General considerations

In the previous version of WIMP simulation, the WimpSimp program by Joakim Edsjö directly produced the muons resulting from interaction in the ice of neutrinos as decay products of the neutralino annihilation. The muon spectrum had a lower cutoff at an energy of 10 GeV.

We now want to include additional features in the simulation. The new WimpSimp include an option to create a file with neutrinos. These can be used to do a more thorough simulation and include the hadronic shower and the energy of the original neutrino in the output as well as the muon, and to simulate neutrino oscillation before interaction. These things are done by the program genniup, written by Carlos P. de los Heros. Genniup makes use of PYTHIA.

There is a problem for the lowest energies, that the interaction can not be simulated with PYTHIA if neutrino energies go under 15 GeV. This limitation also affects WimpSimp when it is used to generate muons.

The reason for this is apparently physics. If the reaction products other than the muon get to small part of the energy the cross section will not be a continuous function, but will oscillate because of resonances.

We can cut the neutrinos below 15 GeV and simulate interaction on the rest that is left. The muon energy will never be closer than a few GeV under the neutrino energy, because of the part taken by the hadronic shower. Few of the muons produced by a 15 GeV neutrino will have energies above ten GeV, and since this is a suitable lower cut for the muon energy spectrum (the detector cannot trigger very short tracks) the neutrino energy cut will have a very small effect on the spectrum of muons used in the further simulation and analysis.

For the lowest neutralino masses this might be a problem, though, since a larger fraction of the total number of events are close to the energy cutoff.

Programs and settings

WimpSimp

WimpSimp 1.2 produces a file of neutrinos Run this for seven neutralino masses (50 GeV, 100 GeV, 250 GeV, 500 GeV , 1000 GeV, 3000 GeV, 5000 GeV) and two decay channels, one soft (b) and one hard (W) for neutralino annihilation in the sun as well as the earth.

My shellscripts to run WimpSimp: ea_soft and ea_hard UPDATED

wf2f2000

w2f2000 I do not let this program spread the events, that is saved for genniup to do.

genniup

GENNIUP This is the new version of the neutrino propagation and interaction program. It generates muons and hadronic showers and distributes the interactions in a cylinder (circular, not quadratic like the previos version called nuprop).

A few bugs have been fixed and a couple of new features added, including writing more information in the file header.

Here is a tarball of genniup, the September version.

Here follows the cylinder dimensions (they are based on the volumes Joakim used in 1999 but with 30m extra in radius to allow for AMANDA-II).
neutralino mass (GeV) radius (m) height (m) # muons (hard / soft)
50 170 800 676868 / 519889
100 190 950 880507 / 688385
250 230 1550 955805 / 833964
500 270 2350 978039 / 902485
1000 290 3500 989173 / 941549
3000 320 6150 996620 / 972783
5000 410 7600 998178 / 980617

Now: the files.

Here are some files after amasim (with string trigger)

Notes on interaction and other things

There was a problem with a distorted muon energy spectrum, but this is solved. Since we force all neutrinos to interact we have to introduce a weight in order to reproduce the variation of cross section with energy. In this iteration we solved this by generating an initial neutrino spectrum that would correspond to interacting neutrinos instead of actual incoming signal neutrinos. This was accomplished by weighting the neutrino spectrum with neutrino energy.

New WIMP files (see above) were produced. They are larger than the previous files by a factor 2. The interaction volume is now wider, taking into account the whole width of AMANDA-II.

Some of the higher energy muons will reach the detector from an interaction point in the rock, under the ice. This is not taken into account by genniup, but since the ratio of protons to neutrons is similar it is only the propagation and not the interaction point that will be affected by the different material.

To take into account the rock, use the option of two materials in mmc.

Anna Davour July-October 2003, slightly updated 2005