Abstract
The inclusive production of charged hadrons in the collisions of quasi-real photons (e+e−→e+e−+X) has been measured using the OPAL detector at LEP. The data were taken at e+e− centre-of-mass energies from 183 to 209 GeV. The differential cross-sections as a function of the transverse momentum and the pseudorapidity of the hadrons are compared to theoretical calculations of up to next-to-leading order (NLO) in the strong coupling constant αs. The data are also compared to a measurement by the L3 Collaboration, in which a large deviation from the NLO predictions is observed.
Highlights
Hadronic interactions of two photons lead to the production of hadrons whose properties in Quantum Chromodynamics (QCD) depend on the underlying partonic processes, as well as on the way in which the partons are transformed into observable hadrons
A drastic discrepancy between data and next-to-leading order (NLO) QCD has recently been observed in this process [1] which would indicate the breakdown of this otherwise so successful theory and requires further study
The same partonic processes are at work in QCD in both cases, but hadronisation is usually treated differently
Summary
Hadronic interactions of two photons lead to the production of hadrons whose properties in Quantum Chromodynamics (QCD) depend on the underlying partonic processes, as well as on the way in which the partons are transformed into observable hadrons. The same partonic processes are at work in QCD in both cases, but hadronisation is usually treated differently. In leading order QCD this model leads to three different event classes for γ γ interactions: direct, singleresolved and double-resolved, where resolved means that the partons (quarks or gluons) inside the hadronic photon take part in the hard interaction. Letter events are considered only if the electrons are scattered at small angles and are not detected. Both photons are quasi-real (Q2 ≈ 0 GeV2). Differential hadron production cross-sections are measured as a function of the transverse mo-. The inclusive cross-sections are compared to Monte Carlo (MC) event generators in leading order αs and theoretical calculations in next-to-leading order (NLO) αs for this process
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