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Title: Direct Photon Production at Next-to–Next-to-Leading Order

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Journal Article: Publisher's Accepted Manuscript
Journal Name:
Physical Review Letters
Additional Journal Information:
Journal Volume: 118; Journal Issue: 22; Related Information: CHORUS Timestamp: 2017-05-31 22:10:13; Journal ID: ISSN 0031-9007
American Physical Society
Country of Publication:
United States

Citation Formats

Campbell, John M., Ellis, R. Keith, and Williams, Ciaran. Direct Photon Production at Next-to–Next-to-Leading Order. United States: N. p., 2017. Web. doi:10.1103/PhysRevLett.118.222001.
Campbell, John M., Ellis, R. Keith, & Williams, Ciaran. Direct Photon Production at Next-to–Next-to-Leading Order. United States. doi:10.1103/PhysRevLett.118.222001.
Campbell, John M., Ellis, R. Keith, and Williams, Ciaran. Wed . "Direct Photon Production at Next-to–Next-to-Leading Order". United States. doi:10.1103/PhysRevLett.118.222001.
title = {Direct Photon Production at Next-to–Next-to-Leading Order},
author = {Campbell, John M. and Ellis, R. Keith and Williams, Ciaran},
abstractNote = {},
doi = {10.1103/PhysRevLett.118.222001},
journal = {Physical Review Letters},
number = 22,
volume = 118,
place = {United States},
year = {Wed May 31 00:00:00 EDT 2017},
month = {Wed May 31 00:00:00 EDT 2017}

Journal Article:
Free Publicly Available Full Text
This content will become publicly available on May 31, 2018
Publisher's Accepted Manuscript

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Cited by: 6works
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  • We present the first calculation of direct photon production at next-to-next-to leading order (NNLO) accuracy in QCD. For this process, although the final state cuts mandate only the presence of a single electroweak boson, the underlying kinematics resembles that of a generic vector boson plus jet topology. In order to regulate the infrared singularities present at this order we use the $N$-jettiness slicing procedure, applied for the first time to a final state that at Born level includes colored partons but no required jet. We compare our predictions to ATLAS 8 TeV data and find that the inclusion of themore » NNLO terms in the perturbative expansion, supplemented by electroweak corrections, provides an excellent description of the data with greatly reduced theoretical uncertainties.« less
  • For large-[ital p][sub [ital T]] direct photon production by a longitudinally polarized beam and target complete next-to-leading-order corrections [higher-order corrections (HOC's)] are determined. For these, one loop corrections to the basic subprocesses [ital [rvec g]] [ital [rvec q]][r arrow][gamma][ital q] and [ital [rvec q]] [bar [rvec q]][r arrow][gamma][ital g], as well as the contributions of [ital [rvec g]] [ital [rvec g]][r arrow][gamma][ital q[bar q]] and [ital [rvec q]] [ital [rvec q]][r arrow][gamma][ital qq], are calculated. For [ital [rvec p]] [ital [rvec p]][r arrow][gamma]+[ital X], [ital K] factors greater than unity and polarized cross sections and asymmetries well measurable are obtained.more » Certain differences in the regularization procedures and the question of dominance of HOC's by soft, collinear, and virtual gluons are also discussed.« less
  • A recent global analysis of direct photon production at hadron collider and fixed target experiments has noted a disturbing trend of disagreement between next-to-leading-order (NLO) calculations and data. The conjecture has been made that the discrepancy is due to explicit multiple parton emission effects which are not accounted for in the theoretical calculations. We investigate this problem by merging a NLO calculation of direct photon production with extra multiple parton emissions via the parton shower (PS) algorithm. Our calculation maintains the integrity of the underlying NLO calculation while avoiding ambiguities due to double counting of multiple parton emissions. We findmore » that the NLO+PS calculation can account for much of the theory-CDF data discrepancy at {radical}{ital s}=1.8 TeV. It can also account for much of the theory-UA2 discrepancy if a very large virtuality is assumed to initiate the initial state parton shower. For lower energy data sets (e.g., {radical}{ital s}{lt}63 GeV), NLO+PS calculations alone cannot account for the data-theory discrepancy, so that some additional nonperturbative {ital k}{sub {ital T}} smearing is needed. {copyright} {ital 1996 The American Physical Society.}« less
  • The production of jets in low Q{sup 2} ep scattering (photoproduction) and in low Q{sup 2} e{gamma}{sup +}e{gamma}{sup -} scattering ({gamma}{gamma} scattering) allows for testing perturbative QCD and for measuring the proton and photon structure functions. This requires exact theoretical predictions for one- and two-jet cross sections. We describe the theoretical formalism, giving sufficient details, for calculating the direct and resolved processes in {gamma}{rho} and {gamma}{gamma} reactions in next-to-leading order QCD. We present the complete analytical results for the Born terms, the virtual, and the real corrections. To separate singular and regular regions of phase space we use the phasemore » space slicing method with an invariant mass cut-off. In this way, all soft and collinear singularities are either canceled or absorbed into the structure functions. Using a flexible Monte Carlo program, we evaluate the cross sections numerically and perform various tests and comparisons with other calculations. We consider the scale dependence of our results and compare them to data from the experiments H1 and ZEUS at HERA and OPAL at LEP.« less
  • We calculate the one-loop squared contributions to the next-to-next-to-leading order O({alpha}{sup 2}{alpha}{sub s}{sup 2}) radiative QCD corrections for the production of heavy quark pairs in the collisions of unpolarized on-shell photons. In particular, we present analytical results for the squared matrix elements that correspond to the product of the one-loop amplitudes. All results of the perturbative calculation are given in the dimensional regularization scheme. These results represent the Abelian part of the corresponding gluon-induced next-to-next-to-leading order cross section for heavy quark pair hadroproduction.