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DOE OSTI2025

Electrical switching of a p-wave magnet

Magnetic states with zero magnetization but non-relativistic spin splitting are outstanding candidates for the next generation of spintronic devices. Their electronvolt (eV)-scale spin splitting, ultrafast spin dynamics and nearly vanishing stray fields make them particularly promising for several applications. A variety of such magnetic states with non-trivial spin textures have been identified recently, including even-parity d-wave, g-wave or i-wave altermagnets and odd-parity p-wave magnets. Achieving voltage-based control of the non-uniform spin polarization of these magnetic states is of great interest for realizing energy-efficient and compact devices for information storage and processing. Spin-spiral type II multiferroics are optimal candidates for such voltage-based control, as they exhibit an inversion-symmetry-breaking magnetic order that directly induces ferroelectric polarization, allowing for symmetry-protected cross-control between spin chirality and polar order. Here we combine photocurrent measurements, first-principles calculations and group-theory analysis to provide direct evidence that the spin polarization of the spin-spiral type II multiferroic NiI 2 exhibits odd-parity character connected to the spiral chirality. The symmetry-protected coupling between chirality and polar order enables electrical control of a primarily non-relativistic spin polarization. Our findings represent an observation of p-wave magnetism in a spin-spiral type II multiferroic, which may lead to the development of voltage-based switching of non-relativistic spin polarization in compensated magnets.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2014

Qweak: First Direct Measurement of the Weak Charge of the Proton

The Qweak experiment at Hall C of Thomas Jefferson National Accelerator Facility has made the first direct measurement of the weak charge of the proton, QWp, through a precision measurement of the parity-violating asymmetry in elastic e-p scattering at low momentum transfer Q2= 0.025 (GeV/c)2 with incident electron beam energy of 1.155 GeV. The Qweak experiment, along with earlier results of parity violating elastic scattering experiments, is expected to determine the most precise value of QWp which is suppressed in the Standard Model. If this result is further combined with the 133Cs atomic parity violation (APV) measurement, significant constraints on the weak charge of the up quark, down quark, and neutron can be extracted. This data will also be used to determine the weak-mixing angle, sin2 θW, with a relative uncertainty of < 0.5% that will provide a competitive measurement of the running of sin2 θW to low Q2. An overview of the experiment and its results using the commissioning dataset, constituting approximately 4% of the data collected in the experiment, are reported here.

Nuruzzaman, NFN↗

DOE OSTI2026

Entire four-graviton EFT from the duality between color and kinematics

The Bern-Carrasco-Johansson (BCJ) double-copy construction reveals a fundamental structural connection between gauge and gravity theories. At its core, the BCJ double copy is directly due to a duality between the algebraic relations of a color root and those of a kinematic root. We generalize this principle beyond the conventional Lie algebra structure of tree-level Yang-Mills theory. By demanding color-kinematics duality for the complete basis of four-point color structures—including those involving the symmetric 𝑑 𝑎⁢𝑏⁢𝑐 constants—we define the universal double copy. We systematically classify the bases of all such parity-even generalized gauge-theory numerators and, independently, the space of all parity-even four-graviton higher-derivative operators. We demonstrate that our universal double-copy construction precisely spans the entire tower of parity-even four-graviton amplitudes in any dimension, except for the Lovelock 𝑅 3 contribution in 𝐷 > 6 which we can express in terms of a particularly simple universal triple-copy involving gauge theories coupled to scalars. Explicit machine-readable expressions for the complete basis of gauge-theory numerators and fundamental gravitational building blocks are provided in the Supplemental Material. This establishes that all possible four-point gravitational interactions can be factorized into products of gauge-theory building blocks governed by this universal notion of color-kinematics duality.

Carrasco, John Joseph M. [Northwestern Univ., Evan↗

DOE OSTI2018

Angular momentum distribution in Rydberg states excited by a strong laser pulse

We study the excitation to Rydberg states in the interaction of the hydrogen atom with a short, strong laser pulse. Utilizing solutions of the time-dependent Schrödinger equation we find that the parity of the populated angular momentum states agrees with the selection rules for multiphoton resonant absorption at low intensities, if the pulse length is not too short. In contrast, the parity effect cannot be observed for ultrashort pulses as well as for long pulses at high intensities. Here, we further identify signatures of the population in the excited states via the line emissions from the populated np states after the end of the pulse exhibiting the parity effect.

74 ATOMIC AND MOLECULAR PHYSICS↗

DOE OSTI2019

Restricted spin-range correction in the Oslo method: The example of nuclear level density and γ -ray strength function from Pu 239 ( d , p γ ) Pu 240

The Oslo method has been applied to particle- γ coincidences following the Pu 239 ( d , p ) reaction to obtain the nuclear level density (NLD) and γ -ray strength function ( γ SF ) of Pu 240 . Thus, the experiment was conducted with a 12 MeV deuteron beam at the Oslo Cyclotron Laboratory. The low spin transfer of this reaction leads to a spin-parity mismatch between populated and intrinsic levels. This is a concern for the Oslo method as it can have a significant impact on the extracted NLD and γ SF . We have developed an iterative approach to ensure consistent results even for cases with a large spin-parity mismatch, in which we couple Green's function transfer calculations of the spin-parity dependent population cross-section to the nuclear decay code rainier . The resulting γ SF shows a pronounced enhancement between 2–4 MeV that is consistent with the location of the low-energy orbital M 1 scissors mode.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2020

Constraining level densities through quantitative correlations with cross-section data

The adopted level densities (LD) for the nuclei produced through different reaction mechanisms significantly impact the accurate calculation of cross sections for the different reaction channels. Many common LD models make simplified assumptions regarding the overall behavior of the total LD and the intrinsic spin and parity distributions of the excited states. However, very few experimental constraints are taken into account in these models: LD at neutron separation energy coming from average spacings of s- and p-wave resonances ( D 0 and D 1 , respectively) whenever they have been previously measured, and the sometimes subjective extrapolation of discrete levels. These, however, constrain the LD only in very specific regions of excitation energy, and for specific spins and parities. This work aims to establish additional experimental constraints on LD through quantitative correlations between cross sections and LD. This allows for fitting and the determination of detailed structures in LD. For this we use the microscopic Hartree-Fock-Bogoliubov (HFB) LD as a starting point as the HFB LD provide a more realistic spin and parity distributions than phenomenological models such as Gilbert-Cameron (GC). We then associate variations predicted by the HFB model with the structure observed in double-differential cross sections at low outgoing neutron energy, a region that is dominated by the LD input. We also use (n, p) on 56 Fe , as an example case where angle-integrated cross sections are extremely sensitive to LD. For comparison purposes we also perform calculations with the GC model. With this approach we are able to perform fits of the LD based on actual experimental data, constraining the model and ensuring its consistency. This approach can be particularly useful in extrapolating the LD to nuclei for which high-excited discrete levels and/or values of D 0 or D 1 are unknown. Finally, it also predicts neutron-induced inelastic γ cross sections that in some cases can differ significantly from more standard phenomenological LD models such as GC.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2020

19 Ne level structure for explosive nucleosynthesis

Ne 19 is an important isotope in nuclear astrophysics due to its role in both the F 18 ( p , α ) O 15 and O 15 ( α , γ ) Ne 19 reactions in novae and Type I x-ray bursts, respectively. The energy levels of Ne 19 near the α and proton thresholds ( S α = 3529 keV, S p = 6410 keV) correspond to resonances in both of these reactions. Previous measurements to study the structure of Ne 19 have focused on both regions in an effort to constrain these reaction rates. Discrepancies in the energies, spins, and parities for levels in Ne 19 from previous measurements contribute to the reaction-rate uncertainties. Gamma rays from the depopulation of excited states in Ne 19 were measured to reduce the level-energy uncertainties and inconsistencies in previous spin-parity assignments.The F 19 ( He 3 , t ) Ne 19 reaction was used to elucidate the structure of Ne 19 levels up to E x = 6.9 MeV. The reaction products were measured using Gammasphere ORRUBA: Dual Detectors for Experimental Structure Studies—a coupling of the Oak Ridge Rutgers University Barrel Array and Gammasphere at Argonne National Laboratory. Tritons produced in the reaction were measured in coincidence with γ rays from the deexcitation of Ne 19 energy levels. Previously unobserved transitions allowed for discrepancies in the resonance properties relevant to these two reactions to be resolved. In total, 41 transitions from 21 energy levels were measured in Ne 19 , with 21 of those transitions being previously unobserved. Of particular importance, transitions from two 3 / 2 + states with energies of 6423(3) and 6441(3) keV, crucial for accurate estimations of the F 18 ( p , α ) O 15 reaction rate, were found. Energies and spin-parities of important energy levels near the proton and α thresholds were measured and some of the discrepancies in previous measurements were resolved. Overall, measurement of the two near-threshold 3 / 2 + states reduced the calculated upper limit of the F 18 ( p , α ) O 15 reaction rate by factors of 1.5–17 in the nova temperature range.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2022

Improved $^{95}\mathrm{Mo}$ neutron resonance parameters and astrophysical reaction rates

We report improved 95 Mo neutron resonance parameters and reaction rates are important for nuclear astrophysics, testing nuclear models, and nuclear criticality safety. However, despite many previous neutron-capture and total cross-section measurements on this nuclide, there still is much room for improvement as well as several discrepancies. For example, there are very few firm resonance spin and parity assignments; average resonance parameters are available only for each parity, the currently recommended astrophysical reaction rate results in disagreements between stellar models and meteoric isotopic anomalies, and there are substantial disagreements in the neutron-capture cross section at low energies important for nuclear criticality safety. To obtain an improved set of neutron resonance parameters and astrophysical reaction rates for 95 Mo. High-resolution neutron-capture and transmission data were measured at the Oak Ridge Electron Linear Accelerator (ORELA) using highly isotopically enriched 95 Mo samples. The neutron-capture apparatus, data reduction, and analysis were improved so that information contained in the γ-ray cascade following neutron capture were used to assign resonance J π values. Following this, simultaneous analysis of the new neutron-capture and transmission data was used to obtain resonance energies, gamma widths, and neutron widths and their uncertainties to a maximum energy of 10 keV. Accurate neutron-capture cross sections also were obtained for the unresolved resonance region to a maximum energy of 500 keV and, together with the new resonance parameters, used to calculate the astrophysical reaction rates in the temperature range from 5 to 30 keV. A vastly improved set of 95Mo neutron resonance parameters and an astrophysical reaction rate accurate to about 3% were obtained. Firm J π assignments were determined for 261 of the 314 observed resonances. This is a very large improvement over the previously published 32 firm J π assignments for 108 resonances. Also, the number of resonances having both firm J π assignments and Γ γ values was increased by almost a factor of 24—from 11 to 261. Neutron- and total-radiation-width distributions and average resonance spacings, average total radiation widths, and neutron strength functions were obtained for the six different s- and p-wave possibilities. Parameters for the lowest s-wave resonance, which is most important for criticality benchmarks, were obtained with high accuracy. Simple modification of the neutron-capture apparatus and expansion and improvement of data analysis techniques led to a large increase in firm J π assignments for 95 Mo neutron resonances. The resulting astrophysical reaction rate is 20%–30% larger than the currently recommended rate at s-process temperatures, which should lead to better agreement between stellar models and meteoric isotopic anomalies. The neutron-capture cross section at low energies is substantially larger than recommended in the latest evaluation, which is problematical for criticality benchmarks. The average resonance spacing as a function of spin and parity is significantly different from current models. The total-radiation-width distributions are significantly broader than predicted by theory and show significant departures from the expected Gaussian shapes.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2023

Event-by-event correlations between Λ ( Λ ¯ ) hyperon global polarization and handedness with charged hadron azimuthal separation in Au + Au collisions at s N N = 27 GeV from STAR

Global polarizations (P) of Λ (Λ¯) hyperons have been observed in non-central heavy-ion collisions. The strong magnetic field primarily created by the spectator protons in such collisions would split the Λ and Λ¯ global polarizations (ΔP=P Λ –P Λ ¯<0). Additionally, quantum chromodynamics (QCD) predicts topological charge fluctuations in vacuum, resulting in a chirality imbalance or parity violation in a local domain. This would give rise to an imbalance (Δn = N L –N R /< N L +N R > ≠0) between left- and right-handed Λ (Λ¯) as well as a charge separation along the magnetic field, referred to as the chiral magnetic effect (CME). This charge separation can be characterized by the parity-even azimuthal correlator (Δγ) and parity-odd azimuthal harmonic observable (Δa 1 ). Measurements of ΔP, Δγ, and Δa 1 have not led to definitive conclusions concerning the CME or the magnetic field, and Δn has not been measured previously. Correlations among these observables may reveal new insights. Furthermore, this paper reports measurements of correlation between Δn and Δa 1 , which is sensitive to chirality fluctuations, and correlation between ΔP and Δγ sensitive to magnetic field in Au+Au collisions at 27 GeV. For both measurements, no correlations have been observed beyond statistical fluctuations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2017

Search for excited states in O 25

Theoretical calculations suggest the presence of low-lying excited states in 25 O. Previous experimental searches by means of proton knockout on 26 F produced no evidence for such excitations. We search for excited states in 25 O using the 24 O(d,p) 25 O reaction. The theoretical analysis of excited states in unbound 25,27 O is based on the configuration interaction approach that accounts for couplings to the scattering continuum. We use invariant-mass spectroscopy to measure neutron-unbound states in 25 O. For the theoretical approach, we use the complex-energy Gamow Shell Model and Density Matrix Renormalization Group method with a finite-range two-body interaction optimized to the bound states and resonances of 23–26 O, assuming a core of 22 O. Here we predict energies, decay widths, and asymptotic normalization coefficients. Our calculations in a large spdf space predict several low-lying excited states in 25 O of positive and negative parity, and we obtain an experimental limit on the relative cross section of a possible J π = 1/2 + state with respect to the ground state of 25 O at σ 1/2+ /σ g.s. = 0.25$^{+1.0}_{-0.25}$. We also discuss how the observation of negative parity states in 25 O could guide the search for the low-lying negative parity states in 27 O. Previous experiments based on the proton knockout of 26 F suffered from the low cross sections for the population of excited states in 25 O because of low spectroscopic factors. In this respect, neutron transfer reactions carry more promise.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2018

Structure of the exotic He 9 nucleus from the no-core shell model with continuum

Here, the exotic 9 He nucleus, which presents one of the most extreme neutron-to-proton ratios, belongs to the N = 7 isotonic chain famous for the phenomenon of ground-state parity inversion with decreasing number of protons. Consequently, it would be expected to have an unnatural (positive) parity ground state similar to 11 Be and 10 Li. Despite many experimental and theoretical investigations, its structure remains uncertain. Apart from the fact that it is unbound, other properties including the spin and parity of its ground state, and the very existence of additional low-lying resonances are still a matter of debate

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2018

Toward complete spectroscopy using β decay: The example of Cl 32 ( β γ ) S 32

$^{32}\textbf{Cl}$ is a neutron-deficient isotope with a $β$-decay half-life of 298 ms and a spin and parity of $J^π=1^+$. Previous measurements of $^{32}\textbf{Cl}$ $β$-delayed $γ$ rays have yielded a $β$-decay scheme with twelve $β$-decay transitions, contributing to studies of nuclear structure and fundamental symmetries. Those experiments have been limited to the observation of $^{32}\textbf{S}$ states with $J^π = 0^+,1^+, 2^+$. Our goal is to search for new $β$-delayed $γ$ rays and $β$-decay transitions of $^{32}\textbf{Cl}$ to $^{32}\textbf{S}$. A measurement of $^{32}\textbf{Cl}$ $β$-delayed $γ$ decay has been performed using the Clovershare array of high-purity germanium detectors at the National Superconducting Cyclotron Laboratory. By acquiring the highest-statistics $^{32}\textbf{Cl}$ $β$-delayed $γ$-ray spectrum to date and exploiting a new sensitivity to $γ-γ$ coincidences, this experiment has enabled the observation of nine previously unobserved $β$-delayed $γ$-ray transitions, leading to the inference of five $β$-decay transitions never before observed in $^{32}\textbf{Cl}$ $β$-delayed $γ$ decay. The set of observed states includes negative-parity states for the first time. By combining the new information with data from previous work, the lifetimes and partial widths of the 8861- and 9650-keV states of $^{32}\textbf{S}$ have been determined. In addition, the $^{31}\textbf{P}$($p,α$)$^{28}\textbf{Si}$ resonance strength of the 9650-keV state has been limited to $ωγ<9.8$ meV, which is an improvement over direct measurements. An enhanced decay scheme has been constructed. Most of the excited bound $^{32}\textbf{S}$ states that would correspond to allowed and first-forbidden $β$-decay transitions have been observed, demonstrating the potential of $β$-decay experiments to approach complete spectroscopy measurements at the next generation of radioactive beam facilities. The observed positive-parity levels are well matched by $sd$ shell-model calculations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2019

Experimental study of Cl 35 excited states via S 32 ( α , p )

The presolar grains originating in oxygen-neon novae may be identified more easily than those of other stellar sources if their sulfur isotopic ratios ($^{33}\mathrm{S}/^{32}\mathrm{S}$ and $^{34}\mathrm{S}/^{32}\mathrm{S}$) are compared with the theoretical ones. The accuracy of such a comparison depends on reliable $^{33}\mathrm{S}(p,{\gamma})^{34}\mathrm{Cl}$ and $^{34}\mathrm{S}(p,{\gamma})^{35}\mathrm{Cl}$ reaction rates at the nova temperature regime. The latter rate has recently been computed based on experimental input, and many new excited states in $^{35}\mathrm{Cl}$ were discovered above the proton threshold. As a result, the experimental $^{34}\mathrm{S}(p,{\gamma})^{35}\mathrm{Cl}$ rate was found to be less uncertain and 2–5 times smaller than the theoretical one. Consequently, the simulated $^{34}\mathrm{S}/^{32}\mathrm{S}$ isotopic ratio for nova presolar grains was predicted to be smaller than that of type II supernova grains by a factor of 1.5 to 3.7. The present study was performed to confirm the existence of these new resonances, and to improve the remaining uncertainties in the S 34 ( p , γ ) Cl 35 reaction rate. Energies and spin-parities of the Cl 35 excited levels were investigated via high-resolution charged-particle spectroscopy with an Enge split-pole spectrograph using the S 32 ( α , p ) Cl 35 reaction. Differential cross sections of the outgoing protons were measured at E α = 21 MeV. Distorted-wave Born approximation calculations were carried out to constrain the spin-parity assignments of observed levels, with special attention to those significant in determination of the S 34 ( p , γ ) Cl 35 reaction rate over the nova temperature regime. The existence of these newly discovered states are largely confirmed, although a few states were not observed in this study. The spins and parities of a few Cl 35 states were assigned tentatively for the first time. The present S 34 ( p , γ ) Cl 35 experimental thermonuclear reaction rate at 0.1–0.4 GK is consistent within 1 σ with the previous evaluation. However, our rate uncertainty is larger than before due to a more realistic treatment of the uncertainties in the rate input. In comparison with the previous rate evaluation, where the high and low rates differed by less than a factor of 2 over the nova temperature regime, the ratio of the present limit rates is at most a factor of 3.5 at 0.12 GK. At temperatures above 0.2 GK, we recommend the future work to focus on determination of the unknown properties of four excited states of Cl 35 : 6643, 6761, 6780, and 6800 keV.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2024

Fluctuations and correlations of baryonic chiral partners

The exploration of critical phenomena in phase transitions of strongly interacting matter governed by quantum chromodynamics (QCD) is one of the goals of present ultrarelativistic heavy-ion collision experiments at BNL and CERN. The key research direction is to locate the putative critical point on the phase diagram of QCD linked to the chiral symmetry restoration at finite temperature and/or density. One of the main theoretical tools used for this purpose is the fluctuations of conserved charges, such as the net-baryon number. However, due to experimental limitations, analyses of heavy-ion collision data suffer from a very doubtful basing of the net-proton number being a proxy for the total net-baryon number fluctuations. In this work, we use the parity doublet model to investigate the fluctuations of the net-baryon number density in hot and dense hadronic matter. The model accounts for chiral criticality within the mean-field approximation. We focus on the qualitative properties and systematics of the first- and second-order susceptibility of the net-baryon number density, and their ratios for nucleons of positive and negative parity, as well as their correlator. We show that the fluctuations of the positive-parity nucleon do not necessarily reflect the fluctuations of the total net-baryon number density at the phase boundary of the chiral phase transition. We also investigate the nontrivial structure of the correlator. Furthermore, we discuss and quantify the differences between the fluctuations of the net-baryon number density in the vicinity of the chiral and liquid-gas phase transition in nuclear matter. We indicate a possible relevance of our results with the interpretation of the experimental data on net-proton number fluctuations in heavy-ion collisions. Published by the American Physical Society 2024

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2024

Dark matter in a mirror solution to the strong C P problem

We study thermal production of dark matter (DM) in a realization of the minimal models of Bonnefoy [], where parity is used to solve the strong C P problem by transforming the entire Standard Model (SM) into a mirror copy. Although the mirror electron e ′ is a good DM candidate, its viability is mired by the presence of the mirror up quark u ′ , whose abundance is intimately related to the e ′ abundance and must be suppressed. This can be achieved through a sequential freeze-in mechanism, where mirror photons are first produced from SM gluons, and then the mirror photons produce e ′ . After computing the details of this double freeze-in, we discuss the allowed parameter space of the model, which lies at the threshold of experimental observations. We find that this origin of e ′ DM requires a low reheating temperature after inflation and is consistent with the baryon asymmetry arising from leptogenesis, providing mirror neutrinos have a significant degeneracy. Finally, we show that this e ′ DM is not compatible with Higgs parity, the simplest scheme with exact parity, unless SM parameters deviate significantly from their central values or the minimal model is extended. Published by the American Physical Society 2024

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2015

POLARBEAR constraints on cosmic birefringence and primordial magnetic fields

Here, we constrain anisotropic cosmic birefringence using four-point correlations of even-parity E-mode and odd-parity B-mode polarization in the cosmic microwave background measurements made by the POLARization of the Background Radiation (POLARBEAR) experiment in its first season of observations. We find that the anisotropic cosmic birefringence signal from any parity-violating processes is consistent with zero. The Faraday rotation from anisotropic cosmic birefringence can be compared with the equivalent quantity generated by primordial magnetic fields if they existed. The POLARBEAR nondetection translates into a 95% confidence level (C.L.) upper limit of 93 nanogauss (nG) on the amplitude of an equivalent primordial magnetic field inclusive of systematic uncertainties. This four-point correlation constraint on Faraday rotation is about 15 times tighter than the upper limit of 1380 nG inferred from constraining the contribution of Faraday rotation to two-point correlations of B-modes measured by Planck in 2015. Metric perturbations sourced by primordial magnetic fields would also contribute to the B-mode power spectrum. Using the POLARBEAR measurements of the B-mode power spectrum (two-point correlation), we set a 95% C.L. upper limit of 3.9 nG on primordial magnetic fields assuming a flat prior on the field amplitude. This limit is comparable to what was found in the Planck 2015 two-point correlation analysis with both temperature and polarization. Finally, we perform a set of systematic error tests and find no evidence for contamination. This work marks the first time that anisotropic cosmic birefringence or primordial magnetic fields have been constrained from the ground at subdegree scales.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2018

Structure of the nucleon’s low-lying excitations

Here, a continuum approach to the three valence-quark bound-state problem in quantum field theory is used to perform a comparative study of the four lightest ( I = 1/2, J P = 1/2 ± ) baryon isospin doublets in order to elucidate their structural similarities and differences. Such analyses predict the presence of nonpointlike, electromagnetically active quark-quark (diquark) correlations within all baryons; and in these doublets, isoscalar-scalar, isovector-pseudovector, isoscalar-pseudoscalar, and vector diquarks can all play a role. In the two lightest (1/2,1/2 + ) doublets, however, scalar and pseudovector diquarks are overwhelmingly dominant. The associated rest-frame wave functions are largely S-wave in nature; and the first excited state in this 1/2 + channel has the appearance of a radial excitation of the ground state. The two lightest (1/2,1/2 – ) doublets fit a different picture: accurate estimates of their masses are obtained by retaining only pseudovector diquarks; in their rest frames, the amplitudes describing their dressed-quark cores contain roughly equal fractions of even- and odd-parity diquarks; and the associated wave functions are predominantly P-wave in nature, but possess measurable S-wave components. Moreover, the first excited state in each negative-parity channel has little of the appearance of a radial excitation. In quantum field theory, all differences between positive- and negative-parity channels must owe to chiral symmetry breaking, which is overwhelmingly dynamical in the light-quark sector. Consequently, experiments that can validate the contrasts drawn herein between the structure of the four lightest (1/2,1/2 ± ) doublets will prove valuable in testing links between emergent mass generation and observable phenomena and, plausibly, thereby revealing dynamical features of confinement.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2018

Possible interpretation of the newly observed Ω ( 2012 ) state

Inspired by the newly observed $Ω (2012)$ state at Belle II, we investigate the two-body strong decays of $Ω$ baryons up to $N = 2$ shell within the chiral quark model. Our results indicate that (i) the newly observed $Ω (2012)$ state could be assigned to the spin-parity $J^P = 3 / 2^-$ state |$70,^{2}10, 1, 1, \frac{3^-}{2}$$\rangle$ and the experimental data can be reasonably described. However, the spin-parity $J^P = 1 / 2^-$ state |$70,^{2}10, 1, 1, \frac{1^-}{2}$$\rangle$ and spin-parity $J^P = 3 / 2^+$ state |$56, ^{4}10, 2, 0, \frac{3^+}{2}$$\rangle$ cannot be completely excluded. (ii) The $D$-wave states in the $N = 2$ shell are most likely to be narrow states with a width of dozens of MeV and have a good potential to be observed in the $\Xi$$K$ and/or $\Xi(1530)K$ channels in future experiments. The $Ω(2250)$ resonance listed in PDG may be a good candidate for the $J^P$ = $5/2^+$ $1D$ wave state |$56$,$^{4}10$, $2, 2$, $5/2^+$ $\rangle$ .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗