Eur. Phys. J. C (2007) 51: 867-873
https://doi.org/10.1140/epjc/s10052-007-0342-3

Regular Article - Theoretical Physics

Initial-state parton shower kinematics for NLO event generators

High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba, Ibaraki, 305-0801, Japan

^* e-mail: shigeru.odaka@kek.jp

Received: 1 March 2007
Revised: 22 May 2007
Published online: 1 August 2007

Abstract

We are developing a consistent method to combine tree-level event generators for hadron collision interactions with those including one additional QCD radiation from the initial-state partons, based on the limited leading-log (LLL) subtraction method, aiming at an application to NLO event generators. In this method, a boundary between non-radiative and radiative processes necessarily appears at the factorization scale (μ_F). The radiation effects are simulated using a parton shower (PS) in non-radiative processes. It is therefore crucial in our method to apply a PS which well reproduces the radiation activities evaluated from the matrix-element (ME) calculations for radiative processes. The PS activity depends on the applied kinematics model. In this paper we introduce two models for our simple initial-state leading-log PS: a model similar to the ’old’ PYTHIA-PS and a p_T-prefixed model motivated by ME calculations. PS simulations employing these models are tested using W-boson production at LHC as an example. Both simulations show a smooth matching to the LLL subtracted W+1 jet simulation in the p_T distribution of W bosons, and the summed p_T spectra are stable against a variation of μ_F, despite that the p_T-prefixed PS results in an apparently harder p_T spectrum.