Transfer learning allows a deep neural network (DNN) trained on one type of data to be adapted for new problems with limited information. We propose to use the transfer learning technique in physics. The DNN learns the details of one process, and after fine-tuning, it makes predictions for related processes. We consider the DNNs, trained on inclusive electron-carbon scattering data, and show that after fine-tuning, they accurately predict cross sections for electron interactions with nuclear targets ranging from helium-3 to iron.

We introduce a new method for the study of fluctuations of partial transition widths based on nuclear resonance fluorescence experiments with quasimonochromatic linearly polarized photon beams below particle separation thresholds. It is based on the average branching of decays of $J=1$ states of an even-even nucleus to the $2_1^{+}$ state in comparison to the ground state. Between 5 and 7 MeV, a constant average branching ratio for $\gamma$ decays from $1^{-}$ states of 0.490(16) is observed for the nuclide ${}^{150}\mathrm{Nd}$. Assuming ${\chi }^2$-distributed partial transition widths, this average branching ratio is related to a degree of freedom of $\nu =1.93(12)$, rejecting the validity of the Porter-Thomas distribution, requiring $\nu =1$. The observed deviation can be explained by nonstatistical effects in the $\gamma$-decay behavior with contributions in the range of 9.4(10)% up to 94(10)%.

Incorporating microscopic nuclear-structure information into the discussion of bulk properties of astronomical objects such as neutron stars has always been a challenging issue in interdisciplinary nuclear astrophysics. Using the $rp$-process nucleosynthesis as an example, we studied the effective stellar ${\beta }^{+}$ and electron capture (EC) rates as well as the corresponding neutrino energy-loss rates of eight waiting-point (WP) nuclei with realistic stellar conditions and presence of strong magnetic fields. The relevant nuclear transition strengths are provided by the projected shell model. We have found that, on average, due to the magnetic field effect, the stellar weak rates can increase by more than an order of magnitude for all combinations of density and temperature, as well as in each of the WPs studied. We relate the onset field strength, at which the weak rates begin to increase, to nuclear structure quantities, $Q$ value or electronic chemical potential ${\mu }_e$. The enhanced weak rates may change considerably over the lifetime of WPs, thereby modifying the current understanding of the $rp$ process.

A crossover involving three-fermion clusters is relevant to the hadron-quark crossover, which, if occurring in a neutron star, could naturally reproduce the dense-matter equation of state recently deduced from simultaneous observations of neutron-star masses and radii. To understand the crossover mechanism, we examine the role of tripling fluctuations induced by the formation of three-fermion clusters. The phase-shift representation of fluctuations manifests an interplay of bound and scattering states, leading to nonmonotonic momentum distributions of baryonlike clusters and peaked sound speed at finite densities. We demonstrate them by applying our approach to a nonrelativistic system of one-dimensional three-color fermions analogous to the hadron-quark matter.

In this Letter, we examine the impact of QCD phase transitions on the quark spin fluctuations and correlations. We propose the quark-antiquark correlation, which relates to the vector meson spin alignment and the $\mathrm{\Lambda }-\overline{\mathrm{\Lambda }}$ correlation, and can be used as a novel probe of the critical end point (CEP) in the QCD phase diagram. Using the Nambu-Jona-Lanisio model, we qualitatively study the properties of quark-antiquark spin correlations. Our findings reveal a peak structure near the CEP of the chiral phase transition, which may serve as an experimental signature of the CEP and account for the non-monotonic behavior of $\varphi$ meson alignment at low collision energies observed recently in experiments.

The color glass condensate (CGC) effective theory and the collinear factorization at high twist (HT) are two well-known frameworks describing perturbative QCD multiple scatterings in nuclear media. It has long been recognized that these two formalisms have their own domain of validity in different kinematic regions. Taking direct photon production in proton-nucleus collisions as an example, we clarify for the first time the relation between CGC and HT at the level of a physical observable. We show that the CGC formalism beyond shock-wave approximation, and with the Landau-Pomeranchuk-Migdal interference effect is consistent with the HT formalism in the transition region where they overlap. Such a unified picture paves the way for mapping out the phase diagram of parton density in nuclear medium from dilute to dense region.

We explore the effects of including the energy dependence determined from evolution equations within the color glass condensate framework on observables in ultrarelativistic heavy-ion collisions. This amounts to integrating the JIMWLK evolution equations into the impact parameter-dependent glasma model, which is then coupled to viscous relativistic hydrodynamics. This methodology allows for a systematic representation of nuclei at specific Bjorken-$x$ values, which are probed at different center-of-mass energies of the collision and rapidities of final state particles. Comparing the methodology to the conventional impact parameter-dependent glasma model, we find significant effects on multiplicity distributions and particle spectra, especially in smaller collision systems at the highest center-of-mass energies. Our results highlight the importance of incorporating nonlinear QCD evolution in the description of heavy-ion collisions at varying center-of-mass energies, as the precise extraction of transport coefficients will be affected. This Letter establishes a robust framework for understanding the quark gluon plasma and nuclear structure at high energy, integrating small-$x$ physics into the initial conditions of heavy-ion collisions.

The previously unknown nucleus ${}^{20}\mathrm{Al}$ has been observed for the first time by detecting its in-flight decays. Tracking trajectories of all decay products with silicon microstrip detectors allowed for a conclusion that ${}^{20}\mathrm{Al}$ is unbound with respect to three-proton ($3p$) emission. The $3p$-decay energy of the ${}^{20}\mathrm{Al}$ ground state has been determined to be $1.93{(}_{-0.10}^{+0.12})\mathrm{MeV}$ through a detailed study of angular correlations of its decay products, ${}^{17}\mathrm{Ne}+p+p+p$. This value is significantly smaller than the predictions inferred from the isospin symmetry by using the known neutron separation energy of its mirror nucleus ${}^{20}\mathrm{N}$, which indicates a possible isospin symmetry breaking in the mirror nuclei ${}^{20}\mathrm{Al}$ and ${}^{20}\mathrm{N}$. This observed isospin symmetry breaking is supported by the calculations of the continuum embedded theoretical frameworks, describing the observed ${}^{20}\mathrm{Al}$ ground state as a $1p$ $s$-wave state with a spin-parity of $1^{-}$, which differs from the spin-parity ($2^{-}$) of the ${}^{20}\mathrm{N}$ ground state. The ${}^{20}\mathrm{Al}$ ground state decays by sequential $1p\text{−}2p$ emission via the intermediate ground state of ${}^{19}\mathrm{Mg}$, which is the first observed case of “daughter” $2p$ radioactivity following $1p$ decay of the parent state.

Reducing uncertainties in the nuclear matrix elements (NMEs) remains a critical challenge in designing and interpreting experiments aimed at discovering neutrinoless double-beta ($0\nu \beta \beta$) decay. Here, we identify a class of observables, distinct from those employed in low-energy nuclear structure applications, that are strongly correlated with the NMEs: momentum correlations among hadrons produced in high-energy nuclear collisions. Focusing on the ${}^{150}\mathrm{Nd}\to {}^{150}\mathrm{Sm}$ transition, we combine a Bayesian analysis of the structure of ${}^{150}\mathrm{Nd}$ with simulations of high-energy ${}^{150}\mathrm{Nd}+{}^{150}\mathrm{Nd}$ collisions. We reveal prominent correlations between the NMEs and features of the quark-gluon plasma formed in these processes, such as spatial gradients and anisotropies, that are accessible via collective flow measurements. Our findings demonstrate collider experiments involving $0\nu \beta \beta$ decay candidates as a platform for benchmarking theoretical predictions of the NMEs.

We identify a new class of three-nucleon forces that arises in the low-energy effective theory of nuclear interactions including pions. We estimate their contribution to the energy of neutron and nuclear matter and find that it can be as important as the leading-order three-nucleon forces previously considered in the literature. The magnitude of this force is set by the strength of the coupling of pions to two nucleons and is presently not well constrained by experiments. The implications for nuclei, nuclear matter, and the equation of state of neutron matter are briefly discussed.

Whether or not femto-scale droplets of quark-gluon plasma (QGP) are formed in so-called small systems at high-energy colliders is a pressing question in the phenomenology of the strong interaction. For proton-proton or proton-nucleus collisions the answer is inconclusive due to the large theoretical uncertainties plaguing the description of these processes. While upcoming data on collisions of ${}^{16}\mathrm{O}$ nuclei may mitigate these uncertainties in the near future, here we demonstrate the unique possibilities offered by complementing ${}^{16}\mathrm{O}+{}^{16}\mathrm{O}$ data with collisions of ${}^{20}\mathrm{Ne}$ ions. We couple both nuclear lattice effective field theory (NLEFT) and projected generator coordinate method (PGCM) ab initio descriptions of the structure of ${}^{20}\mathrm{Ne}$ and ${}^{16}\mathrm{O}$ to hydrodynamic simulations of ${}^{16}\mathrm{O}+{}^{16}\mathrm{O}$ and ${}^{20}\mathrm{Ne}+{}^{20}\mathrm{Ne}$ collisions at high energy. We isolate the imprints of the bowling-pin shape of ${}^{20}\mathrm{Ne}$ on the collective flow of hadrons, which can be used to perform quantitative tests of the hydrodynamic QGP paradigm. In particular, we predict that the elliptic flow of ${}^{20}\mathrm{Ne}+{}^{20}\mathrm{Ne}$ collisions is enhanced by as much as $1.174(8{)}_{\mathrm{stat}}(31{)}_{\mathrm{syst}}$ for NLEFT and $1.139(6{)}_{\mathrm{stat}}(39{)}_{\mathrm{syst}}$ for PGCM relative to ${}^{16}\mathrm{O}+{}^{16}\mathrm{O}$ collisions for the 1% most central events. At the same time, theoretical uncertainties largely cancel when studying relative variations of observables between two systems. This demonstrates a method based on experiments with two light-ion species for precision characterizations of the collective dynamics and its emergence in a small system.

Using the $B\rho$-defined isochronous mass spectrometry technique, we conducted the first mass measurement of the proton dripline nucleus ${}^{22}\mathrm{Si}$. We confirm that ${}^{22}\mathrm{Si}$ is bound against particle emission with $S_p/S_{2p}=+1412(114)/+229(54)\mathrm{keV}$, fixing the proton dripline location for the Si element. By analyzing the mass differences of the neighboring $sd$-shell nuclei, we find that ${}^{22}\mathrm{Si}$ exhibits a doubly magic character similar to its mirror partner ${}^{22}\mathrm{O}$, and that the mirror energy difference of ${}^{22}\mathrm{Si}\text{−}{}^{22}\mathrm{O}$ deviates from the predictions assuming mirror symmetry. Gamow shell-model calculations reveal that the average occupations of valence protons in ${}^{22}\mathrm{Si}$ are nearly identical to those of valence neutrons in ${}^{22}\mathrm{O}$, supporting the $Z=14$ magicity in ${}^{22}\mathrm{Si}$. The observed mirror-symmetry breaking is attributed to the extended proton distribution in ${}^{22}\mathrm{Si}$ arising from a small contribution of the unbound $\pi 2s_{1/2}$ orbital.

We calculate the spatial Wilson line correlator for $2+1$ flavor QCD using highly improved staggered quark discretization for fermions and in quenched QCD for a wide range of temperatures, from the chiral crossover temperature $T_{\mathrm{pc}}\simeq 156\mathrm{MeV}$ or the deconfinement temperature $\simeq 300\mathrm{MeV}$, respectively, up to 2 GeV. Extracting the spatial string tension for different lattice cutoffs and by performing a continuum extrapolation of this observable, we show that the soft (magnetic) gluons interact nonperturbatively even at temperatures $\gtrsim 1\mathrm{GeV}$. We provide incriminating evidences to demonstrate that dimensionally reduced effective theories can describe these soft quark and gluon quasi-particles for both quenched and $2+1$ flavor QCD, at temperatures $T\gtrsim 5T_{\mathrm{pc}}$. We also show for the first time the imprints of the nonperturbative pseudopotential in the properties of mesonic screening masses for temperatures ranging from 0.8 to 164 GeV in the quark-gluon plasma.

A loosely bound hadronic molecule produced by a relativistic heavy-ion collision has been described as a “snowball in hell” since it emerges from a hadron resonance gas whose temperature is orders of magnitude larger than the binding energy of the molecule. This remarkable phenomenon can be explained in terms of a novel thermodynamic variable called the “contact” that is conjugate to the binding momentum of the molecule. The production rate of the molecule can be expressed in terms of the contact density at the kinetic freeze-out of the hadron resonance gas. It approaches a nonzero limit as the binding energy goes to 0.

We employed laser spectroscopy of atomic transitions to measure the nuclear charge radii and electromagnetic properties of the high-spin isomeric states in neutron-rich indium isotopes ($Z=49$) near the closed proton and neutron shells at $Z=50$ and $N=82$. Our data reveal a reduction in the nuclear charge radius and intrinsic quadrupole moment when protons and neutrons are fully aligned in ${}^{129}\mathrm{In}(N=80)$, to form the high spin isomer. Such a reduction is not observed in ${}^{127}\mathrm{In}(N=78)$, where more complex configurations can be formed by the existence of four neutron holes. These observations are not consistently described by nuclear theory.

The neutrinoless double-beta decay ($0\nu \beta \beta$) of two neutrons $nn\to ppee$ is the elementary subprocess of $0\nu \beta \beta$ decay in nuclei. Accurate knowledge of the $nn\to ppee$ amplitude is required to pin down the short-range contributions in the nuclear matrix elements of the candidate nuclei for large-scale $0\nu \beta \beta$ searches. In this Letter, we report the first next-to-leading-order prediction of the $nn\to ppee$ amplitude, with Bayesian uncertainty quantification. This is made possible by the development of the relativistic chiral effective field theory, in which no unknown contact term is required up to next-to-leading order. The theory is validated by reproducing in a parameter-free way the available data on the charge independence and charge symmetry breaking contributions in the two-nucleon scattering. The present work makes an essential step toward addressing the uncertainty in the theoretical calculations of the nuclear matrix elements relevant for $0\nu \beta \beta$ searches.

${}^{76}\mathrm{Ge}$ can $\beta \beta$ decay into three possible excited states of ${}^{76}\mathrm{Se}$, with the emission of two or, if the neutrino is Majorana, zero neutrinos. None of these six transitions have yet been observed. The Majorana Demonstrator was designed to study $\beta \beta$ decay of ${}^{76}\mathrm{Ge}$ using a low background array of high purity germanium detectors. With 98.2 kg-y of isotopic exposure, the demonstrator sets the strongest half-life limits to date for all six transition modes. For $2\nu \beta \beta$ to the $0_1^{+}$ state of ${}^{76}\mathrm{Se}$, this search has begun to probe for the first time half-life values predicted using modern many-body nuclear theory techniques, setting a limit of $T_{1/2}>1.5\times {10}^{24}\mathrm{y}$ (90% CL).

We present the first theoretical study of the polarization of lepton pairs produced in $\sqrt{s_{\mathrm{NN}}}=5.02\mathrm{TeV}$ $\mathrm{Pb}+\mathrm{Pb}$ collisions at the LHC, using next-to-leading order (NLO) dilepton emission rates. These calculations employ a multistage framework to simulate the evolution of relativistic heavy-ion collisions, and to explore the sensitivity of polarization to early times. It is found that the intermediate invariant-mass dileptons are indeed probes of the thermal equilibration process, and go beyond the reach of hadronic observables. We compute the polarization anisotropy coefficient obtained with LO dilepton rates, and show that the LO and NLO results differ radically, both in trend and in magnitude, at low and intermediate lepton pair invariant masses.

A new effective theory framework for fluctuating hydrodynamics in the relativistic regime is derived using standard thermodynamical principles and general properties of nonequilibrium stochastic dynamics. For the first time, we establish clear and concise conditions for ensuring that the resulting effective theories are causal, stable, and well-posed within general relativity. These properties are independent of spacetime foliation and are valid in the full nonlinear regime. Out-of-equilibrium fluctuations are constrained by a relativistically covariant version of the Crooks fluctuation theorem, which determines how the entropy production is distributed even when the system is driven by an external force. This leads to an emerging ${\mathbb{Z}}_2$ symmetry responsible for imposing fluctuation-dissipation relations for n-point correlation functions, which matches the standard constraints for the Schwinger-Keldysh effective action.

The spectroscopic studies of very neutron-rich nucleus ${}^{128}\mathrm{Ag}$ have been performed for the first time at the Radioactive Isotope Beam Factory of RIKEN. A new seniority isomer with a half-life of $1.60(7)\mathrm{\mu }\mathrm{s}$ has been identified and is proposed to have a spin-parity of ${16}^{-}$ with a maximally aligned configuration comprising three proton holes in the $g_{9/2}$ orbital and one neutron hole in the $h_{11/2}$ orbital. The new level structure in ${}^{128}\mathrm{Ag}$ is quite well described by shell model calculations without invoking excitations across the $Z=50$ and $N=82$ shell gaps, and presents a good case of seniority scheme in odd–odd nuclei in the south vicinity of the double-magic nucleus ${}^{132}\mathrm{Sn}$. With a classification of various components of the proton–neutron interaction, the inversion of lowest-lying $9^{-}$ and ${10}^{-}$ states between ${}^{128}\mathrm{Ag}$ and its neighboring isotone ${}^{130}\mathrm{In}$ is found to be dynamically ascribed to the seniority-nonconserving proton–neutron interaction components. The structure above ${10}^{-}$ up to the ${16}^{-}$ isomer in ${}^{128}\mathrm{Ag}$ shows remarkable similarities to seniority structures in the semimagic nuclei ${}^{128}\mathrm{Pd}$ and ${}^{130}\mathrm{Cd}$. These spectroscopic features in ${}^{128}\mathrm{Ag}$ indicate that the $N=82$ shell closure is still robust in silver isotopes.