2021 Impact factor 4.991
Particles and Fields
Eur. Phys. J. C 7, 29-48
DOI 10.1007/s100529800958

Final state photon production at LEP

A. Gehrmann-De Ridder1 - E.W.N. Glover2

1 DESY, Theory Group, D-22603 Hamburg, Germany
2 Department of Physics, University of Durham, Durham DH1 3LE, England

Received: 9 June 1998 / Published online: 21 August 1998

We present a detailed study of photon production in hadronic events in electron-positron annihilation at LEP energies. We show that estimates of the inclusive photon spectrum using the quark-to-photon fragmentation function determined using the ALEPH `photon' + 1 jet data agree well with the observations of the OPAL collaboration. This agreement shows that the photon fragmentation function determined in this way can be used for inclusive observables. We also compare next-to-leading order and beyond leading logarithm predictions obtained using the numerically resummed solutions of the fragmentation function evolution equation of Bourhis, Fontannaz and Guillet and Glück, Reya and Vogt with the data. Moreover, in order to check the general behaviour of the fragmentation function, we consider an analytic series expansion in the strong coupling. We find that the parameterizations are inaccurate at large x values. While the OPAL data is in broad agreement with estimates based on any of these approaches, the ALEPH data prefers the resummed BFG parameterization. Finally, there is some ambiguity as to whether the fragmentation function is treated as ${\cal O}(\alpha)$ or ${\cal O}(\alpha/\alpha_s)$. We show that at present this ambiguity affects mainly the prediction for the `photon' + 1 jet rate at large z.

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