EKHARA: A Monte Carlo generator for and processes

Abstract: We present the EKHARA Monte Carlo event generator of reactions and . The newly added channel () is important for physics and can be used for the pion transition form factor studies at meson factories. Program summary: 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, Queenʼs 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 . The newly added channel, , 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 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 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 events are generated in 78 seconds (no cuts), [•] 105 weighted 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 , Acta Phys. Polon. B 36 (2005) 3425–3434. [[2]] H. Czyz, E. Nowak-Kubat, The reaction 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 , 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. [Copyright &y& Elsevier]