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

We present the EKHARA Monte Carlo event generator of reactions e(+)e(-) -> e(+)e(-)pi(0) and e(+)e(-) -> e(+)e(-)pi(+)pi(-). The newly added channel (e(+)e(-) -> e(+)e(-)pi(0)) is important for gamma*gamma* 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, 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(-)pi(+)pi(-). The newly added channel, e(+)e(-) -> e(+)e(-)pi(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(-)pi(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(-)pi(+)pi(-) 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(-)pi(0) events are generated in 78 seconds (no cuts), 10(5) weighted e(+)e(-)pi(+)pi(-) events are generated in 38 seconds (with cuts [2]). (C) 2011 Elsevier B.V. All rights reserved.