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, Stony Brook, NY Work Performed in Collaboration with Wick Haxton, Institute for Nuclear Theory, UW

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 d l  l=d sec(  ) d l  l = f (x,y)

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

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

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

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

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

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

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

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

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

Comparisons

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,