Hard Photoproduction Research Articles

Erratum: Hard photoproduction of a diphoton with a large invariant mass [Phys. Rev. D 96 , 074008 (2017)

We correct the expression for the $\ensuremath{\gamma}N\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\gamma}{N}^{\ensuremath{'}}$ amplitude in the generalized Bjorken regime, where the diphoton is nearly forward and its invariant mass is the hard scale enabling to factorize the scattering amplitude in terms of generalized parton distributions. This amplitude has a very peculiar and interesting analytic structure, while the cross section estimates are only slightly changed.

Centrality Dependence of Charmed-Meson Photoproduction in Ultrarelativistic Heavy Ion Collisions**Supported by the National Natural Science Foundation of China under Grant No. 11847207, the International Postdoctoral Exchange Fellowship Program of China under Grant No. 20180010, and the China Postdoctoral Science Foundation funded project No. 2017M610663

We calculate the centrality dependence of inclusive cross section of large-pT charmed-meson (D0, D∗, D∗+, and ) from heavy quark fragmentation by the hard photoproduction processes in ultrarelativistic heavy ion collisions. The numerical results indicate that the contribution of the hard photoproduction processes cannot be negligible for the inclusive charmed-meson production in Au-Au collisions at Relativistic Heavy Ion Collider (RHIC) and Pb-Pb collisions at Large Hadron Collider (LHC).

Hard photoproduction of a diphoton with a large invariant mass

The electromagnetic probe has proven to be a very efficient way to access the $3-$dimensional structure of the nucleon, particularly thanks to the exclusive Compton processes. We explore the hard photoproduction of a large invariant mass diphoton in the kinematical regime where the diphoton is nearly forward and its invariant mass is the hard scale enabling to factorize the scattering amplitude in terms of generalized parton distributions. This amplitude has a very peculiar and interesting analytic structure. We calculate unpolarized cross sections and the angular asymmetry triggered by a linearly polarized photon beam.

Heavy quarkonium photoproduction in ultrarelativistic heavy ion collisions

Based on the factorization formalism of nonrelativistic quantum chromodynamics (NRQCD), we calculate the production cross section for the charmonium and the bottomonium produced by the hard photoproduction processes and fragmentation processes in relativistic heavy ion collisions. It is shown that the existing experimental data on heavy quarkonium production at the Large Hadron Collider (LHC) can be described in the framework of the NRQCD formalism, and the phenomenological values of matrix elements for color-singlet and color-octet components give the main contribution. The numerical results of photoproduction processes and fragmentation processes for the heavy quarkonium production become prominent in p-p collisions and Pb-Pb collisions at LHC energies.

Photoproduction of Light Vector Meson in Relativistic Heavy Ion Collisions

We calculate the hard photoproduction of light vector meson from the fragmentation of photon in Pb—Pb collisions. Using the perturbative quantum chromodynamics calculation, we rigorously derive the electromagnetic fragmentation production for ρ, ω and φ in relativistic nucleus-nucleus collisions by the photoproduction processes. It is shown that the differential cross section of photoproduction processes of light vector meson cannot be negligible in relativistic heavy ion collisions at Large Hadron Collider energies.

Diffractive [formula omitted] and continuum [formula omitted] pair production in PHENIX Ultraperipheral Collisions

We report results on high energy photoproduction from the PHENIX experiment. Using Run 4 Au-Au data taken with an ultra-peripheral trigger (requiring a rapidity gap in 3.0 ⩽ η ⩽ 3.9 ). We find 10 ± 3 candidates for diffractive J / ψ photoproduction and of order 40 candidates for continuum e + e − photoproduction in the mass range m e e ⩾ 1.8 GeV / c 2 . We then discuss prospects and rates for hard photoproduction at the LHC with Pb-Pb beam collisions and p-Pb.

Heavy Ion Physics with the ATLAS Detector

Soon after the LHC is commissioned with proton beams the ATLAS experiment will begin studies of Pb-Pb collisions with a center of mass energy of ?sNN = 5.5 TeV. The ATLAS program is a natural extension of measurements at RHIC in a direction that exploits the higher LHC energies and the superb ATLAS calorimeter and tracking coverage. At LHC energies, collisions will be produced with even higher energy density than observed at RHIC. The properties of the resulting hot medium can be studied with higher energy probes, which are more directly interpreted through modification of jet properties emerging from these collisions, for example. Other topics which are enabled by the 30-fold increase in center of mass energy include probing the partonic structure of nuclei with hard photoproduction (in UltraPeripheral collisions) and in p-Pb collisions. Here we report on evaluation of ATLAS capabilities for Heavy Ion Physics.

Theory of hard photoproduction

The author reviews the present theoretical understanding of photons and hard photoproduction processes, discussing the production of jets, light and heavy hadrons, quarkonia, and prompt photons in photon-photon and photon-hadron collisions. Virtual and polarized photons and prompt-photon production in hadron collisions are also discussed. The most important leading-order and next-to-leading-order quantum chromodynamics results are compiled in analytic form. A large variety of numerical predictions is compared to data from TRISTAN, LEP, and HERA and extended to future electron and muon colliders. The sources of all relevant results are collected in an extensive bibliography.

Soft and hard contributions to hard pion photoproduction

Soft and hard contributions to hard pion photoproduction

An investigation of a possible hard contribution to φ photoproduction

We investigate the possibility that the process of φ photoproduction may have a significant hard perturbative QCD component. This suggestion is based on a study of the energy dependence of the forward φ photoproduction cross section followed by a calculation where we show that a coherent sum of the pQCD and conventional soft Pomeron contributions provides an excellent reproduction of the experimental data. Our results suggest that the transition from the predominantly soft photoproduction of light ρ and ω vector mesons to the predominantly hard photoproduction of heavy J/ Ψ and ϒ is smooth and gradual, similar to the transition observed in deep inelastic scattering studies of the proton structure function in the small x limit. Our predictions for higher HERA energies are presented.

J/ψ and γ Photoproduction at Relativistic Heavy-Ion Collider

Hard photoproduction of J/ψ and gamma- at the Relativistic Heavy-Ion Collider Au-Au, I-I, Cu-Cu, Si-Si, and O-O collisions is discussed in the process A+A → A+ J/ψ(gamma-) + X. It shows that in the rang of transverse momentum Pt < 4 GeV the hard photoproduction process can be used to test the gluon distribution in the nucleus. So the process also provides a new way of testing the EMC effects. The large Pt heavy quark Qc and gluon fragmantizing into J/ψ are also studied in the range of 4 < Pt < 10 GeV.

Events with large ETtot in photoproduction at HERA

Hard photoproduction events observed at HERA have a large excesses of transverse energy flow with respect to theoretical predictions. For this paper events with total transverse energy greater than 45 GeV were selected. Jet cross sections and the dependence of the event rate on the photon-proton centre of mass energy W were measured. A multi-parton interaction model can describe the jet cross section but probably not the W distribution while a model without multi-parton interactions describes the W dependence well but not the jet cross section. At the moment, there is no model that describes data satisfactorily in the measured kinematic range.

J/ψ and υ Photoproduction in Pb-Pb Collisions at Large Hadron Collider

Hard photoproduction of J/ψ and T at large hadron collider Pb-Pb collisions with center of mass energy 6300 AGeV is discussed in the process Pb + Pb → Pb + J/ψ(Γ) + X with three types of equivalent photon spectrum function. It turns out that in hard photoproduction the J/ψ cross section is dominated by the gluon and heavy quark fragmentation, especially the gluon fragmentation is very important at large pt, while the T cross section is dominated by the leading order process. It may be conclude from the result that the hard photoproduction processes can be used to test several important problems such as the gluon distribution in the nucleus, gluon and heavy quark fragmentation of J/ψ, and so on. In addition the process also provide a new way of testing the EMC effects.

HERA Workshop on proton, photon and pomeron structure

HERA Workshop on proton, photon and pomeron structure

Diffractive hard photoproduction at HERA and evidence for the gluon content of the pomeron

Inclusive jet cross sections for events with a large rapidity gap with respect to the proton direction from the reaction ep → jet + X with quasi-real photons have been measured with the ZEUS detector. The cross sections refer to jets with transverse energies E T jet > 8 GeV. The data show the characteristics of a diffractive process mediated by pomeron exchange. Assuming that the events are due to the exchange of a pomeron with partonic structure, the quark and gluon content of the pomeron is probed at a scale ∼ ( E T jet) 2. A comparison of the measurements with model predictions based on QCD plus Regge phenomenology requires a contribution of partons with a hard momentum density in the pomeron. A combined analysis of the jet cross sections and recent ZEUS measurements of the diffractive structure function in deep inelastic scattering gives the first experimental evidence for the gluon content of the pomeron in diffractive hard scattering processes. The data indicate that between 30% and 80% of the momentum of the pomeron carried by partons is due to hard gluons.

Parton densities in the photon

The parton densities in the photon have been derived from measurements of the photon structure function and of jet production in two-photon and photoproduction processes. Recent analyses by the H1 and ZEUS collaborations show that hard photoproduction processes at HERA allow to determine the gluon density down to x values of 10−2. For a discrimination of different models the systematic uncertainties in these analyses have still to be reduced.

Soft and hard photoproduction news from H1 at HERA

This report presents some preliminary results from measurements of photoproduction events collected with the H1 detector at the HERA ep colliding storage rings. The results concern the total gamma p cross section, diffractive vector meson production, inclusive particle and jet production, and the partonic content of the photon. Some conclusions on hard parton processes and on their interplay with soft physics are discussed. The data were taken during the autumn of 1992. They correspond to an integrated luminosity of 21.9+or-1.5 nb-1.