title: Single Spin Asymmetries from a Single Wilson Loop.
abstract: We study the leading-power gluon transverse-momentum-dependent distributions (TMDs) of relevance to the study of asymmetries in the scattering off transversely polarized hadrons. Next-to-leading-order perturbative calculations of these TMDs show that at large transverse momentum they have common dynamical origins but that in the limit of a small longitudinal momentum fraction x, only one origin remains. We find that in this limit, only the dipole-type gluon TMDs survive and become identical to each other. At small x, they are all given by the expectation value of a single Wilson loop inside the transversely polarized hadron, the so-called spin-dependent odderon. This universal origin of transverse spin asymmetries at small x is of importance to current and future experimental studies, paving the way to a better understanding of the role of gluons in the three-dimensional structure of spin-polarized protons.
authors.affiliation: Van Swinderen Institute for Particle Physics and Gravity, University of Groningen, Nijenborgh 4, 9747 AG Groningen, Netherlands.
authors.forename: Daniël
authors.initials: D
authors.lastname: Boer
authors.affiliation: Nikhef and Department of Physics and Astronomy, VU Amsterdam, De Boelelaan 1081, NL-1081 HV Amsterdam, The Netherlands.
authors.forename: Miguel G
authors.initials: MG
authors.lastname: Echevarria
authors.affiliation: Nikhef and Department of Physics and Astronomy, VU Amsterdam, De Boelelaan 1081, NL-1081 HV Amsterdam, The Netherlands.
authors.forename: Piet J
authors.initials: PJ
authors.lastname: Mulders
authors.affiliation: Nikhef and Department of Physics and Astronomy, VU Amsterdam, De Boelelaan 1081, NL-1081 HV Amsterdam, The Netherlands.|School of physics, and Key Laboratory of Particle Physics and Particle Irradiation (MOE), Shandong University, Jinan, Shandong 250100, People's Republic of China.
authors.forename: Jian
authors.initials: J
authors.lastname: Zhou