arXiv subjects

Yogiro Hama

Publications and source records attributed to Yogiro Hama.

35 records · Page 2Linked to original sources

arXiv2011

Fluctuating Initial Conditions and Anisotropic Flows

In this work we study the connection between anisotropic flows and lumpy initial conditions for Au+Au collisions at 200GeV. We present comparisons between anisotropic flow coefficients and eccentricities up to sixth order, and between initial condition reference angles and azimuthal particle distribution angles. We also present a toy model to justify the lack of connection between flow coefficients and eccentricities for individual events.

nucl-th↗

arXiv2011

Directed flow at mid-rapidity in event-by-event hydrodynamics

Fluctuations in the initial geometry of a nucleus-nucleus collision have been recently shown to result in a new type of directed flow (v_1) that, unlike the usual directed flow, is also present at midrapidity. We compute this new v_1 versus transverse momentum and centrality for Au-Au collisions at RHIC using the hydrodynamic code NeXSPheRIO. We find that the event plane of v_1 is correlated with the angle of the initial dipole of the distribution, as predicted, though with a large dispersion. It is uncorrelated with the reaction plane. Our results are in excellent agreement with results inferred from STAR correlation data.

nucl-th↗

arXiv2010

Boost-invariant one-tube model for two-particle correlation

We show the in-plane/out-of-plane effect, in the two-particle correlation function, computed with the NexSPheRIO code, in Au+Au collisions at 200AGeV. In order to clarify the origin of the effect, a simplified model, which consists of a peripheral high-energy-density tube in a smooth background with longitudinal boost invariance, is applied.

hep-ph↗

arXiv2010

Fluctuating initial conditions in hydrodynamics for two-particle correlations

Event-by-event hydrodynamics, with fluctuating initial conditions, has shown to nicely reproduce several features of experimentally observed quantities in high-energy nuclear collisions. Here we discuss how it may help to understand, in a unified way, the various structures observed in the long-range two-particle correlations, both in nucleus-nucleus and p-p collisions. Suggestions of how experimentally this description could be tested are also discussed.

hep-ph↗

arXiv2010

Lambda and Antilambda polarization in Au-Au collisions at RHIC

Recent experiments at RHIC have shown that in 200 GeV Au-Au collisions, the Lambda and Antilambda hyperons are produced with very small polarizations [1], almost consistent with zero. These results can be understood in terms of a model that we recently proposed [2]. In this work, we show how this model may be applied in such collisions, and also will discuss the relation of our results with other models, in order to explain the experimental data.

hep-ph↗

arXiv2009

Trying to understand the ridge effect in hydrodynamic model

In a recent paper, the hydrodynamic code NeXSPheRIO was used in conjunction with STAR analysis methods to study two-particle correlations as function of Delta_eta and Delta_phi. Both the ridge-like near-side and the double-hump away-side structures were obtained. However, the mechanism of ridge production was not clear. In order to understand it, we study a simple model with only one high-energy density peripheral tube in a smooth cylindrical back-ground, with longitudinal boost invariance. The results are rather surprising, but the model does produce the triple-ridge structure with one high ridge plus two lower ones placed symmetrically with respect to the former one. The shape of this structure is rather stable in a wide range of parameters.

hep-ph↗

arXiv2008

NeXSPheRIO results on azimuthal anisotropy in Au-Au collisions at 200A GeV

In this work, we present the results obtained by the hydrodynamic code NeXSPheRIO on anisotropic flows. In our calculation, we made use of event-by-event fluctuating initial conditions, and chemical freeze-out was explicitly implemented. We studied directed flow, elliptic flow and forth harmonic coefficient for various hadrons at different centrality windows for Au+Au collisions at 200 AGeV. The results are discussed and compared with experimental data from RHIC.

nucl-th↗

arXiv2007

NeXSPheRIO Results on Elliptic-Flow Fluctuations at RHIC

By using the NexSPheRIO code, we study the elliptic-flow fluctuations in Au+Au collisions at 200A GeV. It is shown that, by fixing the parameters of the model to correctly reproduce the charged pseudo-rapidity and the transverse-momentum distributions, reasonable agreement of with data is obtained, both as function of pseudo-rapidity as well as of transverse momentum, for charged particles. Our results on elliptic-flow fluctuations are in good agreement with the recently measured data in experiments.

hep-ph↗

arXiv2007

An approach to chemical freeze-out scenario of identified particle spectra at 200AGeV Au-Au collisions at RHIC

Thermal model fit indicates early chemical freeze-out of multi-strange hadrons with small collective velocities at 200AGeV Au-Au collisions at RHIC. In this work, we present our recent results by SPheRIO hydrodynamical calculations inspired by this picture. In our model, multi-strange hadrons go through chemical freeze-out when the system reaches some temperature close to the phase transition, stopping to make inelastic collisions, and their abundances are therefore determined only by partonic EOS. At a lower temperature thermal freeze-out takes place where elastic collisions are brought to a halt. We calculate the spectra for various hadrons at different centrality windows, with chemical and thermal freeze-out temperature being fit as a function of centrality. As it is shown, the result provides a reasonable panoramic description of the spectra of identified particles. Chemical freeze-out gives good correction of the multiplicity of certain species of particles, especially for multi-strange hadrons.

nucl-th↗

arXiv2007

Status and Promise of Particle Interferometry in Heavy-Ion Collisions

After five years of running at RHIC, and on the eve of the LHC heavy-ion program, we highlight the status of femtoscopic measurements. We emphasize the role interferometry plays in addressing fundamental questions about the state of matter created in such collisions, and present an enumerated list of measurements, analyses and calculations that are needed to advance the field in the coming years.

nucl-ex↗

arXiv2007

pT distribution of hyperons in 200A GeV Au-Au by smoothed particle hydrodynamics

The transverse momentum distributions for hadrons in 200GeV Au-Au collision at RHIC is calculated using a smoothed particle hydrodynamics code SPheRIO, and are compared with the data from STAR and PHOBOS Collaborations. By employing the equation of state which explicitly incorporate the strangeness conservation and introducing strangeness chemical potential into the code, the transverse spectrums give a reasonable description for the experimental data.

nucl-th↗

arXiv2007

Effect of chemical freeze out on identified particle spectra at 200AGeV Au-Au Collisions at RHIC using SPheRIO

We investigate the effect of chemical freeze-out on identified particle spectra at 200AGeV Au-Au Collisions at RHIC, by utilizing a full three-dimensional hydrodynamical calculation. The hydrodynamical code SPheRIO we employed is based on the smoothed particle hydrodynamic algorithm. In order to describe the spectra of strange hadrons, the code has been further improved by explicitly incorporating the strangeness conservation and a chemical freeze-out mechanism. In our model, strange hadrons such as Lambda, Xi, Omega and phi undergo the chemical freeze-out immediately after the hadronization, and their multiplicities are fixed thereafter. At a lower temperature the thermal freeze-out takes place for all the particles. It is shown that the present model provides a reasonably good description for the spectra of identified particles, in particular, considerable improvement is observed for those of strange hadrons.

nucl-th↗

arXiv2005

3D Relativistic Hydrodynamic Computations Using Lattice-QCD-Inspired Equations of State

In this communication, we report results of three-dimensional hydrodynamic computations, by using equations of state with a critical end point as suggested by the lattice QCD. Some of the results are an increase of the multiplicity in the mid-rapidity region and a larger elliptic-flow parameter v2. We discuss also the effcts of the initial-condition fluctuations and the continuous emission.

hep-ph↗

arXiv2005

Antihyperon polarization in high-energy inclusive reactions

We propose a model for the antihyperon polarization in high-energy proton-nucleus inclusive reactions, based on the final-state interactions between the antihyperons and other produced particles (predominantly pions). To formulate this idea, we use the previously obtained low-energy pion-(anti-)hyperon interaction using effective chiral Lagrangians, and a hydrodynamic parametrization of the background matter, which expands and decouples at a certain freezeout temperature.

hep-ph↗

arXiv2001

Low Energy Pion-Hyperon Interaction

We study the low energy pion-hyperon interaction considering effective non-linear chiral invariant Lagrangians including pions, rho mesons, hyperons and corresponding resonances. Then we calculate the S- and P-wave phase-shifts, total cross sections, angular distributions and polarizations for the momentum in the center-of-mass frame up to k=400 MeV. With these results we discuss the CP violation in the csi-> pi-lambda and omega-> pi-csi weak decays.

hep-ph↗

arXiv2000

Continuous emission versus freeze-out via HBT

The effect of the continuous emission hypothesis on the two-pion Bose-Einstein correlation function is discussed and compared with the corresponding results based on the usual freeze-out. Sizeable differences in the correlation function appear in these different descriptions of the decoupling process. This means that, when extracting properties of the hot matter formed in high-energy heavy-ion collisions from the data, completely different conclusions may be reached according to the description of the particle emission process adopted.

hep-ph↗

arXiv1999

Variational Principle for Relativistic Fluid Dynamics

The variational principle for the special and general relativistic hydrodynamics are discussed in view of its application to obtain approximate solutions to these problems. We show that effective Lagrangians can be obtained for suitable ansatz for the dynamical variables such as density profile of the system. As an example, the relativistic version of spherical droplet motion (Rayleigh-Plesset equation) is derived from a simple Lagrangian. For the general relativistic case the most general Lagrangian for spherically symmetric systems is given.

hep-ph↗