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Hirotsugu Fujii

Publications and source records attributed to Hirotsugu Fujii.

26 records · Page 2Linked to original sources
arXiv2013

Heavy quark pair production in high energy pA collisions: Quarkonium

Quarkonium production in high-energy proton (deuteron)-nucleus collisions is investigated in the color glass condensate framework. We employ the color evaporation model assuming that the quark pair produced from dense small-x gluons in the nuclear target bounds into a quarkonium outside the target. The unintegrated gluon distribution at small Bjorken x in the nuclear target is treated with the Balitsky-Kovchegov equation with running coupling corrections. For the gluons in the proton, we examine two possible descriptions, unintegrated gluon distribution and ordinary collinear gluon distribution. We present the transverse momentum spectrum and nuclear modification factor for J/psi production at RHIC and LHC energies, and those for Upsilon(1S) at LHC energy, and discuss the nuclear modification factor and the momentum broadening by changing the rapidity and the initial saturation scale.

hep-ph↗
arXiv2012

CGC predictions for p+Pb collisions at the LHC

We present predictions for total multiplicities and single inclusive particle production in proton-lead collisions at the LHC. The main dynamical input in our calculations is the use of solutions of the running coupling BK equation tested in e+p data. We use a Monte-Carlo treatment of the nuclear geometry and either $k_t$-factorization or the hybrid formalisms to describe particle production in the central and forward rapidity regions, respectively.

hep-ph↗
arXiv2011

Critical exponents from two-particle irreducible 1/N expansion

We calculate the critical exponent $ν$ in the 1/N expansion of the two-particle-irreducible (2PI) effective action for the O(N) symmetric $ϕ^4$ model in three spatial dimensions. The exponent $ν$ controls the behavior of a two-point function $<ϕϕ>$ {\it near} the critical point $T\neq T_c$, but can be evaluated on the critical point $T=T_c$ by the use of the vertex function $Γ^{(2,1)}$. We derive a self-consistent equation for $Γ^{(2,1)}$ within the 2PI effective action, and solve it by iteration in the 1/N expansion. At the next-to-leading order in the 1/N expansion, our result turns out to improve those obtained in the standard one-particle-irreducible calculation.

hep-ph↗
arXiv2010

Chiral phase transition in a random matrix model with three flavors

The chiral phase transition in the conventional random matrix model is the second order in the chiral limit, irrespective of the number of flavors N_f, because it lacks the U_A(1)-breaking determinant interaction term. Furthermore, it predicts an unphysical value of zero for the topological susceptibility at finite temperatures. We propose a new chiral random matrix model which resolves these difficulties by incorporating the determinant interaction term within the instanton gas picture. The model produces a second-order transition for N_f=2 and a first-order transition for N_f=3, and recovers a physical temperature dependence of the topological susceptibility.

hep-lat↗
arXiv2008

Initial energy density and gluon distribution from the Glasma in heavy-ion collisions

We estimate the energy density and the gluon distribution associated with the classical fields describing the early-time dynamics of the heavy-ion collisions. We first decompose the energy density into the momentum components exactly in the McLerran-Venugopalan model, with the use of the Wilson line correlators. Then we evolve the energy density with the free-field equation, which is justified by the dominance of the ultraviolet modes near the collision point. We also discuss the improvement with inclusion of nonlinear terms into the time evolution. Our numerical results at RHIC energy are fairly consistent with the empirical values.

hep-ph↗
arXiv2006

Quark pair production in high energy pA collisions: General features

A consistent treatment of both multiple scattering and small x quantum evolution effects on pair production in high energy pA collisions is feasible in the framework of the Color Glass Condensate (hep-ph/0402257). We first discuss the properties of quark pair production in the classical effective theory where only multiple scattering effects are included. Explicit results are given for pair production as a function of the invariant mass of pairs, the pair momenta, the atomic mass number A and the quark mass. We relate the logarithms that appear in our formulation of pair production to logarithms that appear in the limit of collinear factorization in QCD. Violations of kT factorization and medium modifications, as represented by the Cronin effect, are also investigated. We next consider how small x quantum evolution (shadowing) effects modify the results for pair production. In particular, we provide results for the rapidity distribution of pairs and the dependence of the Cronin effect on rapidity. We discuss the dependence of our results on the initial conditions for small x evolution and comment on its implications for pair production at RHIC and the LHC.

hep-ph↗
arXiv2005

Quantitative study of the violation of kt-factorization in hadroproduction of quarks at collider energies

We demonstrate the violation of kT-factorization for quark production in high energy hadronic collisions. This violation is quantified in the Color Glass Condensate framework and studied as a function of the quark mass, the quark transverse momentum, and the saturation scale Qsat, which is a measure of large parton densities. At x values where parton densities are large but leading twist shadowing effects are still small, violations of kT-factorization can be significant - especially for lighter quarks. At very small x, where leading twist shadowing is large, we show that violations of kT-factorization are relatively weaker.

hep-ph↗