scholarly journals Predictions for high-energy real and virtual photon–photon scattering from color dipole BFKL–Regge factorization

2002 ◽  
Vol 22 (4) ◽  
pp. 637-646 ◽  
Author(s):  
N.N. Nikolaev ◽  
J. Speth ◽  
V.R. Zoller
Keyword(s):  
Virtual Photon ◽  
High Energy ◽  
Photon Scattering ◽  
Color Dipole ◽  
Regge Factorization

scholarly journals Saturation effects in SIDIS at very forward rapidities

2021 ◽  
Vol 2021 (7) ◽  
Author(s):  
E. Iancu ◽  
A. H. Mueller ◽  
D. N. Triantafyllopoulos ◽  
S. Y. Wei
Keyword(s):  
Inelastic Scattering ◽  
Cross Section ◽  
Cross Sections ◽  
Virtual Photon ◽  
Large Fraction ◽  
Quark Distribution ◽  
High Energy ◽  
Longitudinal Momentum ◽  
Black Disk ◽  
Gluon Saturation

Abstract Using the dipole picture for electron-nucleus deep inelastic scattering at small Bjorken x, we study the effects of gluon saturation in the nuclear target on the cross-section for SIDIS (single inclusive hadron, or jet, production). We argue that the sensitivity of this process to gluon saturation can be enhanced by tagging on a hadron (or jet) which carries a large fraction z ≃ 1 of the longitudinal momentum of the virtual photon. This opens the possibility to study gluon saturation in relatively hard processes, where the virtuality Q2 is (much) larger than the target saturation momentum $$ {Q}_s^2 $$ Q s 2 , but such that z(1 − z)Q2 ≲ $$ {Q}_s^2 $$ Q s 2 . Working in the limit z(1 − z)Q2 ≪ $$ {Q}_s^2 $$ Q s 2 , we predict new phenomena which would signal saturation in the SIDIS cross-section. For sufficiently low transverse momenta k⊥ ≪ Qs of the produced particle, the dominant contribution comes from elastic scattering in the black disk limit, which exposes the unintegrated quark distribution in the virtual photon. For larger momenta k⊥ ≳ Qs, inelastic collisions take the leading role. They explore gluon saturation via multiple scattering, leading to a Gaussian distribution in k⊥ centred around Qs. When z(1 − z)Q2 ≪ Q2, this results in a Cronin peak in the nuclear modification factor (the RpA ratio) at moderate values of x. With decreasing x, this peak is washed out by the high-energy evolution and replaced by nuclear suppression (RpA< 1) up to large momenta k⊥ ≫ Qs. Still for z(1 − z)Q2 ≪ $$ {Q}_s^2 $$ Q s 2 , we also compute SIDIS cross-sections integrated over k⊥. We find that both elastic and inelastic scattering are controlled by the black disk limit, so they yield similar contributions, of zeroth order in the QCD coupling.

scholarly journals Hadronic properties of the photon

2019 ◽  
Vol 204 ◽  
pp. 05012
Author(s):  
Sergey Gevorkyan
Keyword(s):  
High Energy ◽  
Dipole Model ◽  
The Other ◽  
Dominance Model ◽  
Color Transparency ◽  
Vector Dominance ◽  
Color Dipole ◽  
The Impact ◽  
Color Dipole Model ◽  
Hadronic Component

Currently it is no doubt that high energy photons (real or virtual) have a hadronic component leading to photon shadowing in its interaction with nuclei. We shortly consider the difficulties appeared in the models like vector dominance model (VDM) and stress that these problems can be solved in a color dipole model inspired by Quantum Chromodynamics (QCD). From the other hand, the color dipole model allows one to investigate the impact of vector meson polarization on their interaction with nucleons and nuclei, the challenge which is crucial for studying, for instance, such a fundamental effect as color transparency.

scholarly journals Nonlinear corrections on the parametrization methods

2021 ◽  
Vol 81 (9) ◽  
Author(s):  
G. R. Boroun ◽  
B. Rezaei
Keyword(s):  
Cross Sections ◽  
Direct Method ◽  
Nonlinear Behavior ◽  
High Energy ◽  
Structure Functions ◽  
Distribution Functions ◽  
Reduced Cross Section ◽  
Color Dipole ◽  
Wide Range ◽  
Energy Processes

AbstractWe present nonlinear corrections (NLCs) to the distribution functions at low values of x and $$Q^{2}$$ Q 2 using the parametrization $$F_{2}(x,Q^{2})$$ F 2 ( x , Q 2 ) and $$F_{L}(x,Q^{2})$$ F L ( x , Q 2 ) . We use a direct method to extract nonlinear corrections to the ratio of structure functions and the reduced cross section in the next-to-next-to-leading order (NNLO) approximation with respect to the parametrization method (PM). Comparisons between the nonlinear results with the bounds in the color dipole model (CDM) and HERA data indicate the consistency of the nonlinear behavior of the gluon distribution function at low x and low $$Q^{2}$$ Q 2 . The nonlinear longitudinal structure functions are comparable with the H1 Collaboration data in a wide range of $$Q^{2}$$ Q 2 values. Consequently, the nonlinear corrections at NNLO approximation to the reduced cross sections at low and moderate $$Q^{2}$$ Q 2 values show good agreement with the HERA combined data. These results at low x and low $$Q^{2}$$ Q 2 can be applied to the LHeC region for analyses of ultra-high-energy processes.

scholarly journals CHIRAL ANOMALY EFFECTS AND THE BABAR MEASUREMENTS OF THE γγ* → π0 TRANSITION FORM-FACTOR

2011 ◽  
Vol 26 (23) ◽  
pp. 4125-4131 ◽  
Author(s):  
T. N. PHAM ◽  
X. Y. PHAM
Keyword(s):  
Form Factor ◽  
Perturbative Qcd ◽  
Virtual Photon ◽  
Transition Form Factor ◽  
High Energy ◽  
Chiral Anomaly ◽  
Steady Increase ◽  
Transition Form ◽  
Babar Data ◽  
Energy Processes

The recent BaBar measurements of the γγ*→π0 transition form-factor show spectacular deviation from perturbative QCD prediction for large spacelike Q2 up to 34 GeV2. When plotted against Q2, Q2F(Q2) shows steady increase with Q2 in contrast with the flat Q2 behavior predicted by perturbative QCD, and at 34 GeV2 is more than 50% larger than the QCD prediction. Stimulated by the BaBar measurements, we revisit our previous paper on the cancellation of anomaly effects in high energy processes Z0→π0γ, e+e- → π0γ and apply our results to the γ*γ→π0 transition form-factor measured in the e+e- → e+e-π0 process with one highly virtual photon. We find that, the transition form-factor F(Q2) behaves as [Formula: see text] and produces a striking agreement with the BaBar data for Q2F(Q2) with m = 132 MeV which also reproduces very well the CLEO data at lower Q2.

scholarly journals Diffractive Bremsstrahlung in Hadronic Collisions

2015 ◽  
Vol 2015 ◽  
pp. 1-20 ◽  
Author(s):  
Roman Pasechnik ◽  
Boris Kopeliovich ◽  
Irina Potashnikova
Keyword(s):  
Rest Frame ◽  
Parton Model ◽  
High Energy ◽  
Higgs Bosons ◽  
Color Dipole ◽  
Phenomenological Studies ◽  
Main Observation ◽  
Basic Features ◽  
Bremsstrahlung Process ◽  
Hadronic Collisions

Production of heavy photons (Drell-Yan), gauge bosons, Higgs bosons, and heavy flavors, which is treated within the QCD parton model as a result of hard parton-parton collision, can be considered a bremsstrahlung process in the target rest frame. In this review, we discuss the basic features of the diffractive channels of these processes in the framework of color dipole approach. The main observation is a dramatic breakdown of diffractive QCD factorisation due to the interplay between soft and hard interactions, which dominates these processes. This observation is crucial for phenomenological studies of diffractive reactions in high energy hadronic collisions.

The photonuclear cross section at high energies as determined from the nuclear interaction of muons

1968 ◽  
Vol 46 (10) ◽  
pp. S373-S376 ◽  
Author(s):  
R. J. W. Hodgson ◽  
H. S. Murdoch ◽  
H. D. Rathgeber
Keyword(s):  
Form Factor ◽  
Cross Section ◽  
Virtual Photon ◽  
Cosmic Ray ◽  
Nuclear Interaction ◽  
High Energy ◽  
Photon Spectrum ◽  
High Energies ◽  
Deep Underground ◽  
Energy Dependent

Information about the photonuclear cross section σγ, at high energy can be obtained from muon interaction experiments by considering the virtual photon spectrum of the muons. Previous attempts to fit a virtual photon spectrum and form factor to the following experiments are discussed: (1) interaction of machine-produced muons at 2.5 and 5 GeV; (2) interaction of cosmic-ray muons at high energy; (3) the intensity–depth relation of cosmic-ray muons deep underground. It is shown that previous proposals to fit one or more of these experiments are not consistent with all the experimental evidence, particularly in relation to the form factor. It is demonstrated that σγ is energy-dependent above 1 GeV and, with due allowance for this, a form factor may be found which is consistent with the various experiments.

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