1. Underground Muon Intensities for Henderson DUSEL Jeffrey Wilkes Dept of Physics, U. of Washington for Kregg Philpott INT, U. of Washington Henderson DUSEL Capstone Workshop 2006 May 6, 2006 - Stony Brook, NY Work Performed in Collaboration with Wick Haxton, Institute for Nuclear Theory, UW

2. Muon flux estimation ● Muons primarily produced in atmosphere, from decay of mesons produced by Galactic cosmic ray interactions ● At the surface, muon rate dependent on zenith angle (path length through atmosphere) ● Rate underground = rate at surface, attenuated by overburden in muon arrival direction  Ocean experiments are simpler… ●...unfortunately mountains are not flat, even in physics approximations  Must fold in topography, from geodetic survey maps Image from http://www.unine.ch d l  l=d sec(  ) d l  l = f (x,y)

3. Method ● Muon flux at surface has been studied for decades  Good semi-analytic model available (Gaisser 2002) ● Digital Elevation Maps (DEMs) available at 10m resolution for most of the USA, and < 90m resolution for most of the world ● For now, using simple 5 0 by 5 0 (zenith x azimuth) bins* and compute distance from surface to detector for each bin ● Multiply by mean rock density to get slant depth for each bin  Use R=10km as horizontal limit *Runs take 1 day on a garden-variety PC

4. Flat surface ● Benchmark: flux vs depth, summed over all arrival angles for flat surface topography

5. Henderson 3D view ● South-Looking View ● Continental Divide ~5km to the west (right) ● Take lab to be directly under peak of Harrison Mountain

6. Henderson Topography ● Continental Divide* is just beginning to show up on left edge of map; summits along the Divide have major effects on muon flux contours that follow * Continental Divide = boundary between Mississippi River and Pacific Ocean watersheds

7. 8100’ level (2500 mwe nominal) Upper Campus 1 ● Calculated flux under Harrison Mt. of 4.6093e- 8 cm -2 s -1 ● Equivalent Calculated depth of 2.7635 kmwe (for points directly under summit of Harrison Mt.)

8. 7700’ level (3300 mwe nominal) Upper Campus 2 ● Calculated flux under Harrison Mt. of 2.7682e- 8 cm -2 s -1 ● Equivalent Calculated depth of 3.0698 kmwe

9. 6750’ level (4200 mwe nominal) Central Campus ● Calculated flux under Harrison Mt. of 8.7806e- 9 cm -2 s -1 ● Equivalent Calculated depth of 3.8088 kmwe

10. BTW, for comparison: Brand X, 4850’ depth ● Falling terrain to the Northeast means lower backgrounds obtained to the Southwest ● Calculated muon flux of 4.5141e-9 cm -2 s -1 ● Equivalent Calculated Depth : 4.2651 kmwe

11. 4900’ level (6000 mwe nominal) Lower Campus ● Calculated flux under Harrison Mt. of 1.1001e- 9 cm -2 s -1 ● Equivalent Calculated depth of 5.2879 kmwe

12. Comparisons

13. Summary ● Toolkit developed for calculations of muon flux vs (x,y,z) allows preliminary estimates of background at DUSEL experiment locations ● Uniform expression of muon flux in terms of depth below a flat surface allows comparisons in terms of equivalent depth parameter... ● Further info: contact Kregg Philpott, kreggp@u.washington.edu