The continuous spectrum of double beta decay ($\beta \beta$) provides a sensitive probe to test the predictions of the standard model and to search for signatures of new physics beyond it. We present a comprehensive analysis of the ${}^{136}\mathrm{Xe}$ $\beta \beta$ spectrum utilizing $39.1\pm 0.7\mathrm{kg}·\mathrm{yr}$ of ${}^{136}\mathrm{Xe}$ exposure from the PandaX-4T experiment. The analysis yields the most precise measurement to date of the ${}^{136}\mathrm{Xe}$ two-neutrino double beta decay ($2\nu \beta \beta$) half-life, $(2.14\pm 0.05)\times {10}^{21}\mathrm{years}$, the uncertainty of which is reduced by a factor of 2 compared to our previous result. We measure the parameter ${\xi }_{31}^{2\nu }$, defined as the ratio between the subleading and leading components of the ${}^{136}\mathrm{Xe}$ $2\nu \beta \beta$ nuclear matrix element, to be ${0.59}_{-0.38}^{+0.41}$, which is consistent with theoretical predictions. We also search for Majoron-emitting modes of ${}^{136}\mathrm{Xe}$ $\beta \beta$, establishing the most stringent limit for the spectral index $n=7$.

We performed high-precision decay-pion spectroscopy of light $\mathrm{\Lambda }$ hypernuclei at the Mainz Microtron (MAMI) using the A1 spectrometer facility. By measuring the monochromatic ${\pi }^{-}$ momentum from the two-body weak decay ${}_{\mathrm{\Lambda }}{}^3\mathrm{H}\to {}^3\mathrm{He}+{\pi }^{-}$ and referencing it to the ${}_{\mathrm{\Lambda }}{}^4\mathrm{H}\to {}^4\mathrm{He}+{\pi }^{-}$ decay, we determined the $\mathrm{\Lambda }$ binding energy of ${}_{\mathrm{\Lambda }}{}^3\mathrm{H}$ with unprecedented accuracy. The obtained value, $B_{\mathrm{\Lambda }}{(}_{\mathrm{\Lambda }}^3\mathrm{H})=0.523\pm 0.013_{\mathrm{stat}}\pm 0.075_{\mathrm{syst}}.\mathrm{MeV}$, is consistent with the STAR result, but indicates a significantly deeper binding than inferred from earlier measurements. This result implies a stronger $\mathrm{\Lambda }$-deuteron interaction and provides stringent constraints on hyperon-nucleon interactions.

The lifetime of the $J^{\pi }=2^{+}$ state in the self-conjugate ${}^{88}\mathrm{Ru}$ nucleus has been determined in an experiment performed using rare-isotope beams provided by the new Facility for Rare Isotope Beams. This is the heaviest $N=Z$ nucleus for which such a measurement has been achieved. ${}^{88}\mathrm{Ru}$ was populated by both one-neutron knockout and charge-exchange reactions, and the lifetime of ${14.3}_{-3.4}^{+2.5}\mathrm{ps}$ was determined using the triple-foil plunger technique. The extracted electromagnetic transition strength shows that the quadrupole collectivity has dropped significantly compared with the highly deformed $N=Z$ region around $A\sim 80$. These results are compared with state-of-the-art large-scale shell-model and discrete nonorthogonal shell-model calculations. The theoretical calculations indicate a moderate triaxial deformation and suggest that low-lying states in this nucleus are no longer dominated by strong many-particle many-hole excitations, unlike the lighter, highly deformed $N=Z$ nuclei nearby.

The nature of the tetraneutron ($4n$) system remains a pivotal question in nuclear physics. We investigate the $4n$ system using nuclear lattice effective field theory in finite volumes with a lattice size up to $L=30\mathrm{fm}$, employing both a high-precision ${\mathrm{N}}^3\mathrm{LO}$ interaction and a simplified SU(4) symmetric one. The ground-state energy is found to decrease smoothly with increasing box size, showing no plateau characteristic of a resonance. We further compute the dineutron-dineutron scattering phase shift using Lüscher’s finite-volume method. At the smallest relative momenta, the extracted $2n–2n$ $S$-wave phase shift is small, consistent with a weak interaction in the dilute limit. At intermediate momenta, it exhibits a weak attraction with a peak of approximately 10° at relative momentum of 60–84 MeV. While this structure does not constitute a resonance, the corresponding confined $4n$ energy of 1.7–3.3 MeV lies close to the experimentally observed low-energy peak.

This Letter reports the first measurement of photonuclear $D^0$ meson production in ultraperipheral heavy ion collisions. The study is performed using lead-lead collision data, with an integrated luminosity of $1.34{\mathrm{nb}}^{-1}$, collected by the CMS experiment at a nucleon-nucleon center-of-mass energy of 5.36 TeV. Photonuclear events, where one of the colliding nuclei breaks up and the other remains intact, are selected based on breakup neutron emissions and by requiring no particle activity in a large rapidity interval in the direction of the photon-emitting nucleus. The $D^0$ mesons are reconstructed via the $D^0\to K^{-}{\pi }^{+}$ decay channel, with the cross section measured as a function of $D^0$ meson transverse momentum and rapidity. The results are compared with next-to-leading-order perturbative QCD calculations that employ recent parametrizations of the lead nuclear parton distribution functions, as well as with predictions based on the color glass condensate framework. This measurement is the first photonuclear collision study characterizing parton distribution functions of lead nuclei for parton fractional momenta $x$ (relative to the nucleon) ranging approximately from a few ${10}^{-4}$ to ${10}^{-2}$ for different hard energy scale $Q^2$ selections.

Collider experiments involving nuclei provide a direct means of studying exotic states of nuclear matter. Recent measurements of energy correlators in both proton-nucleus (p-A) and nucleus-nucleus (A-A) collisions reveal sizable modifications, attributable to nuclear effects, compared to proton-proton (p-p) collisions. Energy correlators, and their associated light-ray operator product expansion (OPE), allow scaling behaviors of the measured spectrum to be directly mapped to properties of the underlying quantum field theory. Here, we demonstrate for the first time how this mapping occurs in nuclear collisions, and highlight how the light-ray OPE characterizes leading nuclear effects. We show that the leading modification to the energy correlator distribution is characterized by an enhancement of the expectation value of twist-4 light-ray operators, resulting in a scaling for the ratio of the two-point correlator in nuclear matter to that in vacuum of $\sim 1+a{\theta }^2$ up to quantum corrections. We verify that this leading twist-4 correction accurately describes recent A-A and p-A data, and is thus sufficient to capture the scaling behavior within the angular range measured for jet radii used in nuclear experiments. Our light-ray OPE based approach lays the groundwork for a rigorous characterization of nuclear modification to energy correlator observables.

We report measurements of charmonium sequential suppression in $\mathrm{Ru}+\mathrm{Ru}$ and $\mathrm{Zr}+\mathrm{Zr}$ collisions at $\sqrt{s_{\mathrm{NN}}}=200\mathrm{GeV}$ with the STAR experiment at the Relativistic Heavy Ion Collider (RHIC). The inclusive yield ratio of $\psi (2\mathrm{S})$ to $\mathrm{J}/\psi$ as a function of transverse momentum is reported, along with the centrality dependence of the double ratio, defined as the $\psi (2\mathrm{S})$ to $\mathrm{J}/\psi$ ratio in heavy-ion collisions relative to that in $p+p$ collisions. In the 0–80% centrality class, the double ratio is found to be $0.41\pm 0.10(\mathrm{stat})\pm 0.03(\mathrm{syst})\pm 0.02(\mathrm{ref})$, lower than unity with a significance of 5.6 standard deviations. This provides experimental evidence that $\psi (2\mathrm{S})$ is significantly more suppressed than $\mathrm{J}/\psi$ in heavy-ion collisions at RHIC. This sequential suppression pattern seems to increase from peripheral to central collisions, but with no significant dependence on the transverse momentum.

Nuclear radius is a fundamental structural observable that informs many properties of atomic nuclei and nuclear matter. Experimental studies of radii in drip line nuclei are in the forefront of research with radioactive ion beams. Of particular interest are charge radii of proton-unbound nuclei that will soon be approached in laser spectroscopy. In this Letter, using the complex-energy approach and direct time propagation, we investigate the radius of the proton resonance whose size is ill defined in the standard stationary quantum-mechanical description. An early-time plateau is identified during which the radius of the Gamow resonance coincides with the real-energy radius accessible experimentally. We demonstrate a nonmonotonic dependence of the complex radius on decay energy and a local increase of the charge radius across the threshold (a halolike enhancement).

The differential radial flow fluctuation $v_0(p_{\mathrm{T}})$ has emerged as a new probe of the quark-gluon plasma. However, its characteristic rise-and-fall pattern with $p_{\mathrm{T}}$, resembling anisotropic flow, remains unexplained. I introduce a momentum rescaling framework that factorizes $v_0(p_{\mathrm{T}})$ into kinematic and dynamical components: $v_0(p_{\mathrm{T}})/v_0=-[d\ln ⟨n(p_{\mathrm{T}})⟩/d\ln p_{\mathrm{T}}+1]\times g(p_{\mathrm{T}})$. The first factor, determined by spectral shape, generates the rise-and-fall pattern as the spectra transition from exponential to power-law behavior. The dynamical component $g(p_{\mathrm{T}})$ isolates $p_{\mathrm{T}}$-dependent dynamics: $<1$ signals suppressed fluctuations, $>1$ indicates enhancement. Analysis of LHC data reveals $g(p_{\mathrm{T}})$ deviates from unity by 20%–40% in central collisions. Predictions for RHIC show that spectral shape alone generates the rise-and-fall baseline pattern with substantial energy dependence. This framework enables tighter medium property constraints by separating kinematic from dynamical effects, with broad applications to anisotropic flow and higher-order radial flow fluctuations.

Nuclear Schiff moments (NSMs) are sensitive probes for physics beyond the standard model of particle physics signaling violations of time-reversal and parity-inversion symmetries in atomic nuclei. In this Letter, we report the first-ever calculation of a NSM in a nuclear ab initio framework, employing the no-core shell model to study the fluorine isotope ${}^{19}\mathrm{F}$. We further perform quantum-chemistry calculations to evaluate the sensitivity of the hafnium monofluoride cation, ${\mathrm{HfF}}^{+}$, to the NSM of ${}^{19}\mathrm{F}$. Combined with recent high-precision measurements of the molecular electric dipole moment of ${\mathrm{HfF}}^{+}$ [Roussy et al., An improved bound on the electron’s electric dipole moment, Science 381, 46 (2023).], our results enable the first experimental bound on the NSM of ${}^{19}\mathrm{F}$. Although the resulting bounds on the pion-nucleon-nucleon ($\pi \mathrm{NN}$) coupling constants are not yet the most stringent, this Letter establishes the foundation for constraining $\pi \mathrm{NN}$ interactions using nuclear ab initio methods.

We present a novel multimessenger approach to extract the effective radial flow of the quark-gluon plasma (QGP) by jointly analyzing thermal photon and dilepton spectra in heavy-ion collisions. A key feature of this method is that it circumvents the need for a directly unmeasurable reference—the photon temperature in the absence of flow—by establishing, within a calibrated model framework, a stable, approximately linear correlation with the dilepton-inferred temperature. This construction defines an experimentally constructible quantity, $v_r^{\mathrm{eff}}$, which reflects early-time collectivity and exhibits a strong correlation with the spacetime-averaged radial velocity of the QGP. Together with previous results linking dilepton slopes to the initial QGP temperature, our work establishes a consistent framework for electromagnetic tomography of the QGP. Our framework quantifies the experimental precision target, thereby providing a concrete road map for future measurements at RHIC and the LHC and opening a new avenue to probe the early-time dynamics of hot QCD matter.

In an experiment performed at the Facility for Rare Isotope Beams (FRIB) using the FRIB Decay Station initiator, 15 new half-lives of isotopes near ${}^{54}\mathrm{Ca}$ were measured. A new method of extracting lifetimes from experimental data, taking into account the unknown $\beta$-delayed neutron emission branches of very neutron-rich nuclei, was developed to enable systematic uncertainty analysis. The experiment observed a dramatic change in the half-life systematics for the isotopes with neutron number $N=34$. Beyond $N=34$, the decline of nuclear lifetime is much slower, leading to longer than anticipated lifetimes for near-dripline nuclei. State-of-the-art shell-model calculations can explain the experimental results, revealing the imprint of shell effects and the need for modification of single-particle neutron states. The results from a newly developed quasiparticle random phase approximation model with potential for making global predictions were also tested against the experimental results and good agreement was found.

The triply charged thorium-229 ion (${{}^{229}\mathrm{Th}}^{3+}$) has been identified as a promising candidate for the development of ultraprecise nuclear clocks. In this Letter, we investigate how the electron structure of this ion, particularly the single valence electron, influences the nucleus through nuclear hyperfine mixing (NHM)—a phenomenon previously studied almost solely for highly charged ions. We show that NHM opens electric dipole ($E1$) transition channels, which can significantly enhance the efficiency of nuclear isomeric excitation by 2 orders of magnitude. Additionally, NHM accelerates the spontaneous decay rate of the nuclear isomeric state by 1% to 7%, depending on the specific hyperfine level involved.

Incorporating nuclear shell effects within the framework of orbital-free density functional theory (DFT) has remained a long-standing challenge in nuclear physics. While the Hohenberg-Kohn theorem formally guarantees the existence of an orbital-free density functional that is capable of describing all many-body effects, including shell effects, practical attempts since the 1970s have consistently failed to capture such effects. This persistent difficulty has even led to the misconception that the orbital-free DFT is inherently unable to describe nuclear shell effects. Here we develop a nonlocal orbital-free DFT approach for atomic nuclei and demonstrate that nuclear shell effects can be successfully incorporated into the orbital-free DFT through the construction of a nonlocal kinetic energy density functional. In particular, we show that the nonlocal orbital-free functional yields a nucleon localization function that, as an established indicator of shell effects, exhibits consistent behavior with the exact Kohn-Sham solution.

The initial-state geometry in relativistic heavy-ion collisions provides a novel probe to nuclear cluster structure. For ${}^{20}\mathrm{Ne}$, a novel approach is proposed to distinguish between the cluster configurations ($5\alpha$ versus $\alpha +{}^{16}\mathrm{O}$) in order to gain insight into nuclear structure transitions governed by many-body quantum correlations. Through analytical calculations with the microscopic Brink model and event-by-event simulations using the hydrodynamic framework, we establish the normalized symmetric cumulant NSC(3, 2) and the Pearson coefficient ${\rho }_2(v_2^2,\delta [p_{\mathrm{T}}])$ as quantitative discriminators to reveal enhanced cluster degrees of freedom in the ground state of ${}^{20}\mathrm{Ne}$. The ultracentral $\mathrm{Ne}+\mathrm{Ne}$ collisions at the LHC can experimentally identify these two competing configurations via these flow correlation observables, opening a new paradigm for probing clustering in light nuclei.

Recent experimental data show an unexpectedly large spin alignment of $\varphi$ mesons in high-energy heavy-ion collisions, which can be explained by short-distance fluctuations of strong-force fields (vector $\varphi$ fields) within the constituent-quark model. We calculate the hyperon spin correlations within the same model, taking into account hydrodynamic effects and a $\varphi$ field fluctuating in space-time according to a Gaussian distribution. The $\mathrm{\Lambda }\overline{\mathrm{\Lambda }}$ spin correlation induced by the $\varphi$ field is shown to be negative as opposed to that of $\mathrm{\Lambda }\mathrm{\Lambda }$ or $\overline{\mathrm{\Lambda }}\overline{\mathrm{\Lambda }}$. We thus propose a new net spin-correlation observable as a sensitive probe to separate strong-force effects from hydrodynamic ones. With the strength of the field fluctuations extracted from the observed $\varphi$ spin alignment, we predict the collision-energy dependence of the hyperon spin correlations and also investigate the dependence of the net spin correlation on azimuthal-angle and rapidity difference.

Delayed $\gamma$-ray spectroscopy was performed for evaporation residues produced in the ${}^{58}\mathrm{Ni}+{}^{96}\mathrm{Ru}$ reaction. A new isomer in ${}_{70}{}^{150}\mathrm{Yb}$ ($Z=70$, $N=80$) with a half-life of $0.62(5)\mathrm{\mu }\mathrm{s}$ was identified at an excitation energy of 2872(2) keV. Its spin-parity is assigned as (${10}^{+}$) and a decay scheme is proposed based on a strong analogy with that of the isotonic ${}_{68}{}^{148}\mathrm{Er}$. Previously, the ${10}^{+}$ isomers were observed in the $N=80$ even-$Z$ isotones from the neutron-rich ${}_{46}{}^{126}\mathrm{Pd}$ to the neutron-deficient ${}_{68}{}^{148}\mathrm{Er}$. For the first time, by combining experimental data and comprehensive large-scale shell-model calculations, we clearly identify the configurations of these isomers and demonstrate that they all exhibit seniority structures. These findings firmly establish a configuration change in the ${10}^{+}$ isomeric chain, from a pair of maximally aligned $1h_{11/2}$ neutrons (holes) to a pair of maximally aligned $1h_{11/2}$ protons around the $Z=64$ subshell closure. This transition serves as a unique isomeric relay underpinning the persistence of the isomeric chain.

Magnetic dipole, $M1$, strengths were studied in semimagic ${}^{50}\mathrm{Ti}$ up to the neutron-separation threshold by combining data from $(d,p)$ one-neutron transfer, $(\gamma ,{\gamma }^{\prime })$ real-photon scattering, $(e,e^{\prime })$ inelastic scattering at extreme backward angles, and $(p,p^{\prime })$ at $E_p=210\mathrm{MeV}$ and extreme forward angles. The combination of all probes provided unique access to the neutron spin-flip contribution and the possibility to evaluate its role in generating the spin-flip $M1$ strengths. The small contribution of the neutron $(1f_{7/2}{)}^{-1}(1f_{5/2}{)}^{+1}$ spin-flip transitions, which were probed with the $(d,p)$ reaction, to the overall strength in ${}^{50}\mathrm{Ti}$ questions the standard picture for the microscopic origin of spin-flip strength in the $fp$ shell. For ${}^{50}\mathrm{Ti}$, this Letter shows that $J^{\pi }=1^{+}$ states with larger neutron $(1f_{7/2}{)}^{-1}(1f_{5/2}{)}^{+1}$ spectroscopic factors do not correspond to the ones with the largest $B(M1;0_1^{+}\to 1_i^{+})$ strengths.