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

Data Sample

Stdhep files for an Ecm=500 GeV SM data sample assuming a 120 GeV Higgs mass 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

Electron/Positron Beam Properties: Beamstrahlung and LINAC Energy Spread

The following lines in whizard.in control the properties of the colliding electron/positron beams:

USER_spectrum_on = T
USER_spectrum_mode = -2

The first line indicates that a user-supplied function is used to simulate the beams. 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 energy 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 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, and includes both incoming LINAC
energy spread and beamstrahlung.

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 fermions 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

Kinematic cuts are applied to massless particle configurations where some cutoff is required to avoid an infinite cross section. In the WHIZARD event generation stage we set the masses of all first and second generation fermions to zero, so that photons, gluons, electrons, muons and u,d,s,c quarks are all subject to kinematic cuts. The cuts are given by the WHIZARD input parameters default_jet_cut, default_mass_cut and default_q_cut . We use the WHIZARD default value
default_jet_cut=10 GeV for the minimum invariant mass of a pair of colored particles. We use default_mass_cut=4 GeV for the minimum invariant mass of a pair of colorless particles, and we use default_q_cut=4 GeV for the minimum sqrt(-Q**2) for
massless t-channel processes.

The massless assumption for the first and second fermion generations can produce some odd results given the kinematic cut values we have chosen. For example, the cross section for gamma gamma -> tau tau is significantly larger than the cross section for gamma gamma -> mu mu since the cut value of 4 GeV for default_mass_cut and default_q_cut is much larger than the tau mass.
Also the cross section for gamma gamma -> qq is suppressed relative to the corresponding cross section for lepton pair
production because the cut value of 10 GeV for default_jet_cut is larger than the cut value of 4 GeV for default_mass_cut .

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.