[Paper Review] Radiative effects in scattering of polarized leptons by polarized nucleons and light nuclei

Igor Akushevich, A. Ilyichev+1 more|ArXiv.org|Jun 18, 2001

Dark Matter and Cosmic Phenomena1 references3 citations

TL;DR

This paper presents a comprehensive framework for calculating radiative corrections (QED, electroweak, and QCD) in polarized lepton-nucleon and lepton-light nucleus scattering using the Bardin-Shumeiko approach. It derives explicit covariant formulae for inclusive, semi-inclusive, diffractive, and elastic processes, enabling precise data analysis through FORTRAN codes like POLRAD 2.0, RADGEN, DIFFRAD, and MASCARAD, which are validated in experiments at CERN, DESY, SLAC, and TJNAF, showing that asymmetry corrections are small despite large cross-section corrections due to cancellation of leading logarithmic terms.

ABSTRACT

Recent developments in the field of radiative effects in polarized lepton-nuclear scattering are reviewed. The processes of inclusive, semi-inclusive, diffractive and elastic scattering are considered. The explicit formulae obtained within the covariant approach are discussed. FORTRAN codes POLRAD, RADGEN, HAPRAD, DIFFRAD and MASCARAD created on the basis of the formulae are briefly described. Applications for data analysis of the current experiments on lepton-nuclear scattering at CERN, DESY, SLAC and TJNAF are illustrated by numerical results.

Motivation & Objective

• To address the challenge of extracting one-photon exchange contributions from experimental data in high-precision lepton-nucleon scattering by correcting for radiative effects.
• To develop model-independent QED radiative corrections without artificial parameters, using the Bardin-Shumeiko approach to handle infrared divergences.
• To extend radiative correction calculations to polarized processes, including inclusive, semi-inclusive, diffractive, and elastic scattering, with applications to spin asymmetries and structure functions.
• To create and validate FORTRAN codes—POLRAD 2.0, RADGEN, DIFFRAD, MASCARAD—for real-time data processing in current and future experiments at major facilities.
• To estimate higher-order corrections (LO and NLO) and electroweak effects in deep inelastic scattering, particularly near kinematic boundaries where Z-boson exchange becomes significant.

Proposed method

• Uses the Bardin-Shumeiko formalism to compute QED radiative corrections without introducing an artificial soft-hard cutoff, thereby avoiding numerical instabilities.
• Derives explicit covariant expressions for radiative corrections to both lepton and hadronic currents in deep inelastic scattering (DIS), including spin-dependent and spin-averaged cross sections.
• Applies the structure function method and Compton tensor formalism to compute corrections for unpolarized and polarized fermions, including heavy photon contributions.
• Constructs FORTRAN codes—POLRAD 2.0, RADGEN, DIFFRAD, MASCARAD—based on derived formulae to simulate radiative effects and perform iterative radiative correction procedures in experimental data analysis.
• Incorporates electroweak corrections within the on-mass-shell scheme and t’Hooft-Feynman gauge, with results applicable to high-Q² kinematics where Z-exchange effects are non-negligible.
• Employs iterative data processing to extract Born-level observables by correcting for radiative backgrounds, using relative corrections defined via σ_obs = (1+δ)σ₀ + σ_R.

Experimental results

Research questions

• RQ1 How can radiative corrections in polarized lepton-nucleon scattering be calculated without introducing artificial cutoffs for soft and hard photon emissions?
• RQ2 What is the impact of radiative corrections on spin asymmetries in inclusive and semi-inclusive deep inelastic scattering, especially when leading logarithmic terms cancel?
• RQ3 How do electroweak corrections, particularly Z-boson exchange, affect observables in high-Q² kinematic regions of lepton-nucleon scattering?
• RQ4 To what extent do hard-photon bremsstrahlung contributions differ between spin-averaged and spin-dependent cross sections in elastic and diffractive processes?
• RQ5 How can FORTRAN-based codes like POLRAD and RADGEN be used to simulate and correct for radiative effects in real experimental data from CERN, DESY, SLAC, and TJNAF?

Key findings

• Radiative corrections to the unpolarized cross section can be large due to leading logarithmic contributions, but corrections to the asymmetry are significantly smaller due to cancellation of δ in the numerator.
• For longitudinal polarization asymmetries, δ_p > δ_u leads to positive radiative corrections; for transverse asymmetries, the opposite behavior is observed, indicating different correction structures.
• The FORTRAN code POLRAD 2.0 enables complete radiative correction procedures for inclusive and semi-inclusive experiments, with validation through numerical results at SLAC and TJNAF.
• The Monte Carlo generator RADGEN 1.0, derived from POLRAD 2.0, allows event-by-event simulation of radiative effects in inclusive DIS, supporting data analysis at high-precision experiments.
• Codes DIFFRAD and MASCARAD successfully compute radiative corrections for diffractive vector meson electroproduction and elastic ep scattering, respectively, with applications confirmed in experimental data at DESY and TJNAF.
• Electroweak corrections are found to be non-negligible at high Q², particularly near kinematic edges, justifying their inclusion in precision analyses using the on-mass-shell scheme.