(r8) AlpgenRestructuringORDERBY1--AHji < Main

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---++ Introduction

   The !AlpgenInterface is undergoing a complete restructuring, according to the [[http://indico.cern.ch/conferenceDisplay.py?confId=35613][new guidelines for GeneratorInterfaces]].
This page documents this restructuring

---++ New Features

---++ Validation
   * What with using the SLHA mass line? Is this doing something bad?

   * W + jets
      * Basic mother-daughter relations validation.
   * Z + jets
      * Basic mother-daughter relations validation.
      * Basic INORAD validation.
         * Why do we get the complete event record seen by UPVETO?
   * ttbar + jets
      * Basic mother daughter relations validation.
      * Why is it freezing? Why does it stop freezing when I use !FourVectors instead of doing calculations manually.
      * Always bitten by FORTRAN/C-style array differences.

---+++ Issues
   * The PYUPRE subroutine:
<verbatim>
C...PYUPRE
C...Rearranges contents of the HEPEUP commonblock so that
C...mothers precede daughters and daughters of a decay are
C...listed consecutively.
</verbatim>
   In standalone Pythia, a call to UPEVNT is always followed by a call to PYUPRE. In order to mimic that behavior, we do the same in !AlpgenInterface.
   * What is the "phantom event" at the beginning of DBPART?
      * Solved: it was an extra call of DBPART in a wrong place. 
   *  How to make sure the PDF sets are chosen consistently in ALPGEN and PYTHIA?
   * What ALPGEN uses for the jet clustering is the HEPEVT common block, NOT the HEPEUP.

---++ FORTRAN routines

Here we describe the FORTRAN routines responsible for the matching in standalone matching.

---+++ UPINIT routine
   * I/O
   * Call ALSHCD - returns "PYT"
   * I/O
      * Read until "****"
      * Read IHRD
      * Read six masses (mc, mb, mt, mw, mz, mh)
      * Read key-value pairs (PARVAL[NTMP] array)
      * Read until "****"
      * Read xsec, xsec_error, number of unw events, luminosity
   * Call AHSPAR to setup parameters - this sets EBEAM.
      * This sets every parameter except IHRD, the masses and the jet clustering parameters.
   * PBEAM1=DBLE(EBEAM),  PBEAM2=DBLE(EBEAM), IH1=1 --> these are tramp variables to set up HEPRUP later.
   * Call PDFCONVH (what does it do?)
   * Call ALSHCD
   * Prepares INORAD
   * Gets jet matching criteria
   * Sets up the HEPRUP
   * Calls ALSHIN (passes the six masses to PYTHIA)
   * Sets LPRUP (originally it was 661, now it has a meaning).

   * [[%ATTACHURL%/UPINIT.odg][UPINIT.odg]]: UPINIT

---+++ UPVETO routine

-- Main.ThiagoTomei - 24 Feb 2009