Proton Spin Structure from Measurable Parton Distributions

Xiangdong Ji, Xiaonu Xiong, and Feng Yuan

Phys. Rev. Lett. 109, 152005 – Published 10 October 2012

Abstract

We present a systematic study of the proton spin structure in terms of measurable parton distributions. For a transversely polarized proton, we derive a polarization sum rule from the leading generalized parton distributions appearing in hard exclusive processes. For a longitudinally polarized proton, we obtain a helicity decomposition from well-known quark and gluon helicity distributions and orbital angular-momentum contributions. The latter are shown to be related to measurable subleading generalized parton distributions and quantum-phase space Wigner distributions.

Received 25 February 2012

DOI:https://doi.org/10.1103/PhysRevLett.109.152005

Authors & Affiliations

Xiangdong Ji^1,2,3, Xiaonu Xiong^2,4, and Feng Yuan⁴

¹Department of Physics, Shanghai Jiao Tong University, and Shanghai Key Lab for Particle Physics and Cosmology, Shanghai 200240, People’s Republic of China
²Center for High-Energy Physics, Peking University, Beijing 100080, People’s Republic of China
³Maryland Center for Fundamental Physics, University of Maryland, College Park, Maryland 20742, USA
⁴Lawrence Berkeley National Laboratory, Nuclear Science Division, Berkeley, California 94720, USA