Hadron Resonance Research Articles

Finite size effect on the thermodynamics of a hot and magnetized hadron resonance gas

The thermodynamic properties of a non-interacting ideal hadron resonance gas (HRG) of finite volume have been studied in the presence of an external magnetic field. The inclusion of background magnetic field in the calculation of thermodynamic potential is done by the modification of the dispersion relations of the charged hadrons in terms of Landau quantization. The generalized Matsubara prescription has been employed to take into account the finite size effects in which a periodic (anti-periodic) boundary conditions is considered for the mesons (baryons). We find significant effects of the magnetic field as well as system size on the temperature dependence of energy density, longitudinal and transverse pressure especially in low temperature regions. The HRG is found to exhibit diamagnetism (paramagnetism) in the low (high) temperature region whereas the finite size effect is seen to strengthen the diamagnetic behavior of the medium.

Hadronic resonances in heavy-ion collisions at NICA energies and their reconstruction in the MPD setup

The short-lived hadronic resonances are used to study the properties of the hot and dense medium produced in the relativistic heavy-ion collisions. The resonance masses and widths, yields and mean transverse momenta measured in the hadronic decay channels probe different stages of the nuclear collisions and are most sensitive to strangeness production, collective flow and hadronization mechanisms as well as to lifetime and density of the hadronic phase. In this contribution, we discuss line shape modifications for short-lived resonances and their consequences for the yields and shapes of the production spectra measured in heavy-ion collisions at intermediate collision energies, [Formula: see text][Formula: see text]GeV. Capabilities of the MPD facility at NICA to reconstruct resonances in Bi+Bi collisions at [Formula: see text][Formula: see text]GeV are presented and discussed.

System size and flavour dependence of chemical freeze-out temperatures in ALICE data from pp, pPb and PbPb collisions at LHC energies

We present the system size and flavour dependence of the chemical freeze-out temperature (Tch) at vanishing baryo-chemical potential calculated via thermal fits to experimental yields for several multiplicity classes in pp, pPb and PbPb collisions measured by ALICE. Using the Thermal-FIST Hadron Resonance Gas model package, we compare the quality of fits across various treatments of strangeness conservation under different freeze-out conditions as a function of the charged particle multiplicity density 〈dNch/dη〉. Additionally, we examine how the anti-hadron to pion yield ratios of light and strange baryons, as well as the ϕ meson, evolve within a flavour-dependent model. Through a unique two-temperature chemical freeze-out approach, we show that flavour dependence of Tch in a Strangeness Canonical Ensemble leads to a natural explanation of strangeness enhancement from small to large systems at LHC energies without requiring any non-equilibrium particle production at small 〈dNch/dη〉.

Resonance production in partial chemical equilibrium

In high energy collisions, a dense, strongly interacting medium could be created, the quark gluon plasma. In rapid expansion, from the soup of quarks and gluons a gas of resonance and stable particles is formed at the chemical freeze-out and after that, as the system cools down, the kinetic freeze-out takes place and interaction between particles ceases. By measuring resonance ratios one could get information about the dominant physical processes in the intermediate temperature ranges, i.e. between the chemical and kinetic freeze-out. These quantities are measured at RHIC and LHC energies. In the present analysis we employ the hadron resonance gas model assuming partial chemical equilibrium to characterize these measured data. We calculate the ratios of several resonances to their stable counterpart and compare these model calculations to available experimental data.

QCD equation of state with Tsallis statistics for heavy-ion collisions

Nonextensive statistics has attracted attention as a description of particle spectra in nuclear collisions at QCD energies. First, we construct the equation of state by incorporating Tsallis statistics based on the hadron resonance gas and parton gas models. Thermodynamic conditions are found to impose constraints on the $q$-parameter of Tsallis distribution. Next, we apply the equation of state to the relativistic hydrodynamic modeling of nuclear collisions. The Cooper-Frye prescription is consistently modified. Numerical demonstrations indicate that the model may describe charged particle spectra at Large Hadron Collider in the transverse momentum range up to 6-8 GeV. Elliptic flow, on the other hand, suggests a narrower range of applicability.

Diffusion matrix associated with the diffusion processes of multiple conserved charges in a hot and dense hadronic matter

Bulk matter produced in heavy ion collisions has multiple conserved quantum numbers like baryon number, strangeness and electric charge. The diffusion process of these charges can be described by a diffusion matrix describing the interdependence of diffusion of different charges. The diffusion coefficient matrix is estimated here from the Boltzmann kinetic theory for the hadronic phase within relaxation time approximation. In the derivation for the same, we impose the Landau-Lifshitz conditions of fit. This leads to e.g. the diagonal diffusion coefficients to be manifestly positive definite. The explicit calculations are performed within the ambit of hadron resonance gas model with and without excluded volume corrections. It is seen that the off-diagonal components can be significant to affect the charge diffusion in a fluid with multiple conserved charges. The excluded volume correction effects is seen to be not significant in the estimation of the elements of the diffusion matrix.

Search for high-mass resonances decaying to a jet and a Lorentz-boosted resonance in proton-proton collisions at [formula omitted

A search is reported for high-mass hadronic resonances that decay to a parton and a Lorentz-boosted resonance, which in turn decays into a pair of partons. The search is based on data collected with the CMS detector at the LHC in proton-proton collisions at s=13TeV, corresponding to an integrated luminosity of 138fb−1. The boosted resonance is reconstructed as a single wide jet with substructure consistent with a two-body decay. The high-mass resonance is thus considered as a dijet system. The jet substructure information and the kinematic properties of cascade resonance decays are exploited to disentangle the signal from the large quantum chromodynamics multijet background. The dijet mass spectrum is analyzed for the presence of new high-mass resonances, and is found to be consistent with the standard model background predictions. Results are interpreted in a warped extra dimension model where the high-mass resonance is a Kaluza–Klein gluon, the boosted resonance is a radion, and the final state partons are all gluons. Limits on the production cross section are set as a function of the Kaluza–Klein gluon and radion masses. These limits exclude at 95% confidence level models with Kaluza–Klein gluon masses in the range 2.0 to 4.3 TeV and radion masses in the range 0.20 to 0.74 TeV. By exploring a novel experimental signature, the observed limits on the Kaluza–Klein gluon mass are extended by up to about 1 TeV compared to previous searches.

Thermal hadron resonances in chiral and U(1)A restoration

We review recent work on thermal resonances and their connection with chiral symmetry and U(1)A restoration within the QCD phase diagram. In particular, the ƒ0 (500) and K∗ 0 (700) states generated from ππ and πK scattering within Unitarized Chiral Perturbation Theory (ChPT) at finite temperature allow one to describe scalar susceptibilities, which combined with Ward Identities yield interesting conclusions regarding the interplay between chiral and U(1)A restoration, key to understand the nature of the transition.

Can standard model and experimental uncertainties resolve the MiniBooNE anomaly?

We critically examine a number of theoretical uncertainties affecting the MiniBooNE short-baseline neutrino oscillation experiment in an attempt to better understand the observed excess of electronlike events. We reexamine the impact of fake charged current quasielastic events, the background due to neutral current ${\ensuremath{\pi}}^{0}$ production, and the single-photon background. For all processes, we compare the predictions of different event generators (genie, gibuu, nuance, and nuwro) and, for genie, of different tunes. Where MiniBooNE uses data-driven background predictions, we discuss the uncertainties affecting the relation between the signal sample and the control sample. In the case of the single-photon background, we emphasize the uncertainties in the radiative branching ratios of heavy hadronic resonances. We find that not even a combination of uncertainties in different channels adding up unfavorably (an ``Altarelli cocktail'') appears to be sufficient to resolve the MiniBooNE anomaly. We finally investigate how modified background predictions affect the fit of a $3+1$ sterile neutrino scenario. We carefully account for full four-flavor oscillations not only in the signal but also in the background and control samples. We emphasize that, because of the strong correlation between MiniBooNE's ${\ensuremath{\nu}}_{e}$ and ${\ensuremath{\nu}}_{\ensuremath{\mu}}$ samples, a sterile neutrino mixing only with ${\ensuremath{\nu}}_{\ensuremath{\mu}}$ is sufficient to explain the anomaly, even though the well-known tension with external constraints on ${\ensuremath{\nu}}_{\ensuremath{\mu}}$ disappearance persists.

Searching for New Physics in Hadronic Final States with Run 2 Proton–Proton Collision Data at the LHC

The symmetries of the Standard Model give rise to the forces that act on particles, and the corresponding force mediators. While the Standard Model is an excellent description of particle interactions, it has known limitations; it is therefore important to search for new physics beyond the Standard Model, potentially indicating as-of-yet unknown symmetries of nature. The ATLAS and CMS collaborations have detailed physics programmes, involving a large number of searches for new physics in hadronic final states. As the start of Run 3 of the LHC is imminent, now is a good time to review the progress made and the status of hadronic searches during Run 2 at a centre-of-mass collision energy of s=13TeV. This review provides an overview of the motivations and challenges of hadronic final states at the LHC, followed by an introduction to jet reconstruction, calibration, and tagging. Three classes of searches for new physics in hadronic final states are discussed: di-jet searches, searches for missing transverse momentum in association with another object, and searches for hadronic di-boson resonances. The complementarity of these different analysis strategies is discussed, emphasising the importance of a varied hadronic physics programme in the search for new physics.

Entropy per Rapidity in Pb-Pb Central Collisions using Thermal and Artificial Neural Network (ANN) Models at LHC Energies

The entropy per rapidity produced in central Pb-Pb ultra-relativistic nuclear collisions at LHC energies is calculated using experimentally identified particle spectra and source radii estimated from Hanbury Brown-Twiss (HBT) correlations for particles π, k, p, Λ, Ω, and and π, k, p, Λ, and at and TeV, respectively. An artificial neural network (ANN) simulation model is used to estimate the entropy per rapidity at the considered energies. The simulation results are compared with equivalent experimental data, and a good agreement is achieved. A mathematical equation describing the experimental data is obtained. Extrapolation of the transverse momentum spectra at is required to calculate ; thus, we use two different fitting functions, the Tsallis distribution and hadron resonance gas (HRG) model. The success of the ANN model in describing the experimental measurements leads to the prediction of several spectra values for the mentioned particles, which may lead to further predictions in the absence of experiments.

Conserved number fluctuations in interacting hadron resonance gas model

Fluctuations of net-baryon, net-charge and net-strangeness numbers are studied within the framework of ideal hadron resonance gas (IHRG), including attractive and repulsive van der Waals interactions. The binding energy and thermodynamic parameters are calculated for different extended versions of the HRG (E-HRG) model. The susceptibility ratios of conserved numbers are estimated in full phase-space using various HRG models that show a strong dependence on collision energies. The effect of kinematic cuts (transverse momentum (pT) and pseudo-rapidity (η)) on those ratios of conserved numbers are also discussed. It is observed that, the normalized susceptibility ratios as a function of collision energies strongly depend on lower pT cut-off and Δη window. The E-HRG models are very sensitive to kinematic acceptance even for net-proton fluctuations. The susceptibility ratios calculated from different HRG models with proper kinematic acceptances are compared with the experimental measurements, which will help to better understand the phase transition and existence of critical point in the QCD phase diagram.

Collision energy dependence of the critical end point from baryon number fluctuations in the Linear Sigma Model with quarks

We show that the Linear Sigma Model with quarks produces an effective description of the QCD phase diagram and of the system’s equilibrium distribution properties that deviate from those of the Hadron Resonance Gas Model. The deviation is due to the inclusion of plasma screening properties, encoded in the contribution of the ring diagrams and thus to the introduction of a key feature of plasmas near phase transitions, namely, long-range correlations. After fixing the model parameters using input from LQCD for the crossover transition at vanishing chemical potential, we study the location of the Critical End Point in the effective QCD phase diagram. We use the model to study baryon number fluctuations and show that in heavy-ion collisions, the CEP can be located for collision energies $$\sqrt{s_{NN}}\sim 2$$ GeV, namely, in the lowest NICA or within the HADES energy domain.

Hadron resonance gas model with repulsive mean-field interactions: Specific heat, isothermal compressibility and speed of sound

We investigate the effect of repulsive interaction between hadrons on the specific heat (CV), isothermal compressibility (κT) and the speed of sound (Cs2) of hot and dense hadronic matter. The repulsive interactions are included through a mean-field approach where the single particle energy picks correction term due to mean field interactions between hadrons. This correction term is proportional to the number density of hadrons. We assume different mean-field interactions for mesons and baryons. We also confront CV and Cs2 with existing lattice QCD simulation results. We find that the repulsive interactions have very strong effect on CV and Cs2 while its effect on κT is very mild. We finally discuss the implications of our results in the context of heavy-ion collision experiments.

K^{*}(892)^0 meson production in inelastic p+p interactions at 40 and 80 text{ GeV }!/!c beam momenta measured by NA61/SHINE at the CERN SPS

Measurements of K^{*}(892)^0 resonance production via its K^{+}pi ^{-} decay mode in inelastic p+p collisions at beam momenta 40 and 80 text{ GeV }!/!c (sqrt{s_{NN}}=8.8 and 12.3 text{ GeV }) are presented. The data were recorded by the NA61/SHINE hadron spectrometer at the CERN Super Proton Synchrotron. The template method was used to extract the K^{*}(892)^0 signal. Transverse momentum and rapidity spectra were obtained. The mean multiplicities of K^{*}(892)^0 mesons were found to be (35.1 pm 1.3 mathrm {(stat)} pm 3.6 mathrm {(sys))} cdot 10^{-3} at 40 text{ GeV }!/!c and (58.3 pm 1.9 mathrm {(stat)} pm 4.9 mathrm {(sys))} cdot 10^{-3} at 80 text{ GeV }!/!c. The NA61/SHINE results are compared with the Epos1.99 and Hadron Resonance Gas models as well as with world data. The transverse mass spectra of K^{*}(892)^0 mesons and other particles previously reported by NA61/SHINE were fitted within the Blast-Wave model. The transverse flow velocities are close to 0.1–0.2 of the speed of light and are significantly smaller than the ones determined in heavy nucleus-nucleus interactions at the same beam momenta.

Total and Partial Shear Viscosity in Heavy-Ion Collisions at Energies of BES, FAIR and NICA

We calculated the shear viscosity of hot and dense nuclear matter produced in a symmetric system of central gold–gold collisions at energies of BES RHIC, FAIR and NICA. For calculations of the collisions, the transport model UrQMD was employed. The shear viscosity was obtained within the Green–Kubo formalism. The hadron resonance gas model was used to determine temperature and chemical potentials of baryon charge and strangeness out of microscopic model calculations. In contrast to our previous works, we determined the partial viscosity of the main hadron species, such as nucleons, pions, kaons and Lambdas, via the nucleon–nucleon, pion–pion and so forth, correlators. A decrease in the beam energy from Elab=40 to 10 AGeV leads a to rise in baryon shear viscosity accompanied by a drop in the shear viscosity of mesons. The ratio of total shear viscosity to entropy density also decreases.

Neutron stars with crossover to color superconducting quark matter

We follow the idea that the QCD phase diagram may be described by a crossover from a hadron resonance gas to perturbative QCD using the switch function ansatz of Albright, Kapusta and Young [1]. While the switch function could be calibrated at vanishing baryon chemical potential with data from lattice QCD simulations, it has been suggested recently by Kapusta and Welle [2] that in the zero temperature limit, the switch function parameter $\mu_0$ could be constrained by neutron star phenomenology, in particular by massive pulsars like PSR J0740+6620 with a mass exceeding $2~M_\odot$. In this work we demonstrate that this procedure to constrain the QCD phase diagram does crucially depend on the fact that cold dense quark matter is very likely in a color superconducting state.

Pole position of the a1(1260) resonance in a three-body unitary framework

Masses, widths, and branching ratios of hadronic resonances are quantified by their pole positions and residues with respect to transition amplitudes on the Riemann sheets of the complex energy-plane. In this study we discuss the analytic structure in the physical energy region of three-body scattering amplitudes on such manifolds. As an application, we determine the pole position of the $a_1(1260)$ meson from the ALEPH experiment by allowing for $\pi\rho$ coupled channels in S- and D-wave. We find it to be $\sqrt{s_0}=(1232^{+15+9}_{-0-11}-i266^{+0+15}_{-22-27})~\text{MeV}$.

Building a testable shear viscosity across the QCD phase diagram

Current experiments at the Relativistic Heavy Ion Collider (RHIC) are probing finite baryon densities where the shear viscosity to enthalpy ratio $\eta T/w$ of the Quark Gluon Plasma remains unknown. We use the Hadron Resonance Gas (HRG) model with the most up-to-date hadron list to calculate $\eta T/w$ at low temperatures and at finite baryon densities $\rho_B$. We then match $\eta T/w$ to a QCD-based shear viscosity calculation within the deconfined phase to create a table across $\left\{T,\mu_B\right\}$ for different cross-over and critical point scenarios at a specified location. We find that these new $\eta T/w(T,\mu_B)$ values would require initial conditions at significantly larger $\rho_B$, compared to ideal hydrodynamic trajectories, in order to reach the same freeze-out point.

The Hadron Resonance Gas model with the effect of Magnetic field.

The Hadron Resonance Gas model with the effect of Magnetic field.