Field of application

The event generator is suitable for the reaction of:
  1) e p -> e' p &pi⁺ &pi^-    in the Q² range ~0.1--5.0 GeV² and in the W-range from threshold to ~3 GeV;
  2) &gamma p -> p &pi⁺ &pi^-    in the W-range from 1.7 to ~3 GeV;
  3) e p -> e' n &pi⁰ &pi⁺   , where proton is inside deutron The Q² range ~0.1--1.0 GeV² and in the W-range from threshold to ~2.0 GeV. The main purpose of the this generator is to generate a background when studing reaction    e p -> e' n &pi⁰   , where proton is inside deutron Probably it will work somehow in wider W- and Q²-range but quality of data description still need to be checked.

Physics used in event generator

Events are generated according to the model of 5-dim. differential cross section (see Nucl.Phys. A672 220 (2000) and Phys.Atom.Nucl. 64 1292 (2001)) adjusted to experimental data on single differential cross-sections. The model describes reasonably experimental data on integrated and 1-diff. cross sections at Q² values: from 0.0 to 5. GeV². For higher W (W>2.1 GeV) we assume phase space behavior with amplitudes fixed at W=2.1 GeV.

Third generator uses only the very basic features of the reaction, since its main purpose is to generate a background.

Algorithm

The 5-dim differential cross-sections were calculated on W-Q² grid. Two pion events were simulated based on these cross-sections interpolated to required 7-dim kinematics grid composed by Q², W, S(pi+ pi-), S(p pi+), Theta(pi-), Phi(pi-), Psi(pi-). Si are the invariant mass squares for the final hadron pairs. Theta(pi-), Phi(pi-) are CM pi- angles, while the Psi(pi-) is the angle between two planes composed by the free momentum of (pi- p(initial)) and (pi+ p)

Comparison with the available experimental data

Q2		Integrated Cross Section		1-differential Cross Sections
0.000 (prelim. G11A)		int		diff
0.225 (data of E94-005)		int		diff
0.275 (data of E94-005)		int		diff
0.65 (data of E93-006)		int		diff
0.95 (data of E93-006)		int		diff
1.30 (data of E93-006)		int		diff
2.70 (E16 preliminary)		int		diff
3.85 (E16 preliminary)		int		diff
4.60 (E16 preliminary)		int		diff

Comparrison of the missing mass distributions for the third generator.

E1-6 preliminary		Missing mass

Source code

Contacts