Project description

This project is devoted to the study of contributions to scattering processes that are formally of subleading power in the hard scale. The importance of going beyond the leading power accuracy is widely recognized. One reason is that such contributions constrain the ultimate accuracy of QCD description based on leading-power (leading-twist) factorization theorems. They need to be understood for the theory to match the very high data accuracy expected at the experimental facilities of the next generation. This concerns especially exclusive and semi-inclusive reactions at the heart of the physics programs of the EIC and JLAB12, where the bulk of data is and will be concentrated at moderate momentum transfers. Another reason is that higher-twist contributions actually become unsuppressed in certain regions of phase space. A prime example is provided by multiparton scattering processes in hadron-hadron collisions. As their importance grows with the collision energy, they are of considerable interest at the LHC (and even more so at possible future hadron colliders).

We continue the study of power suppressed contributions to hard reactions along the lines outlined in the original proposal. The main difference is that the subproject P3b is not renewed: the research on power corrections in the TMD factorization framework will be continued with minimal DFG support (Mercator Fellowship for Dr. Vladimirov, who is moving from Regensburg to Madrid). The subproject P3c is, on the contrary, considerably extended by adding a broad study program of twist-three GPDs. The general direction will be a transition from formal developments to applications and impact studies.