The physics of hadrons (original) (raw)
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Heavy-Quark Production in the Target Fragmentation Region
Fortschritte der Physik/Progress of Physics, 1997
Fixed-target experiments permit the study of hadron production in the target fragmentation region. It is expected that the tagging of specific particles in the target fragments can be employed to introduce a bias in the hard scattering process towards a specific flavour content. The case of hadrons containing a heavy quark is particularly attractive because of the clear experimental signatures and the applicability of perturbative QCD. The standard approach to one-particle inclusive processes based on fragmentation functions is valid in the current fragmentation region and for large transverse momenta p T in the target fragmentation region, but it fails for particle production at small p T in the target fragmentation region. A collinear singularity, which cannot be absorbed in the standard way into the phenomenological distribution functions, prohibits the application of this procedure. This situation is remedied by the introduction of a new set of distribution functions, the target fragmentation functions. They describe particle production in the target fragmentation region, and can be viewed as correlated distribution functions in the momentum fractions of the observed particle and of the parton initiating the hard scattering process. It is shown in a next-to-leading-order calculation for the case of deeply inelastic lepton-nucleon scattering that the additional singularity can be consistently absorbed into the renormalized target fragmentation functions on the one-loop level. The formalism is derived in detail and is applied to the production of heavy quarks. The renormalization group equation of the target fragmentation functions for the perturbative contribution is solved numerically, and the results of a case study for deeply inelastic lepton-nucleon scattering at DESY (H1 and ZEUS at HERA), at CERN (NA47) and at Fermilab (E665) are discussed. We also comment briefly on the case of an intrinsic heavy-quark content of the proton.
Heavy quark production at collider energies: Some selected topics
Acta Physica Polonica B, Proceedings Supplement
We discuss production of charm quarks and mesons as well as nonphotonic electrons in pp scattering at RHIC. The distributions in rapidity and transverse momentum of charm and bottom quarks/antiquarks are calculated in the k t-factorization approach. The hadronization of heavy quarks is done by means of fenomenological fragmentation functions. The semileptonic decay functions found by fitting semileptonic decay data measured by the CLEO and BABAR collaborations are used. Good description of the inclusive data at large transverse momenta of electrons is obtained and a missing strength at small transverse momenta of electrons is found. Furthermore we discuss kinematical correlations between charged leptons from semileptonic decays of open charm/bottom, leptons produced in the Drell-Yan mechanism as well as some other mechanisms not included so far in the literature. When calculating the Drell-Yan processes we include transverse momenta of q andq, using the Kwieciński parton distributions. Reactions initiated by purely QED γ * γ *-fusion in elastic and inelastic pp collisions as well as diffractive mechanism of exclusive cc production are included. A good description of the dilepton invariant mass spectrum measured by the PHENIX collaboration is achieved. Predictions for the dilepton pair transverse momentum distribution as well as distribution in azimuthal angle between electron and positron are presented.
Perturbative quantum chromodynamic prediction for the heavy quark fragmentation function
Physics Letters B, 1987
Within the framework of a parhcular model for meson production, a perturbatlve QCD analysis is presented for the reclusive production of pseudoscalar and vector mesons to derive the fragmentatmn function of heavy quarks produced in e+e-anmhllatmn. The results are compared with experimental data for bottom and charm quark fragmentatmn functmns. The new generation of high energy e+e-colliders such as TRISTAN, SLC, and LEP, is expected to provide a wealth of information about production and hadronization of heavy quarks (c, b, t). The production of heavy particles in these accelerators will be an important testing ground for the perturbative quantum chromodynamics (QCD) [ 1-3 ]. One of the interesting properties of heavy quarks which can be studied in the framework of perturbative QCD is the evolution of quarks into hadrons. The mechanism responsible for hadronization, in general, is specified by the fragmentation function D~ (z, s) which represents the fragmentation of the quark Q into the final state hadron H with the momentum fraction z= 2E/~s, where E is the energy of the hadron and s is the square of the total e+e-CM energy. Various phenomenological models, like the Lund model [ 4 ], the Cascade model [ 5 ], and the Peterson et al. model [ 6 ], motivated by QCD, have been developed to describe the fragmentation function D~. Since these models [ 4-6 ] involve parameters to fit the experimental data, it is not clear how to check the consistency of their results with a general theorem for the extreme case of heavy quark fragmentation given Work supported by the Department of Energy, contract DE-AC03-76SF00515.
Heavy quark production in gammagamma\gamma\gammagammagamma collisions: a theoretical reappraisal
arXiv (Cornell University), 2000
Heavy quark production in γγ collisions is reanalyzed. It is argued that evaluating the cross section σ(γγ → QQ) in a well-defined renormalization scheme requires the inclusion of direct photon contributions up to the order α 2 α 2 s. The order α 2 α 2 s direct photon contributions are furthermore needed for factorization scale invariance of the sum of direct and resolved photon contributions. The importance of quantitative analysis of renormalization and factorization scale dependence of the approximation currently used for the evaluation of σ(γγ → QQ) is emphasized as the only way of estimating the theoretical uncertainty related to the ambiguity in choosing these scales.
Physical Review D, 1989
The results of a complete analytical calculation of the next-to-leading-order QCD radiative corrections to the inclusive cross sections parton+parton -+ V+X, where V is an on-shell 8'or Z with transverse momentum Qr of order Ms, or a massive virtual photon with Qr of order of its invariant mass, are presented. Numerical predictions for 8', Z, and y production at collider energies are also presented. The dependence of the radiative corrections on the choice of renormalization and factorization scales is discussed. The results presented indicate that the QCD-improved parton model can be used to make firm and reliable predictions for electroweak-boson production at large Qr.
Large-p⊥ hadroproduction of heavy quarks
Nuclear Physics B, 1994
The production of heavy quarks at large p ⊥ (p ⊥ ≫ m) in hadronic collisions is considered. The analysis is carried out in the framework of perturbative fragmentation functions, thereby allowing a resummation at the NLO level of final state large mass logarithms of the kind log(p ⊥ /m). The case of b-quark production is considered in detail. The resulting theoretical uncertainty from factorization/renormalization scales at large p ⊥ is found to be much smaller than that shown by the full O(α 3 s ) perturbative calculation.
Energy and scale dependence of heavy-quark production in QCD
Il Nuovo Cimento A Series 11, 1994
of the heavy quark cross-sections in high-energy photoproduction. evolution. The same holds true when considering the energy and scale dependence crossing point if the gluon structure functions used have proper Altarelli-Parisi u2 cross-sections as functions of the energy for different values of p2 have a common tically depend on the energy for higher values, u2 = 4M 2 + SM 2. The calculated small scale values, [42 M M2, where M is the heavy quark mass, and do not prac butions. The values of K-factors increase significantly with the energy for relatively accounting for leading order and next-to-leading order perturbative QCD contri u2, using different proton structure functions. The cross-sections are computed sections in pp or pp collisions up to (/E = 200 TeV for different values of the scale We consider the energy dependence of charm and beauty production cross Abstract 12) World Laboratory,