Direct photon production in and pp interactions at √s = 24.3 GeV

Sozzi, G.; Ballocchi, G.; Bernasconi, A.; Breedon, R.; Camilleri, L.; Cool, R. L.; Cox, P. T.; Cushman, P.; Dick, L.; Dukes, E. C.; Gabioud, B.; Gaille, F.; Giacomelli, P.; Hubbard, D.; Jeanneret, J.B.; Joseph, C.; Kubischta, W.; Loude, J.-F.; Malamud, E.; Morel, C.; Oberson, P.; Overseth, O. E.; Pagès, J.L.; Perroud, J. P.; Ruegger, D.; Rusack, R.; Singh, V.; Snow, G. R.; Steiner, D.; Studer, L.; Trân, M. T.; Vacchi, A.; Valenti, G.; Werlen, M.

doi:10.1016/0370-2693(93)91600-r

Cited by 16 publications

(6 citation statements)

References 31 publications

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“…GeV, obtained by WA70 [11], NA24 [12], and UA6 [13] collaborations scaled by the nuclear overlap for zero impact parameter for the collision of lead nuclei. The solid curve gives the perturbative QCD results [14] for the pp collisions scaled similarly.…”

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confidence: 99%

Flash of photons from the early stage of heavy-ion collisions

Srivastava

Geiger

1998

Phys. Rev. C

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The dynamics of partonic cascades may be an important aspect for particle production in relativistic collisions of nuclei at CERN SPS and BNL RHIC energies. Within the Parton-Cascade Model, we estimate the production of single photons from such cascades due to scattering of quarks and gluons q g -> q gamma, quark-antiquark annihilation q qbar -> g gamma, or gamma gamma, and from electromagnetic brems-strahlung of quarks q -> q gamma. We find that the latter QED branching process plays the dominant role for photon production, similarly as the QCD branchings q -> q g and g -> g g play a crucial role for parton multiplication. We conclude therefore that photons accompanying the parton cascade evolution during the early stage of heavy-ion collisions shed light on the formation of a partonic plasma.Comment: 4 pages including 3 postscript figure

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confidence: 99%

Flash of photons from the early stage of heavy-ion collisions

Srivastava

Geiger

1998

Phys. Rev. C

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“…We have also shown the production of single photons from pp collisions for √ s ≈ 24 GeV, obtained by WA70 [28], NA24 [29], and UA6 [30] collaborations scaled by the nuclear thickness for zero impact parameter for the collision of lead nuclei. The solid curve gives the perturbative QCD results [27] for the pp collisions scaled similarly.…”

Section: Resultsmentioning

confidence: 99%

Flash of prompt photons from the early stage of heavy-ion collisions

Srivastava

1999

AIP Conference Proceedings

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Abstract. We briefly recall the tremendous strides in the studies of the parton cascade model made by Klaus Geiger. Next, we argue that photons may provide confirmation of several of these ideas. Thus we know that, copious internetted partonic cascades may develop in the wake of relativistic collisions of nuclei at CERN SPS and BNL RHIC energies, We use the parton cascade model to estimate the emission of single photons generated from such cascades due to the branching of quarks q → q γ, scattering of quarks and gluons, and annihilation of quarks. The formation of a hot and dense partonic matter is shown to be preceded by an intense radiation of photons from the QED branching of quarks. This is similar to the QCD branching q → qg which along with the gluon multiplication ( g → gg ) which is known to play a crucial role in the formation of the dense partonic plasma. FROM PCM TO VNI; AN ODE TO KKGIt is incumbent on us to provide a comprehensive and accurate description of relativistic collision of nuclei from the instant of nuclear contact to the formation of hadronic states which are ultimately detected in experiments. Such collisions are expected to create: a) the conditions which prevailed at the time of early universea few micro-seconds after the big-bang, and thus, b) a strongly interacting matter under conditions of extreme temperatures and densities which would throw light on the "hallowed" quark-hadron phase transition. A significant step in this direction was provided by the parton cascade model (PCM) [1] which was proposed to study the time evolution of the parton phase space distribution in relativistic nuclear collisions. In this approach the space-time 1)

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“…This rare process in principle provides information on the intrinsic k T of the partons, by the transverse momentum imbalance of the two photons 22 , although perturbative corrections may destroy the significance [124]. Somewhat later, using an internal hydrogen gas jet target, pp and pp data were also taken at √ s =24.3 GeV by UA6 and the difference σ(pp → γX) − σ(pp → γX) was measured for the first time [125,126]. The difference isolates the leading order qq annihilation term and with the quark distributions known from deep inelastic scattering, this way one could determine the gluon distributions from the other leading order process, the qg → γq Compton scattering, and even α s can be measured [127] In the early 1990s Fermilab experiments CDF and D0 measured prompt photon cross sections in √ s =1.8 TeV pp collisions up to p T =120 GeV/c.…”

Section: Spectramentioning

confidence: 99%

“…Right: xT-scaling of the world data on direct photons in pp and pp as of 2012 (figure taken from [137]). Sources of additional data included here: CMS [140], ATLAS [150], D0 [151], CDF [128,152], PHENIX [92,136,137], UA1 [88], UA2 [153], R807 [147], R108 [154], E704 [155], NA24 [156], UA6 [125].…”

Section: Spectramentioning

confidence: 99%

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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Direct photon production in and pp interactions at √s = 24.3 GeV

Cited by 16 publications

References 31 publications

Flash of photons from the early stage of heavy-ion collisions

Flash of photons from the early stage of heavy-ion collisions

Flash of prompt photons from the early stage of heavy-ion collisions

Direct real photons in relativistic heavy ion collisions

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