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Manuscript Title: An update of the generator of atmospheric muons from parametric formulas (MUPAGE)
Authors: M. Bazzotti, G. Carminati, A. Margiotta, M. Spurio
Program title: MUPAGE
Catalogue identifier: AEBT_v2_0
Distribution format: tar.gz
Journal reference: Comput. Phys. Commun. 181(2010)835
Programming language: C++.
Computer: The code has been developed and tested on Pentium M, 2.0 GHz; 2x Intel Xeon Quad Core, 2.33 GHz.
Operating system: Scientific Linux 3.x; 4.x; 5.x; Slackware 12.0.0.
RAM: 50 MB
Supplementary material: The Table mentioned in the "Summary of revisions" section, can be obtained here.
Keywords: Simulation of atmospheric muons, neutrino telescopes, multiple muons, Monte Carlo generator.
PACS: 95.55.Vj.
Classification: 1.1, 11.3.

External routines: ROOT (http://root.cern.ch)

Does the new version supersede the previous version?: Yes

Nature of problem:
Fast simulation of atmospheric muon bundles for underwater/ice neutrino telescopes.

Solution method:
Atmospheric muon events are generated according to parametric formulas [2] giving the flux, the multiplicity, the radial distribution and the energy spectrum.

Reasons for new version:
We simplified the possible choice of the muon bundle energy, which in the previous version could give a wrong estimation of the equivalent livetime. In addition, in the former version the choice of a virtual cylinder with height much larger than the diameter stopped the program. The problem is now fixed.

Summary of revisions:
The MUPAGE event generator computes automatically the equivalent livetime corresponding to the number of generated events Ngen on the user-defined cylinder (can) surrounding the virtual detector. MUPAGE needs some parameters as input (provided by the user in the file dat/parameters.dat). These parameters refer to the detector configuration, to the medium and to the range of simulation parameters (multiplicity, zenith angle, muon energy), see Table 1 (Supplementary material). In the previous version, the user could change the energy range of each muon in the bundle using Emin and Emax (minimum and maximum of the muon energy at the can level). It has been found that an arbitrary change of these values produces a wrong computation of the livetime. In the new version, these values cannot be changed and have been removed from the data cards. The selection of the energy threshold of the event is now possible with the Ethreshold parameter. It represents the sum of the energy of muons in the same bundle. The default value has been decreased to Ethreshold=0.001 TeV. The user may now increase the threshold value without any corruption of the livetime computation.
A second problem was related to the choice of the can size. The error was due to an uncorrected frame coordinate transformation in the code. MUPAGE produces the muon bundle event kinematics on the surface of the can. If the height was much larger than the can diameter, the program crashed and had to be restarted after increasing the value of MFactor. The new version corrects the error, and this parameter is not necessary anymore. In addition, there is not the need to increase the can radius (using the EnlargedCANr parameter) with a too large value. It is now recommended to define EnlargedCANr equal to Rmax.

Restrictions:
Water vertical depth range from 1.5 to 5 km w.e.; zenith angle range from 0 to 85 degrees.

Additional comments:
The program requires the ROOT libraries for the pseudorandom number generator.

Running time:
Running with the default settings takes only a few seconds.

References:
[1] M. Bazzotti et al. A parameterisation of the flux and energy spectrum of single and multiple muons in deep water/ice. arXiv:0910.4259
[2] Y. Becherini, A. Margiotta, M. Sioli and M. Spurio, Astrop. Phys.25 (2006), 1.