Hard Scattering Processes in QCD

Temple University, Philadelphia PA

Investigators

Abstract

Quantum Chromodynamics (QCD) is the microscopic theory of the strong interactions and allows us to understand how hadrons, such as the proton, neutron and pion, are formed through partons, the building blocks of QCD. High-energy scattering processes can be used to explore how partons (quarks and gluons) that come out of a high-energy scattering make a transition into hadrons. While various aspects of these processes are well understood, many striking puzzles remain. Transverse single-spin asymmetries (SSAs) represent one such puzzle. Early QCD calculations predicted basically vanishing effects, but experiments revealed huge SSAs up to 40%. Despite decades of research, the detailed understanding of single-spin asymmetries in QCD is still missing. In this context, this project will explore the role played by the fragmentation of partons for different single-spin asymmetries. Graduate students and postdoctoral fellows will be involved in this very active field at the frontier of current hadronic physics. This project will make possible extensive numerical studies of transverse SSAs for single-hadron production in proton-proton collisions, where one of the incoming protons is polarized perpendicular to the reaction plane. These studies will make use of existing analytical results that were developed previously by the investigator and one of his graduate students. Not only is this investigation expected to clarify if parton fragmentation can indeed explain the huge SSAs observed experimentally, but also whether a simultaneous description of SSAs in hadronic collisions and in lepton-induced processes can be obtained. This project is closely related to experiments conducted at the Thomas Jefferson National Accelerator Facility, the Relativistic Heavy Ion Collider at Brookhaven National Laboratory, and other accelerator facilities worldwide.