Gluon and charm distributions in the photon

Abstract

We study systematically the sensitivity of the photon structure function data on the gluon contents of the photon, by using the leading order Altarelli-Parisi (AP) equations. Charm quark contribution is studied in the quark parton model and by using the massive quark AP equations of Glück, Hoffmann and Reya. The present photon structure function data are found to allow wide range of gluon distributions in the photon. We give a set of six scale-dependent parton distributions in the photon (WHIT1 to WHIT6), which have systematically different gluon contents. Sensitivity of the structure function at small x and that of the total charm quark production cross section to the effective 1 gluon distribution are discussed.12.38.-t Typeset using REVT E X 2

Constraining gluon shadowing using photoproduction in ultraperipheralpAandAAcollisions

“…Another source of differences is in the choice and scope of experimental data from which F γ 2 is extracted. At present there is an appreciable number of photon parton distribution sets available, both at leading and next-to-leading orders [55][56][57][58][59][60][61][62][63][64][65][66][67][68][69][70]. It should be noted that unlike in the case of a nucleon, there are no valence quarks present in the photon; therefore antiquark distributions are the same as quark distributions.…”

Measurement of the photon structure function F2 at low x

“…The results reported here go down to x = 0.0025. This kinematical region is of particular interest because theoretical predictions differ significantly from each other [5][6][7][8][9][10][11] and because in this region the proton structure function is observed to start to increase as x decreases [12].…”

A high-Q[sup 2] measurement of the photon structure function F[sub 2][sup γ] at LEP2

“…In Figure 3 the data are compared to several theoretical calculations. The leading order parameterisations of F γ 2 from GRV, SaS1d [9] and WHIT1 [10], which all include a contribution from massive charm quarks, are described in detail in reference [2]. The naive quark-parton model (QPM) simulates only the point-like component of F γ 2 , and is calculated for four active flavours with masses of 0.325 GeV for light quarks and 1.5 GeV for charm quarks.…”