SHERPA Interface First Presentation

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SHERPA Interface First Presentation

• Martin Niegel
• Karlsruhe Institute of Technology
• Altan Cakir
• Karlsruhe Institute of Technology
• Markus Merschmeyer
• RWTH Aachen

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SHERPA Event Generator

• SHERPA Event Generator (Simulation for
  High-Energy Reactions of PArticles) F.Krauss et
  al., JHEP02(2004)056
• Multi-purpose event generator written in C
• Offers modularity to divide event into different
  stages, seperated by different scales, i.e.
• - Matrix-element generation by AMEGIC
• - Parton shower by APACIC
• Hadronisation is still Pythia interfaced, but
  will be replaced
• Multiple interactions by AMISIC
• Etc.
• ME PS matching by CKKW (details talk of Altan
  Cakir)

Available models SM, MSSM, ADD
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SHERPA Event Generation
Event generation is divided into 3 steps
Step 1 Feynman diagrams are calculated and
translated into helicity amplitudes, also
suitable phase-space mappings are produced and
stored in library files
All datacards (.dat) are required to be located
in a generic directory. The calculated library
files are stored in a directory Process inside.
Step 2 Libraries are compiled and linked
The makelibs script hast to be executed inside
the generic directory. The compiled libs are
stored in a directory libs inside Process
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SHERPA Event Generation
Step 3 Cross sections are evaluated and events
are generated

• The datacards and a Process directory containing
  library files and libraries are required in order
  to generate events.
• The cross sections are stored in a directory
  Result and can be used for further event
  generation.
• SHERPA provides a HepMC interface in order to
  generate events as a HepMCGenEvent object,
  which can be used in CMSSW.

SherpaInterface performs step 3, i.e. use
precompiled libs and (optional) evaluated cross
sections
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SherpaInterface

• The SherpaInterface provides
• the use of precompiled libs and (optional)
  preevaluated cross sections of available
  processes
• the option to adapt the datacard parameters
  inside the CMSSW configfile
• scripts to generate own process libraries and
  convert the associated datacards to ParameterSets
  of CMSSW configfile language

• The SherpaInterface does not provide
• a solution to generate events from scratch in a
  single CMSSW run

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What is required to generate events?

• SherpaInterface requires
• Run directory defaultSherpaRun (can be changed
  in configfile) which must contain the process
  libs (optional xs).

• cfi-file with datacard parameters

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What happens during cmsRun?

• Datacard parameters are extracted from cfi-file
  and stored in dat-files in SherpaRun directory
• SHERPA generates HepMCGenEvents using
  information of cards, libraries and (optional)
  cross sections
• If cross sections are missing or xs-related
  parameters are changed, the cross section will be
  recalculated

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Datacard Parameters
Sherpa datacard parameters inside cfi-file are
splitted in different ParameterSets (motivated by
Sherpa datacard structure) Beam, Fragmentation,
Hadron, Integration, ISR, Lund, ME, MICuts, MI,
Model, Particle, Processes, Run, Selector, Shower
Changes in ParameterSet Selector (phase-space
related parameters e.g. ptJet,Minv,etc.) affect
the cross section. This yields a cross section
reevaluation during CMSSW runtime.
(time-consuming for certain processes) Changes of
parameters affect the ME calculation. The libs
have to be recalculated and recompiled. This
yields a CMSSW crash! All other parameters can be
changed.
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Workflow with precompiled libs

• precompiled libs and cross sections for certain
  processes are available as archives at CASTOR
• sherpa_process.cfi cfi-file with all parameters
• sherpa_process_libs.tgz Process directory with
  libs
• sherpa_process_crss.tgz Result directory with
  cross section

The Process and Result directory have to be
stored in the SherpaRun directory and the
cfi-file has to be included in the
cfg-file include "GeneratorInterface/SherpaInterf
ace/test/process.cfi"
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Generation of private libraries

• You need
• SHERPA installation (with LHAPDF, HepMC2)
• SHERPA datacards in a tarball
  sherpa_yourprocess_cards.tgz
• The MakeSherpaLibs.sh script
• You do
• MakeSherpaLibs.sh -r your path to SHERPA -p
  yourprocess and wait (sometimes rather long)?
• You get
• sherpa_yourprocess_libs.tgz
• sherpa_yourprocess_crss.tgz
• sherpa_yourprocess.cfi (PrepareSherpaLibs.sh)
• and the zipped log files from SHERPA

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Status

• Yet the SherpaInterface is not in a CMSSW
  release.
• SherpaInterface_setup.sh script available
• Local installation of SHERPA_1.0.11
• SHERPA is linked to CMSSW external tools LHAPDF
  and HepMC
• SHERPA is registered in CMSSW
• The SherpaInterface is installed and registered
  in CMSSW

• Twiki page available
• https//twiki.cern.ch/twiki/bin/view/CMS/SherpaInt
  erface
• SherpaInterface is working for gt CMSSW_1_6_0
• Fast Simulation test runs succeeded for 1_6_8
  ,1_8_0

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Problems

• Time-consuming e.g. WNjets
  24h 0-31-2d 0-4gt4d
• Size of libs e.g. WNjets
  2110MB 0-3200MB 0-4gt1GB
• Zipping of libs gain 50 in size
• Experience Z4jets, ZW4jets, ttbar4jets crash
  due to memory leak, but in principle it should
  work
• SherpaInterface runs fine on any 'lxplus' machine
  but fails when using CRAB (-gt unknown
  exception...)?
• no inclusive SUSY events possible with SHERPA at
  present, every single channel has to be specified
• SHERPA output Intermediate state particles
  (vectorbosons) are NOT stored in the generator
  output!

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Outlook

• SHERPA
• faster generation of SHERPA libs using a local
  grid cluster
• next major SHERPA release will hopefully bring
• more efficient methods for 2-gtN (Ngt5) processes
• possibility of inclusive SUSY events
• valid HepMC2-ASCII ouput for usage with
  'MCFileSource' (IOMC/Input), useful for
  small-scale test productions
• SherpaInterface
• Request SHERPA to be integrated in CMSSW as an
  external package
• Provide more SHERPA processes as precompiled libs
• Get SherpaInterface inside CMSSW release

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SHERPA Contact Persons

• SHERPA Contact Persons
• Markus Merschmeyer (RWTH Aachen)
• Altan Cakir (Karlsruhe Institute of
  Technology)
• Martin Niegel (Karlsruhe Institute of Technology)
• We acknowledge the help of S.Schumann, S. Höche,
  F. Siegert and F. Krauss (IPPP, Durham)

• Questions
• What is required to make the SherpaInterface an
  official CMSSW tool?
• Where to store the precompiled libs ? (Yet
  CASTOR)
• Who will be responsible for production of libs ?