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→∞.     

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.     

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.     

Hadronization and chirality in strongly interacting partonic matter — The future of the RHIC Program

New physics and detector concepts for a future pp and heavy ion program at the RHIC-II accelerator facility will be discussed. I will focus on hadronic observables which enable us to gain a better understanding on the hadronization from a sQGP and the chiral symmetry restoration in a sQGP. The ultimate question of how matter acquires mass can be addressed by this program in a complementary way to the Higgs search in high energy physics. The contributions of the RHIC program to the study of QCD will be discussed in detail.