Theory seminar - Anjie Gao

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Speaker: Anjie Gao (MIT)

Title: Factorization for TMDs in SIDIS at Subleading Power

Abstract: Since shortly after the discovery of partons people have thought about probing their transverse momentum inside hadrons. For example, in 1978 it was shown to give rise to an azimuthal cos(phi) asymmetry of the outgoing hadrons in the process of semi-inclusive DIS (SIDIS), known as the Cahn effect. Such asymmetry is difficult to study since in QCD it first appears at subleading order in the SIDIS power expansion. Besides the cos(phi) distribution, a number of other asymmetries also show up at this power, including some which probe the spin structure of hadrons. In the literature these observables have traditionally been studied at tree level using the parton model. In this talk I show that the use of effective field theory makes it possible to treat these observables systematically. Utilizing the soft-collinear effective theory formalism we completely determine all possible contributions to any order in perturbation theory. Interestingly, we find that dynamical soft gluon contribution remains simple at this power. We identified that the only new distribution functions are a set of the quark-gluon-quark correlators, which come along with only one new Wilson coefficient. Our final results yield factorization formulae for all subleading power azimuthal asymmetries, establishing these as useful observables within QCD, and enabling higher precision predictions.