EKHARA: A Monte Carlo generator for e+e??e+e??0 e + e ? ? e + e ? ? 0 and e+e??e+e??+?? e + e ? ? e + e ? ? + ? ? processes ?
We present the EKHARA Monte Carlo event generator of reactions e+e??e+e??0 e + e ? ? e + e ? ? 0 and e+e??e+e??+?? e + e ? ? e + e ? ? + ? ? . The newly added channel (e+e??e+e??0 e + e ? ? e + e ? ? 0 ) is important for ???? ? ? ? ? physics and can be used for the pion transition form factor studies at meson factories. Program title: EKHARA Catalogue identifier: AEIO_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEIO_v1_0.html Program obtainable from: CPC Program Library, Queen?s University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 23?820 No. of bytes in distributed program, including test data, etc.: 310?673 Distribution format: tar.gz Programming language: FORTRAN 77 with quadruple precision Computer: PC, main frame Operating system: Linux, Unix, MS Windows RAM: up to 10 Megabytes for operation of the compiled program Classification: 11.2, 11.6 Nature of problem:  The first version of EKHARA [1,2] was developed to simulate a background for the pion form factor measurement at meson factories coming from the process e+e??e+e??+?? e + e ? ? e + e ? ? + ? ? . The newly added channel, e+e??e+e??0 e + e ? ? e + e ? ? 0 , will help in the pion transition form factor studies at meson factories [3]. Solution method:  Events consisting of the momenta of the outgoing particles are generated by Monte Carlo methods. The generated events are distributed accordingly to the theoretical cross section. For the e+e??e+e??0 e + e ? ? e + e ? ? 0 mode the Monte Carlo sampling developed in [4] was adopted. Restrictions: In order to compile the code, the FORTRAN 77 compiler should support quadruple precision numbers. Unusual features:  To avoid numerical cancellations in the e+e??e+e??+?? e + e ? ? e + e ? ? + ? ? mode calculations are carried in the quadruple precision. Running time: It depends on the requested mode and applied kinematic cuts. An example: on Intel Core2 Quad CPU Q6600 @ 2.40 GHz, using only one thread, 105 unweighted e+e??0 e + e ? ? 0 events are generated in 78 seconds (no cuts), 105 weighted e+e??+?? e + e ? ? + ? ? events are generated in 38 seconds (with cuts [2]). References: H. Czyz, E. Nowak-Kubat, Radiative return via electron pair production: Monte Carlo simulation of the process e+e???+??e+e? e + e ? ? ? + ? ? e + e ? , Acta Phys. Polon. B 36 (2005) 34253434. H. Czyz, E. Nowak-Kubat, The reaction e+e??e+e??+?? e + e ? ? e + e ? ? + ? ? and the pion form factor measurements via the radiative return method, Phys. Lett. B 634 (2006) 493497. G. Amelino-Camelia, et al., Physics with the KLOE-2 experiment at the upgraded DA?NE DA ? NE , Eur. Phys. J. C 68 (2010) 619681. G.A. Schuler, Two-photon physics with GALUGA 2.0, Comput. Phys. Commun. 108 (1998) 279303.
monte carlo generator pion transition form factor pion pair production two-photon processes e+e? e + e ? annihilation e+e? e + e ? e+e? e + e ? e + e ?