Deep inelastic Compton scattering at theep collider HERA

We study in detail the effects of isolation requirements on expectations for prompt photon production rates at DESY HERA in the first fully consistent study performed completely in next-to-leading order (NLO) of QCD. In particular we examine whether the isolated cross section will give useful information on the gluon content of the photon and proton. We find that the cross section turns out to be hardly sensitive to the gluon distribution of the photon in the kinematically accessible range, but that it depends significantly on the quark content of the photon in some regions of the kinematical variables. We show furthermore that the present knowledge of the proton's parton distributions, in particular, its gluon distribution, has to be improved in order to determine the photonic structure functions in this process.

Section: A T H E Inclusive Cross Sectionmentioning

confidence: 99%

“…l(d)], in LO the contributing subprocesses are the same as those for jet production and are listed, for example, in Refs. [6,8]. There are many new contributions in NLO which were all calculated for inclusive hadron pro-duction in [19].…”

Section: A T H E Inclusive Cross Sectionmentioning

confidence: 99%

Isolated prompt photon production at DESY HERA

Gordon

Vogelsang

1995

“…With this in mind we have calculated all the higher order to tie down important QCD parameters such as structure functions and the much neg Inclusive hadron production is also in itself interesting since it can and has been used soon [3][4][5] and 1rO photoproduction will be an important background to these processes.…”

mentioning

confidence: 99%

Next-to-leading-order corrections to inclusive hadron photoproduction

Gordon

1994

both cross-sections are presented. OCR Output compact analytical expressions for the matrix elements for all the direct contributions to HERA where we study in detail the scale dependence of the cross section. ln addition solved photons and apply the results to ¢r° production at LEP2 as well as at the ep collider hadron photoproduction. We take into account all contributions from resolved and unreWe present a complete calculation of next-to-leading order (NLO) corrections to inclusive February 19921 /gu/g4{O_f·) discussed elsewhere [7][8][9][10], this simple separation is no longer so clear from a theoretical OCR Output thereby providing a means of separating the three classes of processes, but as has been lt may be possible for the photon fragments produced in the reactions to be tagged separate.as defined in Fig.2. As much as possible we will keep the discussions of the two reactions we discuss 7p processes we will use the usual labels of direct and resolved contributions in one or both beam directions, for once-and twice-resolved processes respectively. When either photon, whereas in the latter two cases such fragments are produced in each event, ents (Fig.lc). ln the first case there are no hadronic fragments or spectator jets from the twice-resolved contributions where both photons interact via their partonic constitu is resolved into its partonic constituents before interacting with the other (Fig.1b), and in the hard scattering process (Fig.la), the once-resolved contributions where one photon section: the direct contributions where the photons couple directly to the quarks produced sions, we identify the three following classes of contributions to the inclusive hadron cross couplings. ln this paper we will adopt the convention whereby, when discussing 77 colli case of 77 collisions there is the additional case where both photons interact via point-like the labels direct and resolved are sufficient to define the classes of processes, but in the called direct and resolved processes When considering 7p interactions, for example, coupling from those where it does so via its partonic constituents. This defines the so tributions to the cross-section where the photon interacts via its point-like electromagnetic It is customary when considering photoproduction processes to separate those con and ep machines.(O(cr,)) corrections to the photoproduction of inclusive hadrons relevant for both e+el ected fragmentation functions. With this in mind we have calculated all the higher order to tie down important QCD parameters such as structure functions and the much neg Inclusive hadron production is also in itself interesting since it can and has been used soon [3][4][5] and 1rO photoproduction will be an important background to these processes.it is hoped that the photoproduction of prompt photons will be studied at HERA very of the data will soon be extended and improved at both HERA and LEP2. Furthermore quantitative tests of perturbative QCD. It is also anticipated that the range and quality that they be confronted...

“…''Here we would like to point out that the way of counting the order of QCD calculations in the photoninduced processes is still a subject of discussion (see, e.g., [21,22] and earlier papers [23,24]). The origin of the problem is the presence of a definite parton model prediction in the form of an lnQ 2 contribution, leading to the inhomogeneous term in the Q 2 evolution equations for the quark densities in the photon.…”

Section: Qq Production In Collisionsmentioning

confidence: 99%

Towards understanding bb¯ production in γγ collisions

Chýla¹

2004

The data on the total cross section σ tot (e + e − →e + e − bb) measured at LEP2 represent a serious challenge for perturbative QCD. In order to understand the origin of the discrepancy between the data and QCD calculations, we investigate the dependence of four contributions to this cross section on γγ collision energy. As the reliability of the existing calculations of σ tot (e + e − →e + e − bb) depends, among other things, on the stability of the calculations of the cross section σ tot (γγ → bb) with respect to variations of the renormalization and factorization scales, we investigate this aspect in detail. We show that in most of the region relevant for the LEP2 data the existing QCD calculations of the cross section σ tot (γγ → bb) do not exhibit a region of local stability. Possible source of this instability is suggested and its phenomenological implications for understanding the LEP2 data are discussed.