Emerging Spin and Transverse Momentum Effects in pp and p+A Collisions

While we are measuring large transverse single spin asymmetries in polarized proton-proton collisions at forward rapidities, the mechanisms creating these asymmetries are still not clearly understood. In this workshop we would like to obtain an overview of the status of measurements performed so far and discuss new approaches to improve our understanding. In coordination with the corresponding theorists we would like to review how novel processes such as diffraction, other exclusive measurements and explicit forward jet measurements as well as the connection to proton-nucleus asymmetries can be exploited to understand the origin of these asymmetries. Closely related are new theoretical insights towards the scale dependence of some of the underlying correlation functions and newly suggested correlations in fragmentation which would need to be obtained independently in some other process to provide a viable explanation for the large asymmetries.

Last, at the advent of an electron-ion collider, a discussion of other unique measurements in polarized proton-proton and proton-nucleus collisions is in order. Any remaining measurements could be performed in the early 2020s with dedicated instrumentation in one interaction region at forward and very forward rapidities.

The corresponding topics and sessions are:

1. Hadron + Jet Observables
2. Extraction of TMDs and collinear di-hadron fragmentation
3. TMD evolution
4. Diffractive effects and its relation to resolving the large single transverse spin asymmetries
5. General discussion of remaining p+A physics such as nuclear PDFs (via DY and direct photons) and inclusive pion single spin asymmetries.

Last Modified: October 29, 2021