EKHARA: A Monte Carlo generator for [formula omitted] and [formula omitted] processes

Abstract

We present the EKHARA Monte Carlo event generator of reactions e + e − → e + e − π 0 and e + e − → e + e − π + π − . The newly added channel ( e + e − → e + e − π 0 ) is important for γ ⁎ γ ⁎ 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 e + e − → e + e − π + π − . The newly added channel, e + e − → e + e − π 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 − π 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 − 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, • 10 5 unweighted e + e − π 0 events are generated in 78 seconds (no cuts), • 10 5 weighted e + e − π + π − events are generated in 38 seconds (with cuts [2]).