Hadronization of quark systems

Hadronization in simple models of quark systems is discussed with emphasis on the combinatorial aspects. The numberN of quarks and the numberN _c of colours are the relevant variables. In onedimension and in the meson and baryon sector the problem is completely soluble. When multiquark hadrons are included an iterative procedure still allows a complete solution. Higher dimensions are difficult to treat but global hadronization, without dimensionality constraints, is again soluble. As a general result the baryon/meson ratio is, for large quark densities, rather large, ?1/3 and may grow without limit asN→∞.     

Chiral Singularity in Hadronization

Hadronization at finite temperature and density is discussed in the framework of the Nambu-Jona-Lasinio (NJL) model. The differential cross-section for the conversion of a quark-antiquark pair into two pions to the first order of 1/N_c expansion is calculated as a function of the c.m. energy s, temperature T and the chemical potendal u. The density effect is emphasized.     

Hadronization from color interactions

A quark coalescence model, based on semi-relativistic molecular dynamics with color interactions among quarks, is presented and applied to pp collisions. A phenomenological potential with two tunable parameters is introduced to describe the color interactions between quarks and antiquarks. The interactions drive the process of hadronization that finally results in different color neutral clusters, which can be identified as hadrons based on some criteria. A Monte Carlo generator PYTHIA is used to generate quarks in the initial state of hadronization, and different values of tunable parameters are used to study the final state distributions and correlations. Baryon-to-meson ratio, transverse momentum spectra, pseudorapidity distributions and forward-backward multiplicity correlations of hadrons produced in the hadronization process, obtained from this model with different parameters, are compared with those from PYTHIA.     

Hadronization of expanding QGP

We discuss how the dynamics of an exploding hot fireball of quark-gluon matter impacts the actual phase transition conditions between the deconfined and confined state of matter. We survey the chemical conditions prevailing at hadronization.     

Hadronization in the Nuclear Media

The influence of the nuclear environment on the production of charged pions, kaons and (anti)protons in semi-inclusive deep inelastic scattering has been studied by the HERMES experiment at DESY using a 27.6?GeV positron beam. Identified hadron multiplicities have been measured for helium, neon, krypton and xenon relative to that of deuterium as a function of ??, z and ${p_{t}^{2}}$ . Dependences have been extracted in a one and two-dimensional representation, i.e. in the form of detailed binning over one variable and integrating over all other variable or three slices over the other variable. The most prominent feauteres compared to a one-dimensional analysis are changes of the ??-, ${p_{t}^{2}}$ two-dimensional dependences of ratios, in particular in case of protons. In general pions and negative kaons show similar dependences, however, positive kaons, protons and antiprotons behave quite differently.     

Partial inelasticities from the dual parton model

The question of the energy behavior of the partial inelasticities is studied in the context of the dual parton model. A simple analytical expression is derived which describes the behavior of the partial inelasticities at high energies. A comparison with the results of some other models is also given. The question of the violation of Feynman scaling is considered with reference to the inelasticity problem. Received: 8 August 1997 / Revised version: 12 December 1997 / Published online: 10 March 1998     

Hadronization in heavy-ion collisions: recombination and fragmentation of partons

We argue that the emission of hadrons with transverse momentum up to about 5 GeV/c in central relativistic heavy ion collisions is dominated by recombination, rather than fragmentation of partons. This mechanism provides a natural explanation for the observed constant baryon-to-meson ratio of about one and the apparent lack of a nuclear suppression of the baryon yield in this momentum range. Fragmentation becomes dominant at higher transverse momentum, but the transition point is delayed by the energy loss of fast partons in dense matter.     

Non-relativistic models for inelasticities in the ND−1 equations

Inelasticities in non-relativistic, many-channel scattering problems, due to the existence of non-explicit further channels of the system, are studied in the framework of the matrix ND^?1 representation of partial-wave scattering amplitudes, using the concept of a generalised phase-space matrix. For a system of coupled two-fragment channels driven by an absorptive, effective-potential matrix, general, exact expressions for the phase-space matrix are derived in terms of a matrix generalisation of the Kowalski-Noyes half-off-shell extension factor. Analytically soluble coupled-channel models based on finite-rank interactions are used to illustrate the general formulas, to discuss the problem of CDD singularities, and to numerically test approximation schemes based on Born expansions of the half-off-shell factors. It is concluded that for a large class of problems, the regular part of the phase-space matrix can be calculated in a practical way from low-order Born or multiple-scattering terms, in much the same way as usually done for the left-hand singularities.     

QGP强子化的多粒子玻色–爱因斯坦关联分析

计算了由夸克–胶子等离子体(QGP)颗粒表面强子化所产生的π介子和K介子的多粒子玻色–爱因斯坦关联.对有限初始重子数密度的情况,K⁺介子的多粒子关联比π介子的多粒子关联弱,K^－介子的平均多粒子关联强度随QGP颗粒数目N_d的增加而快速下降.在零初始重子数密度情况下,K⁺和π介子的平均多粒子关联强度的差别随N_d的增加而变得明显.     

Hadronization corrections to helicity components of the fragmentation function

In the hadronic decays of , gluon emission leads to the appearance of the longitudinal component of the fragmentation function, . Measurement of and the transverse component, , could thus provide insight into the gluon fragmentation function. However, hadronization corrections at low x can be significant. Here we present a method of accounting for such corrections, using the Jetset event generator as illustration. Received: 11 April 2001 / Revised version: 4 May 2001 / Published online: 29 June 2001     

Hadronization of excited nucleons in nuclear collisions at ISR energies

Calorimeters downstream of the intersection of pα and αα beams in the ISR have been used to study the hadronization of excited nucleons. These data extend and support the conclusions from previous studies of the A-dependence of particle multiplicities in ultrarelativistic p-nucleus collisions, which provided evidence that the proton hadronizes outside the nuclear volume.