Underground Muon Intensities for Henderson DUSEL

1. 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 Underground Muon Intensities for Henderson DUSEL Work Performed in Collaboration with Wick Haxton, Institute for Nuclear Theory, UW

2. Image from http://www.unine.ch d l=dsec(q) l = f (x,y) l d q q l 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

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 50 by 50 (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