Nuclear Theory·nucl-th
16 papers—8 primary·8 cross-listed
Rika Danjo · Toshimi Suda · Toshio Suzuki
We propose a new method to determine the 4th moment of the nuclear charge-density distribution of 208Pb, with high precision from low-momentum-transfer elastic electron scattering.
A. M. Ankowski · J. Golak · E. Pérez del Rio · S. Sharma · R. Skibiński · K. Topolnicki · H. Witała · W. N. Polyzou · H. Kamada · D. Dutta
The nucleon axial form factor is a primary source of systematic uncertainty in charged-current quasielastic interactions, of critical importance for long-baseline neutrino-oscillation studies. Its low- behavior is particularly problematic to pin down in neutrino measurements. To address this limitation, we investigate the weak process of polarized positron capture on the deuteron, . Employing a relativistic momentum-space formalism, we present predictions for the total cross section. Focusing on the kinematic regime free from pion-production backgrounds, we analyze various differential cross sections and their sensitivity to the variation. Our results demonstrate that thanks to the positron upgrade, Jefferson Lab will gain a unique position to make inroads into determining the low- behavior of the axial form factor.
Yong-Jia Huang · Bikai Gao
Statistical evidence for a continuous hadron-quark transition is found in this work. Confronting microscopic descriptions connecting the Parity Doublet Model and the Nambu--Jona-Lasinio model with observationally constrained non-parametric equations of state, Bayesian model comparison decisively favors a boundary-free crossover over the conventional first-order Maxwell construction () and fixed-boundary crossover (). The preferred crossover decouples the intermediate stiffening from the intrinsic stiffness of each phase, allowing both sectors to exhibit physical self-consistency. The chiral-invariant nucleon mass is large, , as expected for a substantial baryon mass surviving chiral restoration. While the quark sector accommodates a small pairing gap consistent with perturbative QCD limits, avoiding the excessively large gaps required by the other constructions. These results demonstrate that a realistic unified description represents a continuous transition deviating substantially from isolated effective models of hadrons and quarks. Exploring genuine phase boundaries is therefore necessary through the emergence of spinodal instabilities within unified frameworks.
Pengcheng Li · Yongjia Wang · Qingfeng Li
The pair transverse momentum () and collision-energy () dependent difference between and femtoscopic correlations was observed by the HADES and STAR Collaborations. We investigate how much of the observed splitting can be accounted for by Coulomb dynamics in 0-10\% central Au+Au collisions at -5.2 GeV. Using the UrQMD model and the CRAB programme, three transport scenarios that successively include baryon-baryon, baryon-meson, and meson-meson Coulomb interactions are considered. In a separate calculation based on the baryon-baryon reference, we reconstruct the time-dependent effective charge and radius of the residual charged source and propagate each pion from its individual last strong-interaction point through the evolving field. The calculations reproduce the main and dependences of the radii. Baryon--meson Coulomb interactions generate most of the additional charge splitting in the microscopic calculation. The residual-source treatment also enhances the longitudinal and sideward radius ratios relative to the reference, whereas the outward ratio changes little, and the enhancement generally decreases with increasing . Within the present framework, this contribution does not fully account for the data, motivating further investigation of the charged-source geometry and its interplay with strong-interaction dynamics.
S. A. Bhat · Nazira Nazir · W. Tawseef · J. A. Sheikh · G.H. Bhat · S. Jehangir · G. B. Vakil · M. Bhuyan
The microscopic approach of the triaxial projected shell model (TPSM) is employed to investigate the properties of the isomer in the six isotones of Xe, Ba, Ce, Nd, Sm, and Gd. The observed decay pattern of the isomer for these isotones is unexpected with the hindrance factor decreasing with atomic number. It is shown in the present work that multi-quasiparticle mixing into the ground-state configuration is responsible for the observed decreasing trend of the hindrance factor. We have also calculated the excitation energies and in-band transition probabilities of the yrast and the band built on the isomer for the six isotones, and it is shown that TPSM approach reproduces the measured quantities quite satisfactorily.
Rong Wang · Sheng-Ting Sun · Han-Jie Cai · Xun-Chao Zhang · Huan Jia · Yuan He
In this paper, we present a data-driven artificial neural network (ANN) model for describing the double differential cross sections (DDCS) of neutron emission in nuclear spallation reactions. The ANN model is found to be precise, flexible, and efficient in predicting differential cross sections of nuclear reactions and in learning the complex dependence of neutron DDCS on the projectile energy (), target nucleus ( and ), neutron energy (), and neutron emission angle (). The model is trained on replicas of experimental data that incorporate uncertainties. Several regularization schemes are examined during ANN training. The input variables of the constructed ANN framework are also investigated, and the following six key variables are selected for the input layer of the ANN model: , , , , , and . The ANN predictions are compared with training data provided by various experimental collaborations, showing excellent agreement. The resulting model is further tested on test data with projectile energies, target nuclei, and neutron emission angles different from those in the training data, indicating strong predictive power and generalization capability of the ANN framework. As an illustration, the neutron DDCS as functions of , , and projectile energy are predicted and presented for copper target. The proposed high-precision ANN model is expected to be beneficial for accelerator-driven system (ADS) design and many other applications in nuclear physics, astrophysics, and nuclear technology development.
Yuma Kikuchi · Kiyoshi Katō · Takayuki Myo
We apply our complex-scaled time-evolution operator to the two-proton decay of Be. The nucleus is described as an three-body system with explicit Jacobi-coordinate rearrangement and the realistic Argonne NN interaction for the proton-proton subsystem. Starting from a confined initial wave packet, the decay dynamics are described by expansion over the complex-scaled eigenstates of the final Hamiltonian. The decay width extracted from the late-time survival probability agrees closely with that obtained from the CSM resonance pole. The time-dependent densities in different Jacobi coordinates reveal complementary aspects of the evolving three-body geometry, while the spin-singlet component remains dominant during the decay. In particular, the correlated two-proton configuration persists even in the presence of the strong short-range repulsion of the realistic NN interaction. These results demonstrate the applicability of the complex-scaled time-evolution framework to explicit three-body decay dynamics and provide a consistent description of the decay width, spatial evolution, and spin correlations of Be.
Naoki Yamamoto
We study secondary pairing in the two-flavor color-superconducting (2SC) phase, where the residual ungapped quarks form a same-chirality condensate driven by an attractive instanton-induced interaction. We determine its symmetry realization, quasiparticle structure, anomaly matching, and low-energy effective theory. The pairing gap is necessarily nodal; in particular, the complex axial state has two point nodes and realizes a spinful relativistic superfluid. This state preserves the full chiral symmetry while breaking the modified baryon-number symmetry and spatial rotations, with rotations about the nodal axis locked to the condensate phase. This locking gives rise to a Berry term, the Mermin-Ho relation, and a type-B orientational Nambu-Goldstone mode in addition to the superfluid phonon. We also show how anomaly matching is reorganized by secondary pairing: the perturbative mixed anomaly is realized by a Wess-Zumino coupling of the superfluid phonon, whereas the and Witten anomalies are carried by the point-node Bogoliubov-de Gennes flavor doublets. The resulting theory provides a concrete dense-QCD realization of a spinful relativistic superfluid with nodal fermions required by anomaly matching.
V.Martínez-Fernández · B.Pire · P.Sznajder · J.Wagner
Coherent hard exclusive reactions on light nuclei offer access to their quark and gluon structure and provide a framework for three-dimensional nuclear tomography. We analyze deeply virtual Compton scattering on a helium-4 target, including leading-twist contributions as well as kinematical twist-3 and twist-4 effects. We present numerical estimates of cross sections and asymmetries for kinematic regimes relevant to JLab experiments. We emphasize the importance of next to leading order (NLO) and kinematical twist 3 and 4 contributions to interpret data in the JLab kinematics. We deduce a first tomographic image of quarks and gluons in the helium-4 nucleus.
Sanskriti Agrawal · Raktim Abir
We develop an operator-level framework for reconstructing the angular structure of small- diffractive amplitudes from energy-flow measurements. Focusing on coherent diffractive dijet production in the leading-eikonal approximation, we establish the relation between the angular multipoles of the dipole amplitude, the gluon Wigner distribution, and the diffractive scattering amplitude, while keeping their distinct radial transforms explicit. We show that, in the real common-phase sector and away from diffractive zeros, the normalized scattering amplitude can be reconstructed directly, up to a global sign convention, from the square root of the normalized energy-flow distribution. For generic complex amplitudes, the measured intensity instead determines autocorrelations of the amplitude spectrum and phase retrieval is not unique without additional information. We further discuss corrections arising from harmonic-dependent phases, practical conditions for an EIC extraction, and effects beyond the leading-eikonal approximation.
Simin Wu · Leyao Lin · Yilong Xie
We investigate how the transverse initial energy-density distribution controls the second sine harmonic of longitudinal polarization in Pb--Pb collisions at . We use (3+1)-dimensional Particle-In-Cell Relativistic ideal hydrodynamics and the Becattini--Buzzegoli--Palermo isothermal local-equilibrium prescription. Across the twelve selected initial states, the kinematic-vorticity contribution is negative, whereas the kinematic-shear contribution is positive. Changing the initial energy-density normalization , transverse smoothing width , or reduced impact parameter modifies the relative magnitudes of the two contributions rather than merely rescaling their sum. Reducing the transverse smoothing width generally strengthens both contributions, whereas increasing the initial energy-density normalization can preferentially weaken and reverse the total harmonic. At fixed , the impact-parameter dependence is mainly shear driven for narrower transverse smoothing and mainly vorticity driven for broader transverse smoothing. Applying the Liu--Yin prescription to the two tested hydrodynamic backgrounds reverses the total sign, showing that the sign depends on the polarization formula as well as on the fluid fields. Our results obtained with ideal hydrodynamics and the ILE prescription have the same sign and order of magnitude as the ALICE measurements for peripheral Pb--Pb collisions in the -- centrality interval, showing that such a positive harmonic can arise from an initial-state-controlled, shear-dominated balance at decoupling.
Yuki Fujimoto · Volodymyr Vovchenko
We investigate QCD thermodynamics in the intermediate-temperature regime using a gas of confining strings supplemented by excluded volume (EV) corrections. In this description, the discrete hadron resonance spectrum is replaced by an exponentially growing open-string spectrum characterized by a Hagedorn temperature , related to the confining string tension. With a common EV parameter shared by mesons and baryons, the model gives a good description of bulk lattice-QCD thermodynamics above the pseudocritical temperature. Among the values considered, provides the best agreement, lower than the value inferred from ideal-string-gas fits to the vacuum hadron spectrum. A simultaneous calibration of the mesonic and baryonic EV parameters gives and . Within the present spectral ansatz, the larger baryonic EV parameter indicates that stronger effective suppression is required in the baryon sector, although noticeable tensions remain in several conserved-charge observables.
Qi-Fang Lü · Xurong Chen · Yu-Bing Dong · Igor I. Strakovsky · Xiao-Yun Wang · Ju-Jun Xie
We present a phenomenological study of the near-threshold reaction, focusing on the interference effects between the channel resonances and non-resonance background. This reaction provides a complementary probe to photoproduction for investigating the nature of the hidden-charm pentaquark states. Using an effective Lagrangian approach, we construct scattering amplitudes for and states under two spin-parity scenarios, with the background dominated by the channel meson exchange. We find that the interference can produce peaks, dips, or complex line shapes depending on the relative phase, in contrast to the simple resonance peaks commonly reported in previous theoretical studies. The two spin-parity scenarios yield qualitatively similar patterns, indicating that our main conclusion is robust. Given the current scarcity of experimental data for the pion-induced channel, we emphasize the urgent need for future measurements at J-PARC to understand the dynamics of the interaction near threshold and to search for the heavy pentaquark states.
Domingo Gallegos · Roi Klein · Amos Yarom
We study the hydrodynamics of a charged fluid with spin degrees of freedom. We argue that, in a conformal field theory in 3+1 dimensions, the spin density is related to a linear combination of standard second-order transport coefficients, and an additional term quadratic in the gauge- and mixed gauge-gravitational anomaly coefficients. We compute the spin density in several free and holographic theories and compare the results.
S. Chen · M. Petri · S. Paschalis · H. L. Crawford · P. Doornenbal · R. Taniuchi · K. Wimmer · B. A. Brown · J. D. Holt · B. S. Hu · T. Miyagi · T. Otsuka and 27 other authors
High-resolution in-beam -ray spectroscopy of Ca was performed at the Radioactive Isotope Beam Factory (RIBF) at RIKEN. Excited states in Ca were populated via one-neutron and one-proton removal reactions from a Sc radioactive beam, and the emitted rays were detected using the HiCARI hybrid germanium detector array. The lifetime of the first excited state in Ca was measured for the first time through an analysis of Doppler-roadened -ray line shapes arising from relativistic recoil velocities. A lifetime of ps was deduced, corresponding to a reduced transition probability of at the 1 level, with a best-fit value of . The measured transition strength is compared with state-of-the-art shell-model and ab initio calculations, providing a stringent benchmark for shell-model Hamiltonians and effective charges and modern ab initio descriptions of the neutron-rich calcium isotopes approaching the potential = 40 shell closure.
Sinem Küçükyılmaz · Halil Mutuk
We investigate the spectroscopic and decay properties of the meson within a nonrelativistic quark model. We calculate the mass spectrum of radially and orbitally excited states in the -, -, and -wave sectors, the pseudoscalar and vector decay constants with one-loop QCD corrections, the E1 and M1 radiative widths, and radial Regge trajectories. The ground state and its first radial excitation agree well with experiment. The predicted decay constants are in line with relativistic model estimates and yield a corresponding prediction for the leptonic decay . The E1 transition pattern is governed primarily by radial-wave-function overlaps, and the dominant transitions of the lowest -wave multiplet suggest the radiative cascade as a promising pathway to the unobserved -wave states. The model predicts an inverted fine-structure ordering in the - and -wave multiplets, reflecting the competition between the one-gluon-exchange (OGE) and confinement contributions to the spin--orbit interaction. The allowed M1 widths are strongly suppressed by the small predicted hyperfine splittings, highlighting the importance of a direct mass measurement. The radial Regge trajectories are nearly linear across all considered families, with slopes decreasing as the orbital angular momentum increases. These results identify the mass and the fine-structure ordering of the lowest -wave multiplet as the key measurements for testing the spin-dependent dynamics of the system.