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Takeshi Osada

Publications and source records attributed to Takeshi Osada.

13 recordsLinked to original sources
arXiv2026

Radial-flow fluctuations in the geometrical-scaling framework

We discuss radial-flow fluctuations using the $p_{\rm T}$-differential measure \(v_0(p_{\rm T})\), together with its $p_{\rm T}$-integrated counterpart \(v_0\), within the framework of geometrical scaling (GS), where the saturation momentum scale provides the characteristic scale for particle production. We show that the GS framework leads to results similar to those obtained from the momentum-rescaling model proposed by Jiangyong Jia. In the GS picture, event-by-event spectral fluctuations are governed by fluctuations of the saturation momentum scale; consequently, the single-mode ansatz introduced in Jia's model emerges naturally. We also show that the GS picture suggests a possible connection between transverse-momentum correlations and fluctuations of the emission region, which may be probed through Hanbury Brown and Twiss (HBT) analyses. Using the string percolation model, which is closely related to GS, we estimate the multiplicity dependence of radial-flow fluctuations and propose the scaled quantity $A_0(N_{Δy}) \equiv v_0^2 N_{Δy}$, with $N_{Δy}=(dN/dy)Δy$, as a diagnostic observable for testing the role of effective flux-tube fluctuations.

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arXiv2021

Multiplicity-dependent saturation momentum in $p$-Pb collisions at 5.02 TeV

Semi-inclusive transverse momentum spectra observed in proton-proton and proton-lead nuclear collisions at LHC energies obey a geometric scaling with a scaling variable using multiplicity-dependent saturation momentum. The saturation momentum extracted from the experimental data is proportional to the 1/6 power of the hadron multiplicity in the final state. On the other hand, the system's transverse size is proportional to the 1/3 power of the multiplicity, and the saturation momentum and the transverse size of the system are strongly correlated with the hadron multiplicity in the final state. Since the saturation momentum is proportional to the average transverse momentum of hadrons, one predicts average transverse momentum is also proportional to the 1/6 power of the multiplicity, which is consistent with experimental results at the LHC energy. We found that a nuclear modification factor $R_{\rm pPb}$ calculated by the multiplicity-dependent saturation momentum decreases at $p_{\rm T} \lesssim$ 1GeV/$c$ and that our model can partially explain the $R_{\rm pPb}$'s behavior thought to be caused by nuclear shadowing. On the other hand, Cronin enhancement experimentally observed at $2 \lesssim p_{\rm T} \lesssim $ 6 GeV/$c$ is not reproduced. However, the experimental result, including the Cronin effect, can be reproduced well by introducing $p_{\rm T}$ dependence as a 4$\sim$5\% correction to the multiplicity-dependent saturation momentum.We also discuss a relation between the geometric scaling in the semi-inclusive distributions and the string percolation model.

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arXiv2019

Saturation momentum scale extracted from semi-inclusive transverse spectra in high-energy pp collisions

Geometric scaling is well confirmed for transverse momentum distributions observed in proton-proton collisions at LHC energies. We introduced multiplicity dependence on a saturation momentum of the geometrical scaling, assuming the scaling holds for semi-inclusive distributions as well as for inclusive distributions. The saturation momentum is usually given by Bjorken's $x$ variable, but redefinition of the scaling variable can make the saturation momentum a function of collision energy $W$. We treat the energy as a free parameter (denoted $W^*$ to distinguish it from $W$) and associate the energy-dependent saturation momentum $Q_{\rm sat}(W^*)$ with particle number density. By using $Q_{\rm sat}(W^*)$ for a scaling variable $τ$, we show semi-inclusive distributions can be geometrically scaled. i.e., all semi-inclusive spectra observed at $W$=0.90, 2.76 and 7.00 TeV overlap one universal function. The particle density dependences of mean transverse momentum $\langle p_{\rm T} \rangle$ for LHC energies scales in terms of $Q_{\rm sat}(W^*)$. Furthermore, our model explains a scaling property of event-by-event $p_{\rm T}$ fluctuation measure $\sqrt{C_m}/\langle p_{\rm T}\rangle$ at LHC energies for pp collisions, where $C_m$ is two-particle transverse momentum correlator. Our analysis of the $p_{\rm T}$ fluctuation makes possible to evaluate a non-perturbative coefficient of the gluon correlation function.

hep-ph↗
arXiv2017

Event-by-event mean $p_{\rm T}$ fluctuations and transverse size of color flux tube generated in $p$-$p$ collisions at $\sqrt{s}$=0.90TeV

We propose a novel phenomenological model of mean transverse momentum fluctuations based on the Geometrical Scaling hypothesis. Bose-Einstein correlations between two gluons generated from an identical color flux tube are taken into account as a source of the fluctuation. We calculate an event-by-event fluctuation measure $\sqrt{C_m}/\langle p_{\rm T}\rangle$ and show that ALICE data observed at $\sqrt s=$0.90 TeV for $p$+$p$ collisions are reproduced. By fitting our model to the experimental data, we evaluate the transverse size of the color flux tube as a function of the multiplicity.

hep-ph↗
arXiv2015

Separation of equilibrium part from an off-equilibrium state produced by relativistic heavy ion collisions using a scalar dissipative strength

We have proposed a novel way to specify the initial conditions of a dissipative fluid dynamical model for a given energy density $\varepsilon=u_μT^{μν}u_ν$ and baryon number density $n=N^μu_μ$, which does not impose the so-called Landau matching condition for an off-equilibrium state. In addition to usual two parameters for equilibrium part, i.e., $α\equiv μ/T$, $β\equiv1/T$ (where $T$ is separation temperature and $μ$ is separation chemical potential introduced to separate equilibrium part from the off-equilibrium state), a dissipative strength $γ$ is newly introduced to specify the off-equilibrium state. These $α$, $β$ and $γ$ can be uniquely determined by $\varepsilon$, $n$ and $P_{\rm eq}(α,β)+Π=-1/3Δ_{μν}T^{μν}$ consisting of both kinetic theoretical definitions and the thermodynamical stability condition. For $γ<10^{-3}$, $T$ and $μ$ are almost independent of $γ$, which means that the Landau matching condition is approximately satisfied. However, this is not the case for $γ\gtrsim 10^{-3}$.

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arXiv2012

Relativistic dissipative hydrodynamics with extended matching conditions for ultra-relativistic heavy-ion collisions

Recently we proposed a novel approach to the formulation of relativistic dissipative hydrodynamics by extending the so-called matching conditions in the Eckart frame [Phys. Rev. {\bf C 85}, (2012) 14906]. We extend this formalism further to the arbitrary Lorentz frame. We discuss the stability and causality of solutions of fluid equations which are obtained by applying this formulation to the Landau frame, which is more relevant to treat the fluid produced in ultra-relativistic heavy-ion collisions. We derive equations of motion for a relativistic dissipative fluid with zero baryon chemical potential and show that linearized equations obtained from them are stable against small perturbations. It is found that conditions for a fluid to be stable against infinitesimal perturbations are equivalent to imposing restrictions that the sound wave, $c_s$, propagating in the fluid, must not exceed the speed of light $c$, i.e., $c_s < c$. This conclusion is equivalent to that obtained in the previous paper using the Eckart frame [Phys. Rev. {\bf C 85}, (2012) 14906].

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arXiv2008

New Method of Modelling Dissipative Hydrodynamics

We propose to model the dissipative hydrodynamics used in description of the multiparticle production processes ($d$-hydrodynamics) by a special kind of the perfect nonextensive fluid ($q$-fluid) where $q$ denotes the nonextensivity parameter appearing in the nonextensive Tsallis statistics. The advantage of $q$-hydrodynamics lies in its formal simplicity in comparison to the $d$-hydrodynamics. We argue that parameter $q$ describes summarily (at least to some extent) all dynamical effects behind the viscous behavior of the hadronic fluid.

hep-ph↗
arXiv2008

Nonextensive perfect hydrodynamics - a model of dissipative relativistic hydrodynamics?

We demonstrate that nonextensive perfect relativistic hydrodynamics ($q$-hydrodynamics) can serve as a model of the usual relativistic dissipative hydrodynamics ($d$-hydrodynamics) facilitating therefore considerably its applications. As illustration we show how using $q$-hydrodynamics one gets the $q$-dependent expressions for the dissipative entropy current and the corresponding ratios of the bulk and shear viscosities to entropy density, $ζ/s$ and $η/s$.

hep-ph↗
arXiv2008

Causal dissipative hydrodynamics obtained from the nonextensive/dissipative correspondence

We derive the constitutive equations of causal relativistic dissipative hydrodynamics ($d$-hydrodynamics) from perfect nonextensive hydrodynamics ($q$-hydrodynamics) using the nonextensive/dissipative correspondence (NexDC) proposed by us recently. The $q$-hydrodynamics can be thus regarded as a possible model for the $d$-hydrodynamics facilitating its application to high energy multiparticle production processes. As an example we have shown that applying the NexDC to the perfect 1+1 $q$-hydrodynamics, one obtains a proper time evolution of the bulk pressure and the Reynolds number.

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arXiv2008

Dissipative or just Nonextensive hydrodynamics? - Nonextensive/Dissipative correspondence -

We argue that there is correspondence between the perfect nonextensive hydrodynamics and the usual dissipative hydrodynamics, which we call nonextensive/dissipative correspondence (NexDC). It leads to simple expression for dissipative entropy current and allows for predictions for the ratio of bulk and shear viscosities to entropy density, $ζ/s$ and $η/s$.

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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↗
arXiv2000

Entropy and holography constraints for inhomogeneous universes

We calculated the entropy of a class of inhomogeneous dust universes. Allowing spherical symmetry, we proposed a holographic principle by reflecting all physical freedoms on the surface of the apparent horizon. In contrast to flat homogeneous counterparts, the principle may break down in some models, though these models are not quite realistic. We refined fractal parabolic solutions to have a reasonable entropy value for the present observable universe and found that the holographic principle always holds in the realistic cases.

astro-ph↗