Study of the sign change of the Sivers function from STAR collaboration W/Z production data

Here, recent data on the transverse single spin asymmetry $$A_N$$ measured by the STAR Collaboration for $$p ↑\, p \to W^\pm/Z^0 \, X$$ reactions at RHIC allow the first investigation of the Sivers function in Drell-Yan processes and of its expected sign change with respect to SIDIS processes. A critical assessment of the significance of the data is attempted.