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Title: Probing gluon saturation with next-to-leading order photon production at central rapidities in proton-nucleus collisions

Abstract

Here, we compute the cross section for photons emitted from sea quarks in proton-nucleus collisions at collider energies. The computation is performed within the dilute-dense kinematics of the Color Glass Condensate (CGC) effective field theory. Albeit the result obtained is formally at next-to-leading order in the CGC power counting, it provides the dominant contribution for central rapidities. We observe that the inclusive photon cross section is proportional to all-twist Wilson line correlators in the nucleus. These correlators also appear in quark-pair production; unlike the latter, photon production is insensitive to hadronization uncertainties and therefore more sensitive to multi-parton correlations in the gluon saturation regime of QCD. We demonstrate that k and collinear factorized expressions for inclusive photon production are obtained as leading twist approximations to our result. In particular, the collinearly factorized expression is directly sensitive to the nuclear gluon distribution at small x. Other results of interest include the realization of the Low-Burnett-Kroll soft photon theorem in the CGC framework and a comparative study of how the photon amplitude is obtained in Lorenz and light-cone gauges.

Authors:
 [1];  [2];  [3];  [4]
  1. Univ. of Zagreb, Zagreb (Croatia); The Univ. of Tokyo, Tokyo (Japan)
  2. The Univ. of Tokyo, Tokyo (Japan)
  3. Univ. Heidelberg, Heidelberg (Germany)
  4. Brookhaven National Lab. (BNL), Upton, NY (United States)
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL), Upton, NY (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Nuclear Physics (NP) (SC-26)
OSTI Identifier:
1376115
Report Number(s):
BNL-114000-2017-JA
Journal ID: ISSN 1029-8479
Grant/Contract Number:
SC00112704
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Journal of High Energy Physics (Online)
Additional Journal Information:
Journal Name: Journal of High Energy Physics (Online); Journal Volume: 2017; Journal Issue: 1; Journal ID: ISSN 1029-8479
Publisher:
Springer Berlin
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; Heavy Ion Phenomenology; NLO Computations

Citation Formats

Benic, Sanjin, Fukushima, Kenji, Garcia-Montero, Oscar, and Venugopalan, Raju. Probing gluon saturation with next-to-leading order photon production at central rapidities in proton-nucleus collisions. United States: N. p., 2017. Web. doi:10.1007/JHEP01(2017)115.
Benic, Sanjin, Fukushima, Kenji, Garcia-Montero, Oscar, & Venugopalan, Raju. Probing gluon saturation with next-to-leading order photon production at central rapidities in proton-nucleus collisions. United States. doi:10.1007/JHEP01(2017)115.
Benic, Sanjin, Fukushima, Kenji, Garcia-Montero, Oscar, and Venugopalan, Raju. Thu . "Probing gluon saturation with next-to-leading order photon production at central rapidities in proton-nucleus collisions". United States. doi:10.1007/JHEP01(2017)115. https://www.osti.gov/servlets/purl/1376115.
@article{osti_1376115,
title = {Probing gluon saturation with next-to-leading order photon production at central rapidities in proton-nucleus collisions},
author = {Benic, Sanjin and Fukushima, Kenji and Garcia-Montero, Oscar and Venugopalan, Raju},
abstractNote = {Here, we compute the cross section for photons emitted from sea quarks in proton-nucleus collisions at collider energies. The computation is performed within the dilute-dense kinematics of the Color Glass Condensate (CGC) effective field theory. Albeit the result obtained is formally at next-to-leading order in the CGC power counting, it provides the dominant contribution for central rapidities. We observe that the inclusive photon cross section is proportional to all-twist Wilson line correlators in the nucleus. These correlators also appear in quark-pair production; unlike the latter, photon production is insensitive to hadronization uncertainties and therefore more sensitive to multi-parton correlations in the gluon saturation regime of QCD. We demonstrate that k⊥ and collinear factorized expressions for inclusive photon production are obtained as leading twist approximations to our result. In particular, the collinearly factorized expression is directly sensitive to the nuclear gluon distribution at small x. Other results of interest include the realization of the Low-Burnett-Kroll soft photon theorem in the CGC framework and a comparative study of how the photon amplitude is obtained in Lorenz and light-cone gauges.},
doi = {10.1007/JHEP01(2017)115},
journal = {Journal of High Energy Physics (Online)},
number = 1,
volume = 2017,
place = {United States},
year = {Thu Jan 26 00:00:00 EST 2017},
month = {Thu Jan 26 00:00:00 EST 2017}
}

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Cited by: 7works
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  • Within the Color Glass Condensate effective theory, we reconsider the next-to-leading order (NLO) calculation of the single inclusive particle production at forward rapidities in proton-nucleus collisions at high energy. Focusing on quark production for definiteness, we establish a new factorization scheme, perturbatively correct through NLO, in which there is no ‘rapidity subtraction’. That is, the NLO correction to the impact factor is not explicitly separated from the high-energy evolution. Our construction exploits the skeleton structure of the (NLO) Balitsky-Kovchegov equation, in which the first step of the evolution is explicitly singled out. The NLO impact factor is included by computingmore » this first emission with the exact kinematics for the emitted gluon, rather than by using the eikonal approximation. This particular calculation has already been presented in the literature, but the reorganization of the perturbation theory that we propose is new. As compared to the proposal in, our scheme is free of the fine-tuning inherent in the rapidity subtraction, which might be the origin of the negativity of the NLO cross-section observed in previous studies.« less
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