Next-to-leading order fragmentation functions for pions and kaons

We present new sets of fragmentation functions for charged pions and kaons, both at leading and next-to-leading order. They are fitted to TPC data taken at energy =29 GeV and describe excellently a wealth of othere ⁺ e ^– data on charged-hadron production, ranging from =5.2 GeV way up to LEP 1 energy. They also agree with data on the production of neutral pions and kaons, if one makes the natural assumption that the respective fragmentation functions are related to the charged counterparts bySU(2) symmetry. We also list simple parameterizations of thex andQ ² dependence of our results, which may be implemented conveniently in applications.Supported by Bundesministerium für Forschung und Technologie, Bonn, Germany, under Contract 05 6 HH 93P (5), and by EEC ProgramHuman Capital and Mobility through NetworkPhysics at High Energy Colliders under Contract CHRX-CT93-0357 (DG12 COMA)     

The isospin-symmetry-breaking effects in <Emphasis Type="Italic">K</Emphasis><Subscript><Emphasis Type="Italic">e</Emphasis>4</Subscript> decays

The final-state interaction of pions in K _e4 decay allows to obtain the value of the isospin and angular-momentum-zero ππ scattering length a ₀⁰.We take into account the electromagnetic interaction of pions and isospin-symmetry-breaking effects caused by different masses of neutral and charged pions and estimate the impact of these effects on the procedure of scattering-length extraction from K _e4 decays.     

Some information from nucleon-antinucleon annihilation at rest: e+e− annihilation,hadronic fragmentation and deep inelastic structure functions

The experimental spectra of charged pions in $\text{N}\text{N}$ annihilation at rest are described in a model of quasi-two-body decays. The same model predicts the π⁰, ? and ω spectra. We apply a previous calculation to determine in the vector-dominance model, the pions spectra in e⁺e^? annihilation at the same energy. The $\text{N}\text{N}$ system is then used as a heavy hadron in order to describe, in a model-independent way: (i) the projectile fragmentation part in inclusive reactions; (ii) the valence part of the deep inelastic structure function.     

Spotting glueballs in collinear gluon jets

We suggest looking for pure gluon hadronic states (glueballs) in ?→ 3g → low spherically final state (collinear gluon jets). In these events one gluon has the maximum energy, $\text{M?}\text{2}$, favouring fragmentation into a glueball. The signature for a true C = G + glueball is its prominence at the ? resonance in e⁺e^? →? → (glueball → four charged pions) + … and its absence in q$\text{q}$ jets off (we do not expect significant quark fragmentation into glueballs).     

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.     

Isospin symmetry violating effects and scattering length extraction from kaon decays

The isospin symmetry breaking effects in the charged kaons decays to two or three pions are considered. In semileptonic decay K ^± → π ⁺ π ^?e^± ν (called K _e4) these effects turn out to be crucial for correct extraction of ππ scattering lengths. Taking in account electromagnetic interaction between the pions in the final state and isospin symmetry breaking due to different masses of charged and neutral pions allows to adjust the values of scattering lengths obtained from experimental data on K _e4 decay and predictions of Chiral Perturbation Theory (ChPT). Final state interactions of pions in the decay K ^± → π ^± π ⁰ π ⁰ leading to the anomaly (cusp) in the π ⁰ π ⁰ invariant mass distribution in the vicinity of charged pions’ threshold are discussed and recent results of accounting of the electromagnetic interaction among charged pions leading to π ⁺ π ^? bound states (pioniumatom) just under the charged pions’ threshold are presented.     

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.     

Particle distributions in jets

I extend a model of energy flow in hadronic jets to discuss pion production. I fix the parameter ϱ≈2 GeV of the jet model in terms of the height of the rapidity plateau and the typical transverse energy of pions in e⁺e⁻ jets. I find a relation between the jet shape and the fragmentation function for a quark into pions. I relate the height of the rapidity plateau to the power (1 − x_p) that appears in the fragmentation function.     

On kaon production in e<Superscript>+</Superscript>e<Superscript>-</Superscript> and semi-inclusive DIS reactions

We consider semi-inclusive unpolarized DIS for the production of charged kaons and the different possibilities to test the conventionally used assumptions s-s̄=0 and D_d ^K+-K-=0. The tests considered have the advantage that they do not require any knowledge of the fragmentation functions. We also show that measurements of both charged and neutral kaons would allow for the determination of the kaon fragmentation functions D_q ^K++K- solely from SIDIS measurements, and we discuss the comparison of (D_u-D_d)^K+-K- obtained independently in SIDIS and e⁺e^- reactions. All analyses are performed in LO and NLO in QCD. The feasibility of the tests to HERMES SIDIS data is considered. PACS 12.38.Bx; 13.85.Ni     

Inclusive production of charged pions, kaons and protons in υ(4S) decays

Using the detector ARGUS at thee ⁺ e ^– storage ring DORIS II, we have investigated inclusive momentum spectra of charged pions, kaons, and protons from decays of the (4S) meson. The kaon spectra have been measured in two independent ways, by coherently exploiting the detector's particle identification capabilities, and by detecting decays in-flight. The extracted mean multiplicities for charged hadrons are 7.17±0.05±0.14 pions, 1.56±0.03±0.05 kaons and 0.110±0.010±0.007 protons per (4S) decay, where pions and protons fromK _s ^o and decays have been subtracted.Supported in part by the Institute of Physics, University of Lund, Sweden     

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.     

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.     

Flavour separation by means of transverse beam polarization in high-energy e+e- annihilation

Transverse beam polarization is in e⁺e^- annihilation at high energies shown to lead to a strong azimuthal variation in the flavour composition of the produced quark-antiquark pairs. We describe, in the SU(2) × U(1) model, a way in which this could be used to obtain flavour-specific information on the quark fragmentation functions. In inclusive charged particle rates the effect might be much reduced, but still observable.     

Reactions with leading hadrons in meson-proton interactions at 250 GeV/c

Inelastic final states with one or two leading hadrons are studied in π⁺p and K⁺p interactions at 250 GeV/c. In reactions with two leading hadrons, the dependence of the average charge multiplicity of associated pions on their effective mass is essentially consistent with that observed in p?p and γγ-collisions, but differs from that obtained in e⁺e^? -annihilation. The multiplicity and (semi)inclusive characteristics of the π⁺-induced non-diffractive reactions are compared to predictions of current versions of the FRITIOF fragmentation model. We show that the hard-like sub-processes, essentially responsible for the production of leading hadrons with relatively large transverse momentum as well as for the relatively large multiplicity of associated pions, are not properly treated in the model.     

The electromagnetic effects in <Emphasis Type="Italic">K</Emphasis><Subscript><Emphasis Type="Italic">e</Emphasis>4</Subscript> decay

The final-state interaction of pions in K _e4 decay allows to obtain the value of the isospin and angular-momentum-zero ππ scattering length a ₀ ⁰ .We take into account the electromagnetic interaction of pions and isospin-symmetry-breaking effects caused by different masses of neutral and charged pions and estimate the impact of these effects on the procedure of scattering-length extraction from K _e4 decays.     

Inclusive particle photoproduction to next-to-leading order

We study the inclusive photoproduction of neutral and charged pions and at HERA, via the resolved photon mechanism, in QCD to next-to-leading order. We present various distributions of phenomenological interest and study the theoretical uncertainties due to the mass scales, and to photon and proton sets of structure functions. A new set of fragmentation functions for charged pions is also presented.     

(Medium-modified) fragmentation functions

We discuss some of the recent advances in the field of parton fragmentation processes into hadrons as well as their possible modifications in QCD media. Hadron-production data in e ⁺ e ⁻, deep inelastic scattering and hadronic collisions are presented, together with global analyses of fragmentation functions into light and heavy hadrons and developments on parton fragmentation in perturbative QCD at small momentum fraction. Motivated by the recent RHIC data indicating a significant suppression of large-p _⊥ hadron production in heavy-ion collisions, several recent attempts to model medium-modified fragmentation, e.g. by solving “medium” evolution equations or through Monte Carlo studies, have been proposed and are discussed in detail. Finally, we mention the possibility to extract medium-modified fragmentation functions using photon–hadron correlations.     

Factorization and transverse momentum for two-hadron production in inclusive e + e − annihilation

We study the factorization of processes involving two fragmentation functions in the case of very small transverse momenta. We consider two-hadron production in inclusive e ⁺ e ⁻ annihilation and demonstrate a new simple and illustrative method of factorization for such processes, including leading order α _s corrections. The text was submitted by the authors in English.     

Electron production by 4.0 GeV/cπ+p interactions

We have investigated electron production in 4.0 GeV/cπ⁺pinteractions. Limits to direct electron pair production are measured and an example of ?⁰ or ω⁰ decay to e⁺e^? is observed. The ratio of the number of singly produced electrons to the total number of charged pions is less than 6 × 10^-5 (at the 95% confidence level).