Abstract
We investigate the effects of keeping the full color structure for parton emissions in parton showers for both LEP and LHC. This is done within the Herwig 7 dipole shower, and includes gluon emission, gluon splitting, initial state branching processes, as well as hadronization. The subleading Nc terms are included as color matrix element corrections to the splitting kernels by evolving an amplitude-level density operator and correcting the radiation pattern for each parton multiplicity, up to a fixed number of full color emissions, after which a standard leading color shower takes over. Our results are compared to data for a wide range of LEP and LHC observables and show that the subleading Nc corrections tend to be small for most observables probing hard, perturbative dynamics, for both LEP and LHC. However, for some of these observables they exceed 10%. On soft physics we find signs of significantly larger effects.
Highlights
We investigate the effects of keeping the full color structure for parton emissions in parton showers for both LEP and LHC
This is done within the Herwig 7.1 [27] implementation of the dipole shower algorithm [28], giving us a full-fledged general purpose event generator which can be used for studying color matrix element corrections to any process occurring at the LHC and other colliders, in practice up to a limited number of colored partons, restricted by the fast growing complexity in color space, still reaching down to relatively soft emissions
We use the Herwig 7.1 dipole shower, with settings according to the 7.1.3 release [27], with the modified weighted Sudakov veto algorithm outlined in section 5, and with color matrix element corrections as described in section 3, starting from lowest order 2 → 2 processes
Summary
This paper is based on dipole factorization, stating that whenever the gluon to be emitted from an n-parton configuration becomes either soft or collinear to one of the existing partons, the squared amplitude for the n+1-parton case can be approximated with. In the limit where z is small, it is rather the parton with momentum fraction z which is soft and should be seen as radiated and be inserted between the emitter (with the large momentum fraction 1 − z) and the spectator. The initial state emission cases are treated in a standard backward evolution scheme, meaning that if the emitter is an initial state parton, the backward evolution is done by folding in the parton distribution functions (PDFs), using appropriate splitting kernels, and colors are updated as if the resulting (low energy) parton was emitted. To be more precise, denoting the emitter participating in the hard process by i, the radiated parton with j, and the (initial) parton going into the PDF by ij, the used splitting kernel is Pij→ij, and the emission probability is evolved using PDF ratios [35], as described in section 6.5 in [2].
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
