Low transverse momentum photon production in proton-nucleus collisions at 18 GeV/<i>c</i>

Ml, Tincknell; Rl, Clark; Lissauer, D.; Takai, H.; Ray, Anne E.; J, Gomez del Campo; Shapira, D.; C, Erd; Schukraft, J.; Willis, W.

doi:10.1103/physrevc.54.1918

Cited by 12 publications

(6 citation statements)

References 39 publications

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“…The inclusive photon spectra were measured up to 1 GeV/c in p T , in eight bins of rapidity, and compared to the photon spectra expected from hadron decay. While the fitted slopes changed significantly with rapidity, no significant excess was found at any of the rapidities.-Due to the high energy resolution of the BaF 2 array, E855 could also study the very low p T limit (p T < 100 MeV) and found no excess beyond the expected decay yields and Bremsstrahlung from charged hadrons [193]. The result is consistent with what the HELIOS collaboration found in 450 GeV/c p + Be collisions [271].…”

Section: Sps Fnal and Agssupporting

confidence: 83%

“…In contrast to the vigorous photon/dilepton program at CERN SPS only one experiment was dedicated to (low p T ) photon search at BNL AGS, where E855 was looking for soft photons with an 18 GeV/c p beam hitting Be and W targets [189]. The data were taken in 1990, and photons were detected in two small, movable electromagnetic calorimeters, both consisting of 19 hexagonal BaF 2 scintillating crystals, each 9.5X 0 long.…”

Section: A Sps Fnal and Agsmentioning

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: Sps Fnal and Agssupporting

confidence: 83%

Section: A Sps Fnal and Agsmentioning

confidence: 99%

Direct real photons in relativistic heavy ion collisions

David

2020

Rep. Prog. Phys.

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“…The theorem states that for ω → 0 the photons come exclusively from the external hadrons in the process considered. But this poses immediately the question: how close do we have to come to ω = 0 in order to see the behaviour of the photon-emission amplitude predicted by Low? There have been a number of experimental studies trying to verify Low's theorem [2][3][4][5][6][7][8][9][10][11][12]. For a review of the experimental situation see [13].…”

Section: Introductionmentioning

confidence: 99%

High-energy $ππ$ scattering without and with photon radiation

Lebiedowicz,

Nachtmann,

Szczurek

2021

Preprint

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We discuss the processes ππ → ππ and ππ → ππγ from a general quantum field theory (QFT) point of view. In the soft-photon limit where the photon energy ω → 0 we study the theorem due to F.E. Low. We confirm his result for the 1/ω term of the ππ → ππγ amplitude but disagree for the ω 0 term. We analyse the origin of this discrepancy. Then we calculate the amplitudes for the above reactions in the tensor-pomeron model. We identify places where "anomalous" soft photons could come from. Three soft-photon approximations (SPAs) are introduced. The corresponding SPA results are compared to those obtained from the full tensor-pomeron model for c.m. energies √ s = 10 GeV and 100 GeV. The kinematic regions where the SPAs are a good representation of the full amplitude are determined. Finally we make some remarks on the type of fundamental information one could obtain from high-energy exclusive hadronic reactions without and with soft photon radiation.

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“…A measurement of the soft-photon production at the LHC could shed light on a longstanding discrepancy between the theoretical predictions of the bremsstrahlung, based on Low's theorem [7], and the measured soft-photon spectra in several hadronic reactions. For experiments on soft photon production see [8][9][10][11][12][13][14][15][16][17][18][19]. Overviews of the experimental and theoretical status of this "soft photon puzzle" are given in [20] and [4].…”

Section: Introductionmentioning

confidence: 99%

Central exclusive diffractive production of single photon in high-energy proton-proton collisions within the tensor-pomeron approach

Lebiedowicz¹,

Nachtmann²,

Szczurek³

2023

Preprint

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We discuss central-exclusive production (CEP) of photons via different fusion processes in the reaction pp → ppγ at high energies, available at RHIC and LHC, within the tensor-pomeron model. We consider two types of processes, the photoproduction contribution via the photonpomeron and photon-reggeon fusion reactions, and the purely diffractive contribution via the reggeon-pomeron and odderon-pomeron fusion reactions. We present predictions for the measurements of photons at midrapidity, |y| < 2.5, and at relatively low transverse momentum, 0.1 GeV < k ⊥ < 1 GeV. To check the main results of our study the measurement of the outgoing protons is not necessary. This is of relevance, e.g., for the present version of the ALICE detector at the LHC. Several differential distributions, for instance, in y, k ⊥ and ω, the rapidity, the absolute value of the transverse momentum, and the energy of the photon, respectively, are presented. We show that the photoproduction is an important process in the kinematic region specified above. There it gives a much larger cross section than diffractive bremsstrahlung. This is remarkable as the CEP cross section is of order α 3 em whereas the bremsstrahlung one is only of order α em . On the other hand, the soft-photon bremsstrahlung where the basic pp → pp reaction is due to strong interaction diffraction is more important than CEP in the forward rapidity range, |y| > 4, and/or at very low k ⊥ . We leave it as a challenge for the planned ALICE 3 experiment at the LHC to study these two contributions to soft photon production in pp collisions. This could shed new light on the so called "soft photon puzzle" in hadron-hadron collisions.

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Low transverse momentum photon production in proton-nucleus collisions at 18 GeV/c

Cited by 12 publications

References 39 publications

Direct real photons in relativistic heavy ion collisions

Direct real photons in relativistic heavy ion collisions

High-energy $ππ$ scattering without and with photon radiation

Central exclusive diffractive production of single photon in high-energy proton-proton collisions within the tensor-pomeron approach

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