Abstract
The QCD evolution of transverse momentum dependent (TMD) distribution functions has recently been formulated in a parton branching (PB) formalism. In this approach, soft-gluon coherence effects are taken into account by introducing the soft-gluon resolution scale and exploiting the relation between transverse-momentum recoils and branching scales. In this work we investigate the implications of dynamical, i.e., branching scale dependent, resolution scales. We present both analytical studies and numerical solution of PB evolution equations in the presence of dynamical resolution scales. We use this to compare PB results with other approaches in the literature, and to analyze predictions for transverse momentum distributions in Z-boson production at the Large Hadron Collider (LHC).
Highlights
Theoretical predictions for precision physics at high-energy hadron colliders require methods for QCD resummations [1] to all orders in the strong coupling
We present an application of our formalism to the Z-boson transverse momentum distribution in Drell-Yan (DY) production [17] at the Large Hadron Collider (LHC), and study its sensitivity to dynamical resolution scales at low transverse momenta
In the case of integrating over all k⊥ (Fig. 6(right)) we note that MRW-CT10nlo gives rise to a much higher distribution than all other curves, implying that the MRW-CT10nlo high-k⊥ tail has a significant impact at integrated level for most values of x
Summary
Theoretical predictions for precision physics at high-energy hadron colliders require methods for QCD resummations [1] to all orders in the strong coupling. The method is based on the unitarity picture of parton evolution [5,6], and takes into account color coherence of soft-gluon radiation [7,8,9,10] and transverse momentum recoils. Because the transverse momentum generated radiatively in the branching is sensitive to the treatment of the non-resolvable region [11], a supplementary condition is needed to relate the transverse momentum recoil and the scale of the branching This relation embodies the well-known property of angular ordering, and implies that the soft-gluon resolution scale can be dynamical, i.e., dependent on the branching scale.
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