Abstract
Parton shower event generators typically approximate evolution of QCD color so that only contributions that are leading in the limit of an infinite number of colors are retained. Our parton shower generator, Deductor, has used an "LC+" approximation that is better, but still quite limited. In this paper, we introduce a new scheme for color in which the approximations can be systematically improved. That is, one can choose the theoretical accuracy level, but the accuracy level that is practical is limited by the computer resources available.
Highlights
Parton shower event generators for hadron collisions, such as HERWIG [1], PYTHIA [2], and SHERPA [3], are essential for the analysis of experiments at the Large Hadron Collider. They treat QCD color in the leading color (LC) approximation, that is at leading order in an expansion in powers of 1=N2c, where Nc 1⁄4 3 is the number of colors
Previous versions of our parton shower generator, DEDUCTOR [4,5,6,7,8,9,10,11,12,13], use what we call the LC+ approximation [7], which includes some terms suppressed by powers of 1=N2c
This paper concerns improvements in the color treatment in DEDUCTOR that could be applicable to other parton shower generators
Summary
Parton shower event generators for hadron collisions, such as HERWIG [1], PYTHIA [2], and SHERPA [3], are essential for the analysis of experiments at the Large Hadron Collider. One can define an evolution equation for a parton shower with leading order splitting functions such that the evolution is exact in color. This is relatively straightforward [4],. We use the color density operator as the basis for parton shower evolution We note that it is sometimes used explicitly for analytical summations of large logarithms [19,20,21,22]. There is, for instance, a certain choice for the number of partons and their momenta We find it useful to use a notation in which linear operators act on vectors jρÞ in the statistical space.
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