Jun 2 – 7, 2019
Carnegie Mellon University
America/New_York timezone

Probing the nucleon spin structure at RHIC using the Electro-weak interaction

Jun 3, 2019, 11:45 AM
McConomy Auditorium (CMU Cohen University Center)

McConomy Auditorium

CMU Cohen University Center

Invited Few Body Systems MENU-2019 Plenary


Ralf Seidl (RIKEN)


Only a short time after the discovery of the massive bosons of the elctro-weak interaction, they can be used as tool in the study of the nucleon structure at RHIC energies. In particular the maximal parity violation makes W boson production interesting as W bosons only couple to left-handed quarks and right-handed anti-quarks. The W boson production therefore selects the helicity in longitudinally polarized proton-proton collisions. In addition, the charge of the W determines the dominant quark and anti-quark flavors (up and dbar for W+, d and ubar for W^-). The RHIC experiments PHENIX and STAR have successfully used single spin asymmetries of W decay leptons to access the polarized light sea at a very high scale and without the added uncertainties of fragmentation functions. The results strongly indicate an asymmetric polarized light sea of opposite sign to the unpolarized light sea which rules out simple pion-cloud models.
When fully reconstructing Ws or Zs, the STAR experiment managed to measure single transverse spin asymmetries related to the Sivers effect. First results slightly favor a sign change of the Sivers function with respect to semi-inclusive DIS measurements in accordance with theory predictions.
Last, electro-weak boson production also provides information about the unpolarized nucleon structure, again particularly light sea quarks, at higher fractional energies than what is typically probed at the LHC.
An overview over these RHIC measurements will be presented.

Graduate Student No
Early Consideration No

Primary author

Ralf Seidl (RIKEN)

Presentation materials