As an example of dynamically generated resonances we mention the interaction of vector mesons with baryons within the local hidden gauge formalism which gives rise to a large amount of such states, many of which can be associated to known resonances, while others represent predictions for new resonances. The width of these states coming from decay into pseudoscalar baryon is also addressed. We also mention recent states coming from $Δρπ$ interaction obtained with Faddeev equations.
We present the results of the first calculations involving the interaction of vector mesons with baryons, by means of which one generates a large amount of dynamically generated resonances, many of which can be associated to known resonances, while others represent predictions for new states.
The influence of resonance decays on the elliptic flows of stable hadrons is studied in the quark coalescence model. Although difference between the elliptic flow of pions from resonance decays, except the rho meson, and that of directly produced pions is appreciable, those for other stable hadrons are small. Since there are more pions from the decays of rho mesons than from other resonances, including resonance decays can only account partially the deviation of final pion elliptic flow from the observed scaling of hadron elliptic flows, i.e., the hadron elliptic flow per quark is the same at …
A statistical model for decay and formation of heavy hadronic resonances is formulated. The resonance properties become increasingly uncertain with increasing resonance mass. Drawing on analogy with the situation in low-energy nuclear physics, we employ the Weisskopf approach to the resonance processes. In the large-mass limit, the density of resonance states in mass is governed by a universal Hagedorn-like temperature T_H. As resonances decay, progressively more and more numerous lighter states get populated. For T_H \simeq 170 MeV, the model describes data for the hadron yield ratios at the …
We discuss the indirect and direct role of the short-lived resonances as probes of QGP freeze-out process. The indirect effect is the distortion of stable single particle yields and spectra by contributions of decaying resonances, which alter significantly the parameters obtained in fits to experimental data. We than discuss the direct observation of short-lived resonances as a probe of post-hadronization dynamics allowing to distinguish between different hadronization models.
Recent developments in hadron spectroscopy triggers the discussion on various exotic configurations beyond the simple three-quark state for baryons and quark-anti-quark pair for mesons. In particular, the states observed near a two-hadron threshold are often regarded as candidates of hadronic molecules, which are made of constituent hadrons and dynamically generated by the hadronic interactions. However, identification of the hadronic molecules involves several subtle difficulties which are often overlooked or underestimated. Here we summarize these subtleties and present a promising approach …
Some recent developments in chiral dynamics of hadrons and hadrons in a medium are presented. Unitary schemes based on chiral Lagrangians describe some hadronic states as being dynamically generated resonances. We discuss how standard quantum many body techniques can be used to calculate the properties of these dynamically generated and other hadrons in the nuclear medium. We present some results for vector mesons ($ρ$ and $ϕ$), scalar mesons ($σ$, $κ$, $a_0(980)$, $f_0(980)$), the $Λ(1520)$ and for the in-medium baryon-baryon interaction.
The charged hadron multiplicity fluctuations are considered in the canonical ensemble. The microscopic correlator method is extended to include three conserved charges: baryon number, electric charge and strangeness. The analytical formulae are presented that allow to include resonance decay contributions to correlations and fluctuations. We make the predictions for the scaled variances of negative, positive and all charged hadrons in the most central Pb+Pb (Au+Au) collisions for different collision energies from SIS and AGS to SPS and RHIC.
Strongly intensive measures $Δ$ and $Σ$ are used to study event-by-event fluctuations of hadron multiplicities in nucleus-nucleus collisions. The effects of resonance decays are investigated within statistical model and relativistic transport model. Two specific examples are considered: resonance decays to two positively charged particles (e.g., $Δ^{++}\rightarrow p+ π^+$) and to $π^+π^-$-pairs. (e.g., $ρ^0\rightarrow π^-+π^+$). It is shown that resonance abundances at the chemical freeze-out can be estimated by measuring the fluctuations of the number of stable hadrons. These model results ar…
We update our chemical analysis of (strange) hadrons produced at the SPS in Pb--Pb collisions at 158A GeV and and present a first chemical analysis of RHIC results. We report that the shape of (anti)hyperon m_T-spectra in a thermal freeze-out analysis leads to freeze-out conditions found in chemical analysis, implying sudden strange hyperon production. We discuss how a combined analysis of several strange hadron resonances of differing lifespan can be used to understand the dynamical process present during chemical and thermal freeze-outs. In medium resonance quenching is considered.
A nonlinear chiral SU(3) approach including the spin 3/2 decuplet is developed to describe dense matter. The coupling constants of the baryon resonances to the scalar mesons are determined from the decuplet vacuum masses and SU(3) symmetry relations. Different methods of mass generation show significant differences in the properties of the spin-3/2 particles and in the nuclear equation of state.
The development of theoretical photonuclear physics over the last 40 years is illustrated by a few selected examples highlighting a number of important issues like collective motion in nuclei, the role of subnuclear degrees of freedom, relativity and meson production.
Production of strange hadrons in elementary and heavy-ion reactions is studied with the hadronic transport approach SMASH (Simulating Many Accelerated Strongly-interacting Hadrons). The poorly known branching ratios of the relevant hadronic resonances are constrained from the known elementary hadronic cross sections and from invariant mass spectra of dileptons. The constrained model is employed as a baseline to compare to heavy-ion-collision experiments at low energies ($E_\text{kin} = 1-2A\,\text{GeV}$) and to predict some of the upcoming pion-beam results by HADES, which are expected to be s…
Higher moments of multiplicity fluctuations of hadrons produced in central nucleus-nucleus collisions are studied within the hadron-resonance gas model in the canonical ensemble. Exact conservation of three charges, baryon number, electric charge, and strangeness, is enforced in the large volume limit. Moments up to the forth order of various particles are calculated at SPS, RHIC and LHC energies. The asymptotic fluctuations within a simplified model with only one conserved charge in the canonical ensemble are discussed where simple analytical expressions for moments of multiplicity distributi…
We compare and review the theoretical predictions for the $\bar{K}N$ and $ηN$ elastic amplitudes where sizable variations are found among the considered approaches, especially at subthreshold energies relevant for studies of kaonic atoms and meson-nuclear quasi-bound states. Conditions for an appearance of dynamically generated states in meson-baryon multi-channel interactions are established and discussed for the $\bar{K}N$ and $ηN$ systems.
The structure of the hadron resonances attracts much attention, in association with the recent observations of various exotic hadrons which do not fit well in the conventional picture. These findings urge us to consider various new configurations such as the multiquark states and the hadronic molecules. However, it is a subtle problem to define a proper classification scheme for the hadron structure, and the nonzero decay width of the hadron resonances makes the analysis complicated. In this paper, we summarize the recent developments in the studies of the structure of the hadron resonances, f…
We study the production of hadronic resonances and their interaction in the partonic and hadronic medium using the EPOS3 model, which employs the UrQMD model for the description of the hadronic phase. We investigate the centrality dependence of the yields and momentum distributions for various resonances (rho(770),K(892),phi(1020),Delta(1232),Sigma(1385),Lambda(1520),Xi(1530) and their antiparticles) in Pb-Pb collisions at sNN= 2.76 TeV. The predictions for K(892) and phi(1020) will be compared with the experimental data from the ALICE collaboration. The observed signal suppression of the K(89…
We discuss the interacting hadron resonance gas model to describe the thermodynamics of hadronic matter. While the attractive interaction between hadrons is taken care of by including all the resonances with zero width, the repulsive interactions are included by considering density-dependent mean field potentials. The bulk thermodynamic quantities are confronted with the lattice quantum chromodynamics simulation results at zero as well as at finite baryon chemical potential. We further estimate the shear and bulk viscosity coefficients of hot and dense hadronic matter within the ambit of this …
An overview of a hadron resonance gas (HRG) model that includes van der Waals interactions between hadrons is presented. Applications of the excluded volume HRG model to heavy-ion collision data and lattice QCD equation of state are discussed. A recently developed quantum van der Waals hadron resonance gas model is covered as well. Applications of this model in the context of the QCD critical point are elaborated.
We discuss the composite nature of hadrons appearing near the s-wave two-hadron threshold. Generalizing the Weinberg's weak-binding relation for stable bound states, we show that the compositeness of near-threshold resonances and quasi-bound states can be determined by observable quantities.
We study the radiative decay into $γ$ and a baryon of the SU(3) octet and decuplet of nine and ten resonances that are dynamically generated from the interaction of vector mesons with baryons of the octet and the decuplet respectively. We obtain quite different partial decay widths for the various resonances, and for different charge states of the same resonance, suggesting that the experimental investigation of these radiative decays should bring much information on the nature of these resonances. For the case of baryons of the octet we determine the helicity amplitudes and compare them with …
We present a study of the effects of magnetic fields on fluctuations and correlations in hadron resonance gas model. We find significant changes in the fluctuations of net baryon number, electric charge and strangeness. This is also reflected in various fluctuation ratios along the freezeout curve.
In this work we discuss a modified version of Excluded Volume Hadron Resonance Gas model and also study the effect of Lorentz contraction of the excluded volume on scaled pressure and susceptibilities of conserved charges. We find that the Lorentz contraction, coupled with the variety of excluded volume parameters reproduce the lattice QCD data quite satisfactorily.
In this talk I report on the recent developments in the subject of dynamically generated resonances. In particular I discuss the $γp \to K^0 Σ^+$ and $γn \to K^0 Σ^0$ reactions, with a peculiar behavior around the $K^{*0} Λ$ threshold, due to a $1/2^-$ resonance around 2035 MeV. Similarly, I discuss a BES experiment, $J/ψ\to ηK^{*0} \bar K^{*0}$ decay, which provides evidence for a new $h_1$ resonance around 1830 MeV that was predicted from the vector-vector interaction. A short discussion is then made about recent advances in the charm and beauty sectors.
We present, in the framework of the interacting hadron resonance gas, an evaluation of thermodynamical quantities. The interaction is modelled via a correction for the finite size of the hadrons. We investigate the sensitivity of the model calculations on the radius of the hadrons, which is a parameter of the model. Our calculations for thermodynamical quantities as energy and entropy densities and pressure are confronted with predictions using the lattice Quantum Chromodynamics (QCD) formalism.
Hagedorn states are the key to understand how all hadrons observed in high energy heavy ion collisions seem to reach thermal equilibrium so quickly. An assembly of Hagedorn states is formed in elementary hadronic or heavy ion collisions at hadronization. Microscopic simulations within the transport model UrQMD allow to study the time evolution of such a pure non-equilibrated Hagedorn state gas towards a thermally equilibrated Hadron Resonance Gas by using dynamics, which unlike strings, fully respect detailed balance. Propagation, repopulation, rescatterings and decays of Hagedorn states provi…
A detailed discussion of recent results obtained within the hadron resonance gas model with the multi-component hard core repulsion is presented. Among them there are the adiabatic chemical freeze-out criterion, the concept of separate chemical freeze-out of strange particles and the effects of enhancement and sharpening of wide resonances and quark gluon bags occurring in a thermal medium. These findings are discussed in order to strengthen the planned heavy-ion collision experimental programs at low collision energies. We argue, that due to found effects, at the center of mass collision ener…
The description of the production of light (anti-)(hyper-)nuclei in a hadron resonance gas, or statistical-thermal model approach, has proven to be rather successful, despite the fact that the binding energies of these compound objects are small compared to the emitting fireball temperature. We summarise some recent developments and findings in this approach.
The properties of strange pseudoscalar and vectors mesons as well as strange baryon resonances in dense matter are reviewed. Some open questions on the properties of strange hadrons in medium are addressed, such as the experimental signatures of in-medium effects coming from the hadronic phase on the final observables in heavy-ion collisions for the experimental conditions at SIS, RHIC and LHC energies.
We study the interaction of vector mesons with the octet of stable baryons in the framework of the local hidden gauge formalism using a coupled channels unitary approach, including also the pseudoscalar-baryon channels which couple to the same quantum numbers. We examine the scattering amplitudes and their poles, which can be associated to known $J^P=1/2^-,3/2^-$ baryon resonances, and determine the role of the pseudoscalar-baryon channels, changing the width and eventually the mass of the resonances generated with only the basis of vector-baryon states.
Chiral quark models with Polyakov loop at finite temperature have been often used to describe the phase transition. We show how the transition to a hadron resonance gas is realized based on the quantum and local nature of the Polyakov loop.
We compare recent lattice results on fluctuations and correlations of strangeness, baryon number and electric charge obtained with p4 improved staggered action with the prediction of hadron resonance gas model. We show that hadron resonance gas can describe these fluctuations reasonably well if the hadron properties are as calculated on the lattice.
I discuss the deconfinement transition in 2+1 flavor QCD in terms of Polyakov loops as well as the hadron resonance gas for hadrons containing static quarks and charm quarks.
We have explored some phenomenological issues during calculations of transport coefficients for hadronic matter, produced in the experiments of heavy ion collisions. Here, we have used an ideal hadron resonance gas model to demonstrate the issues. On the basis of dissipation mechanism, the hadronic zoo is classified into resonance and non-resonance members, who participate in dissipation via strong decay and scattering channels respectively. Imposing our phenomenological restriction, we are able to provide a rough upper and lower bound estimations of transport coefficients. Interestingly, we f…
Using the EPOS3 model with UrQMD to describe the hadronic phase, we study the production of short-lived hadronic resonances and the modification of their yields and $p_{T}$ spectra in p-Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV. High-multiplicity p-Pb collisions exhibit similar behavior to mid-peripheral Pb-Pb collisions at LHC energies, and we find indications of a short-lived hadronic phase in p-Pb collisions that can modify resonance yields and $p_{T}$ spectra through scattering processes. The evolution of resonance production is investigated as a function of the system size, which is rel…
We present an effective model for the generic behaviour of hadron masses and phase shifts at finite temperature which shares basic features with recent developments within the PNJL model for correlations in quark matter. On this basis we obtain the transition between a hadron resonance gas phase and the quark gluon plasma in the spirit of the generalized Beth-Uhlenbeck approach where the Mott dissociation of hadrons is encoded in the hadronic phase shifts. Here we restrict ourselves to low-lying hadronic channels and perform a discussion of recent lattice QCD thermodynamics results from this p…
We investigate the effects of finite baryon chemical potential on the transport properties of a hadron resonance gas. We find that a hadron resonance gas with large baryon number density is closer to the ideal fluid limit than the corresponding gas with zero baryon number. This suggests that the system created at the Relativistic Heavy Ion Collider (RHIC) at lower collision energies may behave as a fluid, with an effective fluidity close to the one found at RHIC's highest energy near phase transition. This might explain why the differential elliptic flow coefficient measured at lower collision…
The van der Waals interaction is implemented in a Hadron Resonance Gas model. It is shown that this model can describe Lattice QCD data of different thermodynamical quantities satisfactorily with the van der Waals parameters $a = 1250 \pm 150$ MeV fm$^3$ and $r = 0.7 \pm 0.05$ fm. Further, a phase transition is observed in this model with the critical point at temperature, $T = 62.1$ MeV and baryon chemical potential, $μ_B = 708$ MeV.
We analyze the sensitivity of thermal fits to heavy-ion hadron yield data of ALICE and NA49 collaborations to the systematic uncertainties in the hadron resonance gas (HRG) model related to the modeling of the eigenvolume interactions. We find a surprisingly large sensitivity in extraction of chemical freeze-out parameters to the assumptions regarding eigenvolumes of different hadrons. We additionally study the effect of including yields of light nuclei into the thermal fits to LHC data and find even larger sensitivity to the modeling of their eigenvolumes. The inclusion of light nuclei yields…
We discuss baryon resonances which are dynamically generated in hadron dynamics based on chiral coupled channels approach. With the dynamical description of the baryon resonance, we discuss the origin of the resonance pole, finding that for the description of N(1535) some other components than meson and baryon are necessary. Since the chiral unitary model provides a microscopic description in terms of constituent hadrons, it is straightforward to calculate transition amplitudes and form factors of resonances without introducing further parameters. Finally we briefly discuss few-body nuclear ka…
A unified equation of state for quark-hadron matter is presented in the generalized Beth-Uhlenbeck form. It follows from a $Φ-$derivable approach to the thermodynamic potential where the ansatz for the $Φ$ functional contains all 2PI diagrams at two-loop order formed with quark cluster Green's functions for quark, diquark, meson and baryon propagators. We present numerical results using an effective model for the generic behaviour of hadron masses and phase shifts at finite temperature which shares basic features with recent developments within the PNJL model for correlations in quark matter. …
We present a neat example of a meson--baryon system where the vicinity of two different thresholds enhances the binding of a hadronic resonance, a pentaquark. As a consequence the pattern of states may change when moving among different flavor sectors, what poses a warning on naive extrapolations to heavy flavor sectors based on systematic expansions. For this purpose we simultaneously analyze the $N\bar D$ and $NB$ two-hadron systems looking for possible bound states or resonances. When a resonance is controlled by a coupled-channel effect, going to a different flavor sector may enhance or di…
Investigation of hadronic effects on resonance productions in small collision systems using the EPOS4 model
Pusan National University（釜山国立大学）；The University of Tokyo（东京大学）；European Organization for Nuclear Research (CERN)（欧洲核子研究组织（CERN））；Yonsei University（延世大学）
We study the equation of state (EoS) of the hot and dense hadron gas by incorporating the excluded volume corrections into the ideal hadron resonance gas model (HRG). The total hadron mass spectrum of the model is the sum of discrete mass spectrum consisting all the experimentally known hadrons and the exponentially rising continuous Hagedorn states. We confront the EoS of the model with lattice quantum chromodynamics (LQCD) results at finite baryon chemical potential. We find that this modified HRG model reproduce the LQCD results up to T = 160 MeV at zero as well as finite baryon chemical po…
The interactions of $\bar{D}Σ_{c}$-$\bar DΛ_c$, $\bar{D}^{*}Σ_{c}$-$\bar D^*Λ_c$, and related strangeness channels, are studied within the framework of the coupled channel unitary approach with the local hidden gauge formalism. A series of meson-baryon dynamically generated relatively narrow $N^*$ and $Λ^*$ resonances are predicted around 4.3 GeV in the hidden charm sector. We make estimates of production cross sections of these predicted resonances in $\bar{p} p $ collisions for PANDA at the forthcoming FAIR facility.
In this paper we discuss the interacting hadron resonance gas model in presence of a constant external magnetic field. The short range repulsive interaction between hadrons are accounted through van der Waals excluded volume correction to the ideal gas pressure. Here we take the sizes of hadrons as $r_π$ (pion radius) $= 0$ fm, $r_K$ (kaon radius) $= 0.35$ fm, $r_m$ (all other meson radii) $= 0.3$ fm and $r_b$ (baryon radii) $= 0.5$ fm. We analyse the effect of uniform background magnetic field on the thermodynamic properties of interacting hadron gas. We especially discuss the effect of inter…
The quantum van der Waals (QvdW) extension of the ideal hadron resonance gas (HRG) model which includes the attractive and repulsive interactions between baryons -- the QvdW-HRG model -- is applied to study the behavior of the baryon number related susceptibilities in the crossover temperature region. Inclusion of the QvdW interactions leads to a qualitatively different behavior of susceptibilities, in many cases resembling lattice QCD simulations. It is shown that for some observables, in particular for $χ_{11}^{BQ} / χ_2^B$, effects of the QvdW interactions essentially cancel out. It is foun…
We show that a measurement of the reaction energy dependence of relative hadron resonance yields in heavy ion collisions can be used to study the phase structure of the dense QCD matter created in these collisions, and investigate the origin of the trends observed in the excitation functions of certain soft hadronic observables. We show that presence of chemical nonequilibrium in light quark abundance imparts a characteristic signature on the energy dependence of resonance yields, that differs considerably from what is expected in the equilibrium picture.
We investigate net-proton fluctuations as important observables measured in heavy-ion collisions within the hadron resonance gas (HRG) model. Special emphasis is given to effects which are a priori not inherent in a thermally and chemically equilibrated HRG approach. In particular, we point out the importance of taking into account the successive regeneration and decay of resonances below the chemical freeze-out, which lead to a randomization of the isospin of nucleons and thus to additional fluctuations in the net-proton number. We find good agreement between our model results and the recent …
We study the interaction of vector mesons with the octet of stable baryons in the framework of the local hidden gauge formalism using a coupled channels unitary approach. We examine the scattering amplitudes and their poles, which can be associated to known J^P=1/2^-,3/2^- baryon resonances, in some cases, or give predictions in other ones. The formalism employed produces doublets of degenerate J^P=1/2^-,3/2^- states, a pattern which is observed experimentally in several cases. The findings of this work should also be useful to guide present experimental programs searching for new resonances, …
The knowledge of hadron spectrum is based on experimental observations of hadronic resonances. The resonances are normally observed as peaks in certain invariant mass distributions. However, neither is a peak necessarily due to the presence of a resonance, nor does a resonance necessarily lead to a peak. Kinematic singularities can also produce peaks. Here, we discuss such possibilities and methods distinguishing genuine resonances from kinematic effects.
In this review we give a perspective of the theoretical work done recently on the interpretation of results from $B$, $D$, $Λ_b$, $Λ_c$ weak decays into final states that contain interacting hadrons, and how it is possible to obtain additional valuable information that is increasing our understanding of hadron interactions and the nature of many hadronic resonances. The novelty of these processes is that one begins with a clean picture at the quark level which allows one to select the basic mechanisms by means of which the process proceeds. Finally, one has a final state described in terms of …
Eigenvolume effects in the hadron resonance gas (HRG) model are studied for experimental hadronic yields in nucleus-nucleus collisions. If particle eigenvolumes are different for different hadron species, the excluded volume HRG (EV-HRG) improves fits to multiplicity data. In particular, using different mass~-~volume relations for strange and non-strange hadrons we observe a remarkable improvement in the quality of the fits. This effect appears to be rather insensitive to other details in the schemes employed in the EV-HRG. We show that the parameters found from fitting the data of the ALICE C…
We study the effect of charged secondaries coming from resonance decay on the net-baryon, net-charge and net-strangeness fluctuations in high energy heavy-ion collisions within the hadron resonance gas (HRG) model. We emphasize the importance of including weak decays along with other resonance decays in the HRG, while comparing with the experimental observables. The effect of kinematic cuts on resonances and primordial particles on the conserved number fluctuations are also studied. The HRG model calculations with the inclusion of resonance decays and kinematical cuts are compared with the rec…
We develop a theoretical framework to quantify the structure of unstable hadron resonances. With the help of the corresponding system in a finite volume, we define the compositeness of resonance states which can be interpreted as a probability. This framework is used to study the structure of the scalar mesons f_0(980) and a_0(980). In both mesons, the Kbar K component dominates about a half of the wave function. The method is also applied to the Lambda(1405) resonance. We argue that a single energy level in finite volume represents the two eigenstates in infinite volume. The KbarK N component…
In order to get a more realistic description of the hadron spectrum we extend a constituent-quark model by explicit mesonic degrees of freedom. The resulting system of constituent (anti)quarks, which are subject to an instantaneous confining force, and mesons, which couple directly to the quarks, is treated by means of a relativistic coupled-channel framework. It can be formally shown that the mass-eigenvalue problem for such a system is equivalent to a hadronic eigenvalue problem in which the eigenstates of the pure confinement potential (bare hadrons) are coupled via meson loops. Following t…
The Hadron-Resonance Gas (HRG) approach - used to model hadronic matter at small baryon potentials $μ_B$ and finite temperature $T$ - is extended to finite and large chemical potentials by introducing interactions between baryons in line with relativistic mean-field theory defining an interacting HRG (IHRG). Using lattice data for $μ_B=0$ as well as information on the nuclear equation of state at $T=0$ we constrain the attractive and repulsive interactions of the IHRG such that it reproduces the lattice equation of state at $μ_B=0$ and the nuclear equation of state at $T=0$ and finite $μ_B$. T…
Different scenarios for modeling resonances in a thermal model description of hadron yields measured in heavy-ion collisions are explored: the zero-width approximation, the energy independent Breit-Wigner scheme, and the energy dependent Breit-Wigner (eBW) scheme. Application of the eBW scheme leads to a notable suppression in the proton yields, stemming mainly from a reduced feeddown from $Δ$ resonances because of the threshold effects. A significantly improved agreement of thermal model with hadron yields measured in Pb-Pb collisions at $\sqrt{s_{_{NN}}} = 2.76$ TeV by the ALICE collaboratio…
