Speaker
Cedran Bomhof
(Vrije Universiteit Amsterdam)
Description
The Sivers effect is a possible source for many single spin
asymmetries. The appearance of the Sivers distribution function
is also a testinground for our understanding of universality.
A well-known example of the peculiar universality property of
this function is the relative sign difference of the Sivers
function in SIDIS and Drell-Yan scattering. This opposite sign
is a direct consequence of the initial or final state interactions
that give rise to the future (SIDIS) and past (Drell-Yan) pointing
Wilson lines in the Sivers distribution function. The Wilson lines
are path-ordered exponentials with process-dependent integration
paths in the case of transverse momentum dependent functions. When
going beyond the basic electromagnetic scattering processes these
Wilson lines can become quite complicated structures. In turn,
this observation has consequences on the universality of the
transverse momentum dependent Sivers functions, that are still
today not fully understood. However, the complicated Wilson lines
also have well-defined consequences for the transverse moment of
the Sivers function. In particular, they lead to precise predictions
for certain single-spin asymmetries of which experimental
verification or falsification would test our understanding of the
underlying principles. We will present two such observables,
i.e. specific weighted azimuthal asymmetries in hadronic back-to-back
jet or photon+jet production.
Author
Cedran Bomhof
(Vrije Universiteit Amsterdam)
