Multiparton interactions and higher-twist effects

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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). The subject of higher twist effects is very diverse and covers a large variety of processes and methods. In the second funding period, we concentrate on the study of double parton distributions and on higher-twist corrections to the deeply-virtual Compton scattering. The studies in this project complement the calculation of higher-order perturbative corrections in projects P1, P2 and P4 with the goal to achieve highest possible precision for benchmark observables.