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Physics Nuclear Theory

nucl-th Watch Nuclear Theory

Wednesday 30 September

Nuclear Theory · Cross-listed from hep-ph

Glueballs and fractional anomalous determinants at nonzero $\theta$, and the decays of the X(2370)

Francesco Giacosa, Shahriyar Jafarzade, Győző Kovács et al. (+3 more)

Using fractional anomalous determinants, we construct a model of the trace and axial anomalies of a $SU(3)$ gauge theory at nonzero $\theta$ angle through the couplings to scalar and pseudoscalar glueballs. In the pure gauge theory, we reproduce the $\theta$ dependence of the vacuum energy and the scalar-glueball mass from the lattice, and estimate the jump in the topological charge density for the first-order transition at $\theta = \pi$. In QCD, the coupling of a pseudoscalar glueball to fractional anomalous determinants describes all of the four three-pseudoscalar decay channels of the $0^{-+}$ glueball candidate $X(2370)$ measured by the BESIII collaboration. Measuring the decay rates for $\eta \eta \eta$ and $\eta \eta \eta'$ can provide a stringent test of the model.
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All authors Francesco Giacosa, Shahriyar Jafarzade, Győző Kovács, Péter Kovács, Robert D. Pisarski, Fabian Rennecke

Nuclear Theory · Cross-listed from hep-ph

Fractional anomalous determinants and the chiral phase transition

Robert D. Pisarski

At high temperature instantons form a dilute gas, so in QCD-like theories the breaking of the anomalous $U(1)_A$ symmetry is given by integral powers of the anomalous determinant, $\sim (\det \Phi)^{Q}$, where $\Phi\sim \overline{q}_L q_R$ is bilinear in the quark fields, and with untwisted boundary conditions, the topological charge, $Q$, is an integer. A syncretic model is constructed, which is manifestly "beyond Landau". In the chiral limit, at temperatures above the chiral phase transition, $T > T_\chi$, only integral powers of the anomalous determinant appear. Below $T_\chi$, following 't Hooft et al. I assume that the topological charge $Q$ is fractional, as an integer times $1/N_c$, where $N_c$ is the number of colors. I suggest that consequently, fractional powers of the anomalous determinant appear in the chiral effective Lagrangian. For $N_f$ degenerate flavors, this generalizes the Witten-Veneziano term, valid for small $N_f/N_c$, to arbitrary $N_f/N_c$. In this model the chiral phase transition is generically of second order. The two exceptions are for one flavor, where it is probably crossover, and three flavors, where it could well be weakly first order. This can be tested in lattice QCD with $2+1$ flavors by comparing the (known) temperature dependence of the difference of the $\pi^a$ and $a_0^a$ propagators, to the chiral condensate of the strange quark, between $T_\chi$ and $\sim 2 \, T_\chi$. Analogous measurements are possible for one to four degenerate flavors about $T_\chi$. Lastly, I propose an operator for baryon number in the symmetric phase.
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Nuclear Theory

Searching for the QCD critical point with relativistic viscous hydrodynamics

Kevin P. Pala, Surkhab K. Virk, Isabella Danhoni et al. (+3 more)

With the STAR's Beam Energy Scan II, a rich amount of data exists to search for the QCD critical point. However, a central challenge is that the critical point cannot be directly extracted from data but rather is probed dynamically in an expanding, cooling system that may be far-from-equilibrium. In this talk, we show the latest results from equations of state with a movable critical point generated by the MUSES collaboration, run in the 3+1D relativistic viscous hydrodynamics code CCAKE. We discuss numerical improvements to CCAKE that include “glass” initial conditions and adaptive smoothed particle hydrodynamics, allowing us to rapidly and accurately obtain numerical solutions to the hydrodynamic equations of motion. We can quantify the interplay between beam energy, location of the critical point, and rapidity range.
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All authors Kevin P. Pala, Surkhab K. Virk, Isabella Danhoni, Fernando Gardim, Christopher Plumberg, Jacquelyn Noronha-Hostler

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

Nuclear moments, charge radii, and magnetization distribution parameters of Ag isotopes from laser spectroscopy and ab initio electronic-structure calculations

Leonid V. Skripnikov, Bram van den Borne, Michail Athanasakis-Kaklamanakis et al. (+2 more)

The nuclear electromagnetic moments and mean-square charge radii of several silver (Ag) isotopes deduced from recent laser spectroscopy studies in the mass region $A=$ 96-121 are determined using high-accuracy electronic structure calculations performed in this work. We report hyperfine structure and isotope-shift atomic factors calculated with the relativistic coupled cluster approach, including single, double, triple, and perturbative quadruple excitations, CCSDT(Q). Following a systematic theoretical uncertainty analysis, we show that at the precision now achieved (sub-percent uncertainties in some cases), quantum electrodynamic effects become significant. We also show that the isotope-dependent effect in the hyperfine structure due to the non-point-like nuclear magnetization distribution can be extracted with negligible dependence on the assumed nuclear magnetization model at the present level of precision. This also yields a nuclear magnetic dipole moment that is corrected for the hyperfine anomaly induced by the Bohr-Weisskopf effect. In terms of the nuclear electric quadrupole moments, the uncertainty in the electric-field gradient used to extract the quadrupole moments from laser spectroscopy has also been reduced by one to two orders of magnitude relative to values used in previous studies. Finally, the nuclear charge radii of Ag isotopes are extracted using field- and mass-shift factors from our coupled cluster calculations, and the difference in mean-square charge radii between $^{107,109}$Ag agrees with the value deduced from muonic X-ray spectroscopy.
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All authors Leonid V. Skripnikov, Bram van den Borne, Michail Athanasakis-Kaklamanakis, Gleb Penyazkov, Ruben P. de Groote

Nuclear Theory

Comparison of chisquare variants for Poisson-distributed data and ratios

Mate Csanad, Yan Huang, Daniel Kincses et al. (+2 more)

Fits to binned, Poisson-distributed data are common in high-energy and heavy-ion physics, and they are particularly delicate in correlation function measurements, where the fitted observable is the ratio of two histograms. We compare several goodness-of-fit estimators on large toy data sets: the Neyman and Pearson $\chi^2$, their Yates continuity-corrected versions, a Neyman $\chi^2$ with the variance shifted by $1/2$, the Poisson log-likelihood, and the correlation function likelihood in which both the signal and the reference histogram are treated as Poisson distributed. For a single histogram with mean occupancy $\lambda$, the Neyman $\chi^2$ underestimates the bin content by approximately one count, while the Pearson $\chi^2$ overestimates it by approximately half a count; shifting the variance by $1/2$ changes the Neyman result only at order $1/\lambda$, and only the log-likelihood recovers the mean without bias. For the ratio of two histograms, Neyman-type estimators are biased by approximately $-3/\lambda$ in relative terms (3% at $\lambda=100$), whereas the Pearson and likelihood-based fits are unbiased in the symmetric configuration studied here. The Yates correction leaves the fitted values essentially unchanged but systematically deflates the $\chi^2$, resulting in unrealistically high confidence levels. Simple analytic expressions are derived that reproduce all observed biases. Since these biases do not decrease with the number of bins, whereas the statistical uncertainties do, they can dominate the uncertainty of high-statistics, finely binned measurements. We therefore recommend likelihood-based fits, in particular the correlation function likelihood, for femtoscopic and similar ratio analyses.
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All authors Mate Csanad, Yan Huang, Daniel Kincses, Marton I. Nagy, Barnabas Porfy

Nuclear Theory

N = 32 Shell Evolution in Calcium Isotopes: Evidence from Macroscopic to Microscopic Models

A. Anupam, C. Dash, Yashraj et al. (+2 more)

The well-established N=32 subshell closure in calcium serves as an important benchmark for nuclear structure evolution toward neutron-rich nuclei. Recent charge-radius measurements of potassium isotopes [Nat. Phys. 17, 439-443 (2021)] reveal no corresponding signature of enhanced stability at the same neutron number. Motivated by this discrepancy, we investigate the structural evolution of even-even Ca isotopes from N=22 to 36 using macroscopic, relativistic mean-field (RMF), and large-scale shell-model approaches, with the KB3G, GXPF1A, GXPF1B, and FPD6 interactions in the KSHELL framework. The macroscopic analysis, evaluated against seven theoretical frameworks and NNDC data, reveals a coherent change in neutron structure at N=32, most clearly in the shell-gap energy $\Delta E$ and the three-point binding-energy filter, corroborated by the charge-radius filter. The RMF spectrum with NL3* shows a clear $\nu2p_{3/2}$-$\nu2p_{1/2}$ separation consistent with this signature. KB3G and FPD6 reproduce the N=32 enhancement of $E(2_1^+)$ and reduction of $R_{4/2}$, whereas GXPF1A and GXPF1B give a weaker N=32 signature than N=34 signature, the reverse of the experimental pattern, showing that the two subshells depend differently on the monopole interaction. The deformation parameter and B(E2) values have been obtained with above four interactions and are in good agreement with the experimental results.
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All authors A. Anupam, C. Dash, Yashraj, R. P. Singh, B. B. Sahu

Nuclear Theory · Cross-listed from hep-ph

Electromagnetic probes of concurrent minijet-hydrodynamics evolution

Soham Banerjee, Mayank Singh, Charles Gale et al. (+3 more)

We investigate direct photon and dilepton production in a concurrent minijet-hydrodynamics framework that consistently incorporates event-by-event initial-state fluctuations and dynamical minijet-medium interactions. Produced in initial hard scatterings, minijets thermalize more slowly than the bulk medium and persist into the hydrodynamic stage, where they deposit energy and momentum into the evolving plasma, generating wakes that modify its spacetime evolution. Minijets modify the hadronic multiplicity and momentum anisotropy in a manner that can largely be absorbed by adjusting the shear viscosity and the normalization of the system's initial energy-momentum tensor. In contrast, electromagnetic probes are emitted throughout the evolution and remain directly sensitive to the underlying spacetime history. We perform a comprehensive calculation of direct photon and dilepton production with the minijets and bulk medium evolved simultaneously, using PYTHIA to produce minijets, and describing the underlying plasma with IP-Glasma initial conditions, hydrodynamic evolution with MUSIC and hadronic transport with UrQMD. We find that the minijet-induced modification of the hydrodynamic evolution produces measurable effects in both photon and dilepton observables, establishing electromagnetic radiation as a sensitive probe of the interplay between hard partons and the quark-gluon plasma.
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All authors Soham Banerjee, Mayank Singh, Charles Gale, Sangyong Jeon, Daniel Pablos, Jean-François Paquet

Nuclear Theory

Radiative proton capture on ${}^{12}\mathrm{C}$ in cluster effective field theory

Tae-Sun Park, Eunjin In and Young-Ho Song

Radiative proton capture on ${}^{12}\mathrm{C}$ to the ground state of ${}^{13}\mathrm{N}$ is calculated in cluster effective field theory through next-to-leading order. At low energy the reaction is dominated by $s_{1/2}\to p_{1/2}$ $E1$ capture, which we treat in the long-wavelength limit. Its amplitude is strongly hindered by destructive interference between the contribution fixed by gauge invariance and a counter-term $E1$ current, making the capture particularly sensitive to subleading terms. We fit the recent data below $0.95$~MeV, determining the $E1$ transition counter-term coefficients together with the ground-state asymptotic normalization coefficient and the $\frac{1}{2}^+$ resonance and shape parameters. We obtain $S(0)=1.34\pm0.07$~keV\,b and $S(25~\mathrm{keV})=1.43\pm0.07$~keV\,b, the latter in agreement with recent $R$-matrix extrapolations. We also estimate the effects of the omitted $p$-wave $M1$ capture and $\frac{3}{2}^-$ resonance tail, and find that the fitted asymptotic normalization coefficient moves substantially while the $S$ factors remain almost unchanged.
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Nuclear Theory

Emergence of the nuclear halo in $^{22}$C: Bridging shape and shell

Xiang-Xiang Sun

The structure of $^{22}$C remains unsettled more than a decade after the 2010 reaction-cross-section measurement. The nucleus sits at $N=16$, where the spherical closure of $^{24}$O competes with the deformation of $^{20}$C. We develop a multi-reference density functional approach that restores particle number and angular momentum and mixes quadrupole shapes while retaining the continuum. The calculation gives a deformed two-neutron halo with matter radius of 3.29 fm, closer to the carbon-target extraction, and a long $s$-wave tail. The ground state $0_{1}^{+}$ is dominated by oblate configurations, with $B(E2)$ values comparable to those of $^{20}$C. The valence neutrons occupy mixed $sd$ orbits; the $N=16$ closure established in $^{24}$O is substantially weakened in $^{22}$C.
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Nuclear Theory

Are breakup reactions sensitive to spectroscopic factors? (Spoiler alert: they ain't)

Live-Palm Kubushishi and Pierre Capel

Halo nuclei are mostly studied through reactions. In breakup reactions, the projectile is sent upon a target, which induces the dissociation of the loosely-bound halo from the core of the nucleus. In most cases, a spectroscopic factor for the core-halo structure is inferred from experimental data. In this contribution, we present a new analysis of the Coulomb breakup of 11Be on 208Pb at 69A MeV measured at RIKEN. We use an effective multi-channel particle-rotor model of the projectile, which accounts for the excitation of the 10Be core. The calculations are in excellent agreement with the data, independently of the value of the spectroscopic factor. This confirms that breakup cross sections are insensitive to this value and that spectroscopic factors cannot be inferred from such measurements. In the near future, we plan to extend this idea to other reactions.
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Nuclear Theory

Universal empirical coupled channel calculations for capture cross sections in synthesis of superheavy nuclei

H. Yao, Y. J. Duan, N. Wang et al. (+9 more)

A universal empirical coupled channel model, ECC2, is proposed for the systematic description of capture cross sections in heavy-ion fusion reactions. The model combines a modified Broglia–Winther potential, an effective barrier curvature, and a deformation-dependent barrier distribution width. The most probable barrier heights predicted by ECC2 are in good agreement with the extracted values based on measured excitation functions for 367 systems, and the root-mean-square (rms) deviation is 1.39 MeV. ECC2 is applied to 25 fusion reactions ranging from $^{16}$O+$^{197}$Au to $^{54}$Cr+$^{248}$Cm. The predicted capture excitation functions are consistent with the EBD2.2 predictions for all systems and agree well with the available experimental data.
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All authors H. Yao, Y. J. Duan, N. Wang, D. D. Zhang, X. T. He, T. L. Zhao, P. H. Chen, P. W. Wen, L. Zhu, X. J. Bao, J. J. Li, L. Guo

Nuclear Theory

Advancing Nuclear Physics with Machine Learning and Artificial Intelligence

Wanbing He, Qingfeng Li, Yugang Ma et al. (+3 more)

Machine learning (ML) and artificial intelligence (AI) are becoming powerful tools in scientific research across various disciplines. In this review, we summarize recent progress in AI-assisted studies of nuclear structure and reaction observables, heavy-ion collisions and dense nuclear matter properties, many-body wave functions, experimental facilities and data analysis. This review focus on new progress since the last review in 2023, and machine learning in nuclear physics is evolving from purely data inferences to physics informed learning. Future directions on the integration of physical knowledge with modern learning architectures, large foundation models and other emerging methods are also reviewed. These developments suggest that AI is enabling and advancing new approaches towards most challenging nuclear physics problems.
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All authors Wanbing He, Qingfeng Li, Yugang Ma, Zhongming Niu, Junchen Pei, Yingxun Zhang

Tuesday 29 September

Nuclear Theory

Nuclear Deep Inelastic Scattering around $x=0.3$

S.A. Kulagin and R. Petti

Deep-inelastic scattering (DIS) data on nuclei, from deuterium to lead, indicate that nuclear effects on the partonic structure of bound nucleons are remarkably small around $x=0.3$, where valence-quark distributions peak. We present the results of a global analysis of DIS data on the cross-section ratios $\sigma^A/\sigma^{{}^2\text{H}}$ in the range $0.25 \leq x \leq 0.35$, revealing a remarkable cancellation of nuclear effects across the entire range of nuclear targets. We also discuss the interpretation of such an observation within a microscopic model of nuclear modifications of the structure functions.
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Nuclear Theory

Effective Contact Theory for Exotic Loosely Bound States in Strongly Interacting Expanding Matter

Xiaofeng Wang, Zebo Tang, Zhangbu Xu et al. (+2 more)

Short-distance correlations generate universal relations that can be independent of microscopic details. Tan's contact is a prominent example, connecting close pairs, high-momentum constituents, and bound-state formation across atomic, condensed-matter, and nuclear systems. Whether an analogous universality governs the nonequilibrium freeze-out of relativistic QCD matter is an open question. We develop an effective contact theory that relates the production of loosely bound states to continuum two-particle correlations in heavy-ion collisions. The construction replaces the hard relative-momentum cutoff of conventional coalescence by a regulated Bethe–Peierls kernel: freeze-out localization fixes its momentum scale, while the composite yield fixes its contact residue. Bound and continuum observables then become projections of a common two-particle density matrix rather than independent phenomena. Coulomb-bound $K\mu$ atoms provide an ideal realization because their atomic, production, and source scales are widely separated. A contact-theory analysis of STAR $d\Lambda$ correlations supplies a first bound–continuum consistency test and demonstrates how inferred near-threshold parameters can depend on the finite expanding source. The framework establishes a general strategy for relating coalescence, correlations, and exotic bound states in strongly interacting expanding matter.
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All authors Xiaofeng Wang, Zebo Tang, Zhangbu Xu, Chi Yang, Wangmei Zha

Nuclear Theory

Neutron-nucleus scattering in an $L^2$-integrable basis

Bui Minh Loc and Calvin W. Johnson

First-principles calculations of scattering off quantum many-body systems such as atoms and nuclei is important but nontrivial, requiring large-dimension ($10^3$ to $10^8$ or more) bases. For the first time we apply to many-body targets a recently developed approach to find phase shifts in $L^2$-integrable bases, computing neutron-nucleus scattering using the same interactions as ab initio models of nuclei, in very small (dimension 3-6) bases. Our work shows the mean field dominates low-energy nuclear scattering; it also provides a foundation for more efficient future methodologies.
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Nuclear Theory · Cross-listed from hep-th

Detectors in Nonrelativistic Conformal Field Theories

Cyuan-Han Chang, Subham Dutta Chowdhury, Ian Moult et al. (+1 more)

Correlations in asymptotic fluxes provide one of the primary experimental means of studying physical systems. In the context of relativistic QFT, the formalization of such experiments in terms of detector operators has led to significant progress. Motivated by these successes, in this paper we initiate a study of detector operators in nonrelativistic conformal field theories (NRCFTs). In NRCFTs, fluxes are distributed in both angle and velocity, making the natural detector operator the energy flux differential in velocity, $\mathcal{E}_v(\hat{n})$. We provide non-perturbative definitions of these operators in NRCFTs, and study their symmetries and algebra. We calculate one-point functions of these detector observables in a variety of few and many body states of representative NRCFTs, including free fermions, as well as fermions at unitarity. In interacting three-body states, they exhibit a remarkably rich behavior reflective of the Efimov three-body wave-function, including the formation of an enhanced "jet" structure due to the presence of resonant interactions. We use these detectors to derive a nonrelativistic generalization of the Hofman-Maldacena conformal collider bounds by arguing for positivity of $\mathcal{E}_v(\hat{n})$, and imposing this in spin 1 states. We outline a number of future directions for the study of detectors in NRCFTs, and discuss how they can be measured in a variety of experimental platforms from cold atoms to low energy neutron experiments.
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All authors Cyuan-Han Chang, Subham Dutta Chowdhury, Ian Moult, Dam Thanh Son

Nuclear Theory

Bayesian Constraints on Bosonic Dark Matter in Neutron Stars within a Covariant Density-Functional Equation-of-State Ensemble

Davood Rafiei Karkevandi, Alexander Ayriyan and Armen Sedrakian

We investigate neutron stars admixed with repulsively self-interacting bosonic dark matter (DM) using current multi-messenger observations. The dark component is modeled as a complex scalar field coupled to baryonic matter only through gravity, allowing dark-core and dark-halo configurations. To quantify baryonic equation-of-state (EOS) uncertainties, we combine a three-dimensional scan over $(m_\chi,\lambda,F_\chi)$ with 27 DDME2-based covariant density-functional EOSs spanning $L_{\rm sym}=30,50,70$ MeV and $-600\le Q_{\rm sat}\le 1000$ MeV. The models are confronted in a Bayesian framework with NICER mass–radius measurements from the Amsterdam and Maryland/Illinois analyses and the GW170817 tidal-deformability constraint. After Bayesian evidence weighting over the EOS ensemble, the EOS-relevant dark-sector scale $\mu_\chi\equiv m_\chi/\lambda^{1/4}$ is localized around 250 MeV for both NICER data sets. In the $(m_\chi,\lambda)$ parameterization, the marginalized boson-mass posterior peaks at $m_\chi\simeq300$–$330$ MeV, while $\lambda$ remains broadly distributed. Since the bosonic EOS depends on $m_\chi$ and $\lambda$ only through $\mu_\chi$, their separate marginals are conditional on the adopted independent priors. The inferred DM fraction is more data-set dependent, with posterior modes near 4% for Maryland/Illinois and 12% for Amsterdam. Bosonic DM also shifts the inferred $Q_{\rm sat}$ from negative toward intermediate and positive values, whereas the response of $L_{\rm sym}$ is weaker. This indicates a model-dependent trade-off between DM-induced compactification and the high-density stiffness of baryonic matter. These constraints remain conditional on the selected EOS family and the assumption of a common effective $F_\chi$ for all sources.
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Nuclear Theory · Cross-listed from astro-ph.HE

Joint Mass-Radius and Magnetic-Geometry Inference of PSR J0740+6620

Chun Huang, Tuomo Salmi and Alexander Y. Chen

X-ray pulse-profile modeling can measure neutron-star radii, but its physical interpretation remains limited by the largely phenomenological description of the surface hotspots. Here we connect the X-ray hotspots directly to the pulsar magnetospheric structure and jointly infer the mass, radius, and magnetic geometry of the massive millisecond pulsar PSR J0740+6620 from NICER and XMM-Newton observations. Using a GPU-accelerated implementation, we compare two low-dimensional magnetic configurations that can produce non-antipodal emission: a centered axisymmetric dipole–quadrupole and a shifted dipole. The shifted-dipole model is decisively favored under the adopted priors, with $\Delta\ln Z=5.65$ (Bayes factor $\sim285$), and yields $M=2.059^{+0.068}_{-0.069}\,M_{\odot}$ and $R=13.28^{+1.47}_{-1.07}\,\mathrm{km}$, broadly consistent with previous phenomenological analyses, while requiring nearly symmetric heating of the two polar caps. Both the marginalized shifted-dipole posterior and the timing-compatible representative require an effective X-ray-emitting footprint much smaller than the nominal force-free polar cap calibrated for a centered dipole. This compact footprint is not reproduced by our exploratory photon-conversion estimates and instead points to missing physics in the mapping from magnetospheric currents to observable X-ray emission. Our results show that physically motivated hotspots can preserve the mass–radius inference while turning hotspot morphology into a probe of pulsar magnetospheric structure and emission physics.
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Nuclear Theory · Cross-listed from hep-ph

Muon-to-positron conversion from local dimension-nine operators: pion-pole-improved nuclear multipoles

Yi Liao and Hao-Lin Wang

We begin a systematic study of neutrinoless muon-to-positron conversion, $\mu^-+(A,Z)\to e^++(A,Z-2)$, which violates lepton number by two units and changes charged-lepton flavor. This first paper in a series constructs nuclear operators for local dimension-nine interactions containing a scalar or pseudoscalar lepton bilinear and two contracted vector or axial quark currents. The covariant nucleon currents are built with all six vector and axial form factors. For the working nuclear operator we neglect second-class currents and adopt a pion-pole-improved reduction: non-pole recoil terms generated by the displayed one-body currents are retained through second order in inverse nucleon mass, whereas the pion-pole longitudinal axial current is kept intact before the two currents are contracted. We preserve the two independent momentum transfers at the nucleon vertices and the Coulomb-shifted spatial phase of the outgoing positron. Starting from the spacetime transition element, we show explicitly how the interaction-coordinate integral fixes the sum, but not the sharing, of the two current momenta. Unequal form-factor arguments then generate relative-coordinate multipoles absent in the usually used common-momentum approximation. We give an exact recoupling into two-body nuclear tensors and specialize it to the phenomenologically important $0^+\to0^+$ transition. In this case the external nuclear rank is zero and all magnetic sums collapse, although finite-momentum internal orbital and spin tensors remain. The result is expressed in a form directly contractible with charge-changing two-body transition densities. General six-form-factor currents, arbitrary nuclear angular momenta, and power-counting qualifications are collected in appendices.
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Nuclear Theory · Cross-listed from hep-ph

A glueball puzzle explained in terms of $\phi h_1(1380)$ dynamics: Aka $X(2370)$

K. P. Khemchandani, A. Martinez Torres and E. Oset

We study the interaction of $\phi$ with $h_1(1380)$, considering the latter as a $K^*\bar K$ molecular state, and find the generation of a state with the same quantum numbers, together with a mass and width compatible with the experimental results, as those of $X(2370)$, recently advocated as a candidate for a glueball. Within our description, the suppressed decay modes of $X(2370)$ to $\gamma \omega$, $\omega \phi$ and $K^*\bar K$, reported in the experimental paper as clues to its glueball nature, are naturally explained. Conversely, the non $K^* \bar K$ decay to $K \bar K \pi$ (the latter being the invariant mass where the resonance is observed) is shown to be largely enhanced due to the combination of a triangle singularity and the presence of $K(1630)$ in the $\rho \phi \to \bar K$ vertex involved in the triangle loop.
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Nuclear Theory · Cross-listed from nucl-ex

$\pi$-QCD; Proposal for Experiments at the GSI Pion Beam Facility

HADES Collaboration: R. Abou Yassine, J. Adamczewski-Musch, G. Appagere et al. (+126 more)

We propose to investigate the dynamics of hadronic matter in the strong QCD regime using the pion-beam facility at GSI in conjunction with HADES. This program will study hadron physics through elementary pion-nucleon interactions up to $\sqrt{s}\approx$2.35 GeV, bridging cold matter research with detailed analyses of exclusive reactions. Our goals include exploring baryon resonance formation and their electromagnetic structures. This will complement photo-production experiments (e.g., ELSA) and enhance our understanding of emissivity in dense, hot hadronic matter. Key topics include examining baryon couplings to mesons and virtual photons, analyzing hyperon weak decays in exclusive reactions, and using Partial Wave Analyses with differential cross sections and polarization observables to achieve unprecedented precision in baryon-meson coupling data ($\rho$N, $\omega$N). Furthermore, e$^{+}$e$^{-}$ production measurements off nucleons will provide insight into the electromagnetic transition form factors of baryons in the time-like region, revealing the role of vector mesons ($\rho$, $\omega$). Reactions on nuclear targets allow for detailed studies of hadron properties, including vector-meson line shapes and strengths in cold nuclear matter. These measurements provide a critical reference for the interpretation of results from the hot and dense environment created in $A+A$ collisions. This research also has broader implications. It will contribute to the modeling of neutrino-nucleus interactions, facilitate unprecedented investigations into hypernuclei formation, and enhance our understanding of strong interaction dynamics across different energy regimes.
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All authors HADES Collaboration: R. Abou Yassine, J. Adamczewski-Musch, G. Appagere, M. Becker, A. Blanco, C. Blume, M. Bohman, Y. Bondar, L. Chlad, I. Ciepał, S. Deb, M. D. Doncel Monasterio, M. Duerr, W. Esmail, L. Fabbietti, M. Firlej, T. Fiutowski, A. M. Foda, J. Förtsch, P. Fonte, J. Friese, I. Fröhlich, T. Galatyuk, R. Gernhäuser, M. Grunwald, D. Grzonka, M. Gumberidze, S. Harabasz, T. Heinz, C. Höhne, F. Hojeij, R. Holzmann, M. Idzik, B. Kämpfer, K.-H. Kampert, B. Kardan, V. Kedych, S. Kim, V. Kladov, A. Kodym, M. Kohls, J. Kolas, A. Koperwas-Władyszewska, G. Korcyl, G. Kornakov, W. Krueger, A. Kugler, R. Lalik, S. Lebedev, T. Leontiou, S. Linev, F. Linz, L. Lopes, M. Lorenz, A. Malige, P. Marciniewski, J. Markert, T. Matulewicz, S. Mehat, J.G. Messchendorp, V. Metag, J. Michel, A. Molenda, J. Moron, C. Müntz, A. Mukherjee, M. Nabroth, A. Opíchal, J. Orliński, J.-H. Otto, M. Papenbrock, Y. Parpottas, M. Parschau, S. Pattnaik, C. Pauly, D. Pawlowska-Szymanska, V. Pechenov, O. Pechenova, G. Perez Andrade, J. Phan, K. Piasecki, J. Pietraszko, T. Povar, M. Prędota, K. Prościński, A. Prozorov, W. Przygoda, B. Ramstein, N. Rathod, J. T. Rieger, J. Ritman, A. Rost, A. Rustamov, S. Sahu, P. Salabura, J. Saraiva, K. Scharmann, N. Schild, K. Schönning, E. Schwab, F. Seck, I. Selyuzhenkov, J. Smyrski, M. Sobiella, S. Spies, A. Sreejith, A. Strach, H. Ströbele, J. Stroth, P. Subramani, K. Sumara, O. Svoboda, K. Swientek, J. Taylor, P. E. Tegner, P. Tlusty, M. Traxler, S. Treliński, I. C. Udrea, F. Ulrich-Pur, V. Wagner, A.A. Weber, E. Weiler, C. Wendisch, D. Wielanek, P. Wintz, H.P. Zbroszczyk, M. Zieliński, P. Zumbruch

Nuclear Theory · Cross-listed from hep-ph

CGC Fit to HERA DIS and Forward Hadron Production in p+p Collisions

Piotr Korcyl, Truong My Hau Le, Farid Salazar et al. (+1 more)

Many experiments have provided possible hints of gluon saturation, including geometric scaling in deep inelastic scattering (DIS) at HERA, the suppression of forward particle yields in d+Au collisions relative to p+p collisions at RHIC, and the suppression of away-side peaks in di-hadron correlations at forward rapidities in proton-nucleus collisions at RHIC and the LHC. Previous studies within the Color Glass Condensate (CGC) framework have primarily focused on fits to HERA deep inelastic scattering data, using the resulting dipole amplitudes to predict hadronic observables in proton-nucleus and proton-proton collisions. A simultaneous fit of DIS and forward particle production data, and a systematic study of their interplay, has so far been absent. In the work presented here, we focus on two processes: inclusive DIS and forward single inclusive hadron production in p+p collisions, incorporating data from HERA, RHIC, and the LHC. We solve the Balitsky-Kovchegov (BK) small-x evolution equation and perform a global fit to the combined datasets. Our analysis accounts for uncertainties in fragmentation functions and provides final uncertainties for the fitted parameters. The outcomes demonstrate the potential of the CGC formalism to provide a universal description of these diverse processes at the level of the dipole amplitude. In these proceedings, after very briefly summarizing the setup and our results, we highlight one particular aspect of the analysis, namely the complete uncertainty treatment. We validated the final uncertainties with two independent methods: the Hessian method and the Bayesian inference method, finding very good agreement.
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All authors Piotr Korcyl, Truong My Hau Le, Farid Salazar, Tomasz Stebel

Nuclear Theory · Cross-listed from hep-ph

Generalized parton distributions of the nucleon in the chiral quark soliton model: Sum over all quark states at nonzero skewness and momentum transfer

Josuke Minamiguchi

We compute the combinations $E_M=H^{u+d}+E^{u+d}$ and $H_E=H^{u-d}+tE^{u-d}/(4M_N^2)$ of unpolarized generalized parton distributions (GPDs) of the nucleon in the chiral quark soliton model at nonzero skewness $\xi$ and nonzero momentum transfer $t$. The combinations contain the GPDs $H^{u-d}$ and $E^{u+d}$, which are subleading in the expansion in the inverse number of colors. Both combinations are double sums over the quark states. A multipole expansion of the light-cone operators makes the sums computable at every $\xi$ and every $t\le0$. The contribution of the Dirac continuum is summed over the quark states, without an interpolation formula and without a gradient expansion. The first moments satisfy the form-factor sum rules, and the second moments satisfy polynomiality.
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Nuclear Theory · Cross-listed from hep-ph

Impact of Open Heavy-Flavour Production on nCTEQ Nuclear PDFs

Jan Wissmann, Tomáš Ježo, Michael Klasen et al. (+2 more)

We present nCTEQ26OHF, a global analysis of nuclear parton distribution functions (nPDFs) within the nCTEQ framework. In this analysis, constrasting the main nCTEQ26 release, we replace the Crystal-Ball function, an effective matrix element that is used in nCTEQ26 for open heavy-flavor (OHF) and quarkonium production, by an SACOT GM-VFNS calculation for the OHF predictions. The resulting nCTEQ26OHF PDFs are compatible with the nCTEQ26 PDFs within uncertainties, implying that the OHF data alone provide ample constraint.
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All authors Jan Wissmann, Tomáš Ježo, Michael Klasen, Ingo Schienbein, Hubert Spiesberger

Nuclear Theory · Cross-listed from cond-mat.quant-gas

Finite-momentum trimers and Cooper quartets in a one-dimensional Fermi gas with coexistent $s$- and $p$-wave interactions

Yixin Guo

We study finite-momentum trimers and Cooper quartets in a one-dimensional two-component Fermi gas with coexistent $s$- and $p$-wave interactions, regularized in the relative momentum of each pair so that they remain Galilean invariant. Pauli blocking alone then makes the trimer dispersion deviate from free center-of-mass motion, so the trimer energy can be lowest at finite total momentum. Allowing this motion expands the $abb$ region among pairs and trimers and removes the region where an odd-wave pair is lowest. The $aabb$ quartet lies below all these branches at every sampled coupling, and in a strip starting on the crossing of the two dimer-pair channels its lowest breakup channel is a moving $abb$ trimer and an atom. At weak interspecies attraction, a variational bound shows that two odd-wave Cooper pairs bind into a quartet, whose binding exceeds that of the coexisting trimer by orders of magnitude as the attraction weakens. At stronger interspecies attraction, the quartet binding relative to two unlike-species dimers disappears when the odd-wave interaction is switched off, although the even-wave interaction dominates the interaction energy. Relative to the in-vacuum case, the Fermi sea enhances the weak-coupling quartet binding, and at fixed scattering lengths the quartet binding grows with density while the coexisting trimer becomes much shallower. These results show that neither the most strongly bound pair nor the dominant interaction energy alone determines whether the quartet binds.
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Nuclear Theory

Wigner and mirror correlations in nuclear mass predictions with kernel ridge regression

X. H. Wu

Wigner- and mirror-correlated kernel ridge regression (WKRR) and its odd-even extension WKRRoe are developed to improve nuclear mass predictions. The Wigner and mirror correlations are encoded entirely in the kernel functions without introducing more weight parameters. For experimentally known nuclear masses, WKRRoe achieves a leave-one-out root-mean-square deviation of 98.0 keV, which falls below the often-quoted 100-keV scale discussed in connection with chaos-related limits. The gain is mainly concentrated in light nuclei near $N=Z$ and is especially large for mirror pairs. Further tests show that WKRRoe can potentially improve predictions for experimentally unknown nuclei near $N=Z$, particularly when their mirror partners have already been measured.
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Nuclear Theory

Short-range correlated pairs from nucleon density profiles as a new probe of the nuclear equation of state

L. Ponnath, N. Barnea, I. Korover et al. (+6 more)

We investigate to what extent the observed nuclear systematics of Short-Range Correlations (SRCs) can be described by the geometry of the underlying proton and neutron density distributions. Building on previous connections between nuclear SRC contacts and one-body densities, we formulate an explicit density-overlap representation in which proton–proton, proton–neutron, and neutron–neutron SRC source terms are constructed from the full spatial density profiles obtained with Energy Density Functionals (EDFs). The framework contains two global parameters describing the overall SRC pair formation strength and the relative contribution of the spin-singlet channel, while the nucleus-dependent evolution is generated by the density-overlap integrals. The framework simultaneously reproduces several independent experimental SRC observables, including proton–proton to proton–neutron pair ratios, relative SRC pair abundances, and proton and neutron high-momentum double ratios. A comparison between relativistic and Skyrme-type EDF families demonstrates the sensitivity of these observables to the underlying density geometry and allows the effect of the complete density profiles to be distinguished from simple radius-based geometrical estimates. Applied to neutron-rich oxygen isotopes, the framework predicts a pronounced evolution of the neutron–neutron pair abundance. Comparison with an independent calculation based on occupied harmonic-oscillator wave functions and an explicit finite-distance criterion supports the predicted isotopic evolution in neutron-rich oxygen isotopes. This agreement identifies the proton–proton to neutron–neutron SRC pair ratio as a promising experimental probe of neutron-skin thicknesses in neutron-rich nuclei and, through their connection to the symmetry energy, of the nuclear equation of state.
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All authors L. Ponnath, N. Barnea, I. Korover, S. Paschalis, M. Petri, E. Piasetzky, X. Roca-Maza, S. Typel, I. Wischnevsky Shlush

Nuclear Theory

Elliptic flow in an expanding and rotating fireball

Ashutosh Dwibedi, Anupam Panja and Sabyasachi Ghosh

We investigate the role of initial orbital angular momentum in generating elliptic flow in off-central heavy-ion collisions. The conventional expanding fireball picture is extended for the first time to a simultaneously expanding and rotating fireball characterized by an angular velocity. Spherical and spheroidal emission geometries with two different rotating flow profiles, reminiscent of global and differential rotation, are considered for our investigation. While the transverse-momentum spectra at midrapidity are largely insensitive to the geometry and flow profile for realistic values of angular velocity, the elliptic flow is strongly affected by anisotropic expansion and rotation. A spherical fireball generates elliptic flow solely through the momentum anisotropy induced by rotation, but its magnitude remains below the observed values for realistic angular velocities. In contrast, an anisotropically expanding and rotating spheroidal fireball exhibits a $\sim 10\%$ enhancement of elliptic flow for $\sqrt{s_{\rm NN}}=7.7$ GeV, which reduces to a $2\%$ for $\sqrt{s_{\rm NN}}=39$ GeV relative to its non-rotating counterpart. Within our fireball framework, this indicates that vorticity can contribute at the $2-10\%$ level to the observed elliptic flow.
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Nuclear Theory

Semiclassical description of quadrupole-hexadecapole correlation in nuclear shape evolution

Kenichiro Arita

Background: Theoretical investigations of nuclear shapes with realistic effective interactions or mean field potentials have suggested a remarkable systematics in the hexadecapole shape evolution with varying particle number: Within each single-particle shell, from one spherical magic number to the next, a diamond type (beta_4>0) appears in the first half, and then turn into oblong type (beta_4<0) in the second half. Purpose: Nuclear deformation is essentially governed by the single-particle shell structure. In semiclassical periodic orbit theory (POT), level density is expressed as the sum over contributions from classical periodic orbits, and the origins of the gross shell structures can be understood by the contribution of one or a few shortest orbits. Using the POT, I examine how the hexadecapole degree of freedom affect the contribution of the orbits to the deformed shell structure through their bifurcations to explain the mechanism of above shape evolution. Methods: Ground state deformations are systematically investigated by the shell correction method, taking account of axially symmetric quadrupole and hexadecapole shape degrees of freedom. For simplicity, I employ two simplest mean field potentials to obtain the shell corrections: the oscillator and the cavity (infinite well) potentials. After confirming the the systematics in shape evolution under these simplest mean-field models, semiclassical analyses are made, focusing on the role of PO bifurcation. Results and conclusions: Systematics in the hexadecapole shape evolution in each single-particle shell is clearly explained by the bifurcations of two different types of periodic orbits in the cavity model, which suggest strong correlation between quadrupole and hexadecapole parameters. This also ensures the mechanism of nuclear prolate-shape predominance within this simple potential model.
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Monday 28 September

Nuclear Theory · Cross-listed from hep-ph

Full-event anomaly detection for new physics searches at the Electron-Ion Collider

Dimitrios Athanasakos, Sebastian Grieninger, Hongkai Liu et al. (+3 more)

The future Electron-Ion Collider (EIC) will offer new opportunities to search for physics beyond the Standard Model. We study resonant anomaly detection using machine learning and the full particle content of an event. We consider a new neutral gauge boson and a heavy neutral lepton as illustrative signals with different electron-jet topologies. Weakly supervised learning uses this event information to enhance the sensitivity of an invariant-mass search without identifying individual signal events during training. Comparisons with high-level observables show that the electron kinematics account for an important part of the separation, while correlations among the particles provide further sensitivity. We also construct a conditional full-event generator by adapting a model pretrained on LHC jets to produce EIC background events. A scan over signal fractions demonstrates substantial signal enhancement using the learned background reference, providing a proof of concept for this approach at the EIC. Finally, we consider a fully unsupervised graph autoencoder that provides modest signal enhancement but retains sensitivity at signal fractions too small for effective weak supervision. Our results motivate full-event anomaly detection as part of the EIC physics program and identify directions for developing methods suited to its distinct kinematics.
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All authors Dimitrios Athanasakos, Sebastian Grieninger, Hongkai Liu, Tymothy Mangan, Felix Ringer, Robert Szafron