Kaon Fragmentation Functions Research Articles

Theoretical aspects of inclusive light-hadron production

We summarize the key results of a recent global analysis of inclusive single-charged-hadron production in high-energy colliding-beam experiments. In the framework of the parton model of quantum chromodynamics at next-to-leading order (NLO), fragmentation functions (FFs) for charged pions, charged kaons and (anti)protons are extracted from the experimental data of e+e− annihilation at the Z-boson resonance and at centre-of-mass energy √s = 29 GeV. This fit also yields a new NLO value for the strong-coupling constant, namely α(5)s(MZ) = 0.1170 ± 0.0073. The scaling violations encoded in the FFs through the Altarelli–Parisi evolution equations are tested by confronting e+e−-annihilation data from DESY DORIS, DESY PETRA and CERN LEP2 with NLO predictions based on these FFs. Comparisons of pp̄ data from CERN Spp̄S and the Fermilab Tevatron, γp data from DESY HERA and γγ data from LEP2 with the corresponding NLO predictions allow us to test the universality of the FFs predicted by the factorization theorem.

α s from scaling violations in fragmentation functions

We present a new determination of the strong coupling constant α s through the scaling violations in the fragmentation functions for charged pions, charged kaons, and protons. In our fit we include the latest e + e − annihilation data from CERN LEP1 and SLAC SLC on the Z-boson resonance and older, yet very precise data from SLAC PEP at center-of-mass energy ▪ GeV. A new world average of α s is given.

Testing the universality of fragmentation functions

Using fragmentation functions for charged pions, charged kaons, and (anti)protons recently extracted from experimental data of e^+e^- annihilation at the Z-boson resonance and at centre-of-mass energy root(s) = 29 GeV, we perform a global study of inclusive charged-hadron production in p anti-p, gamma p, and gamma gamma collisions at next-to-leading order in the parton model of quantum chromodynamics. Comparisons of our results with p anti-p data from CERN S p anti-p S and the Fermilab Tevatron, gamma p data from DESY HERA, and gamma gamma data from CERN LEP2 allow us to test the universality of the fragmentation functions predicted by the factorization theorem. Furthermore, we perform comparisons with (e^+e^-)-annihilation data from LEP2 so as to test the scaling violations predicted by the Altarelli-Parisi evolution equations.

Strong coupling constant from scaling violations in fragmentation functions.

We present a new determination of the strong coupling constant alpha(s) through the scaling violations in the fragmentation functions for charged pions, charged kaons, and protons. In our fit we include the latest e+e- annihilation data from CERN LEP1 and SLAC SLC on the Z-boson resonance and older, yet very precise, data from SLAC PEP at center-of-mass energy sqaure root of s = 29 GeV. At next-to-leading order, we find alpha(s)(5)(M(Z)) = 0.1170+/-0.0073. A new world average of alpha(s) is given.

Pion and Kaon Fragmentation Functions in the Spectator Model

Fragmentation functions of pions and kaons are studied using the spectator model. We find that by taking account of the multiparticle states in the spectator, the experimental values of the pion and kaon fragmentation functions can be reproduced. We also obtain the relation between the kaon fragmentation functions from the u-quark and the s-quark.

Fragmentation functions for pions, kaons, and protons at next-to-leading order

Abstract We present new sets of fragmentation functions for charged pions, charged kaons, and protons, both at the leading and next-to-leading orders. They are fitted to the scaled-momentum distributions of these hadrons measured in e+e− annihilation on the Z-boson resonance at CERN LEP1 and SLAC SLC. These data partly come as light-, charm-, bottom-quark-enriched and gluon-jet samples, which allows us to treat all partons independently, after imposing the SU(2) flavour symmetry relations. In order to gain sensitivity to the scaling violation in fragmentation, we also include data from SLAC PEP, with center-of-mass energy s =29 GeV, in our fits. This allows us to also determine the strong-coupling constant, with a competitive error. LEP1 data on the longitudinal cross section as well as DESY DORIS and PETRA data at lower energies nicely agree with theoretical predictions based on our fragmentation functions.

Neutral kaon production in e+e-, ep, and pp-bar collisions at next-to-leading order.

We present new sets of fragmentation functions for neutral kaons, both at leading and next-to-leading order. They are fitted to data on inclusive K^0 production in e^+e^- annihilation taken by MARK II at PEP (\sqrt s = 29 GeV) and by ALEPH at LEP. Our fragmentation functions lead to a good description of other e^+e^- data on inclusive K^0 production at various energies. They also nicely agree with the K_S^0 transverse-momentum spectra measured by H1 at the DESY ep collider HERA, by UA5 at the CERN Sp\bar pS Collider, and by CDF at the Fermilab Tevatron.

Pion and kaon production in e+e- and ep collisions at next-to-leading order.

We present new sets of fragmentation functions for charged pions and kaons, both at leading and next-to-leading order. They are fitted to data on inclusive charged-hadron production in $e^+e^-$ annihilation taken by TPC at PEP ($\sqrt s=29$~GeV) and to similar data by ALEPH at LEP, who discriminated between events with charm, bottom, and light- flavour fragmentation in their charged-hadron sample. We treat all partons independently and to properly incorporate the charm and bottom thresholds. Due to the sizeable energy gap between PEP and LEP, we are sensitive to the scaling violation in the fragmentation process, which allows us to extract a value for the asymptotic scale parameter of QCD, $\Lambda$. Recent data on inclusive charged-hadron production in tagged three-jet events by OPAL and similar data for longitudinal electron polarization by ALEPH allow us to pin down the gluon fragmentation functions. Our new fragmentation functions lead to an excellent description of a multitude of other $e^+e^-$ data on inclusive charged-hadron production, ranging from $\sqrt s=5.2$~GeV to LEP energy. In addition, they agree nicely with the transverse-momentum spectra of single charged hadrons measured by H1 and ZEUS in photoproduction at the $ep$ collider HERA, which represents a nontrivial check of the factorization theorem of the QCD-improved parton model.

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 $\sqrt s=29$~GeV and describe excellently a wealth of other $e^+e^-$ data on charged-hadron production, ranging from $\sqrt s=5.2$~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 by SU(2) symmetry. We also list simple parameterizations of the $x$ and $Q^2$ dependence of our results, which may be implemented conveniently in applications.

Inclusive particle production in $$p\bar p$$ collisions

We calculate the inclusive production of charged hadrons in $\pbp$ collisions to next-to-leading order (NLO) in the QCD improved parton model using a new set of NLO fragmentation functions for charged pions and kaons. We predict transverse-momentum distributions and compare them with experimental data from the CERN S$\pbp$S Collider and the Fermilab Tevatron.

Production of charged mesons with large transverse momentum and with an associated lepton pair

The transverse momentum distributions and branching ratios of mesons produced together with a lepton pair are studied in pp and pp collisions. A simple phenomenological formula describing the p T distributions is proposed. The large- p T behaviour of produced mesons can be used to determine the gluon distribution in the proton and to test its Q 2 variation as predicted by QCD. The prediction for the branching ratios are given. They depend on the form of the proton structure function and pion and kaon fragmentation functions at z = 1.

Particle ratios in electroproduction of kaons and symmetry properties of the quark-parton model

Previously (~), we reported a work on the particle ratios of hadrons (7: • K• and ~) produced in electron-proton (cp), electron-neutron (en) and electron-deuteron (ed) scattering in the framework of the quark-par ton model. The assumptions made were the following: i) The distribution functions of the sea quarks are SU3 symmetric, if) There are only one independent favoured fragmentat ion function, D~ and only one independent unfavoured fragmentat ion function, D~ for pions, iii) Similarly, for kaons, there are only two independent fragmentation functions, i.e., one favoured o n e , D K and one unfavoured one, D~:. Among the interesting results we derived, there are, for example, expressions for the rat ios of fragmentation functions which depend only on the experimental particle ratios but not on the distribution functions of quarks within the target . Unfortunately, however, the results could not be checked clearly with the available experimental da ta due to large errors. Based on the same assumptions as in ref. (~), we investigate in this note the further consequences by considering the different particle ratios, K• • off the same target. We shall est imate the approximate values of the fragmentation functions for kaons, ~)K and DE by using the experimental da ta (2). The particle ratios in electroproduction, are expressed as follows: for the proton target