Fujio Takagi

Excluded volume, bag constant and hadron-quark phase transition

The model of hadron-quark phase transitions proposed by Cleymans et al. is modified by taking into account the fact that the nuclear repulsive force is operative between a pair of nucleons or a pair of antinucleons but not between a nucleon and an antinucleon. The phase boundary in the temperature (T)-chemical potential (μ) plane is calculated for some values of the bag constantB and the hard core radiusR. Stability of the normal nuclear matter together with the bag picture for the nucleon yields rather stringent bounds forB as functions ofR. The most probable range of values is estimated to beB1/4≅150∼200 MeV being consistent with the estimate from hadron spectroscopy. For this range ofB, it is improbable to realize the broken chiral phase with deconfining constituent quarks and Goldstone pions at someT and μ.

University of Mean Charged Hadron Multiplicities in Particle and Nuclear Collisions

We propose that mean charged hadron multiplicities in various particle collision processes including hadron-nucleus collisions are described in terms of a universal function F( ), where is the mean square invariant mass of the final state subsystem X which consists of all the produced hadrons other than the leading particles. Leading particle effects in general and nuclear mass effects in hadron-nucleus collisions are most important factors which deter· mine at a given incident energy. It is found that in proton-emulsion interaction the leading particle effects depend strongly on the number of heavily ionizing prongs. Within the framework of our model, the observed values of mean shower particle multiplicities in proton-emulsion interaction indicate that F( ) obeys a power-law.

Effects of friction on the chiral symmetry restoration in high-energy heavy ion collisions

We study the effects of friction on the chiral symmetry restoration which may take place temporarily in high energy heavy ion collisions. The equations of motion with friction are introduced to describe the time evolution of the chiral condensates within the framework of the linear

Thermodynamics of a single bag and quark deconfinement phase transition

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VENEZIANO'S MODEL FOR PSEUDOSCALAR--PSEUDOSCALAR SCATTERING, FACTORIZATION, AND THE NONET ANSATZ.

model. Four types of friction are used to study how the result is sensitive to the choice of the friction. For the thermalization stage, the time dependent temperature is parametrized so as to simulate the result of the parton-cascade model. It is parametrized according to the one-dimensional scaling hydrodynamics for the subsequent cooling stage. The time development of the condensates and the entropy production due to friction are calculated numerically. The time interval in which the chiral symmetry is restored approximately is investigated in detail for four types of friction. It is found that (i) the maximum temperature must be high enough (not lower than 230 MeV) and the friction must be strong enough in order that the chiral symmetry restoration lasts for a long time (not shorter than 3fm/c), (ii) the ratio of time interval in which chiral symmetry is restored, to the time interval in which the temperature is higher than the critical temperature is typically 0.5 when the friction is strong enough, and (iii) the entropy due to the friction is mainly produced in the early stage of the cooling. The effect of freeze-out is discussed briefly.

Collective Quark Tubes in Hadron-Nucleus Collisions at High Energies

Thermodynamics of a single bag is examined in detail in order to obtain new information on the properties of the phase transition between hadronic matter and quark-gluon plasma. With the zero point energy term added to the usual thermodynamical terms, our formalism provides a smooth interpolation between a ground state bag (a lowest-lying hadron) at zero temperature and an excited bag at a critical temperature. In the simplest case where there is no surface energy, the bag radius diverges like (Tc−T)−1/4 as the temperatureT approaches the critical temperatureTc from below, implying a second order transition into the quark deconfining phase at higher temperature. If there is negative surface energy, the bag radius diverges like (Tc−T)−1. If the surface energy is positive, the radius approaches a finite value asT goes to another critical temperatureT2c (>Tc) and there is no finite radius solution forT>T2c, indicating a first order phase transition. The temperature-dependence of both the internal energy and the free energy is examined in connection with the problem of mass shift of hadrons at high temperature. Virial theorems play an important role. Effects of the quark chemical potential are discussed briefly.

Nuclear effects in the semi-inclusive cross section of high energy neutrino-nucleus interactions

Crossing·symmetric, Regge behaved amplitudes of the Veneziano type are constructed for Ps-Ps scattering, where Ps denotes the pseudoscalar meson octet. Factorization of the parent and the first (odd) daughter Regge trajectories is investigated in detail. Several relations for the VgPSPS and the TgPsPs coupling constants which are equivalent to or consistent with the SU(3) symmetry and Okubos nonet ansatz are obtained, where Vg and Tg denote the vector and the tensor meson nonets, respectively. Positive definiteness of the square of the first daughter-Ps-Ps coupling constant leads to inequalities for the trajectories or the masses which are well satisfied by experiment. Factorization condition for the first daughter trajectories leads to trajectory or mass relations which are well satisfied experimentally. In particular the requirement of the universality for the parent and the first daughter p couplings leads to the broken SU(6) mass relations which have bee~ obtained by Kawarabayashi, Kitakado and Yabuki using Adlers PCAC consistency conditions applied to the Veneziano model. Consequences from the requirement of the PCAC conditions on the 1l-meson processes are discussed briefly.

Collective Quark Tubes and Multiplicity Distributions in α-α Collisions at High Energies

The big hadron model (collective tube model) for hadron production off nuclei is reformulated in terms of the constituent Quark picture. Predictive power of the model is considerably strengthened as the main free parameters of the original model are now calculable. The new version is applied to the mean multiplicities in hadron-nucleus collisions with satisfactory results.

Is multiple production in proton-proton collisions similar to that ine+e− annihilation?

Abstract In high energy neutrino scattering off nuclei, the cross sections σ ( x ) show experimentally a remarkable dependence on the presence or the absence of slow recoil protons. It is found that the effect is explained by the kinematics of slow protons directly produced by diquark fragmentation and the rescattering of leptoproduced nucleons.

DIPS IN TWO-BODY AND QUASI-TWO-BODY HADRONIC PROCESSES AND DUAL GEOMETRICAL MODEL.

Cross sections for various configurations of inelastic a-a collisions at the quark level are calculated by using the standard multiple scattering formula at the nucleon level with the quark additivity approxima· tion for nucleon·nucleon collisions. The result is used to calculate the multiplicity distribution of charged hadrons within the framework of the collective quark tube model (CQTM) i.e., a quark·version of the collective tube model. The calculated distribution is in good agreement with the recent experimental result obtained at CERN ISR. The effect of the collectivity characteristic of CQTM is, however, negligibly small in the a-a case.