On Deeply Virtual Compton Scattering at Next-to-Leading Order

Deeply virtual Compton scattering in the near forward kinematic region is the golden access to Generalized Parton Distributions. We studied the \({\mathcal{O}(\alpha_S)}\) corrections to the scattering amplitude for both spacelike and timelike kinematics relevant respectively to the leptoproduction of a real photon and to the photoproduction of a lepton pair. It turns out that these corrections are phenomenologically important and that the gluonic contributions are by no means negligible, even in the moderate energy range of JLab12 and of the COMPASS-II experiment at CERN.     

Virtual Compton Scattering off Spin-Zero Particles at Low Energies

We discuss the low-energy behaviour of the virtual Compton scattering amplitude off a spin-zero target. We first compare various methods of obtaining a low-energy expression based either on the soft-photon approximation or the use of Ward-Takahashi identities. We point out that structure-dependent terms are defined with respect to a low-energy approximation of the pole terms, which commonly is separated from the full amplitude. We derive a general expression for the structure-dependent terms in an expansion in terms of the momenta and of the initial and final virtual photon, respectively, up to and including terms of order . At order two terms appear that are related to the usual electric and magnetic polarizabilities of real Compton scattering. At order we find nine new structures of which five can only be determined using virtual photons. Received October 23, 1997; accepted for publication December 29, 1997     

Generalized Parton Distributions from Deeply Virtual Compton Scattering at HERMES

The HERMES Collaboration has recently published a set of (correlated) beam charge, beam spin and target spin asymmetries for the Deeply Virtual Compton Scattering (DVCS) process. This reaction allows in principle to access the Generalized Parton Distributions (GPDs) of the nucleon. We have fitted, in the QCD leading-order and leading-twist handbag approximation, but in a model-independent way, this set of data and we report our results for the extracted Compton form factors. In particular, we are able to extract constrains on the H GPD.     

Backward timelike Compton scattering to decipher the photon content of the nucleon

The European Physical Journal C - We consider invisible neutrino decay $$nu _H rightarrow nu _l + phi $$ in the ultra-relativistic limit and compute the neutrino anisotropy loss rate relevant...     

Virtual Compton scattering at low energies with a positron beam

The European Physical Journal A - Using a transport model that includes a first-order chiral phase transition between the partonic and the hadronic matter, we study the development of density...     

Scattering and absorption differential cross sections for double photon Compton scattering

The scattering and absorption differential cross sections for nonlinear QED process such as double photon Compton scattering have been measured as a function of independent final photon energy. The incident gamma photons are of 0.662 MeV in energy as produced by an 8 Ci¹³⁷Cs radioactive source and thin aluminum foils are used as scatterer. The two simultaneously emitted photons in this process are detected in coincidence using two Nal(T1) scintillation detectors and a slow-fast coincidence set-up of 30 nsec resolving time. The measured values of scattering and absorption differential cross sections agree with theory within experimental estimated error.     

利用虚光子散射对回旋脉塞自发辐射的分析

利用电磁场变换分析了带电粒子在磁场中的螺旋运动,基于康普顿散射理论和多普勒公式分析了虚光子与带电粒子的康普顿散射,并推导了在磁场中做螺旋运动的带电粒子的自发辐射波长公式.结果表明,当带电粒子在回旋脉塞的磁场中作螺旋运动时,在粒子静止系中可以观察到运动的周期性变化电场和磁场,即运动的虚光子.通过与带电粒子发生康普顿散射,虚光子能够转化为实光子辐射出去.     

Relativistic double differential cross sections for Compton scattering by bound electrons: Test at low photon energies and predictions at intermediate photon energies

Cross section profiles d²σ/dΩdω′ for Compton scattering of photons by bound electrons are calculated for all subshells of the atom. Results obtained from the form factor approximation and from a relativistic version of the impulse approximation are compared with experimental data for Cu and Pb at a scattering angle ofθ=145° and a photon energy of 662 keV. The impulse approximation proves to be superior to the form factor approximation and is used to predict cross section profiles for a primary energy of 50 MeV and different scattering angles and charge numbers. It is shown that only for the heaviest atoms and scattering angles belowθ=5° there is a non-negligible contribution of Compton scattering to the elastic peak.     

Exclusive electroproduction and the quark structure of the nucleon

The natural interpretation of deep inelastic scattering is in terms of hard scattering on QCD constituents of the target. We examine the relation between amplitudes measured in exclusive lepto-production and the quark content of the nucleon. We show that in the Bjorken limit, the natural interpretation of amplitudes measured in these hard exclusive processes is in terms of the quark content of the meson cloud and not the target itself. In this limit, the most efficient representation of these exclusive processes is in terms of leading Regge amplitudes.     

Theoretical Description of Deeply Virtual Compton Scattering off 3He

Recently, coherent deeply virtual Compton scattering (DVCS) off ³He nuclei has been proposed to access the neutron generalized parton distributions (GPDs). In impulse approximation (IA) studies, it has been shown, in particular, that the sum of the two leading twist, quark helicity conserving GPDs of ³He, H and E, at low momentum transfer, is dominated by the neutron contribution, so that ³He is very promising for the extraction of the neutron information. Nevertheless, such an extraction could be not trivial. A technique, able to take into account the nuclear effects included in the IA analysis in the extraction procedure, has been therefore developed. In this work, the IA calculation of the spin dependent GPD \({\tilde H}\) of ³He is presented for the first time. This quantity is found to be largely dominated, at low momentum transfer, by the neutron contribution, which could be extracted using arguments similar to the ones previously proposed for the other GPDs. The known forward limit of the IA calculation of \({\tilde H}\) , yielding the polarized parton distributions of ³He, is correctly recovered. The knowledge of the GPDs H, E and \({\tilde H}\) of ³He will allow now the evaluation of the cross section asymmetries which are relevant for coherent DVCS off ³He at Jefferson Lab kinematics, an important step towards the planning of possible experiments.     

磁逆多光子非线性Compton微分散射截面的特性

应用电子与光子非弹性碰撞模型,分析、计算了磁逆多光子非线性Compton微分散射截面的特性。结果表明：该微分散射截面随与电子同时作用光子数及电子与光子碰撞非弹性成分的增大而减小,散射光子的频率逐渐趋于共振频率,但不具有共振性;当电子被光场俘获时,磁逆多光子非线性Compton微分散射截面为一恒定值。     

On the photon production in nucleus-nucleus collisions at high energy

A modified Landau hydrodynamical model is applied to study hard thermal photon production in central heavy-ion collisions at LHC, RHIC and SPS energies. It is shown that the phase transition from quark-gluon plasma into hadrons in consequence of the thermodynamical expansion is close to the second order phase transition if a resonance production is taken into account. Hard direct photon emission is also investigated with consideration of nuclear shadowing effect on structure function of quarks and gluons. Also π^π photon background is investigated. It is demonstrated that at the LHC energy photon yield from the quark-gluon plasma in the photon transversal momentumk _⊥ range from 5 to 25 GeV/c exceeds both the background and the direct photon yield. This conclusion may be important for the quark-gluon plasma diagnostic aims. It is also shown that for the LHC energy the thermal photon yield in the present model essentially exceeds this yield obtained in the Bjorken scaling model.