Paolo Bartalini (University of Florida)

1. Introduction to the October LCG GENERATOR Meeting(dedicated to Monte Carlo Validation at the LHC) Paolo Bartalini (University of Florida)

2. Mandate(s) of LCG Generator • Library of Generator Services (WP1/WP2) • Quarterly GENSER releases • Forthcoming release of GENSER 1.2.0  (Alexander’s talk) • Contribution to the development of OO MC (WP1/WP2) • Herwig++/ThePEG, Pythia 8, EvtGen, etc. • Monte Carlo Validation (WP4) • Validation of MC packages in GENSER  Alexander’s talk • Specific collaborations • NRQCD in Pythia 6.3  Marianne’s talk • HIJING on RHIC data  Vladimir’s talk • Permanent Forum on Software & Physics Validation • Allows LHC collaborations to exchange MC validation experiences • Ex. CMS and ATLAS talks on ALPGEN validation • LCG Generator Meetings: Last working Thursday of each month • Public MC event files for x-checks, benchmarks etc. (WP3) • LCG MCDB technically ready: http://mcdb.cern.ch • Allows LCG collaborations to share MC samples • End of the years LCG MCDB presentations to LHC collaborations P.Bartalini (University of Florida)

3. “Default” Parameters in Monte Carlo Models • Monte Carlo Models typically come with their set of default parameters • i.e. the first tuning effort is provided by Monte Carlo authors • Reasonable criteria but no clear prescription • Typically the parameters of not frozen MC packages are refreshed following the most recent phenomenology • Workshops, Literature • Parameters change with MC versions • No easy way to keep track of changes. One should probably book-keep ALL the parameters, even the current default ones. P.Bartalini (University of Florida)

4. Optimizing parameters in MC Models • Why should we change the MC default parameters ? • Optimization to the environment: beams, sqrt(s) etc. • Variation of the parameters within their boundaries to estimate the Theoretical Uncertainties • see for example CMS Note 2005/013 • Examples • Fragmentation: • LEP measurements are typically adopted. • Is the LEP legacy so clear ? Is it reflected in default values ? What are the errors ? • Minimum Bias & Underlying Event: • ENERGY DEPENDENCY OF THE PARAMETERS! • TUNE A from CDFCANNOT BE ADOPTED AS IT IS SOURCE OF QUITE FEW ERRORS AT THE LHC • Appropriate tuning available [A.M.Moraes, C.Buttar and I.Dawson (ATLAS) hep-ph/0403100, pgg 8-16] • How to estimate the uncertainties ? • Parton Distribution Functions • Uncertainties usually estimated using error sets from CTEQ & MRST • Is the methodology clear ? Symmetric or Asymmetric uncertainties ? • LHC Experiments need to discuss/share experiences/methodologies on a regular basis • LCG Generator would act as a LHC Working group providing a permanent forum for these issues P.Bartalini (University of Florida)

5. Backup P.Bartalini (University of Florida)

6. Organisational Issues WEB page http://lcgapp.cern.ch/project/simu/generator  Links to relevant documentation, CVS repository, release.notes etc. CDS Agenda Home>Projects>LHC Computing Grid>Physics Generators  Minutes of meetings, slides of presentations Meetings:  Last Thursday of the month at 5 PM in CERN-32-1-A24 & VRVS  Next meeting on November 24th Simulation project mailing list: project-lcg-simu@cern.ch P.Bartalini (University of Florida)