Constraining the pion distribution amplitude using Drell-Yan reactions on a proton

Abstract

Using a reaction model that incorporates pion bound state effects and continuum results for proton parton distributions and the pion distribution amplitude, φπ, we deliver parameter-free predictions for the μ+ angular distributions in πN→μ+μ−X reactions on both unpolarised and polarised targets. The analysis indicates that such angular distributions are sensitive to the pointwise form of φπ and suggests that unpolarised targets are practically more favourable. The precision of extant data is insufficient for use in charting φπ; hence, practical tests of this approach to charting φπ must await data with improved precision from new-generation experiments. The reaction model yields a nonzero single-spin azimuthal asymmetry, without reference to T-odd parton distribution functions (DFs). This may necessitate additional care when attempting to extract such T-odd DFs from data.

Keywords

• Continuum Schwinger function methods
• Drell-Yan process
• Dyson-Schwinger equations
• Emergence of mass
• Pion structure
• Quantum chromodynamics