Abstract
We present an antenna shower formalism including contributions from initial-state partons and corresponding backwards evolution. We give a set of phase-space maps and antenna functions for massless partons which define a complete shower formalism suitable for computing observables with hadronic initial states. We focus on the initial-state components: initial–initial and initial–final antenna configurations. The formalism includes comprehensive possibilities for uncertainty estimates. We report on some preliminary results obtained with an implementation in the Vincia antenna-shower framework.
Highlights
Parton-shower algorithms offer a universal and fully exclusive perturbative resummation framework for high-energy processes
The central point is that an initial-state parton defined at a high factorization scale, QF, can be evolved “backwards”, towards earlier times, to find the parton from which it originated at some low scale, Q0 ∼ 1 GeV. During this evolution, which is governed by the Altarelli-Parisi splitting kernels [3] supplemented by PDF ratios, initial-state radiation is emitted, which in turn gives rise to its own final-state radiation, and Preprint submitted to Physics Letters B
The step will be to interface the hadronization and underlying-event models in Pythia, and compare to experimental studies, such as the one by CDF [27]
Summary
Parton-shower algorithms offer a universal and fully exclusive perturbative resummation framework for high-energy processes. In the context of Monte Carlo event generators [1], they provide the perturbative input for hadronization models As such, they are complementary to more inclusive techniques, such as fixed-order calculations (limited to small numbers of hard and wellseparated partons) and more inclusive resummation approaches (limited to a fixed set of observables). There, initial-state radiation does not rely on backwards evolution Instead, it is treated essentially as final-state radiation off dipoles stretched between the hard process and the beam remnants, and depends on the non-perturbative makeup of the remnants. We present all the ingredients necessary to construct a consistent initial-state shower based on QCD antennæ. A further important ingredient is comprehensive possibilities for uncertainty estimates, in line with the framework for automated theory uncertainties proposed in ref. [15]
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