On timelike and spacelike deeply virtual Compton scattering at next to leading order

We study timelike and spacelike virtual Compton scattering in the generalized Bjorken scaling regime at next to leading order in the strong coupling constant, in the medium energy range which will be studied intensely at JLab12 and in the COMPASS-II experiment at CERN. We show that the Born amplitudes get sizeable O(\alpha_s) corrections and, even at moderate energies, the gluonic contributions are by no means negligible. We stress that the timelike and spacelike cases are complementary and that their difference deserves much special attention

Timelike vs spacelike DVCS from JLab, Compass to ultraperipheral collisions and AFTER@LHC

Timelike and spacelike virtual Compton scattering in the generalized Bjorken scaling regime are complementary tools to access generalized parton distributions. We stress that the gluonic contributions are by no means negligible, even in the medium energy range which will be studied intensely at JLab12 and in the COMPASS-II experiment at CERN. Ultraperipheral collisions with proton or ion beams may also be used at RHIC and at collider or fixed target experiments at LHC.Comment: 7 pages, Presented at the Low x workshop, May 30 - June 4 2013, Rehovot and Eilat, Israe

NLO QCD corrections for DVCS and TCS

The inclusion of QCD corrections to the Born amplitude of deeply virtual Compton scattering in both spacelike (DVCS) and timelike (TCS) regimes modifies the extraction process of generalized parton distributions (GPDs) from observables. In particular, gluon contributions are by no means negligible even in the medium energy range accessible at JLab12. We emphasize the complementarity of spacelike and timelike measurements and raise the question of factorization scale dependence of the O(alpha_S) results.Comment: 6 pages, 6 figures, Proceedings of the conference Photon 2013, 20-24 May 2013 Paris, France, to be published in Proceedings of Scienc

Sudakov Resummations in Mueller-Navelet Dijet Production

In high energy hadron-hadron collisions, dijet production with large rapidity separation proposed by Mueller and Navelet, is one of the most interesting processes which can help us to directly access the well-known Balitsky-Fadin-Kuraev-Lipatov evolution dynamics. The objective of this work is to study the Sudakov resummation of Mueller-Navelet jets. Through the one-loop calculation, Sudakov type logarithms are obtained for this process when the produced dijets are almost back-to-back. These results could play an important role in the phenomenological study of dijet correlations with large rapidity separation at the LHC.Comment: 20 pages, 5 figures; v2, refs adde

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 O(alphaS) 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.Comment: 10 pages, conference LIGHTCONE 2013, 20-24 May 2013, Skiathos, Greec

Spin dynamics in the Kapitza-Dirac effect

Electron spin dynamics in Kapitza-Dirac scattering from a standing laser wave of high frequency and high intensity is studied. We develop a fully relativistic quantum theory of the electron motion based on the time-dependent Dirac equation. Distinct spin dynamics, with Rabi oscillations and complete spin-flip transitions, is demonstrated for Kapitza-Dirac scattering involving three photons in a parameter regime accessible to future high-power X-ray laser sources. The Rabi frequency and, thus, the diffraction pattern is shown to depend crucially on the spin degree of freedom

Metrology for MRI Safety

. Magnetic Resonance Imaging (MRI) has become an indispensable medical imaging modality with about 30 million patient exams in the EU every year and an excellent history of safe use. Nevertheless, it is continuously evolving and recent technological developments such as ultrahigh magnetic fields, parallel transmission, or MRI guided radiotherapy promise to significantly enhance the quality and the range of applicability of MRI. A major reason why these technological developments are not yet used in the clinical practice are unresolved safety issues. If the patient risk cannot be quantified reliably, a ‘safety first’ attitude naturally prevails preventing the routine use of new technologies or the scanning of subjects at high risk, e.g. carriers of metallic medical implants. The EMRP joint research project HLT 06 "Metrology for MRI Safety" aimed at providing such risk assessments for certain new developments or applications in MRI. The project was concluded in 2015 and some key results will be presented here

Radiation spectra of laser-driven quantum relativistic electrons

A procedure to calculate the radiation spectrum emitted by an arbitrarily prepared Dirac wave packet is developed. It is based on the Dirac charge current and classical electrodynamic theory. Apart from giving absolute intensity values, it is exact in terms of relativistic retardation effects and angular dependence. We employ a laser driven free electron to demonstrate the advantages of our method as compared to traditional ones that merely rely on the Fourier transform of the dipole operator's expectation value. Classical reference calculations confirm the results obtained for the low-frequency part of the spectrum, especially in terms of the observed red-shifts, which clearly deviate from non-relativistic calculations. In the high-frequency part of the spectrum, we note appreciable deviations to the purely classical calculations which may be linked to quantum averaging effects.Comment: 30 pages, 7 figure

Polarization of the electron and positron produced in combined Coulomb and strong laser fields

The process of $e^+e^-$ production in the superposition of a Coulomb and a strong laser field is considered. The pair production rate integrated over the momentum and summed over the spin projections of one of the particles is derived exactly in the parameters of the laser field and in the Born approximation with respect to the Coulomb field. The case of a monochromatic circularly polarized laser field is considered in detail. A very compact analytical expression of the pair production rate and its dependence on the polarization of one of the created particles is obtained in the quasiclassical approximation for the experimentally relevant case of an undercritical laser field. As a result, the polarization of the created electron (positron) is derived.Comment: 16 pages, no figure