We report on new measurements establishing the existence of low-lying isomeric states in ${}^{136}\mathrm{Cs}$ using $\gamma$ rays produced in ${}^{136}\mathrm{Xe}(p,n){}^{136}\mathrm{Cs}$ reactions. Two states with $\mathcal{O}(100)\mathrm{ns}$ lifetimes are placed in the decay sequence of the ${}^{136}\mathrm{Cs}$ levels that are populated in charged-current interactions of solar neutrinos and fermionic dark matter with ${}^{136}\mathrm{Xe}$. Xenon-based experiments can therefore exploit a delayed-coincidence tag of these interactions, greatly suppressing backgrounds to enable spectroscopic studies of solar neutrinos and dark matter.

The transverse-momentum ($p_T$) spectra and coalescence parameters $B_2$ of (anti)deuterons are measured in p-p collisions at $\sqrt{s}=13\mathrm{TeV}$ for the first time in and out of jets. In this measurement, the direction of the leading particle with the highest $p_T$ in the event ($p_T^{\mathrm{lead}}>5\mathrm{GeV}/c$) is used as an approximation for the jet axis. The event is consequently divided into three azimuthal regions, and the jet signal is obtained as the difference between the toward region, that contains jet fragmentation products in addition to the underlying event (UE), and the transverse region, which is dominated by the UE. The coalescence parameter in the jet is found to be approximately a factor of 10 larger than that in the underlying event. This experimental observation is consistent with the coalescence picture and can be attributed to the smaller average phase-space distance between nucleons in the jet cone as compared with the underlying event. The results presented in this Letter are compared to predictions from a simple nucleon coalescence model, where the phase-space distributions of nucleons are generated using pythia8 with the Monash 2013 tuning, and to predictions from a deuteron production model based on ordinary nuclear reactions with parametrized energy-dependent cross sections tuned on data. The latter model is implemented in pythia8.3. Both models reproduce the observed large difference between in-jet and out-of-jet coalescence parameters, although the almost flat trend of the $B_2^{\text{Jet}}$ is not reproduced by the models, which instead give a decreasing trend.

We study the polarization of inclusive $J/\psi$ produced in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02\mathrm{TeV}$ at the LHC in the dimuon channel, via the measurement of the angular distribution of its decay products. We perform the study in the rapidity region $2.5<y<4$, for three transverse momentum intervals ($2<p_T<4$, $4<p_T<6$, $6<p_T<10\mathrm{GeV}/c$) and as a function of the centrality of the collision for $2<p_T<6\mathrm{GeV}/c$. For the first time, the polarization is measured with respect to the event plane of the collision, by considering the angle between the positive-charge decay muon in the $J/\psi$ rest frame and the axis perpendicular to the event-plane vector in the laboratory system. A small transverse polarization is measured, with a significance reaching $3.9\sigma$ at low $p_T$ and for intermediate centrality values. The polarization could be connected with the behavior of the quark-gluon plasma, formed in Pb-Pb collisions, as a rotating fluid with large vorticity, as well as with the existence of a strong magnetic field in the early stage of its formation.

Polarized quarks and antiquarks in high-energy heavy-ion collisions can lead to the spin alignment of vector mesons formed by quark coalescence. Using the relativistic spin Boltzmann equation for vector mesons derived from Kadanoff-Baym equations with an effective quark-meson model for strong interaction and quark coalescence model for hadronizaton, we calculate the spin density matrix element ${\rho }_{00}$ for $\varphi$ mesons and show that anisotropies of local field correlations with respect to the spin quantization direction lead to $\varphi$ meson’s spin alignment. We propose that the local correlation or fluctuation of $\varphi$ fields is the dominant mechanism for the observed $\varphi$ meson’s spin alignment and its strength can be extracted from experimental data as functions of collision energies. The calculated transverse momentum dependence of ${\rho }_{00}$ agrees with STAR’s data. We further predict the azimuthal angle dependence of ${\rho }_{00}$ which can be tested in future experiments.

The nuclear modification factor of neutral pions is measured in proton-lead collisions collected at a center-of-mass energy per nucleon of 8.16 TeV with the LHCb detector. The ${\pi }^0$ production cross section is measured differentially in transverse momentum ($p_T$) for $1.5<p_T<10.0\mathrm{GeV}$ and in center-of-mass pseudorapidity (${\eta }_{\mathrm{c}.\mathrm{m}.}$) regions $2.5<{\eta }_{\mathrm{c}.\mathrm{m}.}<3.5$ (forward) and $-4.0<{\eta }_{\mathrm{c}.\mathrm{m}.}<-3.0$ (backward) defined relative to the proton beam direction. The forward measurement shows a sizable suppression of ${\pi }^0$ production, while the backward measurement shows the first evidence of ${\pi }^0$ enhancement in proton-lead collisions at the LHC. Together, these measurements provide precise constraints on models of nuclear structure and particle production in high-energy nuclear collisions.

The $\beta$ decays from both the ground state and a long-lived isomer of ${}^{133}\mathrm{In}$ were studied at the ISOLDE Decay Station (IDS). With a hybrid detection system sensitive to $\beta$, $\gamma$, and neutron spectroscopy, the comparative partial half-lives ($\log ft$) have been measured for all their dominant $\beta$-decay channels for the first time, including a low-energy Gamow-Teller transition and several first-forbidden (FF) transitions. Uniquely for such a heavy neutron-rich nucleus, their $\beta$ decays selectively populate only a few isolated neutron unbound states in ${}^{133}\mathrm{Sn}$. Precise energy and branching-ratio measurements of those resonances allow us to benchmark $\beta$-decay theories at an unprecedented level in this region of the nuclear chart. The results show good agreement with the newly developed large-scale shell model (LSSM) calculations. The experimental findings establish an archetype for the $\beta$ decay of neutron-rich nuclei southeast of ${}^{132}\mathrm{Sn}$ and will serve as a guide for future theoretical development aiming to describe accurately the key $\beta$ decays in the rapid-neutron capture ($r$-) process.

The excitation energy of the $1/2^{-}$ isomer in ${}^{99}\mathrm{In}$ at $N=50$ is measured to be 671(37) keV and the mass uncertainty of the $9/2^{+}$ ground state is significantly reduced using the ISOLTRAP mass spectrometer at ISOLDE/CERN. The measurements exploit a major improvement in the resolution of the multireflection time-of-flight mass spectrometer. The results reveal an intriguing constancy of the $1/2^{-}$ isomer excitation energies in neutron-deficient indium that persists down to the $N=50$ shell closure, even when all neutrons are removed from the valence shell. This trend is used to test large-scale shell model, ab initio, and density functional theory calculations. The models have difficulties describing both the isomer excitation energies and ground-state electromagnetic moments along the indium chain.

Bulk nuclear structure properties, such as radii and deformations, leave distinct signatures in the final state of relativistic heavy-ion collisions. Isobaric collisions offer an easy route to establish explicit connections between the colliding nuclei’s structure and the observable outcomes. Here, we investigate the effects of nuclear skin thickness and nuclear deformations on the elliptic flow ($v_2$) and its fluctuations in high-energy ${}^{96}\mathrm{Ru}+{}^{96}\mathrm{Ru}$ and ${}^{96}\mathrm{Zr}+{}^{96}\mathrm{Zr}$ collisions. Our findings reveal that the difference in skin thickness between these isobars only influences the inherent ellipticity of the collision systems, $v_2^{\mathrm{rp}}$. In contrast, differences in nuclear deformations solely impact the fluctuations of $v_2$ around $v_2^{\mathrm{rp}}$. Hence, we have identified a data-driven method to disentangle the effects of nuclear skin and nuclear deformations, marking a significant step toward assessing the consistency of nuclear phenomena across energy scales.

We develop an approach to chiral kinetic theories for electrons close to equilibrium and neutrinos away from equilibrium based on a systematic power counting scheme for different timescales of electromagnetic and weak interactions. Under this framework, we derive electric and energy currents along magnetic fields induced by neutrino radiation in general nonequilibrium states. This may be regarded as an effective chiral magnetic effect (CME), which is present without a chiral chemical potential, unlike the conventional CME. We also consider the so-called gain region of core-collapse supernovae as an example and find that the effective CME enhanced by persistent neutrino emission in time is sufficiently large to lead to the inverse cascade of magnetic and fluid kinetic energies and observed magnitudes of pulsar kicks. Our framework may also be applicable to other dense-matter systems involving nonequilibrium neutrinos.

The hadrochemistry of bottom quarks ($b$) produced in hadronic collisions encodes valuable information on the mechanism of color neutralization in these reactions. Since the $b$-quark mass is much larger than the typical hadronic scale of $\sim 1\mathrm{GeV}$, $b\overline{b}$ pair production is expected to be well separated from subsequent hadronization processes. A significantly larger fraction of $b$ baryons has been observed in proton-proton ($pp$) and proton-antiproton ($p\overline{p}$) reactions relative to $e^{+}{e}^{-}$ collisions, challenging theoretical descriptions. We address this problem by employing a statistical hadronization approach with an augmented set of $b$-hadron states beyond currently measured ones, guided by the relativistic quark model and lattice-QCD computations. Assuming relative chemical equilibrium between different $b$-hadron yields, thermal densities are used as fragmentation weights of $b$ quarks into various hadron species. With quark model estimates of the decay patterns of excited states, the fragmentation fractions of weakly decaying $b$ hadrons are computed and found to agree with measurements in $p\overline{p}$ collisions at the Tevatron. By combining transverse-momentum ($p_T$) distributions of $b$ quarks from perturbative QCD with thermal weights and independent fragmentation toward high $p_T$, a fair description of the $p_T$-dependent ${\overline{B}}_s^0/B^{-}$ and ${\mathrm{\Lambda }}_b^0/B^{-}$ ratios measured in $pp$ collisions at the LHC is obtained. The observed enhancement of ${\mathrm{\Lambda }}_b^0$ production is attributed to the feeddown from thus far unobserved excited $b$ baryons. Finally, we implement the hadrochemistry into a strongly coupled transport approach for $b$ quarks in heavy-ion collisions, utilizing previously determined $b$-quark transport coefficients in the quark-gluon plasma, to highlight the modifications of hadrochemistry and collective behavior of $b$ hadrons in Pb-Pb collisions at the LHC.

Jets provide us with ideal probes of the quark-gluon plasma (QGP) produced in heavy-ion collisions, since its dynamics at its different scales is imprinted into the multiscale substructure of the final state jets. We present a new approach to jet substructure in heavy-ion collisions based on the study of correlation functions of energy flow operators. By analyzing the two-point correlator of an in-medium quark jet, we demonstrate that the spectra of correlation functions robustly identify the scales defined by the properties of the QGP, particularly those associated with the onset of color coherence.

The elliptic ($v_2$) and triangular ($v_3$) azimuthal anisotropy coefficients in central ${}^3\mathrm{He}+\mathrm{Au}$, $d+\mathrm{Au}$, and $p+\mathrm{Au}$ collisions at $\sqrt{s_{\mathrm{NN}}}=200\mathrm{GeV}$ are measured as a function of transverse momentum ($p_T$) at midrapidity ($|\eta |<0.9$), via the azimuthal angular correlation between two particles both at $|\eta |<0.9$. While the $v_2(p_T)$ values depend on the colliding systems, the $v_3(p_T)$ values are system independent within the uncertainties, suggesting an influence on eccentricity from subnucleonic fluctuations in these small-sized systems. These results also provide stringent constraints for the hydrodynamic modeling of these systems.

For the first time, the $(d,{}^2\mathrm{He})$ reaction was successfully used in inverse kinematics to extract the Gamow-Teller transition strength in the ${\beta }^{+}$ direction from an unstable nucleus. The new technique was made possible by the use of an active-target time-projection chamber and a magnetic spectrometer, and opens a path to addressing a range of scientific challenges, including in astrophysics and neutrino physics. In this Letter, the nucleus studied was ${}^{14}\mathrm{O}$, and the Gamow-Teller transition strength to ${}^{14}\mathrm{N}$ was extracted up to an excitation energy of 22 MeV. The data were compared to shell-model and state-of-the-art coupled-cluster calculations. Shell-model calculations reproduce the measured Gamow-Teller strength distribution up to about 15 MeV reasonably well, after the application of a phenomenological quenching factor. In a significant step forward to better understand this quenching, the coupled-cluster calculation reproduces the full strength distribution well without such quenching, owing to the large model space, the inclusion of strong correlations, and the coupling of the weak interaction to two nucleons through two-body currents.

The $\beta$-delayed proton decay of ${}^{13}\mathrm{O}$ has previously been studied, but the direct observation of $\beta$-delayed $3\alpha p$ decay has not been reported. Rare $3\alpha p$ events from the decay of excited states in ${}^{13}{\mathrm{N}}^{\star }$ provide a sensitive probe of cluster configurations in ${}^{13}\mathrm{N}$. To measure the low-energy products following $\beta$-delayed $3\alpha p$ decay, the Texas Active Target (TexAT) time projection chamber was employed using the one-at-a-time $\beta$-delayed charged-particle spectroscopy technique at the Cyclotron Institute, Texas A&M University. A total of $1.9\times {10}^5$ ${}^{13}\mathrm{O}$ implantations were made inside the TexAT time projection chamber. A total of 149 $3\alpha p$ events were observed, yielding a $\beta$-delayed $3\alpha p$ branching ratio of 0.078(6)%. Four previously unknown $\alpha$-decaying excited states were observed in ${}^{13}\mathrm{N}$ at 11.3, 12.4, 13.1, and 13.7 MeV decaying via the $3\alpha +p$ channel.

We investigate the response of the near-equilibrium quark-gluon plasma (QGP) to perturbation at nonhydrodynamic gradients. We propose a conceivable scenario under which sound mode continues to dominate the medium response in this regime. Such a scenario has been observed experimentally for various liquids and liquid metals. We further show that this extended hydrodynamic regime (EHR) indeed exists for both the weakly coupled kinetic equation in the relaxation time approximation (RTA) and the strongly coupled $\mathcal{N}=4$ supersymmetric Yang-Mills (SYM) theory. We construct a simple but nontrivial extension of Müller-Israel-Stewart (MIS) theory—namely MIS*—and demonstrate that it describes the EHR response for both the RTA and SYM theory. This indicates that MIS* equations can potentially be employed to search for QGP EHR via heavy-ion collisions.

State-of-the-art hydrodynamic simulations of the quark-gluon plasma are unable to reproduce the elliptic flow of particles observed at the BNL Relativistic Heavy Ion Collider (RHIC) in relativistic ${}^{238}\mathrm{U}+{}^{238}\mathrm{U}$ collisions when they rely on information obtained from low-energy experiments for the implementation of deformation in the colliding ${}^{238}\mathrm{U}$ ions. We show that this is due to an inappropriate treatment of well-deformed nuclei in the modeling of the initial conditions of the quark-gluon plasma. Past studies have identified the deformation of the nuclear surface with that of the nuclear volume, though these are different concepts. In particular, a volume quadrupole moment can be generated by both a surface hexadecapole and a surface quadrupole moment. This feature was so far neglected in the modeling of heavy-ion collisions, and is particularly relevant for nuclei like ${}^{238}\mathrm{U}$, which is both quadrupole deformed and hexadecapole deformed. With rigorous input from Skyrme density functional calculations, we show that correcting for such effects in the implementation of nuclear deformations in hydrodynamic simulations restores agreement with BNL RHIC data. This brings consistency to the results of nuclear experiments across energy scales, and demonstrates the impact of the hexadecapole deformation of ${}^{238}\mathrm{U}$ on high-energy collisions.

We report here the first observation of directed flow ($v_1$) of the hypernuclei ${}_{\mathrm{\Lambda }}{}^3\mathrm{H}$ and ${}_{\mathrm{\Lambda }}{}^4\mathrm{H}$ in mid-central $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{\mathrm{NN}}}=3\mathrm{GeV}$ at RHIC. These data are taken as part of the beam energy scan program carried out by the STAR experiment. From $165\times {10}^6$ events in 5%–40% centrality, about 8400 ${}_{\mathrm{\Lambda }}{}^3\mathrm{H}$ and 5200 ${}_{\mathrm{\Lambda }}{}^4\mathrm{H}$ candidates are reconstructed through two- and three-body decay channels. We observe that these hypernuclei exhibit significant directed flow. Comparing to that of light nuclei, it is found that the midrapidity $v_1$ slopes of ${}_{\mathrm{\Lambda }}{}^3\mathrm{H}$ and ${}_{\mathrm{\Lambda }}{}^4\mathrm{H}$ follow baryon number scaling, implying that the coalescence is the dominant mechanism for these hypernuclei production in the 3 GeV $\mathrm{Au}+\mathrm{Au}$ collisions.

The rate of the final step in the astrophysical $\alpha \mathrm{p}$ process, the ${}^{34}\mathrm{Ar}(\alpha ,\mathrm{p}){}^{37}\mathrm{K}$ reaction, suffers from large uncertainties due to a lack of experimental data, despite having a considerable impact on the observable light curves of x-ray bursts and the composition of the ashes of hydrogen and helium burning on accreting neutron stars. We present the first direct measurement constraining the ${}^{34}\mathrm{Ar}(\alpha ,\mathrm{p}){}^{37}\mathrm{K}$ reaction cross section, using the Jet Experiments in Nuclear Structure and Astrophysics gas jet target. The combined cross section for the ${}^{34}\mathrm{Ar},\mathrm{Cl}(\alpha ,\mathrm{p}){}^{37}\mathrm{K},\mathrm{Ar}$ reaction is found to agree well with Hauser-Feshbach predictions. The ${}^{34}\mathrm{Ar}(\alpha ,2\mathrm{p}){}^{36}\mathrm{Ar}$ cross section, which can be exclusively attributed to the ${}^{34}\mathrm{Ar}$ beam component, also agrees to within the typical uncertainties quoted for statistical models. This indicates the applicability of the statistical model for predicting astrophysical $(\alpha ,\mathrm{p})$ reaction rates in this part of the $\alpha \mathrm{p}$ process, in contrast to earlier findings from indirect reaction studies indicating orders-of-magnitude discrepancies. This removes a significant uncertainty in models of hydrogen and helium burning on accreting neutron stars.