A new approach to multi-jet calculations in hadron collisions
F. Caravaglios, M. L. Mangano, M. Moretti, R. Pittau
TL;DR
The paper introduces the ALPHA algorithm to compute exact tree-level multi-jet QCD amplitudes with improved scaling, addressing the challenge of generating multi-parton final states for hadron collisions. It demonstrates a framework to sum over colour configurations and couple matrix-element calculations to parton-shower evolution, enabling fully exclusive hadron-level descriptions of multi-jet final states. Tests show feasibility for 2→n parton processes with up to n=9 final-state partons and provide results for eight-parton final states, highlighting the method's potential for accurate background modeling and new-physics signatures. The work lays groundwork for future fully interfaced event generators and targeted optimizations in QCD color and Lorentz structure.
Abstract
We present an algorithm to evaluate the exact, tree-level matrix elements for multi-parton processes in QCD. We tested this technique, based on the recursive evaluation of the S-matrix, on processes such as gg -> n gluons and q qbar -> n gluons, with n up to 9. The summation over colour configurations is designed to allow the construction of parton-level event generators suitable to interfacing with a parton-shower evolution including the effects of colour-coherence. This leads to a fully exclusive, hadron-level description of multi-jet final states, accurately incorporating the dynamics of large jet-jet separation angles. Explicit results for the total rates and differential distributions of processes with 8 final-state partons are given.