Parton Showers beyond the Leading Order: a Factorization Approach *

نویسنده

  • F Hautmann
چکیده

We discuss recent work on methods for incorporating nonleading QCD corrections in parton shower algorithms. Parton shower Monte Carlo event generators are the main practical tool to describe multi-particle final states in high energy collisions. These event generators couple a leading-order (LO) hard scattering to a showering, treated basically in the leading logarithm approximation. Many nonleading effects are also included in these event generators: for instance, through the exact multi-parton kinematics; through the angular ordering of gluon emission; through optimal choices of the renormal-ization scale in the running coupling. In some cases there are also treatments (see, e.g., refs. 1,2,3,4) to approximately include next-to-leading-order (NLO) corrections to the hard scattering. Nevertheless, there is as yet no method for going beyond the leading approximation systematically. This implies that event generators cannot incorporate fully the known NLO (and NNLO) calculations of hard-scattering cross sections. Recent papers 5,6,7 have started to investigate systematic subtractive methods as a way to tackle this problem. This talk describes some of the work in this direction. To discuss this, let us schematically represent the cross section in an event generator as σ[W ] = final states X W (X) PS ⊗ ˆ H. (1) Here W is a weight function that specifies the definition of the particular cross section under consideration. The symbol PS denotes the parton shower and the symbol ⊗ denotes its action on the initial and final partons in the hard scattering, whose cross section is denoted byˆH. In a standard Monte Carlo, the hard scattering is taken to the leading order, H (LO) , and PS denotes showering from the partons in H

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تاریخ انتشار 2000