EKHARA: A Monte Carlo generator for e+e−→e+e−π0e+e−→e+e−π0 and e+e−→e+e−π+π−e+e−→e+e−π+π− processes

We present the EKHARA Monte Carlo event generator of reactions e+e−→e+e−π0e+e−→e+e−π0 and e+e−→e+e−π+π−e+e−→e+e−π+π−. The newly added channel (e+e−→e+e−π0e+e−→e+e−π0) is important for γ⁎γ⁎γ⁎γ⁎ physics and can be used for the pion transition form factor studies at meson factories.Program summaryProgram title: EKHARACatalogue identifier: AEIO_v1_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEIO_v1_0.htmlProgram obtainable from: CPC Program Library, Queenʼs University, Belfast, N. IrelandLicensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 23 820No. of bytes in distributed program, including test data, etc.: 310 673Distribution format: tar.gzProgramming language: FORTRAN 77 with quadruple precisionComputer: PC, main frameOperating system: Linux, Unix, MS WindowsRAM: up to 10 Megabytes for operation of the compiled programClassification: 11.2, 11.6Nature 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−π+π−e+e−→e+e−π+π−. The newly added channel, e+e−→e+e−π0e+e−→e+e−π0, 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−π0e+e−→e+e−π0 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−π+π−e+e−→e+e−π+π− 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−π0e+e−π0 events are generated in 78 seconds (no cuts),
• 105 weighted e+e−π+π−e+e−π+π− events are generated in 38 seconds (with cuts [2]).References:[1]H. Czyz, E. Nowak-Kubat, Radiative return via electron pair production: Monte Carlo simulation of the process e+e−→π+π−e+e−e+e−→π+π−e+e−, Acta Phys. Polon. B 36 (2005) 3425–3434.[2]H. Czyz, E. Nowak-Kubat, The reaction e+e−→e+e−π+π−e+e−→e+e−π+π− and the pion form factor measurements via the radiative return method, Phys. Lett. B 634 (2006) 493–497.[3]G. Amelino-Camelia, et al., Physics with the KLOE-2 experiment at the upgraded DAΦNEDAΦNE, Eur. Phys. J. C 68 (2010) 619–681.[4]G.A. Schuler, Two-photon physics with GALUGA 2.0, Comput. Phys. Commun. 108 (1998) 279–303.