Measurement of direct-photon production at the Fermilab Tevatron fixed target energies

Abstract

Measurements of the production of high transverse momentum direct photons by a 515 GeV=c ÿ beam and 530 and 800 GeV=c proton beams in interactions with beryllium and hydrogen targets are presented. The data span the kinematic ranges of 3:5 < p T < 12 GeV=c in transverse momentum and 1.5 units in rapidity. The inclusive direct-photon cross sections are compared with next-to-leading-order perturbative QCD calculations and expectations based on a phenomenological parton-k T model.

Inclusiveπ0,η, and direct photon production at high transverse momentum inp+pAbelev1, Aggarwal2, Ahammed3 et al. 2010Phys. Rev. C393130View full textAdd to dashboardCite

“…Whereas the ratio data/theory from Ref. [70] shows an increase of up to a factor of 4 toward low x T , our results at still lower x T constrain such a potential deviation from theory to less than a factor of 2. It should be noted, however, that the data have been taken at significantly different √ s. We have included both prompt and fragmentation components in the pQCD calculations because our measurement was based on an inclusive sample of photons.…”

“…Those data show a strong discrepancy with pQCD calculations, which was attributed to multiple soft gluon radiation and phenomenologically described as an additional transverse impulse k T to the incoming partons [70]. It has also been argued that this discrepancy might be attributable to nuclear modifications present even in the light berillium nucleus used 064904-23 [71], although the p + p data by E706 show similar behavior at the same √ s NN .…”

“…Earlier measurements of direct photon production in proton-nucleus collisions have been performed by the E706 experiment [70] by scattering protons on a fixed beryllium target, with proton beam energies of 530 and 800 GeV. Those data show a strong discrepancy with pQCD calculations, which was attributed to multiple soft gluon radiation and phenomenologically described as an additional transverse impulse k T to the incoming partons [70].…”

Direct real photons in relativistic heavy ion collisions

“…All these data provided input for incremental improvement of NLO, then NNLO calculations [130][131][132] without any major surprises. However, one particular fixed target experiment (FNAL E706 [133,134]) strongly disagreed with the calculations, triggering speculations that the effect of intrinsic k T is much larger than previously assumed, and, to lesser extent, the results from WA70 [135] also deviated from the general trend, shown below. Due to this discrepancy, photon data in pp and pp were omitted from global-fit analyses of proton PDFs for about a decade [103].…”

“…11, left panel). Apart of two (controversial) datasets from Fermilab E706 [134] and to some lesser extent the D0 results [145] the data are well described from √ s N N = 23 GeV to 1.96 TeV, covering 9 orders of magnitude in cross section. In Fig.…”