Polarizing the Dipoles

TL;DR

This paper extends the dipole subtraction formalism to include arbitrary helicity states for improved numerical efficiency in NLO calculations, specifically for unpolarized scattering, with implementation in Helac-Phegas.

Contribution

It introduces a helicity-dependent extension of the dipole formalism for unpolarized scattering, enhancing Monte Carlo integration efficiency in NLO computations.

Findings

Extension reduces computational complexity.

Implementation in Helac-Phegas facilitates practical use.

Applicable to LHC background studies.

Abstract

We extend the massless dipole formalism of Catani and Seymour, as well as its massive version as developed by Catani, Dittmaier, Seymour and Trocsanyi, to arbitrary helicity eigenstates of the external partons. We modify the real radiation subtraction terms only, the primary aim being an improved efficiency of the numerical Monte Carlo integration of this contribution as part of a complete next-to-leading order calculation. In consequence, our extension is only applicable to unpolarized scattering. Upon summation over the helicities of the emitter pairs, our formulae trivially reduce to their original form. We implement our extension within the framework of Helac-Phegas, and give some examples of results pertinent to recent studies of backgrounds for the LHC. The code is publicly available. Since the integrated dipole contributions do not require any modifications, we do not discuss them, but they are implemented in the software.