The determination of total multiplicity distribution ine + e − annihilation via charged hadron multiplicity distribution

The correspondence between the moments of distribution of primary particles total multiplicity and the moments of partial distribution of charged hadrons multiplicity is obtained. This dependence permits to describe the data on the charged hadrons multiplicity moments by means of negative binomial distribution (NBD) for total hadron multiplicity. The NBD parameterk is fitted as a rational function of c.m. energy.     

Multiplicity distributions in hadron interactions derived from the statistical bootstrap model

We give a self-contained (though sketchy) derivation of the charged multiplicity distribution of final hadrons in a simplified (only pions) version of the statistical bootstrap model (SBM). The analytical form of this distribution is determined by two prominent features of SBM: a singularity at some temperatureT ₀ (related to the phase transition hadrons → quark-gluon plasma) and the production of Poisson-distributed hadron clusters with well-defined decay structure. The multiplicity distribution of final hadrons has two free parameters: an average temperatureT and the mean number \(\bar N\) of clusters, both depending on the collision energy √s such that for √s→∞, the temperature tends to the limitT ₀ while \(\bar N\) may grow (very slowly) without bound. With these two free parameters we obtain reasonable to good fits to experimental data at energies ranging from √s=7.87 to 900 GeV (full and in some cases cut pseudorapidity). The average cluster sizes found in our fits are compatible with those inferred from (pseudo) rapidity correlations in the data. We discuss the relation of this model to the negative binomial distribution (NBD).     

Hadronic spectral function and charm meson production

At the chiral restoration/deconfinement transition, most hadrons undergo a Mott transition from being bound states in the confined phase to resonances in the deconfined phase. We investigate the consequences of this qualitative change in the hadron spectrum on final state interactions of charmonium in hot and dense matter, and show that the Mott effect for D-mesons leads to a critical enhancement of the J/ψ dissociation rate. Anomalous J/ψ suppression in the NA50 experiment is discussed as well as the role of the Mott effect for the heavy-flavor kinetics in future experiments at the LHC. The status of our calculations of hadron–hadron cross sections using the quark interchange and chiral Lagrangian approaches is reviewed, and an ansatz for a unification of these schemes is given.     

Collective Perspective on Advances in Dyson–Schwinger Equation QCD

We survey contemporary studies of hadrons and strongly interacting quarks using QCD's Dyson-Schwinger equations, addressing the following aspects: confinement and dynamical chiral symmetry breaking; the hadron spectrum; hadron elastic and transition form factors, from small-to large-Q2; parton distribution functions; the physics of hadrons containing one or more heavy quarks; and properties of the quark gluon plasma.     

Collective Perspective on Advances in Dyson-Schwinger Equation QCD

We survey contemporary studies of hadrons and strongly interacting quarks using QCD's Dyson-Schwinger equations, addressing the following aspects: confinement and dynamical chiral symmetry breaking; the hadron spectrum; hadron elastic and transition form factors, from small- to large-Q²; parton distribution functions; the physics of hadrons containing one or more heavy quarks; and properties of the quark gluon plasma.     

One-loop factorization for inclusive hadron production in p-A collisions in the saturation formalism

We demonstrate the QCD factorization for inclusive hadron production in p-A collisions in the saturation formalism at one-loop order, with explicit calculation of both real and virtual gluon radiation diagrams. In particular, we find that the cross section can be written into a factorization form in the coordinate space at the next-to-leading order, while the naive form of the convolution in the transverse momentum space does not hold. The collinear divergences associated with the incoming parton distribution of the nucleon and the outgoing fragmentation function of the final-state hadron, as well as the rapidity divergence with small-x dipole gluon distribution of the nucleus are factorized into the splittings of the associated parton distribution and fragmentation functions and the energy evolution of the dipole gluon distribution function. The hard coefficient function is evaluated at one-loop order, and contains no divergence.     

Penetrating flavors

Hadrons made of heavy flavor quarks are expected to have small cross sections and perhaps reduced energy loss in collisions, leading to their being more “penetrating” than ordinary hadrons. Some effects of this in cosmic ray phenomena are considered. If the heavy particle lives long enough it can become the dominant hadron component in the atmosphere. With particles of short lifetime there is a threshold effect in energy where the penetrating hadron travels far enough to become important. Some of the anomalous effects in 10² – 10³ TeV phenomena could be caused via this mechanism by a particle with lifetime ～ 10^?11 s. An ～ 150 cm thick iron absorber would provide a substantial enhancement in the charm/proton ratio in the 10–100 TeV range. If free quarks are produced and have the same cross section as bound quarks, they act as highly penetrating hadrons.     

A NLO calculation of the hadron-jet cross section in photoproduction reactions

We study the photoproduction of large charged hadrons in e p collisions, both for the inclusive case and for the case where a jet in the final state is also measured. Our results are obtained by a NLO generator of partonic events. We discuss the sensitivity of the cross section to the renormalisation and factorisation scales, and to various fragmentation function parametrisations. The possibility to constrain the parton densities in the proton and in the photon is assessed. Comparisons are made with H1 data for inclusive charged hadron production. Received: 25 June 2002 / Published online: 18 October 2002     

A New Qualitative Prediction of the Parton Model for High-Energy Hadron Collisions

Inclusive single jet production in hadron collisions is considered. It is shown that the QCD parton model predicts a nonmonotonic dependence of the inclusive cross section on the fraction of the energy deposited in the jet registered, if it is normalized on the same cross section measured at another collision energy. Specifically, if the cross section is normalized by the one measured at a higher collision energy, it possesses a minimum which depends on jet rapidity. This prediction can be tested at the Fermilab Tevatron, at the CERN LHC, and at the Very Large Hadron Collider under discussion.     

Polarized coincidence electroproduction scaling laws for the final state

We study the inclusive electroproduction of single hadrons off a polarized target. Bjorken scaling laws and the hadron azimuthal distribution are derived from the quark parton model.The polarization asymmetries scale when the target spin is along the direction of the virtual photon, and (apart from one significant exception) vanish for transverse spin. These results have a simple explanation; emphasis is given both to the general mathematical formalism and to intuitive physical reasoning.Through this framework we consider other cases: quarks with anomalous magnetic moment; renormalization group effects and asymptotic freedom; production of vector mesons (whose spin state is analysed by their decay); relation to large transverse momentum hadron production; and a covariant parton model calculation. We also look into spin-0 partons and Regge singularities.All of these cases (apart from the last two) modify the pattern of conclusions. Vector meson production shows polarization enhancements in the density matrix element ?₀₊; the renormalization group approach does not lead to any significant suppressions. They are also less severe in parton models for large p_T hadrons, and are not supported by the covariantly formulated calculation. The origins of these differences are isolated and used to exemplify the sensitivity that polarized hadron electroproduction has to delicate detail that is otherwise concealed.     

Longitudinal broadening of quenched jets in turbulent color fields

The nearside distribution of particles at intermediate transverse momentum, associated with a high momentum trigger hadron produced in a high energy heavy-ion collision, is broadened in rapidity compared with the jet cone. This broadened distribution is thought to contain the energy lost by the progenitor parton of the trigger hadron. We show that the broadening can be explained as the final-state deflection of the gluons radiated from the hard parton inside the medium by soft, transversely oriented, turbulent color fields that arise in the presence of plasma instabilities. The magnitude of the effect is found to grow with medium size and density and diminish with increasing energy of the associated hadron.     

Two problems concerning hot hadronic matter and high energy collisions (Equilibrium formation,plasma deflagration)

This paper addresses two questions concerning the hydrodynamical approach to high energy collisions producing large multiplicities of hadrons. The first one concerns the difficulty of understanding in terms of successive parton interactions the formation of local thermal equilibrium for the small and short-lived blobs of excited hadronic matter created in such collisions. We argue that the number of successive parton interactions is not the only relevant factor for equilibrium formation, another factor being the early randomization present in all experiments which observe a subsystem of the complete final state and average over many unobserved degrees of freedom. This conjecture helps to understand the high degree of universality of hadronic jets and the fact that quite different dynamical models manage to describe the same data. The second problem concerns the hadronization of a blob of quark-gluon plasma as could be produced in a very high energy collision. Assuming the transition of plasma to hadron gas to have high latent heat, we show for small chemical potential that the plasma can deflagrate and convert a fraction of its latent heat into collective flow of the hadron gas. In such deflagrations very little entropy is produced, but the flow velocity of the hadron gas with respect to the plasma can be more than half of the velocity of light.     

Modified dihadron fragmentation functions in hot and nuclear matter

Medium modification of dihadron fragmentation functions due to gluon bremsstrahlung induced by multiple partonic scattering is studied in both deep-inelastic scattering (DIS) off large nuclei and high-energy heavy-ion collisions within the same framework of twist expansion. The modification for dihadrons is found to closely follow that for single hadrons, leading to a weak nuclear suppression of their ratios in DIS experiments. A mild enhancement of the near-side correlation of two high transverse momentum hadrons with increasing centrality is found in heavy-ion collisions due to trigger bias and the rise in parton energy loss with centrality. Successful comparisons between theory and experiment for multihadron observables in both confining and deconfined media offer comprehensive evidence for partonic energy loss as the mechanism of jet modification in dense matter.     

Statistical hadronization model and transverse momentum spectra of hadrons in high energy collisions

A detailed analysis of transverse momentum spectra of several identified hadrons in high energy collisions within the canonical framework of the statistical model of hadronization is performed. The study of particle momentum spectra requires an extension of the statistical model formalism used to handle particle multiplicities, which is described in detail starting from a microcanonical treatment of single hadronizing clusters. Also, a new treatment of extra strangeness suppression is presented which is based on the enforcement of fixed numbers of pairs in the primary hadrons. The considered center-of-mass energies range from to 30 GeV in hadronic collisions ( and Kp) and from 15 to 35 GeV in collisions. The effect of the decay chain following hadron generation is accurately and exhaustively taken into account by a newly proposed numerical method. The exact conservation at low energy and the increasing hard parton emission at high energy bound the validity of the presently taken approach within a limited center-of-mass energy range. However, within this region, a clear consistency is found between the temperature parameter extracted from the present analysis and that obtained from fits to average hadron multiplicities in the same collision systems. This finding indicates that in the hadronization process the production of different particle species and their momentum spectra are two closely related phenomena governed by one parameter. Received: 31 October 2001 / Published online: 15 February 2002     

Sum rules for light-by-light scattering

We derive a set of sum rules for the light-by-light scattering and fusion: γγ→all, and verify them in lowest order QED calculations. A prominent implication of these sum rules is the superconvergence of the helicity-difference total cross section for photon fusion, which in the hadron sector reveals an intricate cancellation between the pseudoscalar and tensor mesons. An experimental verification of superconvergence of the polarized photon fusion into hadrons is called for, but will only be possible at e+ e- and γγ colliders with both beams polarized. We also show how the sum rules can be used to measure various contributions to the low-energy light-by-light scattering.     

Hadron production in 200 GeV μ-copper and μ-carbon deep inelastic interactions

The measurements of the z and p_T² distribution of hadrons produced in the interactions of 200 GeV muons with copper and carbon nuclei are shown in different x_Bj and virtual photon energy intervals. Effects of the jet scattering are seen at the lowest virtual photon energies while for energies above 70 GeV there is no evidence of these effects. Comparison with a theoretical model indicates that at high jet energies the parton fragmentation distance is greater than the nuclear radius and that the parton absorption cross section is less than 10 mb.     

Electron-positron annihilation above 2 GeV and the new particles

This paper reviews the experimental and phenomenological aspects of electron-positron annihilation into hadrons at center-of-mass energies above 2 GeV. The behavior of the total cross section for hadron production as a function of energy is described; and the important parameter R - the ratio of this cross section to the muon-pair production cross section - is discussed. Data on charged particle multiplicities, particle production ratios, and single particle inclusive distributions is also summarized. The paper than summarizes our knowledge of the newly discovered ψ particles; and examines the various theories as to their nature and their relation to conventional hadronic physics.     

Parton model predictions for two-particle correlations in e+e− annihilation

The parton model predicts a jet structure for e⁺e^? annihilation into hadrons. This is obscured at low energies by the presence of finite transverse momentum effects. We suggest studying e+⁺e^? → h₁+h₂+X, where at least one hadron is near the kinematical boundary; this defines a jet axis. Numerous predictions for correlations among mesons follow from Feynman's parton fragmentation suggestion. We also give sum rules which check for the quantum numbers of the partons.     

Effect of nuclear matter on the production of hadrons in deep-inelastic neutrino scattering

The inclusive spectra of hadrons are measured with the aid of the SKAT propane-freon bubble chamber irradiated with a beam of 3-to 30-GeV neutrinos from the Serpukhov accelerator. The resulting data indicate that the intranuclear absorption of leading quark-fragmentation products is enhanced as the energy transfer to the quark involved decreases or as the quark-energy fraction z acquired by the product hadron increases. An analysis of the data on the basis of the color-string model reveals that the cross section for the intranuclear absorption of positively charged hadrons that are characterized by z values in the range between 0.7 and 0.9 is close to the inelastic cross section for pion-nucleon interaction.