Generic User Process Interface for Event Generators
E. Boos, M. Dobbs, W. Giele, I. Hinchliffe, J. Huston, V. Ilyin, J. Kanzaki, K. Kato, Y. Kurihara, L. Lonnblad, M. Mangano, S. Mrenna, F. Paige, E. Richter-Was, M. Seymour, T. Sjostrand, B. Webber, D. Zeppenfeld
TL;DR
Boos et al. present a generic Fortran common-block interface that modularizes event generation by enabling communication between matrix-element generators and shower/hadronization generators. The design introduces two blocks, HEPRUP for run-wide information and HEPEUP for per-event data, and formalizes multiple master weight models (via IDWTUP) with corresponding XWGTUP, XMAXUP, and XSECUP to control subprocess mixing and event unweighting. The interface supports detailed per-particle information (ID, momentum, mass, lifetime, spin, color flow, and history) and provides mechanisms to preserve intermediate resonances during showering, with concrete examples. Implemented in Pythia 6.2 (with dummy UPINIT/UPEVNT routines), the approach aims for flexible interoperability without replacing the standard HEPEVT interface, thereby enabling user-defined processes while maintaining compatibility.
Abstract
Generic Fortran common blocks are presented for use by High Energy Physics event generators for the transfer of event configurations from parton level generators to showering and hadronization event generators.