March 19, 1999

Colleagues,

I took some rate measurements today for my own work, but since others are studying the response of the muon/hadron layer, I thought I should send along a short note to everyone--for those of you who don't care about this, delete now.  For the rest of you, you may find the data of interest to compare with Monte Carlo predictions. 

I chose 2 patches near the center of the muon/hadron layer of Milagro to study, patches 37 and 38.  I measured the rate in each patch with a patch multiplicity trigger using the low-threshold.  Note the window was 200 ns for coincidence.  These results are in the attached figure, a .ps file.  Patch 37 has 12 of 16 PMTs operating, and patch 38 has 14 of 16.  You can see a clear decrease in the rate near 12(or 14) PMT coincidence; also you see that patch 37 has fewer operating PMTs as its rate decreases more quickly than patch 38 as the multiplicity is raised.

It may turn out that an "optimal" trigger (see recent memo on patch triggering) is one in which a well defined pattern of patches, rather than simply one patch, becomes the trigger criterion.  I chose neighboring patches to study the rate of two patch coincidences.  I required that both patches have >NPMT hits in coincidence as well.  These data are also shown in the attached figure. 

Note the interesting fact that these data do not show any "break" in the rate, as has often been ascribed in other situations to a transition from triggers on muons to triggers on showers.  A back-of-the-envelope estimate is that about 50kHz of muons goes through an area of effective size of about 1 patch, so the single patch rates at low NPMTs are consistent with being due (mostly) to muons.  At higher coincidence levels, the rates should be dominated by showers.  This break not being observed here either argues against the muon/shower discriminant, or that my interpretation is incorrect.

Cheers,

Todd