Appendix A. Event store in /PYJETS/

Each line in the PYTHIA event store has the following meaning according to the PYTHIA convention.

Line number	Meaning
1,2	Beam particles (1:$p$, 2:$e^{\pm}$)
3,4	Partons from the beam particles before ISR
	(3:from $p$, 4:from $e^{\pm}$)
5,6	Partons from the beam particles after ISR;
	the initial state in the matrix element calculation
	(5:from $p$, 6:from $e^{\pm}$)
7,8,9,10	Final state particles before FSR;
	the final state in the matrix element calculation
	(7:$p$, 8:$e^{\pm}$, 9:$l^{\mp}$, 10:$l^{\pm}$)
11$\sim$	Final state particles after FSR, fragmentation and decay

In case of the (quasi-)elastic process,

• a parton from the beam proton is the proton itself, i.e. the 1st and the 3rd lines are the same,
  
• the beam proton always makes no ISR, so that the 1st, 3rd and 5th lines are the same,
  
• the 2nd and the 4th lines are also the same.

In case of the DIS process with both ISR and FSR, all of the lines have different contents in general.

As for di-$e$ events, there are 2 identical particles in the final state. In GRAPE, those 2 particles are distinguished in the following way;

• in case of $e^{\pm}e^{\pm}$ interference off, a particle stored in the 8th line is a scattered lepton, and one in the 10th line comes from the 2-$\gamma$ collision ( i.e. a produced lepton),
  
• in case of $e^{\pm}e^{\pm}$ interference on, a lepton stored in the 8th line has smaller transverse momentum than that of a lepton in the 10th line.