The Experts below are selected from a list of 39294 Experts worldwide ranked by ideXlab platform
Toshitaka Kajino - One of the best experts on this subject based on the ideXlab platform.
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Compton Scattering of γ ray vortex with laguerre gaussian wave function
2019Co-Authors: Tomoyuki Maruyama, Takehito Hayakawa, Toshitaka KajinoAbstract:In this work, we report calculation for Compton Scattering of a γ-ray vortex with a wave function of Laguerre Gaussian on an electron in the framework of the relativistic quantum mechanics. We consider the coincidence measurement of the scattered photon and the scattered electron from each Compton Scattering. The momentum of the scattered photon distributes outside of the reaction plane determined by the incident photon and the scattered electron, and the energy of the scattered photon also distributes, when the scattered angle of the electron is simultaneously measured. These distributions depend on the angular momentum and the node number of the Laguerre Gaussian function of the incident photon. Thus, the coincident measurement for Compton Scattering is useful to identify the nature of the vortex photon wave function.
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Compton Scattering of Gamma-Ray Vortex with Laguerre Gaussian Wave Function
2017Co-Authors: Tomoyuki Maruyama, Takehito Hayakawa, Toshitaka KajinoAbstract:In this work, we report calculation for Compton Scattering of a gamma-ray vortex with Laguerre Gaussian wave function on an electron in the framework of the relativistic quantum mechanics. We have found the following unexpected feature. The momentum of scattered photon distributes outside of the reaction plane determined by the incident photon and the scattered electron, and hence the energy of the scattered photon also distributes. This novel result indicates that one can identify a gamma-ray vortex by measuring coincidentally the scattered angles of the electron and photon.
F Sabatie - One of the best experts on this subject based on the ideXlab platform.
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timelike and spacelike deeply virtual Compton Scattering at next to leading order
2013Co-Authors: H. Moutarde, F Sabatie, B Pire, L Szymanowski, J WagnerAbstract: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 $O({\ensuremath{\alpha}}_{s})$ 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.
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from hard exclusive meson electroproduction to deeply virtual Compton Scattering
2013Co-Authors: P Kroll, H. Moutarde, F SabatieAbstract:We systematically evaluate observables for hard exclusive electroproduction of real photons and compare them to experiment using a set of Generalized Parton Distributions (GPDs) whose parameters are constrained by Deeply Virtual Meson Production data, nucleon form factors and parton distributions. The Deeply Virtual Compton Scattering amplitudes are calculated to leading-twist accuracy and leading order in QCD perturbation theory while the leptonic tensor is treated exactly, without any approximation. This study constitutes a check of the universality of the GPDs. We summarize all relevant details on the parameterizations of the GPDs and describe its use in the handbag approach of the aforementioned hard Scattering processes. We observe good agreement between predictions and measurements of deeply virtual Compton Scattering on a wide kinematic range, including most data from H1, ZEUS, HERMES, Hall A and CLAS collaborations for unpolarized and polarized targets when available. We also give predictions relevant for future experiments at COMPASS and JLab after the 12 GeV upgrade.
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from hard exclusive meson electroproduction to deeply virtual Compton Scattering
2012Co-Authors: P Kroll, H. Moutarde, F SabatieAbstract:We systematically evaluate observables for hard exclusive electroproduction of real photons and compare them to experiment using a set of Generalized Parton Distributions (GPDs) whose parameters are constrained by Deeply Virtual Meson Production data, nucleon form factors and parton distributions. The Deeply Virtual Compton Scattering amplitudes are calculated to leading-twist accuracy and leading order in QCD perturbation theory while the leptonic tensor is treated exactly, without any approximation. This study constitutes a check of the universality of the GPDs. We summarize all relevant details on the parametrizations of the GPDs and describe its use in the handbag approach of the aforementioned hard Scattering processes. We observe a good agreement between predictions and measurements of deeply virtual Compton Scattering on a wide kinematic range, including most data from H1, ZEUS, HERMES, Hall A and CLAS collaborations for unpolarized and polarized targets when available. We also give predictions relevant for future experiments at COMPASS and JLab after the 12 GeV upgrade.
Vladimir Pascalutsa - One of the best experts on this subject based on the ideXlab platform.
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nucleon polarizabilities from Compton Scattering to hydrogen atom
2016Co-Authors: Franziska Hagelstein, Rory Miskimen, Vladimir PascalutsaAbstract:Abstract We review the current state of knowledge of the nucleon polarizabilities and of their role in nucleon Compton Scattering and in hydrogen spectrum. We discuss the basic concepts, the recent lattice QCD calculations and advances in chiral effective-field theory. On the experimental side, we review the ongoing programs aimed to measure the nucleon (scalar and spin) polarizabilities via the Compton Scattering processes, with real and virtual photons. A great part of the review is devoted to the general constraints based on unitarity, causality, discrete and continuous symmetries, which result in model-independent relations involving nucleon polarizabilities. We (re-)derive a variety of such relations and discuss their empirical value. The proton polarizability effects are presently the major sources of uncertainty in the assessment of the muonic hydrogen Lamb shift and hyperfine structure. Recent calculations of these effects are reviewed here in the context of the “proton-radius puzzle”. We conclude with summary plots of the recent results and prospects for the near-future work.
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predictive powers of chiral perturbation theory in Compton Scattering off protons
2010Co-Authors: Vadim Lensky, Vladimir PascalutsaAbstract:We study low-energy nucleon Compton Scattering in the framework of baryon chiral perturbation theory (BχPT) with pion, nucleon, and Δ(1232) degrees of freedom, up to and including the next-to-next-to-leading order (NNLO). We include the effects of order p 2, p 3, and p 4/Δ, with Δ≈300 MeV the Δ-resonance excitation energy. These are all “predictive” powers in the sense that no unknown low-energy constants enter until at least one order higher (i.e., p 4). Estimating the theoretical uncertainty on the basis of natural size for p 4 effects, we find that uncertainty of such a NNLO result is comparable to the uncertainty of the present experimental data for low-energy Compton Scattering. We find an excellent agreement with the experimental cross-section data up to at least the pion-production threshold. Nevertheless, for the proton’s magnetic polarizability we obtain a value of (4.0±0.7)×10−4 fm3, in significant disagreement with the current PDG value. Unlike the previous χPT studies of Compton Scattering, we perform the calculations in a manifestly Lorentz-covariant fashion, refraining from the heavy-baryon (HB) expansion. The difference between the lowest order HBχPT and BχPT results for polarizabilities is found to be appreciable. We discuss the chiral behavior of proton polarizabilities in both HBχPT and BχPT with the hope to confront it with lattice QCD calculations in a near future. In studying some of the polarized observables we identify the regime where their naive low-energy expansion begins to break down, thus addressing the forthcoming precision measurements at the HIGS facility.
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predictive powers of chiral perturbation theory in Compton Scattering off protons
2009Co-Authors: Vadim Lensky, Vladimir PascalutsaAbstract:We study low-energy nucleon Compton Scattering in the framework of baryon chiral perturbation theory (B$\chi$PT) with pion, nucleon, and $\Delta$(1232) degrees of freedom, up to and including the next-to-next-to-leading order (NNLO). We include the effects of order $p^2$, $p^3$ and $p^4/\varDelta$, with $\varDelta\approx 300$ MeV the $\Delta$-resonance excitation energy. These are all "predictive" powers in the sense that no unknown low-energy constants enter until at least one order higher (i.e, $p^4$). Estimating the theoretical uncertainty on the basis of natural size for $p^4$ effects, we find that uncertainty of such a NNLO result is comparable to the uncertainty of the present experimental data for low-energy Compton Scattering. We find an excellent agreement with the experimental cross section data up to at least the pion-production threshold. Nevertheless, for the proton's magnetic polarizability we obtain a value of $(4.0\pm 0.7)\times 10^{-4}$ fm$^3$, in significant disagreement with the current PDG value. Unlike the previous $\chi$PT studies of Compton Scattering, we perform the calculations in a manifestly Lorentz-covariant fashion, refraining from the heavy-baryon (HB) expansion. The difference between the lowest order HB$\chi$PT and B$\chi$PT results for polarizabilities is found to be appreciable. We discuss the chiral behavior of proton polarizabilities in both HB$\chi$PT and B$\chi$PT with the hope to confront it with lattice QCD calculations in a near future. In studying some of the polarized observables, we identify the regime where their naive low-energy expansion begins to break down, thus addressing the forthcoming precision measurements at the HIGS facility.
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effective theory of theδ 1232 resonance in Compton Scattering off the nucleon
2003Co-Authors: Vladimir Pascalutsa, Daniel R PhillipsAbstract:We formulate a new power-counting scheme for a chiral effective field theory of nucleons, pions, and Deltas. This extends chiral perturbation theory into the Delta-resonance region. We calculate nucleon Compton Scattering up to next-to-leading order in this theory. The resultant description of existing $\gamma$p cross section data is very good for photon energies up to about 300 MeV. We also find reasonable numbers for the spin-independent polarizabilities $\alpha_p$ and $\beta_p$.
V Suleimanov - One of the best experts on this subject based on the ideXlab platform.
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x ray bursting neutron star atmosphere models using an exact relativistic kinetic equation for Compton Scattering
2012Co-Authors: V Suleimanov, Juri Poutanen, K WernerAbstract:Context. Theoretical spectra of X-ray bursting neutron star (NS) model atmospheres are widely used to determine the basic NS parameters such as their masses and radii. Compton Scattering, which plays an important role in spectra formation at high luminosities, is often accounted for using the differential Kompaneets operator, while in other models a more general, integral operator for the Compton Scattering kernel is used. Aims. We construct accurate NS atmosphere models using for the first time an exact treatment of Compton Scattering via the integral relativistic kinetic equation. We also test various approximations to the Compton Scattering redistribution function and compare the results with the previous calculations based on the Kompaneets operator. Methods. We solve the radiation transfer equation together with the hydrostatic equilibrium equation accounting exactly for the radiation pressure by electron Scattering. We use the exact relativistic angle-dependent redistribution function as well as its simple approximate representations. Results. We thus construct a new set of plane-parallel atmosphere models in local thermodynamic equilibrium (LTE) for hot NSs. The models were computed for six chemical compositions (pure H, pure He, solar H/He mix with various heavy elements abundances Z = 1, 0.3, 0.1, and 0.01 Z , and three surface gravities log g = 14.0, 14.3, and 14.6. For each chemical composition and surface gravity, we compute more than 26 model atmospheres with various luminosities relative to the Eddington luminosity LEdd computed for the Thomson cross-section. The maximum relative luminosities L/LEdd reach values of up to 1.1 for high gravity models. The emergent spectra of all models are redshifted and fitted by diluted blackbody spectra in the 3−20 keV energy range appropriate for the RXTE/PCA. We also compute the color correction factors fc. Conclusions. The radiative acceleration grad in our luminous, hot-atmosphere models is significantly smaller than in corresponding models based on the Kompaneets operator, because of the Klein-Nishina reduction of the electron Scattering cross-section, and therefore formally “super-Eddington” model atmospheres do exist. The differences between the new and old model atmospheres are small for L/LEdd < 0.8. For the same grad/g, the new fc are slightly larger (by approximately 1%) than the old values. We also find that the model atmospheres, the emergent spectra, and the color correction factor computed using angle-averaged and approximate Compton Scattering kernels differ from the exact solutions by less than 2%.
Stanley J Brodsky - One of the best experts on this subject based on the ideXlab platform.
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local two photon couplings and the j 0 fixed pole in real and virtual Compton Scattering
2009Co-Authors: Stanley J Brodsky, Felipe J Llanesestrada, Adam P SzczepaniakAbstract:The local coupling of two photons to the fundamental quark currents of a hadron gives an energy-independent contribution to the Compton amplitude proportional to the charge squared of the struck quark, a contribution which has no analog in hadron Scattering reactions. We show that this local contribution has a real phase and is universal, giving the same contribution for real or virtual Compton Scattering for any photon virtuality and skewness at fixed momentum transfer squared t. The t dependence of this J=0 fixed Regge pole is parameterized by a yet unmeasured even charge conjugation form factor of the target nucleon. The t=0 limit gives an important constraint on the dependence of the nucleon mass on the quark mass through the Weisberger relation. We discuss how this 1/x form factor can be extracted from high-energy deeply virtual Compton Scattering and examine predictions given by models of the H generalized parton distribution.
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light cone wavefunction representation of deeply virtual Compton Scattering
2001Co-Authors: Stanley J Brodsky, Markus Diehl, Dae Sung HwangAbstract:Abstract We give a complete representation of virtual Compton Scattering γ ∗ p→γp at large initial photon virtuality Q 2 and small momentum transfer squared t in terms of the light-cone wavefunctions of the target proton. We verify the identities between the skewed parton distributions H(x,ζ,t) and E(x,ζ,t) which appear in deeply virtual Compton Scattering and the corresponding integrands of the Dirac and Pauli form factors F 1 (t) and F 2 (t) and the gravitational form factors A q (t) and B q (t) for each quark and anti-quark constituent. We illustrate the general formalism for the case of deeply virtual Compton Scattering on the quantum fluctuations of a fermion in quantum electrodynamics at one loop.
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light cone wavefunction representation of deeply virtual Compton Scattering
2000Co-Authors: Stanley J Brodsky, Markus Diehl, Dae Sung HwangAbstract:We give a complete representation of virtual Compton Scattering $\gamma^* p \to \gamma p$ at large initial photon virtuality $Q^2$ and small momentum transfer squared $t$ in terms of the light-cone wavefunctions of the target proton. We verify the identities between the skewed parton distributions $H(x,\zeta,t)$ and $E(x,\zeta,t)$ which appear in deeply virtual Compton Scattering and the corresponding integrands of the Dirac and Pauli form factors $F_1(t)$ and $F_2(t)$ and the gravitational form factors $A_{q}(t)$ and $B_{q}(t)$ for each quark and anti-quark constituent. We illustrate the general formalism for the case of deeply virtual Compton Scattering on the quantum fluctuations of a fermion in quantum electrodynamics at one loop.