Parton distributions in the photon

Abstract

We discuss in detail the photon structure function beyond the leading logarithm approximation. Of special concern is the factorization scheme and the hadronic input ; we show h o w to naturally absorb large terms due to the MS factorization scheme in a modied hadronic component. The eect of the charm quark mass threshold is also discussed in relation to the phenomenology. A comparison with data shows that the modied hadronic component can be reasonably described by a VDM-type input.

A NLO calculation of the large-p $_T$ photon + photon $\to$ photon + jet cross section

“…in agreement with DIS γ γ experiments [17]. For a virtual photon, Q 2 0 must be replaced by max(Q 2 , Q 2 0 ) and the convolution with the spectrum of the photon emitted by the electron takes the form…”

“…We also use the AFG parton distributions [17] and the value Λ For the scales µ = M = p Tγ used here the single resolved contribution is larger than the double resolved contribution by a factor 3 to 6 which increases when p Tγ increases. The single resolved contribution constitutes about 70 % of the total cross Figure 2: The NLO single resolved, double resolved and direct cross sections dσ γ+X /dp Tγ .…”

Dijet photoproduction at HERA and the structure of the photon

“…The number of flavours was set to 5 and the renormalisation and factorisation scales, µ, were set to half the sum of the transverse energies of the final-state partons, E T /2. Two different parameterisations of the photon parton density were used 3 : GRV-HO [34] and AFG-HO [51]. The parton densities in the proton were parameterised using CTEQ5M1 [35]; the value α s (M Z ) = 0.118 used therein was adopted for the central prediction.…”

Pionic parton distributions revisited

“…To conclude let us recall that an improvement of f π (x, Q 2 ) is particularly important in view of its central role in the construction of the photon structure function and the photonic parton distributions [14,15,16,17,18]. Furthermore, recent (large rapidity gap) measurements of leading proton and neutron production in deep inelastic scattering at HERA [19] …”