Complete O(α) QED corrections to the process ep → eX in mixed variables

The complete set of O(α) QED corrections with soft photon exponentiation to the process ep → eX in mixed variables (y = yh, Q2 = Ql2) is calculated in the quark-parton model, including the lepton-quark interference and the quarkonic corrections which were unknown so far. The interference corrections amount to a few percent or less and become negligible at small x. The leading logarithmic terms proportional to ln(Q2mq2) from radiation off quarks are discussed and the non-logarithmic quarkonic corrections are found to be negligible for almost all experimentally accessible x and y.