Drell-Yan lepton pair production at low invariant masses: transverse-momentum resummation and non-perturbative effects in QCD

We consider the transverse-momentum (q(T)) distribution of Drell-Yan lepton pairs produced with invariant masses (M) from low values up to the Z-boson peak (4 <= M <= 116 GeV). We present perturbative predictions obtained by consistently combining the resummation of logarithmically enhanced QCD corrections at small q(T) (q(T) << M) up to next-to-next-to-next-to-next-to-leading logarithmic accuracy with the available fixed-order calculations at next-to-next-to-leading order (i.e. O (alpha(3)(S)) valid at large q(T). For very low q(T) (q(T) similar to Lambda(QCD)), non-perturbative (NP) QCD effects become dominant and have been included through a NP form factor with a small number of free-parameters. We compare our results with multiple experimental datasets from hadron colliders, finding excellent agreement between theory and data. By fitting the NP parameters, we achieve a precise extraction of the NP form factor and the so-called Collins-Soper kernel.