Baryon Resonances Research Articles

Anatomy of critical fluctuations in hadronic matter

Critical phenomena in phase transitions of strongly interacting matter, governed by quantum chromodynamics, are inherently encoded in the fluctuations of conserved charges. In this work, we study the net-baryon number density fluctuations, including the lowest-lying nucleon and the baryonic resonance Δ(1232), based on the parity doublet model in the mean-field approximation. We focus on the qualitative features of the second-order susceptibility of the net-baryon number density in dense hadronic matter and how the inclusion of Δ(1232) affects it. We demonstrate that the fluctuations of the individual baryons do not necessarily reflect the total net-baryon number fluctuations at finite density, due to the nontrivial correlations between different particle species. Our results highlight the role of baryonic correlations in the interpretation of data from heavy ion collision experiments. Published by the American Physical Society 2024

Searching for the first radial excitation of the Δ(1232) in lattice QCD

We present a lattice QCD analysis of the Δ-baryon spectrum, with the goal of finding the position of the 2s radial excitation of the Δ(1232) ground state. Using smeared three-quark operators in a correlation matrix analysis, we report masses for the ground, first and second excited states of the J P = 3/2+ spectrum across a broad range of mπ2 . We identify the lowest lying state as being a 1s state, consistent with the well known Δ(1232). The first excitation is identified as a 2s state, but is found to have a mass of approximately 2.15 GeV on our ∼3 fm lattice, which does not appear to be associated with the Δ(1600) resonance in a significant manner. We also report on the spin-1/2 and odd-parity states accessible via our methods. The large excitation energies of the radial excitations provide a potential resolution to the long-standing missing baryon resonances problem.

Intriguing aspects of light baryon resonances

We discuss that some light baryon resonances exhibit properties which cannot be described when attributing a three-valence quark structure to them. Besides pointing out the hadron resonances which clearly require description beyond the quark model, we focus on the third s11, N∗ state and its decay to final states consisting of the lightest hyperon resonances which have a partial width comparable to that for the decay to πN. Such properties of the mentioned nucleon resonance get manifested in the cross sections and other observables related to processes producing the lightest hyperon resonances. We show that all these findings arise from the strong association of the baryon resonances to the dynamics among the ground-state hadrons.

Extraction of polarization observables in two pion photoproduction reactions

The relevance of the study of polarization observables to gather insight on the features of baryonic resonances, and the procedure applied for the extraction of this information from the data, are illustrated. The reference reaction is the photoproduction of two charged pions with both a polarized beam and target, experimental conditions that were met in the g14 (2012) run of the CLAS experiment at Jefferson Lab. The method for the determination of the I⊙ observable is discussed and illustrated utilizing previously published data.

Dilepton production in proton-proton reaction at 4.5 GeV with the HADES spectrometer

Spectra of dileptons emitted in hadron collisions are important tool to study electromagnetic decays of resonances and the validity of the Vector Meson Dominance model. Furthermore, they provide reference spectra for the hot and dense (heavy-ion A+A collisions) and cold nuclear matter (p+A collisions). In February 2022, proton-proton reactions at 4.5 GeV beam kinetic energy were measured by HADES experiment. The aim of the analysis is to study the specific channels that produced dileptons, such as baryonic resonance Dalitz decays (Δ/N* → Ne+e−) and vector meson decays (ρ/ω/φ→ e+e−). In addition, the investigations of dielectron production above the φ meson mass will be enabled. In this contribution, different steps of the e+e− pair reconstruc tion are discussed.

Studies of Time-like Electromagnetic Structure of Baryons with HADES

We present results of studies of Dalitz decays of baryon resonances (R→Ne+e−) in proton-proton (pp) and pion-proton (πp) collisions performed by the HADES collaboration. They provided the first measurement of electromag netic transition form factors of baryons in the time-like region and contribute to the understanding of the photon-baryon coupling and the role of Vector Dom inance Model in a baryonic sector. We discuss also implications of the results to the understanding of the emissivity of dense and hot QCD matter created in heavy-ion collisions and the role played by the in-medium modification of the ρ meson. Further prospects for future studies with pion beams at GSI with HADES are given in the outlook.

The light baryon resonance spectrum in a coupled-channel approach – Recent results of the Jülich-Bonn model

We present recent results from the Jülich-Bonn dynamical coupledchannel approach, where the spectrum of nucleon and Delta resonances is extracted based on a combined study of the pion- and photon-induced production of πN, ηN, KΛ and KΣ final states. The amplitudes of the Jülich-Bonn model also enter the study of electroproduction reactions as constraints at Q2 = 0.

Partial Wave Amplitude Analysis in Pion-Induced Reactions at the HADES Experiment

The High Acceptance Di-Electron Spectrometer (HADES) collaboration at GSI employs a pion beam to examine the characteristics of baryonic resonances and their decay channels. This pion-beam facility enables the generation of baryonic resonances at a fixed center of mass energy (√s), i.e. in the S-channel. In anticipation of conducting a more comprehensive exploration of the resonance regions in pion-proton collisions, a new implementation of the K-matrix & D-matrix frameworks is currently under development. This updated implementation aims to offer a refined mapping of these regions. Example fits are presented showing the current status and the potential of the new framework.

Effects of multiple single-particle basis states in scattering systems

Low-lying baryon resonances have been explored using Hamiltonian Effective Field Theory (HEFT), in a formalism where resonances with a three-quark component are described by both two-particle meson–baryon states and a bare basis state. Here, we investigate the use of multiple bare states in the Hamiltonian, to extend the formalism to higher energy ranges, and represent a larger portion of the low-lying baryon spectrum. Introducing a second bare state into a toy model extension of the low-energy Δ(1232) system, we explore the influence of the second bare state on the position of poles in the infinite-volume T-matrix. Considering the same system in a finite-volume, we analyse the finite-volume energy spectrum in the presence of a second bare state, providing insight into the interplay between two bare basis states, representing quark-model states, and the relationship between infinite-volume poles and finite-volume eigenstates.

Study of Static Properties of $$\Delta $$ Baryon Resonances in the Relativistic Potential Model Formalism

Study of Static Properties of $$\Delta $$ Baryon Resonances in the Relativistic Potential Model Formalism

Exploring the hadronic phase of relativistic heavy-ion collisions with resonances in ALICE

Hadronic resonances, having short lifetimes, are useful for studying the hadrongas phase that characterizes the late-stage evolution of high-energy nuclear collisions. Indeed, regeneration and rescattering processes occurring in the hadron gas modify the measured yields of hadronic resonances and can be studied by measuring resonance yields as a function of system size and comparing them to model predictions with and without hadronic interactions. Measurements of the differential yields of resonances with different lifetime, mass, quark content, and quantum numbers help in understanding particle production mechanisms, the lifetime of the hadronic phase, strangeness production, parton energy loss, rapidity yield asymmetry, and collective effects. With its excellent tracking and particle identification capabilities, the ALICE experiment measured a comprehensive set of mesonic and baryonic resonances. We present recent results on resonance production in pp, p–Pb, Xe–Xe and Pb–Pb collisions at various center-of-mass energies, highlighting new results of K*±, Λ(1520), and Σ*±(1385). The results are also compared to lower energy measurements and model calculations.

Light baryon resonances from a coupled-channel study including mathbf {KSigma } photoproduction

The Jülich-Bonn dynamical coupled-channel approach is extended to include KSigma photoproduction off the proton. Differential cross section and (double) polarization data for K^+Sigma ^0 and K^0Sigma ^+ are analysed simultaneously with the pion- and photon-induced production of pi N, eta N, KLambda , and KSigma final states, totaling almost 72,000 data points for center-of-mass energies W<2.4 GeV. Based on the fit results the spectrum of N^* and Delta resonances is extracted in terms of pole positions and residues. We discuss the impact of the gamma prightarrow KSigma channels in detail and investigate the influence of recent polarization data for eta p photoproduction.

Anomaly-induced chiral mixing in cold and dense matter

We construct the spectral functions for light vector mesons at finite density and temperature in the presence of a novel mixing between parity partners, induced by baryon density via the Wess-Zumino-Witten action. As the main origin of in-medium broadening, a set of baryon resonances that strongly couple to the vector mesons and the modifications of kaons and anti-kaons due to the Kaplan-Nelson term are included. It is shown that the vector spectra, even with the broadening effects, exhibit sizable signatures of chiral symmetry restoration thanks to the chiral mixing depending on three-momenta carried by the vector mesons. Those spectral functions are used to calculate the integrated production rates of lepton pairs, and a proper binning in momenta and potential decrease in the vector-meson masses due to chiral symmetry restoration are discussed in quantifying the signatures.

In-medium effects in ϕ meson production in heavy-ion collisions from subthreshold to relativistic energies

We investigate the hidden strange $\phi$ meson production in heavy-ion collisions from subthreshold ($E_{kin}\approx 1$ A GeV) to relativistic ($E_{kin}\approx 21$ A TeV) energies as well as its coupling to the open strange mesons (kaons, antikaons) and their productions. Our study is based on the off-shell microscopic Parton-Hadron-String Dynamics (PHSD) transport approach which is applicable for the dynamical description of strongly interacting hadronic and partonic degrees-of-freedom created in heavy-ion collisions. Implementing novel meson-baryon and meson-hyperon production channels for $\phi$ mesons, calculated within a T-matrix coupled channel approach based on the extended SU(6) chiral effective Lagrangian model, along with the collisional broadening of the $\phi$-meson in-medium spectral function, we find a substantial enhancement of $\phi$ meson production in heavy-ion collisions, especially at sub- and near-thresholds. This allows to describe the experimentally observed strong enhancement of the $\phi/K^-$ ratio at low energies without including hypothetical decays of heavy baryonic resonances to $\phi$ as in alternative approaches. Moreover, we show that in spite of a stronger contribution from enhanced $\phi$ to $K^-$ production, the majority of the experimental data for different A+A systems at low energies favor the scenario with in-medium modifications of the kaon and antikaon properties in the hot and dense environment. Moreover, we study the influence of the final state interactions of $K, \bar K$ mesons on the reconstruction of $\phi$'s by the by invariant mass method.

Systematic study of Δ (1232) resonance excitations using single isobaric charge-exchange reactions induced by medium-mass projectiles of Sn

The fragment separator FRS has been for the first time used to measure the (n,p) and (p,n)-type isobaric charge-exchange cross sections of stable 112,124Sn isotopes accelerated at 1A GeV with an uncertainty of 3% and to separate quasi-elastic and inelastic components in the missing-energy spectra of the ejectiles. The inelastic contribution can be associated to the excitation of isobar {\Delta}(1232) resonances and to the pion emission in s-wave, both in the target and projectile nuclei, while the quasi-elastic contribution is associated to the nuclear spin-isospin response of nucleon-hole excitations. The data lead to interesting results where we observe a clear quenching of the quasi-elastic component and their comparisons to theoretical calculations demonstrate that the baryonic resonances can be excited in the target and projectile nuclei. To go further in this investigation, we propose to study the excitation of baryonic resonances taking advantage of the combination of high-resolving power magnetic spectrometers with the WASA calorimeter. These new measurements will allow us to determine the momenta of the ejectiles and pions emitted in coincidence after the single isobaric charge-exchange collisions, providing us unique opportunities to study the evolution of the baryonic resonance dynamics with the neutron-proton asymmetry through the use of exotic radioactive ion beams.

Electromagnetic transition amplitude for Roper resonance from holographic QCD

The Roper resonance, the first excited state of the nucleon, Is one of the best-established baryon resonances. Yet, its properties have not been consistently explained by effective models of QCD, such as the non-relativistic quark model. In this letter, we propose an alternative approach in the Sakai-Sugimoto model that is one of the holographic models of QCD. In particular, we analyze the helicity amplitude of the electromagnetic transitions at the leading of 't~Hooft coupling $1/\lambda$. The model incorporates baryon structure at short distance by non-linear mesons surrounded by meson clouds at long distance. We demonstrate that the recently observed data by CLAS are explained in the present approach.

Hyperon physics at HADES as a fair phase-0 experiment

The HADES experiment investigates the nuclear matter and the properties of baryonic resonances. As part of the FAIR Phase-0 program, HADES is being upgraded to enable a wide range of experiments, including investigating electromagnetic decays of hyperons produced in proton-induced reactions. Feasibility studies show that the newly installed forward detectors are crucial for hyperon reconstruction. The detector upgrade and feasibility studies in preparation for the upcoming beamtimes are presented.

Strong decays of multistrangeness baryon resonances in the quark model

Decay properties of multistrangeness $\mathrm{\ensuremath{\Xi}}$ and $\mathrm{\ensuremath{\Omega}}$ baryon resonances are investigated within the constituent quark model by including relativistic corrections. The strong decay widths of various $\mathrm{\ensuremath{\Xi}}$ and $\mathrm{\ensuremath{\Omega}}$ resonances are computed and tested for internal quark configurations to pin down their spin-parity (${J}^{P}$) quantum numbers and internal structures. We found that the Roper-like resonances in the multistrangeness sector have large decay widths bearing resemblances to their siblings in light and heavy baryon sectors. In addition, we obtained the decay ratio for the $\mathrm{\ensuremath{\Omega}}(2012)$ as $\mathrm{\ensuremath{\Gamma}}(\mathrm{\ensuremath{\Omega}}\ensuremath{\rightarrow}\mathrm{\ensuremath{\Xi}}\overline{K}\ensuremath{\pi})/\mathrm{\ensuremath{\Gamma}}(\mathrm{\ensuremath{\Omega}}\ensuremath{\rightarrow}\mathrm{\ensuremath{\Xi}}\overline{K})=4.5%$, which is consistent with the experimental data when ${J}^{P}=3/{2}^{\ensuremath{-}}$ is assigned. This observation holds the possibility that the $\mathrm{\ensuremath{\Omega}}(2012)$ could naturally be explained as a three-quark state in the quark model. The decays of other low-lying $\mathrm{\ensuremath{\Xi}}$ and $\mathrm{\ensuremath{\Omega}}$ resonances are systematically analyzed, which would be useful to unveil the structure of these resonances in future experiments.

Chiral symmetry restoration and Δ matter formation in neutron stars

We analyze the effects of chiral symmetry restoration in hadronic matter, including the lowest-lying baryonic resonance $\Delta$ based on the parity doublet model. We study the role of $\Delta$ and its chiral partner on the equation of state (EoS) of dense matter under neutron star (NS) conditions of $\beta$-equilibrium and charge neutrality. We find that the softening of the EoS driven by the early onset of $\Delta$ matter due to partial restoration of chiral symmetry allows accommodating the modern multi-messenger astrophysical constraints on the mass, radius, and tidal deformability. The softening above the saturation density is accompanied by subsequent stiffening at high densities. We also find that the matter composition in the NS cores may be different upon variations of the repulsive interactions of $\Delta$ baryons in hadronic matter.

Study of neutrino-nucleus reactions with crisp model ( 0&lt;Eν&lt;3 GeV )

The neutrino-nucleus reactions are studied at energies from 0 to 3 GeV, using the CRISP program. To simulate these reactions, CRISP uses the Monte Carlo method through an intranuclear cascade model. Quase-elastic and baryonic resonance formation channels for the neutrino-nucleon interaction are considered. The total and differential particle emission cross-sections were obtained, obtaining a good agreement with the values reported by the MiniBooNE experiment. The influence of nuclear effects on the studied reactions, such as fermionic motion, the Pauli blocking mechanism, and the nucleonic separation energy, was shown. It was not possible to simultaneously reproduce the $\nu_\mu + D$ and $\nu_\mu + ^{12}C$ reactions using the same axial mass value. For the charged current quasi-elastic channel, $M_A = 0.95 \ GeV$ for the $\nu_\mu + D$ reaction, and $M_A = 1.35 \ GeV$ for the $\nu_\mu + ^{12}C$ reaction. This can be solved if one considers, in addition to the neutrino-nucleon interaction, the neutrino interaction with a pair of nucleons, just as we demonstrate in the last part of this work.