11/6/2022 0 Comments Photonium particle structureThe kinematics chosen is characterized by the electron scattered at large angles and the positron at very small angles thus providing a calculable flux of quasi-real photons (Weizsäcker–Williams approximation). The experiments utilize the so-called two-photon reactions at electron–positron colliders e −e + → e −e ++ h, where h includes all hadrons of the final state. Up to now the photon structure function has only been investigated experimentally by electron scattering off a beam of quasi-real photons. In this asymptotic regime the photon structure function is predicted uniquely in QCD to logarithmic accuracy. However, the asymptotic behavior is approached steadily with increasing Q for x away from zero as demonstrated next. the logarithm of Q being much larger than the logarithm of the quark masses. The quantitative representation of the photon structure function introduced above is strictly valid only for asymptotically high resolution Q, i.e. The complexity of these scattering processes, due to the superposition of many subprocesses, renders the analysis of the gluon content of the photon quite complicated. Gluons as components of the photon may scatter off gluons residing in the proton, and generate two hadron jets in the final state. While electron scattering off photons maps out the quark spectra, the electrically neutral gluon content of the photons can best be analyzed by jet pair production in photon–proton scattering. They are the origin of the excitement associated with the photon structure function. These characteristics, dramatically different from the proton parton density, are unique features of the photon structure function within QCD. To order unity, leaving the logarithmic behavior in the resolution Q untouched apart from superficially introducing the fundamental QCD scale Λ, but tilting the shape of the structure function f B( x) → f ( x) by damping the momentum spectrum at large x. The characteristic behaviorį 2, B γ ( x, Q 2 ) = f B ( x ) log Q 2 / Λ 2 +. Quantum mechanics predicts the number of quark pairs in the photon splitting process to increase logarithmically with the resolution Q, and (approximately) linearly with the momenta x. QCD refines the picture by modifying the shape of the spectrum, to order unity unlike the small modifications naively expected as a result of asymptotic freedom. 1, regulates the essential characteristics of the photon structure function, the number and the energy spectrum of the quark constituents within the photon. The primary splitting of photons to quark pairs, cf. Photon structure function can be described quantitatively in quantum chromodynamics (QCD), the theory of quarks as constituents of the strongly interacting elementary particles, which are bound together by gluonic forces. Quark and antiquark finally transform to hadrons. The impinging electron is scattered off the quark to large angles, the scatter pattern revealing the internal quark structure of the photon. The incoming target photon splits into a nearly collinear quark–antiquark pair. Electron–photon scattering generic Feynman diagram. The intrinsic quark structure of the target photon beam is revealed by observing characteristic patterns of the scattered electrons in the final state.įigure 1. In high-energy, large-angle scattering the experimental facility can be viewed as anĮlectron microscope of very high resolution Q, corresponding to the momentum transfer in the scattering process according to Heisenberg's uncertainty principle. The classical technique for analyzing the virtual particle content of photons is provided by scattering electrons off the photons. Light on teraelectronvolt electron beams in a linear collider facility. Exceedingly high photon energies may be generated in the future by shining laser High energy photon beams have been generated by photon radiation off electron beams in e − e + circular beam facilities such as PETRA at DESY in Hamburg and LEP at CERN in Geneva. the tenfold radius of a proton, for light hadrons. At high energies E the lifetime t of such quantum fluctuations of mass M becomes nearly macroscopic: t ≈ E/M 2 this amounts to flight lengths as large as one micrometer for electron pairs in a 100 GeV photon beam, and still 10 fermi, i.e. Photons with high photon energy can transform in quantum mechanics to lepton and quark pairs, the latter fragmented subsequently to jets of hadrons, i.e.
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