Multiplicities of secondary hadrons produced in vp and vp charged current interactions

In an experiment with the hydrogen bubble chamber BEBC at CERN multiplicities of hadrons produced in νp and $\text{v}\text{p}$ interactions have been investigated. Results are presented on the multiplicities of charged hadrons and neutral pions, forward and backward multiplicities of charged hadrons and correlations between forward and backward multiplicities. Comparisons are made with hadronic reactions and e⁺e^? annihilation. In the framework of the quark-parton model the data imply similar charged multiplicities for the fragments of a u- and a d-quark, and a larger multiplicities for the fragments of a uu- than for a ud-diquark. The correlation data suggest independent fragmentation of the quark and diquark for hadronic masses above ～ 7 GeV and local charge compensation within an event.     

Charged multiplicities of hadrons in hadronic and leptonic reactions

Experimental data on average charged multiplicities of hadrons produced ine ⁺ e ^? annihilations,v N and \(\bar vN\) reactions and non-diffractive π^± p andpp interactions over a wide energy range are found to satisfy simple relationships obtained by expressing the multiplicity of each reaction as a sum of single-quark and diquark jet multiplicities. The observed difference between these two terms can be attributed to the leading nucleon effect.     

Comparison of antiproton diffraction dissociation with inelastic\bar pp interactions ande + e − annihilation into hadrons

Experimental multiplicity distributions of antiproton diffraction dissociation and inelastic antiproton-proton interactions at 22.4 GeV/c with leading particles removed are compared withe ⁺ e ^? annihilation into hadrons. We find agreement with the predictions of the dual parton model.     

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

A model is constructed to simulate recent experimental finding that distributions of hadrons produced in proton-proton collisions are similar to those ine ⁺ e ^? annihilation if the leading proton effects are subtracted properly in the former process. It is found that the predicted multiplicity distribution in proton-proton collisions is too narrow compared to experimental data. As an alternative, we propose a simple quark model that produces correctly the observed multiplicity distribution including the approximate KNO scaling in proton-proton collisions.     

Annihilation of e+−e− into hadrons in a hydrodynamic model

A hydrodynamic model with modified boundary conditions is proposed for the two-jet component of e⁺?e^? annihilation into hadrons. Satisfactory agreement with data for charged multiplicity and inclusive distributions of hadrons is obtained with three energy-independent parameters.     

Z boson effects in electron positron scattering at epic energies at 14 GeV

We discuss the problem of testing the intermediate vector boson effects in the reactions e^?e⁺ → e^?e⁺ + hadrons, e^?e⁺ → e^?e⁺ + μ^?μ⁺, e^?p → e^?x with the next generation of accelerators, and conclude that these reactions must be considered. The differential cross sections for the one lepton at large four-momentum transfer are obtained, and a significant contribution of Z effects is found.     

Multiplicity distributions in a thermodynamical model of hadron production ine + e − collisions

Predictions of a thermodynamical model of hadron production for multiplicity distribution ine ⁺ e ^? annihilations at LEP and PEP-PETRA centre of mass energies are shown. The production process is described as a two-step process in which primary hadrons emitted from the thermal source decay into final observable particles. The final charged tracks multiplicity distributions turn out to be of Negative Binomial type and are in quite good agreement with experimental observations. The average number of clans calculated from fitted Negative Binomial coincides with the average number of primary hadrons predicted by the thermodynamical model, suggesting that clans should be identified with primary hadrons.     

Higher twist contributions from the direct pion coupling ine + e − annihilation,photoproduction and π− p Drell-Yan

We present calculations of normalized higher twist contributions in three processes in which the central sub-processes are related by crossing: the production of hadrons at high transverse momentum relative to the thrust axis ine ⁺ e ^? annihilation, photoproduction of high transverse momentum pions from a proton target, and high transverse momentum lepton pair production in π^? p collisions. The last of these is most interesting, not only because the higher twist contribution is significant, but also the QCD interpretation of the data is uncertain.     

Charged pion,kaon, proton and antiproton production in high energy e+e− annihilations

Production of pions, kaons, protons and antiprotons has been studied in e⁺e^? annihilations at 12 and 30 GeV centre of mass energy using time of flight techniques. The fractional yield of charged kaons and baryons appears to rise with outgoing particle momentum. At our highest energy at least 40% of e⁺e^? annihilations into hadrons are estimated to contain baryons.     

Dual topology in large-pT reactions

We investigate a dual-string approach to the study of jets in large-p_T proton-proton collisions. The model is discussed for the dominant planar topology of valence quark-valence quark scattering where final hadrons may be viewed as fragments of two strings stretched between quarks and forward- or backward-moving diquarks. We assume that in the string c.m. frame, its fragments form a jet analogous to that observed in e⁺e^?→hadrons. Going back to the overall c.m. frame we recover the four-jet structure of large-p_T reactions. We discuss away side multiplicity distributions and show that the string approach which unifies the treatment of large-p_T and background secodaries, is equivalent to the naïve approach when the secondary momentum is large enough compared to its mass. Specific effects emerge for small enough momentum secondaries which result in widening of multiplicity rapidity distributions. Comparison with ISR data shows that this improves the agreement with experiment. Non-dominant contributions are also briefly considered.     

The parton model,duality and deep-inelastic single-particle distributions

Within the quark parton model the two-component duality idea is generalized to single hadron inclusive distributions in deep-inelastic scattering. The discussion is limited to the current fragmentation region. The number of independent distribution functions is reduced. Relations as well as inequalities among the structure functions are obtained. In particular, the excess of π⁺ over π^? in the electroproduction off a proton comes out as a consequence and the differential cross section for e⁺e^? → π+ anything is fully determined by the electroproduction of pions on nucleons.     

QCD jets ine + e −-annihilation and the transition into hadrons

A model has been developed describing QCD jets in the leading logarithmic approximation (LLA) and the subsequent transition into hadrons via a chain decay model. Besides of the production of mesons, the model is also able to describe baryon production. Agreement with recent data frome ⁺ e ^?-annihilation is found. This includes average multiplicities, average transverse momenta and transverse momentum distributions, longitudinal momentum distributions as well as particle production ratios π^α:K ^π : p(0070), charge compensation probabilities and energy flux correlations. The model is compared to similar models developed by other authors.     

Multiplicities in electroproduction and e+e− annihilation

It is shown how more sophisticated versions of the parton model can replace the naive expectation of final state hadrons being produced in ep or e⁺e^? collisions in two jets of finite multiplicity, well-separated in rapidity, with a picture that permits the rapidity gap to be filled in and allows the multiplicity to rise with energy, even up to the limit imposed by energy conservation. Large multiplicity is shown to imply a rather slow approach to scaling and a significant tail in the transverse momentum distribution.     

Multihadron production in a cascade model for e+e− annihilation: I. Total cross section and multiplicity distribution

We consider a simple dynamical model for e⁺e^? annihilation in which the production of pions is the result of a kind of bremsstrahlung process, each step of the cascade being characterized by the decay of a (massive) spin-one system into a pion plus a similar spin-one system. We study the high-energy behaviour of the n-particle and total cross sections as well as the multiplicity distribution for a large class of transition form factors. The model is found to include features familiar from the uncorrelated jet, the multiperipheral and the thermodynamical models. In particular, it is able to accomodate a logarithmically increasing multiplicity as well as a constant total cross section.     

A QCD model for jet fragmentation including soft gluon interference

A new model for hadronic jet fragmentation in hard processes is presented. It is based on a QCD parton branching mechanism with correct treatment of leading collinear and infra-red singularities (i.e. including soft gluon interference). Hadronization occurs via preconfinement of colour singlet clusters, which decay according to a simple phase-space scheme. Although tightly constrained, the model gives a good account of existing e⁺ e^? annihilation data. It predicts significant differences between quark and gluon jets. Comparisons with datadata on the CERN p?p collider jets suggest that a large fraction of them are gluon jets. The model predicts soft gluon interference effects in hadron distributions which are probably not yet observable for pions but should be clear for kaons and baryons.     

A model for multiplicity distributions in high energy collisions

A phenomenological model is presented which regards the system after collision as a single entity that emits hadrons directly. The evolution of this entity gives a new two parameter distribution which fits the high energypp, \(\bar pp\) ,e ⁺ e ^?, π⁺ p andK ⁺ p data reasonably well. The entity emits hadrons along the rapidity axis and exhibits intermittency behaviour under certain conditions.     

Collins and sivers effects in p↑p → jet πX: Universality and process dependence

In this paper we briefly review the transverse momentum dependent generalized parton model and its application to the study of azimuthal asymmetries in the distribution of leading hadrons (mainly pions) inside large transverse momentum jets inclusively produced in polarized proton-proton collisions. We put particular emphasis on the phenomenological interest of these observables, in combination with similar asymmetries measured in semi-inclusive deeply inelastic scattering, Drell-Yan processes and e ⁺ e ^? collisions, for the study of the universality properties of the transverse momentum dependent parton distribution and fragmentation functions. We present results for RHIC kinematics at center-of-mass energies √s = 200 and 500 GeV, for central and mainly forward jet rapidities, in particular for the Sivers distribution and the Collins fragmentation function, that are believed to be responsible for many of the largest asymmetries measured in the last years. We also briefly discuss the case of inclusive jet production and recent phenomenological applications of other theoretical approaches, like the colour gauge invariant generalized parton model and the collinear twist-three approach, aiming at clarifying the issues of the universality and process dependence of transverse momentum dependent functions.