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Vladyslav Pauk

Publications and source records attributed to Vladyslav Pauk.

10 recordsLinked to original sources
arXiv2020

Low energy doubly-virtual Compton scattering from di-lepton electroproduction on a nucleon

We propose a new way to experimentally determine the subleading low-energy structure constant of doubly-virtual Compton scattering on a proton. Such empirical determination will reduce the theoretical model error in estimates of the hadronic correction to the muonic hydrogen Lamb shift. We demonstrate that the di-lepton forward-backward asymmetry in the $e^- p \to e^- p \, e^- e^+$ process, which can be accessed at electron scattering facilities, yields a large sensitivity to this so far unknown low-energy constant.

hep-ph↗
arXiv2018

Dilepton photoproduction on a deuteron target

We investigate the sensitivity of the cross section for lepton pair production off a deuteron target, $γd \to l^+ l^- d$, to the deuteron charge radius. We show that for small momentum transfers the Bethe-Heitler process dominates, and that it is sensitive to the charge radius such that a cross section ratio measurement of about $0.1 \%$ relative accuracy could give a deuteron charge radius more accurate that the current electron scattering value and sufficiently accurate to distinguish between the electronic and muonic atomic values.

hep-ph↗
arXiv2017

Beam normal spin asymmetry for the $e p \to e Δ(1232)$ process

We calculate the single spin asymmetry for the $e p \to e Δ(1232)$ process, for an electron beam polarized normal to the scattering plane. Such single spin asymmetries vanish in the one-photon exchange approximation, and are directly proportional to the absorptive part of a two-photon exchange amplitude. As the intermediate state in such two-photon exchange process is on its mass shell, the asymmetry allows one to access for the first time the on-shell $Δ\to Δ$ as well as $N^\ast \to Δ$ electromagnetic transitions. We present the general formalism to describe the $e p \to e Δ$ beam normal spin asymmetry, and provide a numerical estimate of its value using the nucleon, $Δ(1232)$, $S_{11}(1535)$, and $D_{13}(1520)$ intermediate states. We compare our results with the first data from the Qweak@JLab experiment and give predictions for the A4@MAMI experiment.

hep-ph↗
arXiv2015

Lepton universality test in the photoproduction of $e^- e^+$ versus $μ^- μ^+$ pairs on a proton target

In view of the significantly different proton charge radius extracted from muonic hydrogen Lamb shift measurements as compared to electronic hydrogen spectroscopy or electron scattering experiments, we study in this work the photoproduction of a lepton pair on a proton target in the limit of very small momentum transfer as a way to provide a test of the lepton universality when extracting the proton charge form factor. By detecting the recoiling proton in the $γp \to l^- l^+ p$ reaction, we show that a measurement of a ratio of $e^-e^+ + μ^-μ^+$ over $e^-e^+$ cross sections with a relative precision of around 2%, would allow for a test to distinguish between the two different proton charge radii currently extracted from muonic and electronic observables.

hep-ph↗
arXiv2014

Two-loop massive scalar three-point function in a dispersive approach

We present a dispersion relation formalism to calculate a massive scalar two-loop vertex function. Such calculation is of direct relevance in the evaluation of the hadronic light-by-light contribution to the muon's anomalous magnetic moment due to meson poles. The discontinuity of the two-loop diagram is obtained by a sum of two- and three-particle cut contributions, which involve a phase space integration over the physical intermediate states. The real part of the vertex function is subsequently reconstructed through evaluation of a dispersion integral. We explicitly demonstrate that the dispersive formalism yields exactly the same result as the direct two-loop calculation.

hep-ph↗
arXiv2014

Anomalous magnetic moment of the muon in a dispersive approach

We present a new general dispersive formalism for evaluating the hadronic light-by-light scattering contribution to the anomalous magnetic moment of the muon. In the suggested approach, this correction is related to the imaginary part of the muon's electromagnetic vertex function. The latter may be directly related to measurable hadronic processes by means of unitarity and analyticity. As a test we apply the introduced formalism to the case of meson pole exchanges and find agreement with the direct two-loop calculation.

hep-ph↗
arXiv2014

Single meson contributions to the muon's anomalous magnetic moment

We develop the formalism to provide an improved estimate for the hadronic light-by-light correction to the muon's anomalous magnetic moment a_μ, by considering single meson contributions beyond the leading pseudo-scalar mesons. We incorporate available experimental input as well as constraints from light-by-light scattering sum rules to estimate the effects of axial-vector, scalar, and tensor mesons. We give numerical evaluations for the hadronic light-by-light contribution of these states to a_μ. The presented formalism allows to further improve on these estimates, once new data for such meson states will become available.

hep-ph↗
arXiv2012

Light-by-light scattering sum rules constraining meson transition form factors

Relating the forward light-by-light scattering to energy weighted integrals of the γ* γ-fusion cross sections, with one real photon (γ) and one virtual photon (γ*), we find two new exact super-convergence relations. They complement the known super-convergence relation based on the extension of the GDH sum rule to the light-light system. We also find a set of sum rules for the low-energy photon-photon interaction. All of the new relations are verified here exactly at leading order in scalar and spinor QED. The super-convergence relations, applied to the γ* γ-production of mesons, lead to intricate relations between the γγ-decay widths or the γ* γ-transition form factors for (pseudo-) scalar, axial-vector and tensor mesons. We discuss the phenomenological implications of these results for mesons in both the light-quark sector and the charm-quark sector.

hep-ph↗