500 fb ^-1 SM Data Sample at Ecm=500 GeV

Data Sample

Stdhep files for an Ecm=500 GeV SM data sample are
available at ftp://ftp-lcd.slac.stanford.edu/ilc/ILC500/StandardModel/ .
There are 487,603,537 events (250 fb ^-1 luminosity) with -80% electron/ +30% positron polarization,
and 474,837,805 events (250 fb ^-1 luminosity)  with +80% electron/ -30% positron polarization.
The WHIZARD Monte Carlo version 1.40 is used for parton generation. The Makefile and build log files for
this implementation of WHIZARD can be found in ftp://ftp-lcd.slac.stanford.edu/ilc/ILC500/StandardModel/whizard-v1r4p0 .

Event Weight

Due to the presence of some high cross section processes the events are not completely unweighted.
The event weight must therefore always be considered when analyzing events.
This weight is stored in the variable EVENTWEIGHTLH in the stdhep common block HEPEV4.

Process Identification

Events corresponding to hundreds of different processes are stored in random order in the stdhep files. For each event
the variable IDRUPLH from the stdhep common block HEPEV4 is used to identify the process.

Suppose that an event has IDRUPLH=14995 . The information about the generation of this event
can be found in the directory ftp://ftp-lcd.slac.stanford.edu/ilc/ILC500/StandardModel/run_output/w14995/run_01/ .
For example the log file is ftp://ftp-lcd.slac.stanford.edu/ilc/ILC500/StandardModel/run_output/w14995/run_01/whizard.log ,
the whizard input file is ftp://ftp-lcd.slac.stanford.edu/ilc/ILC500/StandardModel/run_output/w14995/run_01/whizard.in
and cross section information is in ftp://ftp-lcd.slac.stanford.edu/ilc/ILC500/StandardModel/run_output/w14995/run_01/whizard.n3n3n3n3ss_o.out

Beamstrahlung

The following lines in whizard.in control the beamstrahlung simulation:

USER_spectrum_on = T
USER_spectrum_mode = -2

The first line indicates that a user-supplied function is used to simulate beamstrahlung. A copy of this function can
be found in ftp://ftp-lcd.slac.stanford.edu/ilc/ILC500/StandardModel/whizard-src/user.f90

The absolute value of USER_spectrum_mode determines which beamstrahlung spectrum is used, with the sign +/- indicating
electron/positron beam, respectively. For the 500 fb ^-1 SM data sample this absolute value is always 2, and corresponds
to the Guinea-Pig beamstrahlung data contained in the directory ftp://ftp-lcd.slac.stanford.edu/ilc/ILC500/StandardModel/guinea-pig/ilc_0500_may05_run05_seed06/
This spectrum represents the default ILC design for Ecm=500 GeV circa August 2005.

Final State Parton Showering and Fragmentation

PYTHIA 6.205 is used for final state QED/QCD parton showering and for the fragmentation of quarks and gluons. Parton showering is done for all final state ferminons with the exception of electrons. Final state QED showering of electrons is turned off because the PYTHIA final state showering code indiscriminately uses the invariant mass of final state fermion-antifermion pairs for the maximum virtuality scale.

The interface to PYTHIA is contained in ftp://ftp-lcd.slac.stanford.edu/ilc/ILC500/StandardModel/whizard-src/user.f90 . The source code for referenced subroutines can be found in ftp://ftp-lcd.slac.stanford.edu/ilc/ILC500/StandardModel/a6f/include .

Color flow information was not available in WHIZARD 1.40, and so kinematic and parton id information is used to identify color singlet systems (see ftp://ftp-lcd.slac.stanford.edu/ilc/ILC500/StandardModel/a6f/include/ilc_fragment_call.f90 and ftp://ftp-lcd.slac.stanford.edu/ilc/ILC500/StandardModel/a6f/include/calc_a1sq_a2sq.f90 ).

Kinematic Cuts

Requests for additional Ecm=500 GeV Samples

FAQ

Whizard has no gluon emission by default, leading to potentially incorrect multiplicity distributions.

This is true for WHIZARD but irrelevant for this sample since the parton showering was done with PYTHIA.

Whizard has an incorrect implementation of the CKM matrix. Only diagonal terms of the matrix are present (and = 1!), giving wrong W decays.

Although true, it is extremely doubtful that this will have any effect on the current analyses. When we regenerate these datasets, we will be using the latest version of Whizard, which has corrected this.

This sample has generator level cuts a la SiD, providing a potential bias when used for ILD.

There are, indeed, some kinematical cuts for processes with divergent cross-sections, which can be seen by looking at the whizard.in file as described above. However, the only kinematic cut that leads to a genuine loss of events is a 4 GeV minimum invariant mass cut on final state fermion-antifermion pairs.