Search

17 pp. (1996)., The next-to-leading-order (NLO) cross section for the production of heavy quarks at large transverse momenta ( p ⊥ in γγ collisions is calculated with perturbative fragmentation functions (PFFs). This approach allows for a resummation of terms ∝ α s ln( p 2 ⊥ / m 2 ) which arise in NLO from collinear emission of gluons by heavy quarks at large p ⊥ or from almost collinear branching of photons or gluons into heavy-quark pairs. We present single-inclusive distributions in p ⊥ and rapidity including direct and resolved photons for γγ production of heavy quarks at e + e − colliders and at high-energy γγ colliders. The results are compared with the fixed-order calculation for m finite including QCD radiative corrections. The two approaches differ in the definitions and relative contributions of the direct and resolved terms, but essentially agree in their sum. The resummation of the α s ln( p 2 ⊥ / m 2 ) terms in the PFF approach leads to a softer p ⊥ distribution and to a reduced sensitivity to the choice of the renormalization and factorization scales.

Proceedings, Workshop, Annecy, Gran Sasso, Hamburg, Hamburg, Germany, 4 Feb 1995 - 1 Sep 1995 ; (1995).

37 pp. (1994)., We analyze the prospects of measuring the parity of Higgs particles in the Standard Model and its supersymmetric extensions. Higgs decays are discussed in this context as well as production processes including, in particular, the fusion of Higgs particles in linearly polarized photon--photon collisions.

7 pp. (1994)., Non-strongly interacting particles in supersymmetric theories — sleptons, charginos/neutralinos, and charged Higgs bosons — are difficult to detect at the Large Hadron Collider. We therefore examine the possibility of producing particles of this type in virtual γγ collisions at the LHC. Since photons can be emitted from protons which do not break up in the radiation process, very clean events can be generated, compensating to some extent for the small event numbers. Higher rates are expected, at the expense of stray hadrons, for events in which one or both protons break up.

24 pp. (1991)., We have measured the cross section and $Q^2$-dependence of the reaction γγ→ multihadrons, using the CELLO detector at DESY, for visible final-state masses between 4 and 9 GeV. The data are well fitted by an incoherent sum of Generalised Vector Meson Dominance and Quark Parton Model terms, but at lowQ2 require the addition of a third component which resembles the QPM but is less two-jet-like. With and without this term, the GVDM cross section atQ2=0 is found to be 200±20 and 250±25 nb, respectively.

Workshop, Munich, German, München, Germany, 4 Feb 1991 - 3 Sep 1991 ; (1991).

188 pp. (1991).

28 pp. (1979).

38 pp. (1980)., A thorough study of lepton-pair production from two-photon annihilation in p⊆)p collisions is presented. The differential cross section is calculated over a large range of energies (27⩽√ s ⩽800 GeV as a function of the dilepton mass M as well as the dilepton transverse momentum Q T and the Feynman variable x F . No kinematical approximations (such as the equivalent photon approximation) are made. For Q T ≈ 0 the two-photon mechanism represents an important fraction of the pp→e + e − X cross section already at ISR energies, whereas at ISABELLE energies it dramatically dominates in the interval 0⩽ Q T ⪅1 GeV. At ISR energies these conclusions follow from a direct comparison of the two-photon contribution with pp→e + e − X data. For the ISABELLE energy range the expected O( α s ) QCD contribution to pp→ℓ + ℓ − X, corrected for soft gluon radiation to all orders (in leading bilogarithmic approximation), was taken as a reference. At larger Q T and ISR energies the γγ contribution is negligible, whereas at √ s = 800 GeV γγ /QCD≅ 10–20% almost everywhere. Furthermore, two-photon candidate events from the ISR are shown to be in reasonable agreement with theory. A decomposition of the γγ cross section into contributions from both proton vertices being elastic, inelastic and of mixed configuration is given. The results provide important clues for a future isolation of the two-photon mechanism.

120 pp. (1988).

100 pp. (1980).

113 pp. (1986)., This paper summarizes experimental results on exclusive hadron production in two-photon collisions at electron-positron storage rings and attempts some interpretation. Experimental know-how is described and new suggestions are made for future analyses. New model calculations on resonance form factors and pair production amplitudes are presented. The two-photon vertex is decomposed such that experiments can be parameterized with the minimal number of free parameters. Selection rules for off-shell photon collisions are given in addition to Yang’s theorems.

155841 (1980)., The analysis of two photon physics at the e+e− storage ring PETRA is reviewed. Higher order QED processes e+e−→e+e−e+e−(e+e−μ+μ−) have been measured in good agreement with the QED calculations. The production of the f0 resonance has been invstigated and the radiative width has been determined. The total cross section σ(Q2,W) of the inelastic electron photon scattering has been studied in some detail. Evidence for the production of large PT jets in the reaction γγ→qq̄ is reported and a first measurement of the photon structure function in deep inelastic eγ scattering is discussed.

71 pp. (1986).

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54 pp. (1980)., Scitation is the online home of leading journals and conference proceedings from AIP Publishing and AIP Member Societies

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34 pp. (1983)., A total of 26 papers have been contributed to the experimental discussion session. I will discuss some of the tools needed for 2γ experimentation and then point to highlights and regions of particular

17 pp. (1983)., I review experimental results on the reactions e+e− → e+e−e+e− and e+e− → e+e− μ+μ− from PETRA and PEP. Recent high statistics measurements are compared to QED predictions in the form of diagrammatic

40 pp. (1982).

Physics reports 276(5-6), 224 - 405 (1996). doi:10.1016/S0370-1573(96)00008-7, The impact of the ARGUS experiment to elementary particle physics is reviewed. More than ten years of data taking has allowed ARGUS to contribute significantly to our understanding of beauty and charmed hadrons, τ Leptons, ϒ mesons, ϒϒ interactions and fragmentation processes. In particular the ARGUS measurements of CKM matrix elements opened up a new window on the Standard Model., Published by Elsevier Science, North-Holland, Amsterdam [u.a.]