HOWTO Use genr8

genr8 uses a simple t-channel model for generating meson-baryon qausi-two-body production where the meson and baryon can decay via sequential two-body processes. The t-slope parameter and all the particles involved in the production and decay are specified in an input text file. Here is a sample input file for a fixed photon beam energy of 9 GeV and a t-slope parameter of 5 GeV^-2:

%%%%%%%%%%%%%%%%% Start Input Values %%%%%%%%%%%%%%%%%%%%
% beamp.x beamp.y beamp.z beamMass  
0 0 9 0
% targetp.x targetp.y targetp.z targetMass
0 0 0 0.938
% t-channelSlope
      5.0
% number of particles needed to describe the isobar decay of X
4
% 
% particle# 0&1 are always the X&Y 
%part#  chld1#  chld2#  parent# Id     nchild   mass    width   charge  flag
% baryon (Y) decay
 0       *      *       *       14       0       0.938     0.0   +1       11  
% meson (X) decay
 1       2      3       *       0       2       0.77     0.150    0       00
 2       *      *       1       9       0       0.140   0       -1      11
 3       *      *       1       8       0       0.140   0       +1      11
!EOI
%%%%%%%%%%%%%%%%%%%%% End Input Values %%%%%%%%%%%%%%%%%%%%%%%
% for narrow widths particles(stable to strong interactions) 
%  set width to zero (i.e. eta, pi's).
%
%flag 00 =isobar or resonance
%flag  01 = production particle that decays i.e. eta, pizero ..
%flag  11 = production particle that does not decay i.e. piplus,...
%flag  10 = final state particle not in production i.e. gamma
% 

genr8 creates a text file containing the four-vectors for each particle in each event.

genr8 usage: [-A<name>]   < infile 
        -d debug flag
        -n Use a particle name and not its ID number (ascii only) 
        -M<max> Process first max events
        -l<lfevents> Determine the lorentz factor with this many number of events (default is 10000)
        -r<runNo> default runNo is 9000. 
        -P save flag= 11 & 01 events(default saves 11 & 10 events) 
        -A<filename> Save in ascii format. 
        -s<seed> Set random number seed to <seed>. 
                 (default is to set using current time + pid) 
        -h Print this help message

To convert the text file to hddm format, run genr8_2_hddm.

Usage:
       genr8_2_hddm [options] file.ascii

Convert an ascii file of events generated by genr8 into HDDM
for use as input to hdgeant.

 options:

  -r#                       Set the run number (overiding what's in input file)
  -V"x  y  z_min  z_max"    set the vertex for the interaction.
                            (default: x=0 y=0 z_min=65 z_max=65)
  -b"beam_particle_name"    set the beam particle type [gamma].
  -t"target_particle_name"  set the target particle type [proton].
  -P#                       Set the incident particle momentum in GeV.
                            (default: calculate from momentum of
                            final state particles.)
  -s#                       Set the momentum resolution of the beam
                            in MeV. [5MeV]. (Only used if -P option
                            is present.)
  -h                        print this usage statement.