The field of fragmentation functions of light quarks and gluons is reviewed. In addition to integrated fragmentation functions, attention is paid to the dependence of fragmentation functions on transverse momenta and on polarization degrees of freedom. Higher-twist and di-hadron fragmentation functions are considered as well. Moreover, the review covers both theoretical and experimental developments in single-inclusive hadron production in electron-positron annihilation, deep-inelastic lepton-nucleon scattering, and proton-proton collisions.

/pdf/parton-fragmentation-functions-33z4y02wdl.pdf

Parton Fragmentation Functions

The current status of tests of the theory of strong interactions, quantum chromo dynamics (QCD), with data from hadron production in e+e− annihilation experiments is reviewed. The LEP experiments ALEPH, DELPHI, L3 and OPAL have published many analyses with data recorded on the Z0 resonance at and above up to 200\,{\rm GeV} SRC=http://ej.iop.org/images/0034-4885/69/6/R04/rpp98972in002.gif/>. There are also results from SLD at and from reanalysis of data recorded by the JADE experiment at . The results of studies of jet and event shape observables, particle production and quark gluon jet differences are compared with predictions by perturbative QCD calculations. Determinations of the strong coupling constant from jet and event shape observables, scaling violation and fragmentation functions (FFs), inclusive observables from Z0 decays, hadronic τ decays and hadron production in low-energy e+e− annihilation are discussed. Updates of the measurements are performed where new data or improved calculations have become available. The best value of is obtained from an average of measurements using inclusive observables calculated in NNLO QCD: where the error is dominated by theoretical systematic uncertainties. The other measurements of are in good agreement with this value. Finally, investigations of the gauge structure of QCD are summarized and the best values for the colour factors are determined: with errors dominated by systematic uncertainties and in good agreement with the expectation from QCD with the SU(3) gauge symmetry.

https://iopscience.iop.org/article/10.1088/0034-4885/69/6/R04/pdf

Tests of quantum chromo dynamics at e+e? colliders

In the last five years ample evidence has been found supporting the idea that the quark-parton structure of hadrons is relevant for multiple production in soft hadronic collisions. Starting from the experimental foundations, the authors compare the most successful models applying this idea. Implications are discussed on special type reactions like diffraction dissociation and collisions on nuclei, and the models are confronted with recent data leading to new insight and modifications. Relative yields of particles in the central region may be understood as reflecting their valence quark structure in the framework of quark combinatorics, and the comparison of the valence structure of initial and final hadrons allows one to understand yields in the fragmentation regions. From the structure functions of initial hadrons and/or the fragmentation functions of (di)quarks into final hadrons as seen in deep inelastic lepton-hadron or e+e- collisions, one can deduce the shape of fragmentation spectra in soft hadronic collisions. However, hadronic oscillations also prove a very rich independent source of information on parton structure. Work to be done on the theoretical side is on a solid foundation of the two successful pictures of quark fragmentation and quark recombination as well as on an explanation of their apparent complementarity. On the experimental side, apart from further results from the pp collider, high statistics is needed on hydrogen and on heavier nuclei at rho lab>200 GeV/c in particular from strange beams.

https://iopscience.iop.org/article/10.1088/0034-4885/46/11/001/pdf

Parton models of low momentum transfer processes

The observation of quark and gluon jets has played a crucial role in establishing Quantum Chromodynamics [QCD] as the theory of the strong interactions within the Standard Model of particle physics. The jets, narrowly collimated bundles of hadrons, reflect configurations of quarks and gluons at short distances. Thus, by analysing energy and angular distributions of the jets experimentally, the properties of the basic constituents of matter and the strong forces acting between them can be explored. In this review, which is primarily a description of the discovery of the quark and gluon jets and the impact of their observation on Quantum Chromodynamics, we elaborate, in particular, the role of the gluons as the carriers of the strong force. Focusing on these basic points, jets in e
 +
 e
 − collisions will be in the foreground of the discussion and we will concentrate on the theory that was contemporary with the relevant experiments at the electron-positron colliders. In addition we will delineate the role of jets as tools for exploring other particle aspects in ep and \hbox{$pp/p\bar{p}$}pp / p
 p collisions  −  quark and gluon densities in protons, measurements of the QCD coupling, fundamental 2-2 quark/gluon scattering processes, but also the impact of jet decays of top quarks, and W
  ± , Z bosons on the electroweak sector. The presentation to a large extent is formulated in a non-technical language with the intent to recall the significant steps historically and convey the significance of this field also to communities beyond high energy physics.

/pdf/jets-and-qcd-a-historical-review-of-the-discovery-of-the-53bai4xoar.pdf

JETS and QCD: a historical review of the discovery of the quark and gluon jets and its impact on QCD

We use the reaction e-italic/sup +/e/sup -/..-->..hadrons, in the Mark J detector at the DESY electron-positron collider PETRA, to determine the hadronic cross section up to 46.78 GeV. The production of a top quark with a charge equal to (2/3) is excluded up to 46.6 GeV with 95% C.L. The observed rise in the cross section at higher energies is consistent with the electroweak prediction for a Z-italic/sup 0/ mass of 93 GeV. We describe some unusual muon inclusive events.

Study of hadron and inclusive muon production from e+e- annihilation at 39.79 <= sqrt s <= 46.78 GeV.

Measurements of R, sphericity and thrust are presented for c.m. energies between 12 and 31.6 GeV. A possible contribution of a t {Mathematical expression} continuum can be ruled out for c.m. energies between 16 and 31 GeV. © 1980 Springer-Verlag.

/pdf/e-e-annihilation-at-high-energies-and-search-for-the-t-quark-162l8clcin.pdf

E+ e- Annihilation at High-Energies and Search for the t-Quark Continuum Contribution

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E+ e- Annihilation at High-Energies and Search for the t-Quark Continuum Contribution