New information on photon fragmentation functions

Klasen, M.; König, F.

doi:10.1140/epjc/s10052-014-3009-x

Cited by 19 publications

(25 citation statements)

References 29 publications

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“…Note that -in contrast to the Pb+Pb case -dependence on collision centrality is not shown. In fact, determination of the collision centrality in small-on-large systems became controversial since 2012 33 . We will discuss this and the role of photons in eliminating possible centrality biases in Sec.…”

Section: Nuclear Modification Factormentioning

confidence: 99%

“…IV B), but it provided only upper limits in the "thermal" region due to the limitations of the calorimetric measurement. 56 Note that below 2 GeV/c the validity of NLO pQCD is questionable, primarily due to the poorly constrained yield of fragmentation photons, although they are predicted to exceed the prompt photon yield by a factor of 2-3 [33]. within uncertainties by the two-component fit…”

Section: "Thermal" Photon Yields and Effective Temperaturesmentioning

confidence: 99%

“…Other sources include photons from jet fragmentation in vacuum, well known and measured in pp [19,[30][31][32][33]. They should be distinguished from jet Bremsstrahlung which occurs while the parton is still traversing the (QGP) medium and losing energy in it [19].…”

mentioning

confidence: 99%

“…This explanation was supported by the observation that the exponents n at high-p T of the power-law spectra p −n T were very similar in pp and Au+Au, therefore, the difference between the A+A and N coll -scaled pp yields could be interpreted as a δp T shift in the p T -scale[201] 32. The deviation from unity at large rapidities may reflect a nuclear modification of the parton densities (nPDF vs free proton PDF), but there are not enough data yet to settle this issue, which quite possibly will only be resolved at a future electron-ion collider (EIC) 33. Now often replaced by the (purely experimental) "event activity" or some other non-geometric quantity.…”

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confidence: 99%

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Direct real photons in relativistic heavy ion collisions

David

2020

Rep. Prog. Phys.

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Direct real photons are arguably the most versatile tools to study relativistic heavy ion collisions. They are produced, by various mechanisms, during the entire space-time history of the strongly interacting system. Also, being colorless, most the time they escape without further interaction, i.e. they are penetrating probes. This makes them rich in information, but hard to decypher and interpret. This review presents the experimental and theoretical developments related to direct real photons since the 1970s, with a special emphasis on the recently emerged "direct photon puzzle", the simultaneous presence of large yields and strong azimuthal asymmetries of photons in heavy ion collisions, an observation that so far eluded full and coherent explanation. CONTENTS arXiv:1907.08893v1 [nucl-ex] 21 Jul 2019 21. Hydrodynamical models 48 2. Initial state, (fast) thermalization 50 3. Transport calculations 50 4. Other ideas 52 VII. Concluding remarks 54 VIII. Acknowledgements 55 References 56 3 I. INTRODUCTIONThe centuries old quest to reveal the "ultimate" constituents of matter and the laws of Nature governing them, and the realization from quantum mechanics that mapping smaller and smaller objects requires ever larger energy probes, made high energy physics one of the dominant scientific disciplines of the XXth century. At first we took advantage of the Universe as an "accelerator" providing high energy probes (cloud chamber and emulsion experiments), but soon we started to build our own accelerators, constantly increasing their energy and luminosity. The most spectacular and best known results came in elementary particle physics, but astrophysics and nuclear physics were a close second, benefiting enormously from the progress in experimental and theoretical tools. The central question in particle physics was the substructure of hadrons and the nature of confinement, while high energy nuclear physics' foremost concern was the behavior of high density nuclear matter, including its collectivity and possible phase transition into partonic matter, which in turn evoked the early stages of the Universe. Albeit particle and nuclear physics came with different perspectives, both were concerned with the strong interaction and its underlying theory, quantum chromodynamics (QCD), so the birth of a new discipline at their intersection, relativistic heavy ion physics, was almost inevitable. From Princeton and Berkeley to Dubna the race for larger and larger ions, energies and luminosities was on. Hadrons and nuclear fragments were studied extensively, and the applicability of thermo-and hydrodynamics gradually recognized. An excellent review of these first facilities and early developments -both experimental and theoretical -can be found in [1] by Goldhaber, while a (literally) insightful account of the genesis and achievements of RHIC and LHC was given by Baym in [2].Although lepton and photon production in hadronic and nuclear collisions was studied almost since the birth of quantum mechanics and quantum electrodynamics [3][4][...

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Section: Nuclear Modification Factormentioning

confidence: 99%

Section: "Thermal" Photon Yields and Effective Temperaturesmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Direct real photons in relativistic heavy ion collisions

David

2020

Rep. Prog. Phys.

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“…Unfortunately, PDFs and FFs are non-perturbative and must be fitted to experimental data [23]. Due to the lack of a new electron-positron collider, few improvements have been made on photon FFs over the last decades [24,25]. NLO calculations for Zγ+jet and Zγγ [29] have recently become available in MCFM, followed by predictions at next-to-next-to-leading order (NNLO) for diphoton [26,27] and Zγ [28] production.…”

Section: Jhep03(2018)081mentioning

confidence: 99%

Prompt photon production and photon-jet correlations at the LHC

Klasen

Klein-Bösing

Poppenborg

2018

J. High Energ. Phys.

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Next-to-leading order predictions matched to parton showers are compared with recent ATLAS data on isolated photon production and CMS data on associated photon and jet production in pp and pPb collisions at different centre-of-mass energies of the LHC. We find good agreement and, as expected, considerably reduced scale uncertainties compared to previous theoretical calculations. Predictions are made for the ratio of inclusive photons over decay photons R γ , an important quantity to evaluate the significance of additional photon sources, e.g. thermal radiation from a Quark-Gluon-Plasma, and for distributions in the parton momentum fraction in lead ions x obs Pb , that could be determined by ALICE, ATLAS, CMS and LHCb in ongoing analyses of photon+jet production in pPb collisions at √ s N N = 5.02 TeV. These data should have an important impact on the determination of nuclear effects such as shadowing at low x.

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Prompt photon production and photon-hadron jet correlations with POWHEG

Ježo

Klasen

König

2016

J. High Energ. Phys.

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We present a calculation of direct photon production at next-to-leading order of QCD and a matching of this calculation with parton showers using POWHEG BOX. Based on simulations with POWHEG+PYTHIA, we perform a detailed phenomenological analysis of PHENIX data on prompt photon production and photon-hadron jet correlations in pp collisions at RHIC, considerably improving the description of these data with respect to previous calculations, and we suggest additional interesting analyses.

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New information on photon fragmentation functions

Cited by 19 publications

References 29 publications

Direct real photons in relativistic heavy ion collisions

Direct real photons in relativistic heavy ion collisions

Prompt photon production and photon-jet correlations at the LHC

Prompt photon production and photon-hadron jet correlations with POWHEG

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