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Physics Nuclear Theory

nucl-th Watch Nuclear Theory

Thursday 6 August

Nuclear Theory

Momentum Distributions and Spatial Signatures of Proton Halos in the sd Shell

Taslima S.C. Diba, Carlos A. Bertulani and Ronaldo V. Lobato

We perform a theoretical study of intermediate-energy quasifree one-proton knockout reactions on proton targets. Single-particle wave functions constrained by the experimental proton separation energies are employed to calculate longitudinal momentum distributions, one-proton removal cross sections, and full momentum-space profiles for $^{26}$P, $^{27}$S and $^{31}$Ar nuclei. To establish robust criteria to identify proton halos, the analysis is extended beyond the traditional momentum-width approach by investigating the spatial extension of the valence proton through root-mean-square radii and the probability that the proton resides outside the core nucleus, $P(r>R_{\rm core})$. We also examine Coulomb-barrier systematics, mirror-nucleus comparisons, realistic spectroscopic mixtures, finite experimental momentum resolution, and uncertainties associated with the proton separation energy. Our calculations indicate that proton-halo structure cannot be identified reliably from a single observable. A consistent interpretation emerges only when momentum distributions, spatial observables, Coulomb effects, and many-body structure are considered simultaneously. Within the present model, $^{26}$P exhibits the strongest proton-halo signatures, while $^{27}$S retains pronounced halo-like features despite its larger Coulomb barrier. The more strongly confined $^{31}$Ar provides a useful comparison and illustrates the progressive suppression of halo observables with increasing binding and core charge.
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Nuclear Theory · Cross-listed from hep-ph

Quantum Computers will constrain the Equation of State of Neutron Stars

Adrián Castaño-García, Nahia J. Dios-Bilbao, J. J. Gálvez-Viruet et al. (+4 more)

The Equation of State (EoS) of Nuclear Matter at high densities, and particularly that of neutron stars, resists $\mathit{ab}$ $\mathit{initio}$ Quantum Chromodynamics (QCD) computations due to the notorious sign problem of Lattice Gauge Theory at finite chemical potential. A quantum computer deploying QCD in canonical quantization should be able to make substantial progress. We set some basic goals for a future quantum computer to predict the EoS, and thus the basic static observables of the star (mass, radius and Tidal deformability, for example). We then develop the basic theory to address the canonical Hamiltonian in Weyl (time-axial) gauge expressed in normal modes, together with the squared Gauss operator $\mathcal{G}^2$ necessary to execute energy minimization algorithms restricted to the physical Fock subspace. Finally, we deploy our particle-quantum register encoding of a generic field theory to demonstrate QCD at finite chemical potential for a few (three-four) particles with a modest number of momentum modes, by simulating the quantum computer on a classical cluster. This opens the possibility for effective quantum computers to constrain the microscopic physics of neutron stars simultaneously to the operation of third–generation gravitational wave detectors such as the Einstein Telescope, providing more detailed predictions than has been possible until now.
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All authors Adrián Castaño-García, Nahia J. Dios-Bilbao, J. J. Gálvez-Viruet, Felipe J. Llanes-Estrada, Marío Logrosán-Álvarez, Nicolás M. Arenaza, María Gómez-Rocha

Nuclear Theory

Reconstructability and directed flow of short-lived resonances in Au+Au collisions at 19.6 and 200 GeV

Junyi Han, Xialei Jiang, Hongcan Li et al. (+1 more)

We present a systematic study of the reconstructability and directed flow of hadronic resonances in Au+Au collisions within the UrQMD transport model. The main objective of this work is to investigate how the hadronic stage influences both resonance reconstructability and the final-state directed flow. A set of short-lived hadronic resonances, including $\rho^0$, $K^{*0}$, and $\Lambda(1520)$, is investigated to quantify their yields and reconstructable fractions as a function of charged-particle multiplicity, characterized by $(dN_{ch}/d\eta)^{1/3}$. We compare results at $\sqrt{s_{NN}} = 19.6$ and $200 ~\mathrm{GeV}$ to investigate possible energy-dependent differences in the reconstructability. Such differences reflect variations in the properties of the hadronic medium. The results are further examined as a function of resonance lifetime, revealing a clear ordering of reconstructability among different resonances. Overall, the reconstructability is found to be primarily governed by resonance lifetime. The directed-flow analysis reveals clear differences between resonances and their corresponding stable hadrons in mid-central collisions, while these differences become significantly weaker in peripheral collisions, highlighting the important role of hadronic evolution in shaping the final-state directed flow. These studies provide a unified picture of how the hadronic stage influences both resonance reconstructability and directed flow, offering new insights into resonance observables in relativistic heavy-ion collisions.
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All authors Junyi Han, Xialei Jiang, Hongcan Li, Yaping Wang

Nuclear Theory

Benchmarking electromagnetic observables in angular-momentum projected Hartree-Fock

Raul Bernal-Gonzalez and Calvin W. Johnson

We benchmark electromagnetic transitions and moments (electric quadrupole and magnetic dipole) in angular-momentum projected-after-variation Hartree-Fock calculations against full configuration-interaction diagonalization results in a shell model basis. For such a simple approximation we find reasonably good agreement, including for many odd-$A$ and odd-odd nuclides. As previous work on excitation spectra found, results are frequently improved in cases with shape coexistence. Here we considered select cases from the $sd$- and $pf$-valences spaces. While electric quadrupole moments and transitions are, as one might expect, frequently (though not always) well reproduced, especially in even-even nuclides, magnetic dipole moments and transitions are overall better than expected. This continues the benchmarking of projected Hartree-Fock as a simple yet effective alternative to full configuration-interaction as well as an underlying foundation for many other many-body methods.
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Nuclear Theory

Quark matter at finite temperature and proto-quark stars with the axion effects in SU(3) Nambu-Jona-Lasinio model

Peng-Cheng Chu, Jiao-Jiao Wang, Ke Liu et al. (+8 more)

We investigate the thermodynamical properties of strange quark matter (SQM) and proto-quark stars (PQSs) within the SU(3) Nambu-Jona-Lasinio (NJL) model at finite temperature, specifically incorporating the effects of axion fields and vector interactions. Our results demonstrate that these interactions significantly influence the equation of state (EoS), constituent quark masses, entropy density, and the maximum star mass of PQSs at the isentropic stages along the star evolution line. Furthermore, we reveal a distinct thermodynamic signature in the early evolution: the presence of trapped neutrinos leads to a substantial increase in electron number density while simultaneously suppressing the core temperature compared to the neutrino-free case. These findings may highlight the crucial role of the axion effects, flavor-dependent vector interactions, and particle composition in determining the observable properties of compact stars at finite temperature.
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All authors Peng-Cheng Chu, Jiao-Jiao Wang, Ke Liu, Peng Wu, Yu-Heng Liu, He Liu, Hong-Ming Liu, Xiao-Hua Li, Min Ju, Xu-Hao Wu, Ying Zhou

Nuclear Theory · Cross-listed from astro-ph.HE

The impact of nuclear equations of state on the dynamics and multi-messenger emission of magnetorotational stellar explosions

Andrea Celati, Matteo Bugli, Luca Del Zanna et al. (+2 more)

The gravitational collapse of massive stars at the end of their life leads to powerful supernova explosions that produce compact objects, regulate the dynamics of host galaxies, and contribute to cosmic chemical evolution. In the presence of fast rotation and strong magnetic fields, such explosions can reach extreme energies, explaining sources such as hypernovae and long gamma-ray bursts. We investigate the impact of variations in the nuclear equation of state (EoS) on magnetorotational explosions and their multimessenger emission, including neutrinos and gravitational waves. Differences in stiffness, composition, and finite-temperature behavior of the EoS affect the collapse, bounce, and jet-launching phases. Using the Aenus-Alcar code, which includes relativistic magnetohydrodynamics, two-moment neutrino transport, neutrino-matter interactions, and general-relativistic corrections, we perform axisymmetric simulations with different EoSs. All models start from the same pre-supernova progenitor with solar metallicity, a zero-age main sequence mass of 20 solar masses, a dipolar magnetic field, and a shellular rotation profile. The different EoSs produce significant variations in explosion dynamics, proto-neutron star properties, ejecta mass, and multimessenger signals. Our results show that magnetorotational core-collapse supernova signatures depend not only on the cold stiffness of the EoS, but also on its thermal and compositional properties, highlighting the importance of combining gravitational-wave and neutrino observations to constrain dense matter physics and the explosion mechanism.
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All authors Andrea Celati, Matteo Bugli, Luca Del Zanna, Marco Cusinato, Martin Obergaulinger

Nuclear Theory · Cross-listed from hep-lat

QCD Chiral Crossover Line from Lee-Yang Edge Singularities

Heng-Tong Ding, Swagato Mukherjee, Peter Petreczky et al. (+1 more)

We propose a universality-based reconstruction of the QCD chiral crossover line from Lee-Yang edge singularities in the complex baryon chemical potential plane. The framework maps lattice-extracted complex Lee-Yang-zero estimates, treated as proxies for edge singularities, to the universal chiral Lee-Yang edge and thereby determines the $\mu_B$ dependence of both the chiral critical line in the light-quark chiral limit and the pseudo-critical crossover line at physical quark masses. As an illustration, we apply the framework to Lee-Yang-zero estimates recently obtained by the Wuppertal-Budapest collaboration from high-statistics lattice QCD simulations. Without imposing the previously determined small-$\mu_B$ expansion of the crossover line as input, the reconstructed curvature is consistent with existing continuum lattice-QCD results at small $\mu_B$. The fitted chiral-limit transition temperature is also compatible with existing chiral-scaling analyses. These results demonstrate that lattice information on Lee-Yang singularities, combined with universal chiral scaling, provides a quantitatively consistent constraint on the QCD crossover line within the present temperature window and establishes a framework that can be systematically improved with future Lee-Yang-zero determinations.
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All authors Heng-Tong Ding, Swagato Mukherjee, Peter Petreczky, Kai-Fan Ye

Nuclear Theory · Cross-listed from nucl-ex

Three-baryon femtoscopy as an effective 3$\rightarrow$3 scattering experiment

ALICE Collaboration

Scattering experiments have long been the gold standard for constraining hadron$-$hadron interactions, providing direct information on the angular momentum and spin dependence over a wide range of kinematic configurations. However, experimental constraints on three-body dynamics remain limited, specifically for unbound systems and systems involving short-lived hadrons. In this work, the three-proton correlation function is measured in pp collisions at $\sqrt{s}=13.6$ TeV with ALICE at the LHC and presented as a novel approach to access hadronic interactions in three-body systems. A new analysis strategy is employed to isolate the p$-$p$-$p contribution to the correlation function by correcting for background channels and experimental effects, and enabling a direct comparison with state-of-the-art three-body continuum calculations. The extracted correlation function provides the first direct access to the isospin $3/2$ three-body system. The measured observable is found to be sensitive to the partial-wave structure of the nucleon$-$nucleon interaction and indicates that the nuclear interaction acts even at high angular momentum and parity states of the three-body system, revealing an effective long-range attractive component, observed experimentally for the first time in a three-proton continuum system. Hence, three-hadron femtoscopy emerges as an effective 3$\rightarrow$3 scattering experiment with three unbound hadrons in initial and final states. The copious production of hyperons at the modern high-energy colliders ensures the possibility of extending such measurements beyond nucleons, opening a new avenue for future precision studies of three-body dynamics in the strangeness sector.
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Nuclear Theory · Cross-listed from astro-ph.HE

Influence of effective mass of the relativistic mean field theory on core collapse supernovae and compact objects

Kohsuke Sumiyoshi, Hajime Togashi, Shun Furusawa et al. (+4 more)

We study the influence of the effective mass in the relativistic mean field (RMF) theory on the properties of the central core of collapse-driven supernovae and the formation of compact objects. Influence of the effective mass has been so far studied within the non-relativistic frameworks. In order to clarify the role of the effective mass in the relativistic frameworks, which is different from non-relativistic ones, we adopt the set of equation of state (EOS) tables using the parameterizations TM1e and TM1m, which have different effective masses but with the same saturation properties, in the RMF theory. We show that choices of the effective mass in supernova matter affect both the stiffness of the EOS through pressure and the thermodynamical behavior through temperature under the RMF frameworks. We explore differences in matter evolution with neutrino emissions by performing a set of numerical simulations of the gravitational collapse and bounce of massive stars and the cooling of the proto-neutron stars. The EOS with large effective mass leads to compact proto-neutron stars and early collapse to black holes with high densities and temperatures due to the softness. It leads to high energy neutrinos in long emission from the proto-neutron star cooling and in short burst from the black hole formation.
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All authors Kohsuke Sumiyoshi, Hajime Togashi, Shun Furusawa, Shuying Li, Hong Shen, Ken'ichiro Nakazato, Hideyuki Suzuki

Nuclear Theory · Cross-listed from physics.plasm-ph

Millisecond-Scale Neural Operator Surrogates for Double-Null Free-Boundary Grad-Shafranov Equilibria

Plamen G. Krastev

The Grad-Shafranov (GS) equation governs ideal magnetohydrodynamic equilibrium in tokamak plasmas. Free-boundary GS solvers are central to diverted-equilibrium modeling, but nonlinear Picard iteration introduces computational cost and sample-dependent latency that can become prohibitive in optimization, modeling, and control-oriented loops. Here we train a geometrically conditioned Fourier Neural Operator (FNO) to learn a constrained forward map from spatial coordinates, scalar operating parameters $(P_{\mathrm{axis}}, I_p, f_{\mathrm{vac}})$, and prescribed X-point locations to the poloidal-flux field $\psi(R,Z)$. The model is trained on a controlled family of constrained double-null free-boundary equilibria generated with FreeGS for a single fixed machine geometry and prescribed topology. The best model achieves a mean relative $L^2$ error of $0.05\%$, with test error following an empirical $N^{-0.68}$ power law over $N_{\mathrm{train}}\in\{500,1000,2000,5000\}$. It recovers both X-points to within $0.2$ cm and localizes the O-point to $0.03$ cm. As a physics-consistency diagnostic, the predicted fields satisfy an external finite-difference GS residual evaluation at the same level as the ground-truth fields, with mean normalized residual $2.29$, indistinguishable from the $2.29\pm0.06$ FreeGS baseline using the same diagnostic. The trained FNO evaluates one equilibrium in $2.77$ ms on GPU and $25.6$ ms on CPU, corresponding to speedups of ${\sim}640\times$ and ${\sim}69\times$ relative to FreeGS as configured here, with near-deterministic latency (p95/median $=1.01$). These results show that neural-operator surrogates can provide accurate, geometrically precise, millisecond-scale equilibrium evaluations for magnetic-confinement fusion workflows within a prescribed topology and machine geometry.
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Wednesday 5 August

Nuclear Theory · Cross-listed from physics.chem-ph

Ground-State Energy Estimation of HeH$^{+}$, ArH$^{+}$, and H$_2$O via Sample-Based Quantum Diagonalization

Jubin Park, Chae-Hyun Yoon, Minkyu Lee et al. (+1 more)

Accurate ground-state energies are essential for understanding molecular structure, chemical bonding, and reaction energetics in quantum chemistry. In this work, we investigate the ground-state properties of the molecular systems HeH$^+$, ArH$^+$, and H$_2$O using Sample-Based Quantum Diagonalization (SQD), a hybrid quantum-classical framework designed for near-term quantum devices. Unlike variational approaches such as VQE, which require deep parameterized circuits and repeated expectation-value measurements, SQD reconstructs a low-energy determinant subspace directly from measured bitstrings. For the present calculations, bitstrings were generated on IBM quantum hardware using shallow local unitary cluster Jastrow (LUCJ) circuits whose parameters were constructed from the $t_1$ and $t_2$ amplitudes of coupled-cluster singles and doubles (CCSD) calculations based on restricted Hartree–Fock (RHF) references. From these samples, we compute ground-state potential-energy curves of HeH$^+$, ArH$^+$, and H$_2$O with the 6-31G and cc-pVDZ basis sets. For all three systems, the SQD results obtained with the cc-pVDZ basis closely follow the corresponding same-basis CCSD energies and reproduce the equilibrium-region trends of the potential-energy curves. HeH$^+$ and ArH$^+$ were chosen as simple yet astrophysically important molecular-ion benchmarks, while H$_2$O was included as a representative polyatomic molecule to assess the applicability of SQD beyond diatomic ionic systems. At the adopted equilibrium geometries, the deviations from the same-active-space CASCI references are 0.00, 2.51, and 6.34 mHa for HeH$^+$, ArH$^+$, and H$_2$O, respectively. These results demonstrate the feasibility of hardware-assisted SQD for the present benchmark systems and motivate further studies of its accuracy and computational scaling for larger molecular active spaces.
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All authors Jubin Park, Chae-Hyun Yoon, Minkyu Lee, Myung-Ki Cheoun

Nuclear Theory

TITAN mass measurements of neutron-rich Cs, Ba and r-process lanthanide abundances

T.-H. Yeh, J.D. Cardona, Y. Wang et al. (+26 more)

We present measurements for the masses of five neutron-rich isotopes, $^{149-151}$Cs and $^{151, 152}$Ba, probed for the first time by TITAN at TRIUMF with time-of-flight measurement techniques. We propagate these masses to the nuclear reaction and decay data required for the simulation of the rapid neutron capture process (r-process) nucleosynthesis in neutron star mergers. We show that these neutron-rich masses affect the abundance predictions near mass number $A\sim148-152$ corresponding to lanthanide element abundances at $Z=60,\,62$ and $63$. We demonstrate that these new TITAN masses smooth out the odd-even effect in isotopic abundance predictions near $A\sim150$ in both fission cycling astrophysical conditions and conditions that do not reach actinides. We further show that these new masses adjust how fission fragments settle into place when forming the final abundances, and consider the effect on comparisons with stellar abundance ratios such as [Ag/Eu], [Sm/Eu], and [Nd/Eu].
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All authors T.-H. Yeh, J.D. Cardona, Y. Wang, J. Ash, B. Ashrafkhani, I. Belosovic, J. Bergmann, E. Dunling, L. Egoriti, G. Gelinas, G. Gwinner, Z. Hockenbery, C. Izzo, A. Jacobs, S. Kakkar, B. Kootte, E. M. Lykiardopoulou, T. Murbock, A. Mollaebrahimi, A. Ridley, S. F. Paul, W. S. Porter, M. P. Reiter, J. Ringuette, R. Simpson, C. Walls, M. R. Mumpower, N. Vassh, A.A. Kwiatkowski

Nuclear Theory · Cross-listed from hep-ph

Photon-nucleon entanglement in Compton scattering at low and high energies

Yoshitaka Hatta and Víctor Martínez-Fernández

We study spin-spin entanglement in the final state photon-nucleon system in Compton scattering, both at low energy below the pion threshold and at high energy in perturbative QCD to next-to-leading order. We first establish a no-go theorem showing that, for any spin-$\frac{1}{2}$ target, entanglement cannot be generated in unpolarized Compton scattering if the scattering amplitudes are real. We then consider polarized Compton scattering off the electron, the proton and the neutron. At low energy, we uncover a rich variety of maximally entangled Bell states and their unitary equivalents realized across different regions of the kinematic plane. Interestingly, the proton and neutron targets exhibit distinct patterns of entanglement. In the neutron case, the electric and magnetic polarizabilities dramatically influence the pattern and even the existence of entanglement. This suggests that entanglement can serve as a novel tool for investigating the detailed electromagnetic properties of the nucleons.
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Nuclear Theory · Cross-listed from nucl-ex

First Results on Nucleon Resonance Electroexcitation Amplitudes from $ep \to e'\pi^+\pi^-p'$ Cross Sections at $W$ from $1.56-1.76$ GeV and $Q^2$ from $2.0-5.0$ GeV$^2$

V.I.Mokeev, P.Achenbach, V.D.Burkert et al. (+6 more)

The first results on the electroexcitation amplitudes or the $\gamma_vpN^*$ electrocouplings for nucleon resonances ($N^*$s) in the third resonance region are presented. They were obtained from $\pi^+\pi^-p$ electroproduction differential cross sections measured with the CLAS detector and analyzed using the Jefferson Lab-Moscow State University (JM) reaction model. The analysis covers the invariant mass range of the final-state hadrons $W$ from 1.56 to 1.76~GeV and virtual photon four-momentum squared $Q^2$ from 2.0 to 5.0~GeV$^2$. Consistent results on the electroexcitation amplitudes of the $N(1675)5/2^-$ and $N(1680)5/2^+$ obtained from independent analyses of both $\pi N$ and $\pi^+\pi^-p$ final states, demonstrate the capability of reaction models to extract the $\gamma_v p N^*$ electrocouplings for $N^*$s in the third resonance region. Also, for the first time, the electrocouplings of the $\Delta(1700)3/2^-$ and $N(1720)3/2^+$, which predominantly decay into $\pi\pi N$ final states, have become available for $Q^2 > 2.0$~GeV$^2$. Finally, contributions from a new $N'(1720)3/2^+$ baryon state to the $\pi^+\pi^-p$ differential cross sections have been observed for $Q^2 < 5.0$~GeV$^2$. The new results on resonance electrocouplings in the third resonance region offer new opportunities to explore various aspects of the strong QCD regime responsible for the generation of nucleon excited states, in particular, shedding light on the emergence of hadron mass in connection with dynamical chiral symmetry breaking.
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All authors V.I.Mokeev, P.Achenbach, V.D.Burkert, D.S.Carman, R.W.Gothe, E.L.Isupov, K.Joo, K.Neupane, Y.Wunderlich

Nuclear Theory · Cross-listed from astro-ph.HE

Bayesian Inference of fine-features of dense matter EOS from future high-precision data of neutron star radii

Bao-An Li, Xavier Grundler, Wen-Jie Xie et al. (+1 more)

Future high-precision X-ray and gravitational wave observatories are expected to measure the radii of neutron stars (NSs) with an accuracy better than about 0.1 km. However, it remains unclear what particular aspects of the Equation of State (EOS) and to what precision they will be better constrained. Within a Bayesian framework using a meta-model EOS and mock high-precision NS data, the posterior probability distribution functions (PDFs) of NS matter EOS parameters for both hadronic and quark phases and the transition between them were recently studied. We report here a few highlights of these studies.
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All authors Bao-An Li, Xavier Grundler, Wen-Jie Xie, Nai-Bo Zhang

Nuclear Theory · Cross-listed from math.NA

A commutant gate for spectral fitting through symmetry forced degeneracy

Stelios Savva

Learned spectral models fail at symmetry forced degenerate sectors for two distinct reasons. Where symmetry forces levels to coincide exactly, the per level observable one would normally fit is not well defined, since every unit vector of that shared space is an eigenvector; and near a symmetry protected crossing, the eigenvector observable gradient carries a factor 1/(lambda_i - lambda_j) that is genuinely singular as the gap closes. The usual response is to regularize the divergence or threshold the gap, and both carry a real cost: a fixed gap cannot both protect a forced multiplet and keep two genuinely distinct levels apart. We show a different fix, on synthetic operator families with a known symmetry answer key. A gate reads the symmetry structure directly from the observed operators, as the linear commutant of the family, one singular value decomposition nullspace, following the simultaneous block diagonalization of Maehara and Murota. Block identity is read from the centre of that commutant rather than from eigenvalue clustering, which makes the forced versus accidental distinction structural rather than metric, and the objective switches between a projector trace through forced blocks and a per level target elsewhere. Under operator estimation noise the gate classifies correctly to epsilon of about 0.3, where energy clustering already fails by 0.02. Gated fitting reaches the truth at machine precision in both the symmetric and the symmetry breaking regime, in the latter converging to a truth that is a singularity of the ungated objective, and observable bias sits at the noise floor. Validation off the regular representation, where multiplicity and dimension separate, eliminated two defective estimators that all regular representation tests had passed. The demonstrated object is a gated estimator; a full parametric matrix model, with the matrices learned, is the next experiment.
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Nuclear Theory · Cross-listed from hep-ph

Separating Equation-of-State Dynamics from Hadronic Rescattering in Low-Mass Dileptons

Apiwit Kittiratpattana, Ayut Limphirat, Yupeng Yan et al. (+1 more)

We investigate low-mass dilepton emission as a probe of the QCD equation of state and phase structure within non-equilibrium chiral fluid dynamics, comparing first-order phase-transition and crossover scenarios at $\sqrt{s_{\rm NN}}=2.20-6.20$~GeV. To disentangle effects of the macroscopic equation-of-state dynamics from conventional hadronic in-medium modifications, the $\rho$ and $\omega$ meson self-energies are calculated from the same resonance-driven forward-scattering amplitudes in both scenarios. We find two temporally distinct signatures of the first-order phase transition: an early enhancement in the vector-meson pole region associated with the non-equilibrium evolution through the phase transition, and a later enhancement of the low-mass continuum driven by reheating and the prolonged fireball evolution. Both effects survive integration over the complete space-time evolution, with the pole-mass region retaining the strongest sensitivity to the phase structure. Across the investigated beam energies, the pole-mass excitation function retains a pronounced sensitivity to first-order transition dynamics at low collision energies, identifying this mass region as a promising target for future dilepton beam-energy scans.
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All authors Apiwit Kittiratpattana, Ayut Limphirat, Yupeng Yan, Christoph Herold

Nuclear Theory · Cross-listed from nucl-ex

Directed Flow of Protons and Deuterons in Xe+Cs(I) Collisions: Preliminary BM@N Data and THESEUS Modeling

M. E. Kozhevnikova, M. V. Mamaev, I. A. Zhavoronkova et al. (+2 more)

Preliminary BM@N results on the directed flow ($v_1$) of protons and deuterons in Xe+Cs(I) collisions at 3.8$A$ GeV are presented for the 10-40% centrality interval. The measured rapidity dependence of $v_1$ is compared with calculations from the THESEUS event generator, where deuterons are produced thermodynamically on an equal basis with hadrons using a late freeze-out scenario. While THESEUS well describes the proton $v_1$ data, it shows a slight but systematic overestimation of the deuteron flow at low and intermediate rapidities. This comparison tests both the collective dynamics of baryon-rich matter and the thermodynamic mechanism of light-nucleus formation at Nuclotron energies.
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All authors M. E. Kozhevnikova, M. V. Mamaev, I. A. Zhavoronkova, A. V. Taranenko, Yu. B. Ivanov

Nuclear Theory · Cross-listed from hep-ph

A large size of the pion-like excitations in the stringy fluid above $T_{ch}$ is model independent and required by current algebra

L. Ya. Glozman

Multiple lattice evidences support the existence of a confining but chirally symmetric stringy fluid regime of QCD above the chiral symmetry restoration temperature at T_{ch} ~ 155 MeV. This regime is characterized by an approximate chiral spin symmetry and its extensions which means that the propagating excitations represent the chirally symmetric quarks connected into color singlets by the chromoelectric string. Clear \pi,\pi' peaks above T_{ch} were extracted on the lattice from the spatial and temporal correlators, which become broader with temperature and disappear roughly at $3T_{ch}$. The meson-like excitations above T_{ch} were studied within the manifestly confining and chirally symmetric model. It has been demonstrated that the chiral symmetry restoration in the confining regime happens because of Pauli blocking of the levels, required for the existence of the quark condensate, by the thermal quark excitation. The same Pauli blocking leads to a huge swelling of the low-spin mesons above T_{ch} which become infinitely large in the chiral limit. This property should be crucial for the explanation of the high collectivity and a very small mean-free path of the constituents above $T_{ch}$ seen experimentally. Here we demonstrate that the swelling of pions above T_{ch} is a model-independent effect required by current algebra.
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Nuclear Theory · Cross-listed from quant-ph

State-resolved quantum-information fingerprints of partial dynamical symmetry in the interacting boson model

Dhritimalya Roy

Partial dynamical symmetry (PDS) is an algebraic structure in which a symmetry is neither exact nor fully broken: a subset of eigenstates keeps good quantum numbers and stays solvable while the rest mix. It is currently identified from spectroscopy. We ask whether it also leaves a purely structural mark in the eigenstates, and find, for the $sd$-IBM Hamiltonians studied here, that it does, though not in the magnitude of entanglement. The diagnostic is the variance of a symmetry Casimir, the label variance $\Var\,\C[G]$, which shares its zero with a block-coherence entropy and a block impurity: all three vanish when a state occupies a single Casimir sector, a single irreducible representation once conjugate representations are resolved by the cubic Casimir. Resolved state by state, the variance is numerically zero on the symmetry-selected subset and large on the mixed states, isolating the PDS states from the wavefunctions alone; the separation does not close as the boson number grows and persists at Leviatan's first- and second-order critical points, whereas the magnitude of bipartite $s|d$ entanglement does not separate the two families. We anchor the analysis in $^{168}$Er, reproducing Leviatan's fitted $\su3$ admixtures and his Hamiltonian-parameter-independent $\gamma\!\to\! g$ $B(E2)$ ratios. The diagnostic also has an exact dynamical form, a Casimir Loschmidt echo rigid on the symmetry-pure states, and we demonstrate its readout on an IBM superconducting processor at $N=3$, where a single solvable/mixed exemplar reproduces the predicted pattern within finite-shot uncertainties.
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Tuesday 4 August

Nuclear Theory · Cross-listed from hep-ph

Direct versus resolved photons in DPS in photoproduction on proton and nuclei

B. Blok and R. Segev

We study the process of double parton scattering (DPS) associated with the photoproduction at a future Electron-Ion collider (EIC) and HERA. We show that in the case of the resolved photon the 1 to 2 processes lead, even at small transverse momenta of the hard processes , to the increase of the DPS by a factor of order 1.6 in the significant part of the phase space, relative to the predictions of the mean field based models . Moreover we study the kinematic region where direct photon contribution is dominant and show it s boundaries for charm and light quark jets. For charmed jets we see that the relevant region is $x_\gamma\ge 0.2-0.4$. This region is even enhanced if we consider the photoproduction on the nuclei.
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Nuclear Theory · Cross-listed from hep-ph

Quarkoniumlike states above open-flavor thresholds in Born-Oppenheimer EFT

Nora Brambilla, Roberto Bruschini, Abhishek Mohapatra et al. (+2 more)

Many quarkoniumlike states have been observed above open-flavor thresholds, but their organization and internal structure remain unsettled. We study the isoscalar hidden-charm and hidden-bottom sectors in Born–Oppenheimer effective field theory (BOEFT), between the spin–isospin averaged $S+S$ and $S+P$ thresholds. At leading order, heavy-quark spin decouples, and the quarkonium static potential mixes through string breaking with the lowest tetraquark/open-flavor BO potentials of the same quantum numbers. These potentials are constrained by QCD symmetries, their short- and long-distance behavior, and lattice-QCD data. The only calibrated parameter is the lowest $1^{--}$ adjoint meson mass, fixed from the shallow multiplet associated with the $\chi_{c1}(3872)$. Using $T$-matrix, $K$-matrix, and complex-scaling methods, we determine bound states and resonance poles, their masses, pole widths from the included nonstrange $S+S$ channels, normalized pole couplings, and prescription-dependent quarkonium–open-flavor composition measures. Uncoupled hybrid BOEFT multiplets are included as reference levels. The spectrum exhibits a common heavy-quark-spin-symmetry multiplet organization. Most poles are predominantly quarkonium resonances localized at short distances, with the largest open-flavor components closest to threshold. The same equations also generate shallow, spatially extended, open-flavor-dominated states with molecular long-distance characteristics. Their binding energies, radii, and small quarkonium components are highly sensitive to the adjoint meson mass, whereas the higher spectrum is more stable. Together with the hybrid reference levels, the spectrum provides multiplet assignments for most candidates. States not naturally accommodated point to the need for hidden-strange and $S+P$ tetraquark/open-flavor BO sectors and for hybrid–tetraquark and hybrid–quarkonium mixings.
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All authors Nora Brambilla, Roberto Bruschini, Abhishek Mohapatra, Fang-Zheng Peng, Tommaso Scirpa

Nuclear Theory

Local Spin Polarization in Anisotropic Gubser Flow: Suppression Mechanism and Formulation Dependence

Kenji Fukushima, Shi Pu and Dong-Lin Wang

We analytically study the longitudinal spin polarization in relativistic heavy-ion collisions using a perturbed Gubser flow solution. In the large-system-size limit, we derive analytical expression of the local spin polarization along the beam direction. In our treatment, the contributions from thermal vorticity and thermal shear are of comparable magnitudes. The thermal vorticity yields the polarization with a sign opposite to that observed experimentally, while the thermal shear counteracts this effect, helping recover the desired sign. We find that the choice of the reference unit vector aligned with the fluid velocity gives the experimentally observed sign only at low transverse momenta, whereas another formulation with the unit vector fixed along the laboratory time direction yields the desired sign for a wide range of transverse momenta. Notably, a recent formulation with the unit vector normal to the freeze-out hypersurface exhibits an exact cancellation between contributions from thermal vorticity and thermal shear at leading order in the large-system-size limit. We identify a general cancellation pattern with acceleration dominance, which is manifest particularly in the latter two formulations. Thus, the total polarization originates from non-acceleration effects, which need not be substantial even when the elliptic flow is finite, as clearly demonstrated in our analytical results. For comparison, we also discuss the spin polarization in the Hubble flow with rotation.
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Nuclear Theory · Cross-listed from nucl-ex

Statistical and non-statistical $\gamma$-decay properties of $^{64}$Zn

A. C. Larsen, M. Guttormsen, T. K. Eriksen et al. (+23 more)

We present a study on the $\gamma$-decay properties of $^{64}$Zn using the Oslo method on $^{64}$Zn($p,p^\prime \gamma$) data combined with $^{64}$Zn$(\gamma,n)$ cross-section measurements at the NewSUBARU facility. With the Oslo method, we have measured the $\gamma$-ray strength function ($\gamma$SF) and the nuclear level density (NLD) below the neutron threshold. We observe that the NLD trend in the quasi-continuum region of $^{64}$Zn is best characterized by a constant-temperature-like model. %with temperature parameter $T_{\rm CT}=1.21(5)$ MeV. Surprisingly, we find that $\gamma$-ray transitions from the quasi-continuum decaying directly to the $0^+$ ground state seem to be strongly hindered with a hindrance factor of $\kappa \approx 0.5$, which could be an indication of non-statistical effects in the ground-state decay due to, e.g., differences in nuclear shapes. For $\gamma$ energies above the neutron separation energy, the NewSUBARU ($\gamma, n$) data set probes a significant part of the giant dipole resonance. Furthermore, we find that the Oslo-method $\gamma$SF shows a rather smooth behavior, with a clear low-energy enhancement (LEE) for $E_{\gamma} < 4$ MeV.
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All authors A. C. Larsen, M. Guttormsen, T. K. Eriksen, G. M. Tveten, H. Utsunomiya, J. K. Dahl, N. Shimizu, T. Ari-izumi, F. L. Bello Garrote, L. T. Bell, M. M. Bjørøen, F. W. Furmyr, D. Gjestvang, A. Görgen, V. W. Ingeberg, K. C. W. Li, E. Lima, M. Markova, E. F. Matthews, A. H. Mjøs, S. Miyamoto, V. Modamio, T. Renstrøm, E. Sahin, S. Siem, M. Wiedeking

Nuclear Theory

Constructing Effective Interactions via Projection-Based Inversion

Hang Yu, Serdar Elhatisari, Sebastian König et al. (+3 more)

We present a numerical prescription for extracting continuum scattering information from discrete spectra by constraining effective interactions inspired by effective field theory (EFT). Using a Multiparameter Eigenvalue Problem (MEP) emulator, we map energies to a sum of contact potentials by recasting the inverse problem as a linear eigenvalue equation. Because our method determines the effective interaction rather than the scattering amplitude, it can handle non-perturbative Coulomb interactions and different types of truncated Hilbert spaces without analytic quantization conditions. It therefore allows standard bound-state codes to be used for scattering calculations without modification. We validate this prescription across multiple ab initio frameworks using neutron-alpha scattering, alpha-alpha scattering with full Coulomb, and a prediction of proton-$^{14}$O resonances.
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All authors Hang Yu, Serdar Elhatisari, Sebastian König, Dean Lee, Yuan-Zhuo Ma, Takayuki Miyagi

Nuclear Theory

Finite-spectrum Lorentz integral transform calculation of the $^{4}$He photoabsorption cross section in the no-core shell model

P. Yin, H. T. Zhao, C. Y. Zhai et al. (+11 more)

We develop and validate a finite-spectrum implementation of the Lorentz integral transform (LIT) within the ab initio no-core shell model (NCSM) for calculating the photoabsorption cross section of $^4$He. A large set of $1^-$ eigenstates is explicitly calculated in the NCSM, and the LIT is constructed from their excitation energies and the corresponding $E1$ transition strengths. This finite-spectrum approach is complementary to conventional inhomogeneous-equation and Lanczos-based implementations of the LIT method for photoabsorption cross sections. Using the Daejeon16 interaction, we extract the photoabsorption cross section and examine its stability with respect to the model-space truncation, excitation-energy cutoff, and LIT parameters. The reliability of the finite-spectrum extraction is assessed by comparing the $E1$ polarizability and bremsstrahlung sum rule obtained from the discrete NCSM spectrum with the same quantities obtained by integrating the extracted cross section. The extracted cross section captures the principal features of the available $^4$He photonuclear data in the giant-dipole-resonance region and is consistent, in the low-energy rise and main-peak region, with earlier chiral-interaction NCSM-LIT results obtained from Lanczos-based evaluations, while the present calculation with the Daejeon16 interaction exhibits a more pronounced high-energy shoulder. The present work provides a controlled finite-spectrum NCSM-LIT route from explicitly calculated many-body eigenstates and transition strengths to photoabsorption cross sections.
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All authors P. Yin, H. T. Zhao, C. Y. Zhai, J. P. Vary, H. Li, J. M. Dong, H. J. Ong, X. Zhao, P. J. Fasano, A. M. Shirokov, J. Chen, D. Y. Tao, B. Zhou, C. Ji

Nuclear Theory

Microscopic Statistical Calculation of Nuclear Level Density Based on Relativistic Density Functional Theory

Zi-Cheng Wang, Peng-Xiang Du, Jian Li et al. (+2 more)

A microscopic statistical model based on the relativistic density functional theory (RDFT) is developed to calculate the nuclear level density (NLD). The approach employs self-consistent single-particle levels obtained from RDFT as input, incorporates pairing correlations within a finite-temperature Bardeen-Cooper-Schrieffer (BCS) theory, and accounts for rotational and vibrational collective enhancement effects. The spin cut-off parameter is calculated from the single-particle levels, thereby naturally retaining the shell effects and the structural characteristics of different nuclei. Using the shape-coexisting nucleus 98Sr as a representative example, the microscopic origin of the deformation effect on the NLD is investigated. In addition, the calculated NLDs are systematically compared with those from various phenomenological and microscopic models, as well as with available experimental data. The results indicate that although certain discrepancies exist among different models, they exhibit consistent overall evolutionary trends. Meanwhile, the RDFT-based microscopic statistical approach is capable of providing a reasonable description of the experimental NLDs as well as the s- and p-wave neutron resonance spacings.
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All authors Zi-Cheng Wang, Peng-Xiang Du, Jian Li, T. M. Shneidman, Shan-Gui Zhou

Nuclear Theory · Cross-listed from hep-ph

On the nature of fully-charmed four-quark exotic state $X(6900)$ from its photoproduction off nuclei

E. Ya. Paryev

The possibility to study the nature of fully-charmed tetraquark state $X(6900)$ from its inclusive photoproduction off nuclei near the kinematic threshold is investigated within the collision model based on the nuclear spectral function. The model accounts for $X(6900)$ production in direct photon–nucleon interactions as well as three different scenarios for its internal structure: compact tetraquark, molecule of the two hidden-charm $J/\psi$ and $\psi(3770)$ mesons and the mixture of both of them. We calculate within these scenarios the absolute and relative excitation functions on $^{12}$C and $^{184}$W nuclei at near-threshold photon energies of 30–40 GeV, the absolute momentum differential cross sections and ratios of them for the $X(6900)$ meson production off these target nuclei at laboratory polar angles of 0$^{\circ}$–5$^{\circ}$ and for photon energy of 35 GeV as well as the A-dependences of its transparency ratios at photon energy of 35 GeV. We show that these observables reveal a definite sensitivity to the $X(6900)$ intrinsic structure. Therefore, they might be useful for the determination of this structure from the comparison of them with the experimental data from the future experiments at the upcoming experimental facilities, such as the planned electron-ion colliders in the United States and China.
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Nuclear Theory · Cross-listed from hep-ph

Faddeev equations for the $J/\psi\,NN$ and $\phi\,NN$ three-body systems in momentum space

Xu Zhang

We construct Faddeev equations for the $J/\psi\,NN$ and $\phi\,NN$ three-body systems in momentum space. The two-body subsystem $t$-matrix is obtained by solving the Lippmann-Schwinger equations. The $NN$ interactions are constructed using the Malfliet-Tjon potential. The $J/\psi\,N$ interaction potentials in the ${}^4S_{3/2}$ and ${}^2S_{1/2}$ channels are taken from HAL QCD. The $\phi\,N$ interaction potential in the ${}^4S_{3/2}$ channel is also taken from HAL QCD. The ${}^2S_{1/2}$ $\phi N$ interaction is obtained from the combination of the $\phi p$ correlation function analysis and the HAL QCD results, as well as from the assumption that the spin-spin parts of the $\phi N$ and $J/\psi N$ interactions are inversely proportional to the respective hadron masses. The Faddeev equations are solved to find bound states in the $J/\psi\,NN$ and $\phi\,NN$ three-body systems. The numerical results suggest that there exist bound states in the $\phi\,NN$ three-body system, while there is no bound state in the $J/\psi\,NN$ system.
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Nuclear Theory

Does strange meson condensation reduce the moment of inertia of massive proto neutron stars? insights at S = 1 and YL = 0.4

Nie-Cheng Jian and Xian-Feng Zhao

We investigate the effects of strange mesons (sigma-star and phi) on the structural and rotational properties of massive proto neutron stars (PNSs) within the relativistic mean-field (RMF) framework. Using the TW99 parametrization with entropy per baryon S=1 and lepton fraction YL=0.4, we solve the TOV equations and compute the moment of inertia via the Hartle-Thorne approximation. Among eight parametrizations, TW99 is chosen as it gives the largest maximum mass. Our results show that strange mesons soften the equation of state at high densities, reducing both the maximum mass and radius. The moment of inertia peaks at a lower central density than the maximum mass, and strange mesons shift this peak toward higher densities while slightly lowering its value. The relative change in I is negligible for PNSs below 2.1 solar mass, but decreases to about -0.6 at 2.7 solar mass, indicating that strangeness effects are most relevant for the most massive stars. Our findings provide useful constraints on the rotational evolution of massive PNSs and their potential gravitational-wave signatures.
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