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Abstract We present a factorization theorem of the partonic Drell-Yan off-diagonal processes g q ¯ qg → γ ∗ + X $$ g\overline{q}(qg)\to {\gamma}^{\ast }+X $$ in the kinematic threshold regime z = Q 2 / s ̂ → 1 $$ z={Q}^2/\hat{s}\to 1 $$ at general subleading powers in the (1 − z) expansion. Focusing on the first order of the expansion (next-to-leading power accuracy with respect to the leading power q q ¯ $$ q\overline{q} $$ channel), we validate the bare factorization formula up to O α s 2 $$ \mathcal{O}\left({\alpha}_s^2\right) $$ . This is achieved by carrying out an explicit calculation of the generalized soft function in d-dimensions using the reduction to master integrals and the differential equations method. The collinear function is a universal object which we compute from an operator matching equation at one-loop level. Next, we integrate the soft and collinear functions over the convolution variables and remove the remaining initial state collinear singularities through PDF renormalization. The resulting expression agrees with the known cross section in the literature.

We present a method of merging the exclusive LO-matched high energy resummation of High Energy Jets (HEJ) with the parton shower of PYTHIA which preserves the accuracy of the LO cross sections and the logarithmic accuracy of both resummation schemes across all of phase space. Predictions produced with this merging prescription are presented with comparisons to data from experimental studies and suggestions are made for further observables and experimental cuts which highlight the importance of both high energy and soft-collinear effects.