Abstract
Transverse single-spin asymmetries are among the most intriguing observables in hadronic physics. Though such asymmetries were already measured for the first time about four decades ago, their origin is still under debate. Here we consider transverse single-spin asymmetries in semi-inclusive lepton-nucleon scattering, in nucleon-nucleon scattering, and in inclusive lepton-nucleon scattering. It is argued that the single-spin asymmetries for those three processes may be simultaneously described in perturbative QCD, where the re-scattering of the active partons plays a crucial role. A comparison of single-spin asymmetries in different reactions can also shed light on the universality of transverse momentum dependent parton correlation functions. In particular, we discuss what existing data tells us about the predicted process dependence of the Sivers function.
Highlights
The first evidence of a nonzero transverse single-spin asymmetry (SSA) in a hard semi-inclusive process was the observed polarization of neutral Λ-hyperons in the process p Be → Λ↑X at FermiLab.[1]
Transverse SSAs have been studied in semi-inclusive deep-inelastic lepton-nucleon scattering (DIS) by HERMES, COMPASS, and at JLab
A nonzero transverse SSA requires the interference between two amplitudes having a different phase
Summary
The first evidence of a nonzero transverse single-spin asymmetry (SSA) in a hard semi-inclusive process was the observed polarization (up to about 30 %) of neutral Λ-hyperons in the process p Be → Λ↑X at FermiLab.[1]. Two important transverse SSAs in semi-inclusive DIS (the Sivers effect[5] and the Collins effect6) are twist-2 observables Those SSAs can be generated by re-scattering of active partons.[7] In QCD factorization in terms of transverse momentum dependent parton distributions (TMDs), the re-scattering effects render the TMDs gauge invariant and imply a process dependence of certain TMDs.[8] While this underlying picture is very appealing from a theoretical point of view, we want to discuss how it compares with existing data. Before doing so we briefly review some features of TMDs and of the QS function
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callMore From: International Journal of Modern Physics: Conference Series
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
