurement of an astrophysical reaction using a radioactive beam of isomeric nuclei. In particular, we have measured the strength of the key 447-keV resonance in the ${}^{26m}\mathrm{Al}(p,\gamma ){}^{27}\mathrm{Si}$ reaction to be ${432}_{-226}^{+146}\mathrm{meV}$ and find that this resonance dominates the thermally averaged reaction rate for temperatures between 0.3 and 2.5 GK. This work represents a critical development in resolving one of the longest standing issues in nuclear astrophysics research, relating to the measurement of proton capture reactions on excited quantum levels, and offers unique insight into the destruction of isomeric ${}^{26}\mathrm{Al}$ in astrophysical plasmas.

Hydrodynamics and jet quenching are responsible for the elliptic flow $v_2$ and suppression of large transverse momentum ($p_T$) hadrons, respectively, two of the most important phenomena leading to the discovery of a strongly coupled quark-gluon plasma in high-energy heavy-ion collisions. A consistent description of the hadron suppression factor $R_{AA}$ and $v_2$, especially at intermediate $p_T$, however, remains a challenge. We solve this long-standing $R_{AA}\otimes v_2$ puzzle by including quark coalescence for hadronization and final state hadron cascade in the coupled linear Boltzmann transport-hydro model that combines concurrent jet transport and hydrodynamic evolution of the bulk medium. We illustrate that quark coalescence and hadron cascade, two keys to solving the puzzle, also lead to a splitting of $v_2$ for pions, kaons, and protons in the intermediate $p_T$ region. We demonstrate for the first time that experimental data on $R_{AA}$, $v_2$, and their hadron flavor dependence from low to intermediate and high $p_T$ in high-energy heavy-ion collisions can be understood within this coupled framework.

Collinear laser spectroscopy is performed on the nickel isotopes ${}^{58-68,70}\mathrm{Ni}$, using a time-resolved photon counting system. From the measured isotope shifts, nuclear charge radii $R_c$ are extracted and compared to theoretical results. Three ab initio approaches all employ, among others, the chiral interaction ${\mathrm{NNLO}}_{\mathrm{sat}}$, which allows an assessment of their accuracy. We find agreement with experiment in differential radii $\delta ⟨r_c^2⟩$ for all employed ab initio methods and interactions, while the absolute radii are consistent with data only for ${\mathrm{NNLO}}_{\mathrm{sat}}$. Within nuclear density functional theory, the Skyrme functional SV-min matches experiment more closely than the Fayans functional $\mathrm{Fy}(\mathrm{\Delta }r,\mathrm{HFB})$.

We present the first fully unrestricted microscopic calculations of the primary fission fragment intrinsic spins and of the fission fragments’ relative orbital angular momentum for ${{}^{236}\mathrm{U}}^{*}$, ${{}^{240}\mathrm{Pu}}^{*}$, and ${}^{252}\mathrm{Cf}$ using the time-dependent density functional theory framework. Within this microscopic approach, free of restrictions and unchecked assumptions and which incorporates the relevant physical observables for describing fission, we evaluate the triple distribution of the fission fragment intrinsic spins and of their fission fragments’ relative orbital angular momentum and show that their dynamics is dominated by their bending collective modes in contradistinction to the predictions of the existing phenomenological models and some interpretations of experimental data.

In the hydrodynamic model description of heavy-ion collisions, the elliptic flow $v_2$ and triangular flow $v_3$ are sensitive to the quadrupole deformation ${\beta }_2$ and octupole deformation ${\beta }_3$ of the colliding nuclei. The relations between $v_n$ and ${\beta }_n$ have recently been clarified and were found to follow a simple parametric form. The STAR Collaboration has just published precision $v_n$ data from isobaric ${}^{96}\mathrm{Ru}+{}^{96}\mathrm{Ru}$ and ${}^{96}\mathrm{Zr}+{}^{96}\mathrm{Zr}$ collisions, where they observe large differences in central collisions $v_{2,\mathrm{Ru}}>v_{2,\mathrm{Zr}}$ and $v_{3,\mathrm{Ru}}<v_{3,\mathrm{Zr}}$. Using a transport model simulation, we show that these orderings are a natural consequence of ${\beta }_{2,\mathrm{Ru}}\gg {\beta }_{2,\mathrm{Zr}}$ and ${\beta }_{3,\mathrm{Ru}}\ll {\beta }_{3,\mathrm{Zr}}$. We reproduce the centrality dependence of the $v_2$ ratio qualitatively and $v_3$ ratio quantitatively and extract values of ${\beta }_2$ and ${\beta }_3$ that are consistent with those measured at low-energy nuclear structure experiments. STAR data provide the first direct evidence of strong octupole correlations in the ground state of ${}^{96}\mathrm{Zr}$ in heavy-ion collisions. Our analysis demonstrates that flow measurements in high-energy, heavy-ion collisions, especially using isobaric systems, are a new precision tool to study nuclear structure physics.

Deep learning techniques have the power to identify the degree of modification of high energy jets traversing deconfined QCD matter on a jet-by-jet basis. Such knowledge allows us to study jets based on their initial, rather than final, energy. We show how this new technique provides unique access to the genuine configuration profile of jets over the transverse plane of the nuclear collision, both with respect to their production point and their orientation. By effectively removing the selection biases induced by final-state interactions, one can analyze the potential azimuthal anisotropies of jet production associated to initial-state effects. Additionally, we demonstrate the capability of our new method to locate with precision the production point of a dijet pair in the nuclear overlap region, in what constitutes an important step forward toward the long term quest of using jets as tomographic probes of the quark-gluon plasma.

We show that the inclusion of a recently found additional term of the spin polarization vector at local equilibrium which is linear in the symmetrized gradients of the velocity field, and the assumption of hadron production at constant temperature restore the quantitative agreement between hydrodynamic model predictions and local polarization measurements in relativistic heavy ion collisions at $\sqrt{s_{NN}}=200\mathrm{GeV}$. The longitudinal component of the spin polarization vector turns out to be very sensitive to the temperature value, with a good fit around 155 MeV. The implications of this finding are discussed.

Strange matter is believed to exist in the cores of neutron stars based on simple kinematics. If this is true, then hyperon-nucleon interactions will play a significant part in the neutron star equation of state. Yet, compared to other elastic scattering processes, there is very little data on $\mathrm{\Lambda }\text{−}N$ scattering. This experiment utilized the CEBAF Large Acceptance Spectrometer (CLAS) detector to study the $\mathrm{\Lambda }p\to \mathrm{\Lambda }p$ elastic scattering cross section in the incident $\mathrm{\Lambda }$ momentum range $0.9–2.0\mathrm{GeV}/c$. These are the first data on this reaction since the 1970s. The new cross sections have significantly better accuracy and precision than the existing world data, and the techniques developed here can also be used in future experiments.

The ground state to ground state electron-capture $Q$ value of ${}^{159}\mathrm{Dy}$ ($3/2^{-}$) has been measured directly using the double Penning trap mass spectrometer JYFLTRAP. A value of 364.73(19) keV was obtained from a measurement of the cyclotron frequency ratio of the decay parent ${}^{159}\mathrm{Dy}$ and the decay daughter ${}^{159}\mathrm{Tb}$ ions using the novel phase-imaging ion-cyclotron resonance technique. The $Q$ values for allowed Gamow-Teller transition to $5/2^{-}$ and the third-forbidden unique transition to $11/2^{+}$ state with excitation energies of 363.5449(14) keV and 362.050(40) keV in ${}^{159}\mathrm{Tb}$ were determined to be 1.18(19) keV and 2.68(19) keV, respectively. The high-precision $Q$ value of transition $3/2^{-}\to 5/2^{-}$ from this work, revealing itself as the lowest electron-capture $Q$ value, is used to unambiguously characterize all the possible lines that are present in its electron-capture spectrum. We performed atomic many-body calculations for both transitions to determine electron-capture probabilities from various atomic orbitals and found an order of magnitude enhancement in the event rates near the end point of energy spectrum in the transition to the $5/2^{-}$ nuclear excited state, which can become very interesting once the experimental challenges of identifying decays into excited states are overcome. The transition to the $11/2^{+}$ state is strongly suppressed and found unsuitable for measuring the neutrino mass. These results show that the electron-capture in the ${}^{159}\mathrm{Dy}$ atom, going to the $5/2^{-}$ state of the ${}^{159}\mathrm{Tb}$ nucleus, is a new candidate that may open the way to determine the electron-neutrino mass in the sub-eV region by studying electron-capture. Further experimental feasibility studies, including coincidence measurements with realistic detectors, will be of great interest.

We present the first measurement of the timelike Compton scattering process, $\gamma p\to p^{\prime }{\gamma }^{*}({\gamma }^{*}\to e^{+}{e}^{-})$, obtained with the CLAS12 detector at Jefferson Lab. The photon beam polarization and the decay lepton angular asymmetries are reported in the range of timelike photon virtualities $2.25<Q^{\prime 2}<9{\mathrm{GeV}}^2$, squared momentum transferred $0.1<-t<0.8{\mathrm{GeV}}^2$, and average total center-of-mass energy squared $s=14.5{\mathrm{GeV}}^2$. The photon beam polarization asymmetry, similar to the beam-spin asymmetry in deep virtual Compton scattering, is sensitive to the imaginary part of the Compton form factors and provides a way to test the universality of the generalized parton distributions. The angular asymmetry of the decay leptons accesses the real part of the Compton form factors and thus the $D$-term in the parametrization of the generalized parton distributions.

According to first-principle lattice QCD calculations, the transition from quark-gluon plasma to hadronic matter is a smooth crossover in the region ${\mu }_B\le T_c$. In this range the ratio, $C_6/C_2$, of net-baryon distributions are predicted to be negative. In this Letter, we report the first measurement of the midrapidity net-proton $C_6/C_2$ from 27, 54.4, and 200 GeV $\mathrm{Au}+\mathrm{Au}$ collisions at the Relativistic Heavy Ion Collider (RHIC). The dependence on collision centrality and kinematic acceptance in ($p_T$, $y$) are analyzed. While for 27 and 54.4 GeV collisions the $C_6/C_2$ values are close to zero within uncertainties, it is observed that for 200 GeV collisions, the $C_6/C_2$ ratio becomes progressively negative from peripheral to central collisions. Transport model calculations without critical dynamics predict mostly positive values except for the most central collisions within uncertainties. These observations seem to favor a smooth crossover in the high-energy nuclear collisions at top RHIC energy.

The strong suppression of high-$p_T$ jets in heavy-ion collisions is a result of elastic and inelastic energy loss suffered by the jet multiprong collection of color charges that are resolved by medium interactions. Hence, quenching effects depend on the fluctuations of the jet substructure that are probed by the cone-size dependence of the spectrum. In this Letter, we present the first complete, analytic calculation of the inclusive $R$-dependent jet spectrum in PbPb collisions at LHC energies, including resummation of energy loss effects from hard, vacuumlike emissions occurring in the medium and modeling of soft energy flow and recovery at the jet cone. Both the geometry of the collision and the local medium properties, such as the temperature and fluid velocity, are given by a hydrodynamic evolution of the medium, leaving only the coupling constant in the medium as a free parameter. The calculation yields a good description of the centrality and $p_T$ dependence of jet suppression for $R=0.4$ together with a mild cone-size dependence, which is in agreement with recent experimental results. Gauging the theoretical uncertainties, we find that the largest sensitivity resides in the leading logarithmic approximation of the phase space of resolved splittings, which can be improved systematically, while nonperturbative modeling of the soft-gluon sector is of relatively minor importance up to large cone sizes.

Starting from chiral nuclear interactions, we evaluate the contribution of the leading-order contact transition operator to the nuclear matrix element (NME) of neutrinoless double-beta decay, assuming a light Majorana neutrino-exchange mechanism. The corresponding low-energy constant (LEC) is determined by fitting the transition amplitude of the $nn\to pp{e}^{-}{e}^{-}$ process to a recently proposed synthetic datum. We examine the dependence of the amplitude on similarity renormalization group scale and chiral expansion order of the nuclear interaction, finding that both dependences can be compensated to a large extent by readjusting the LEC. We evaluate the contribution of both the leading-order contact operator and standard long-range operator to the neutrinoless double-beta decays in the light nuclei ${}^{6,8}\mathrm{He}$ and the candidate nucleus ${}^{48}\mathrm{Ca}$. Our results provide the first clear demonstration that the contact term enhances the NME in calculations with commonly used chiral two- plus three-nucleon interactions. In the case of ${}^{48}\mathrm{Ca}$, for example, the NME obtained with the $\mathrm{EM}(1.8/2.0)$ interaction is enhanced from 0.61 to 0.87(4), where the uncertainty is propagated from the synthetic datum.