Speaker
John Collins
(Penn State University)
Description
In using transverse-momentum-dependent (TMD) parton densities and
fragmentation functions, important non-perturbative information is at
large transverse position $b_T$. This concerns both the TMD functions
and their evolution. Fits to high energy data tend to predict too
rapid evolution when extrapolated to low energies where larger values
of $b_T$ dominate. I summarize a new analysis of the issues. It
results in a proposal for much weaker $b_T$ dependence at large $b_T$
for the evolution kernel, while preserving the accuracy of the
existing fits. The results are particularly important for using
transverse-spin-dependent functions like the Sivers function.
Author
John Collins
(Penn State University)
