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Renan Hirayama

Publications and source records attributed to Renan Hirayama.

5 recordsLinked to original sources

Updated Hadron List for Transport Simulations of Heavy-Ion Collisions

Hadronic transport approaches used in heavy-ion collision simulations rely on a consistent and accurate hadron list with decay channels. Hadron lists in common use are often experimentally outdated, or, as with the Particle Data Group (PDG) compilations, incompatible with transport codes without further adaptation. We construct PDG2021+, an updated hadron list including all states from the 2021 Particle Data Booklet, together with a binary-decay list designed for direct use in the SMASH transport framework. Using the hadron resonance gas model, we validate the PDG2021+ list against lattice quantum chromodynamics results and experimental yield data. We show that employing $1 \to 2$-body decay chains as a proxy for the full decay processes has a suppressing effect in the low-$p_T$ region of the pion spectrum and introduces a $\sim 3\%$ systematic uncertainty in the pion $\langle p_T \rangle$. Moreover, the inclusion of additional states in PDG2021+ further shifts the pion $\langle p_T \rangle$. These result establish PDG2021+ as a robust, transport-ready hadron list and quantify the systematic effects of decay modeling on key heavy-ion observables.

nucl-th↗

Distinguishing the sources of dielectron anisotropic flow at low beam energies

We present calculations of dielectron anisotropic flow in heavy-ion collisions at HADES beam energies from a hadronic transport approach. The ongoing experimental analysis employs the traditional reaction plane method to evaluate the flow coefficients $v_n$ and claims to see isotropic radiation from the thermal quark-gluon plasma. We show in this work, that in the region above the pion mass, the dilepton flow measurement might suffer from cancellation effects that mask the complicated underlying dynamics. Contributions from different baryonic and mesonic resonances show collective behaviour with different signs and lead to an overall vanishing elliptic flow. To differentiate the different contributions, we propose to employ the scalar product method, which exploits the previously measured hadronic flow to create different reference planes. As a proof of concept, we calculate the $v_2$ of dielectrons for Ag+Ag collisions at $\sqrt{s_{NN}}=2.55$ $\mathrm{GeV}$ with both methods and investigate the contribution of each source, concluding that the scalar product method provides the proton and pion tagged flow coefficients as two distinct measurements, disentangling the various dilepton sources.

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Theoretical and Experimental Constraints for the Equation of State of Dense and Hot Matter

This review aims at providing an extensive discussion of modern constraints relevant for dense and hot strongly interacting matter. It includes theoretical first-principle results from lattice and perturbative QCD, as well as chiral effective field theory results. From the experimental side, it includes heavy-ion collision and low-energy nuclear physics results, as well as observations from neutron stars and their mergers. The validity of different constraints, concerning specific conditions and ranges of applicability, is also provided.

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Effective spectral function of vector mesons via lifetime analysis

Effective spectral functions of the $ρ$ meson are reconstructed by considering the lifetimes inside different media using the hadronic transport SMASH (Simulating Many Accelerated Strongly-interacting Hadrons). Due to inelastic scatterings, resonance lifetimes are dynamically shortened (collisional broadening), even though the employed approach assumes vacuum resonance properties. Analyzing the $ρ$ meson lifetimes allows to quantify an effective broadening of the decay width and spectral function, which is important in order to distinguish dynamical effects from additional genuine medium modifications to the spectral functions, indicating e.g. an onset of chiral symmetry restoration. The broadening of the spectral function in a thermalized system is shown to be consistent with other theoretical calculations. The effective $ρ$ meson spectral function is also presented for the dynamical evolution of heavy-ion collisions, finding a clear correlation of the broadening to system size, which is explained by an observed dependence of the width on the local hadron density. Furthermore, the difference in the results between the thermal system and full collision dynamics is explored, which may point to non-equilibrium effects.

hep-ph↗

Cumulants of conserved charges in hydrodynamic simulations

We introduce a fast and simple method of computing cumulants of net-proton or net-charge fluctuations in event-by-event hydrodynamic simulations of heavy-ion collisions. One evaluates the mean numbers of particles in every hydrodynamic event. Cumulants are then expressed as a function of these mean numbers. We implement the corrections due to global conservation laws. The method is tested using ideal hydrodynamic simulations of Au+Au collisions at $\sqrt{s_{NN}}=200$ AGeV with the NeXSPheRIO code. Results are in good agreement with experimental data on net-proton and net-charge fluctuations by the STAR collaboration.

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