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Vanderhaeghen, Marc

Publications and source records attributed to Vanderhaeghen, Marc.

11 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Radiative corrections: from medium to high energy experiments

Abstract Radiative corrections are crucial for modern high-precision physics experiments, and are an area of active research in the experimental and theoretical community. Here we provide an overview of the state of the field of radiative corrections with a focus on several topics: lepton–proton scattering, QED corrections in deep-inelastic scattering, and in radiative light-hadron decays. Particular emphasis is placed on the two-photon exchange, believed to be responsible for the proton form-factor discrepancy, and associated Monte-Carlo codes. We encourage the community to continue developing theoretical techniques to treat radiative corrections, and perform experimental tests of these corrections.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

The proton charge radius

Nucleons (protons and neutrons) are the building blocks of atomic nuclei and are responsible for more than 99% of the visible matter in the Universe. Despite decades of efforts in studying its internal structure, there are still a number of puzzles surrounding the proton such as its spin and charge radius. Accurate knowledge about the proton charge radius is not only essential for understanding how QCD works in the nonperturbative region but also important for bound state QED calculations of atomic energy levels. It also has an impact on the Rydberg constant, one of the most precisely measured fundamental constants in nature. This review examines the latest situation concerning the proton charge radius in light of the new experimental results from both atomic hydrogen spectroscopy and electron-scattering measurements, with particular focus on the latter. Further, theoretical backgrounds and recent developments concerning the determination of the proton charge radius using different experimental techniques are also presented. Upcoming experiments are discussed, and the deuteron charge radius puzzle is mentioned at the end.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Beam normal spin asymmetry for the e p → e Δ ( 1232 ) process

Here, we calculate the single spin asymmetry for the $e p \to e \Delta(1232)$ 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 $\Delta \to \Delta$ as well as $N^\ast \to \Delta$ electromagnetic transitions. We present the general formalism to describe the $e p \to e \Delta$ beam normal spin asymmetry, and provide a numerical estimate of its value using the nucleon, $\Delta(1232)$, $S_{11}(1535)$, 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.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2013

Lamb shift in muonic deuterium

We consider the two-photon exchange contribution to the 2P-2S Lamb shift in muonic deuterium in the framework of forward dispersion relations. The dispersion integrals are evaluated with minimal model dependence using experimental data on elastic deuteron form factors and inelastic electron-deuteron scattering, both in the quasielastic and hadronic range. The subtraction constant that is required to ensure convergence of the dispersion relation for the forward Compton amplitude T{sub 1} (ν,Q{sup 2}) is related to the deuteron magnetic polarizability β(Q{sup 2}) and represents the main source of uncertainty in our analysis. We obtain for the Lamb shift ΔE{sub 2P-2S} = 1.620±0.190 meV and discuss ways to further reduce this uncertainty.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2011

Higher-order proton structure corrections to the Lamb shift in muonic hydrogen

The recent conundrum with the proton charge radius inspires reconsideration of the corrections that enter into determinations of the proton size. We study the two-photon proton-structure corrections, with special consideration of the nonpole subtraction term in the dispersion relation and using fits to modern data to evaluate the energy contributions. We find that individual contributions change more than the total and present results with error estimates.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Soft spectator scattering in the nucleon form factors at large Q{sup 2} within the soft collinear effective theory approach

The proton form factors at large momentum transfer are dominated by two contributions which are associated with the hard and soft rescattering, respectively. Motivated by a very active experimental form factor program at intermediate values of momentum transfers, Q{sup 2}{approx}5-15 GeV{sup 2}, where an understanding in terms of only a hard rescattering mechanism cannot yet be expected, we investigate in this work the soft rescattering contribution using soft collinear effective theory (SCET). Within such a description, the form factor is characterized, besides the hard scale Q{sup 2}, by a hard-collinear scale Q{Lambda}, which arises due to the presence of soft spectators, with virtuality {Lambda}{sup 2} ({Lambda}{approx}0.5 GeV), such that Q{sup 2}>>Q{Lambda}>>{Lambda}{sup 2}. We show that in this case a two-step factorization can be successfully carried out using the SCET approach. In a first step (SCET{sub I}), we perform the leading-order matching of the QCD electromagnetic current onto the relevant SCET{sub I} operators and perform a resummation of large logarithms using renormalization group equations. We then discuss the further matching onto a SCET{sub II} framework, and propose the factorization formula (accurate to leading logarithmic approximation) for the Dirac form factor, accounting for both hard and soft contributions. We also present a qualitative discussion of the phenomenological consequences of this new framework.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Study of two-photon corrections in the pp{yields}e{sup +}e{sup -} process: Hard rescattering mechanism

We investigate the two-photon corrections to the process pp{yields}e{sup +}e{sup -} at large momentum transfer, aimed to access the timelike nucleon form factors. We estimate the two-photon corrections using a hard rescattering mechanism, which has already been used to calculate the corresponding corrections to elastic electron-proton scattering. Using different nucleon distribution amplitudes, we find that the two-photon corrections to the pp{yields}e{sup +}e{sup -} cross sections in the momentum transfer range 5-30 GeV{sup 2} is below the 1% level.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Sum Rules for Light-by-Light Scattering

We derive a set of sum rules for the light-by-light scattering and fusion: {gamma}{gamma}{yields}all, and verify them in lowest order QED calculations. A prominent implication of these sum rules is the superconvergence of the helicity-difference total cross section for photon fusion, which in the hadron sector reveals an intricate cancellation between the pseudoscalar and tensor mesons. An experimental verification of superconvergence of the polarized photon fusion into hadrons is called for, but will only be possible at e{sup +}e{sup -} and {gamma}{gamma} colliders with both beams polarized. We also show how the sum rules can be used to measure various contributions to the low-energy light-by-light scattering.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2010

Electromagnetic moments of quasistable particle

We deal with the problem of assigning electromagnetic moments to a quasistable particle (i.e., a particle with mass located at the particle's decay threshold). In this case, an application of a small external electromagnetic field changes the energy in a nonanalytic way, which makes it difficult to assign definitive moments. On the example of a spin-1/2 field with mass M{sub *} interacting with two fields of masses M and m, we show how a conventionally defined magnetic dipole moment diverges at M{sub *}=M+m. We then show that the conventional definition makes sense only when the values of the applied magnetic field B satisfy |eB|/2M{sub *}<<|M{sub *}-M-m|. We discuss implications of these results to existing studies in electroweak theory, chiral effective-field theory, and lattice QCD.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗