Underground Muon Intensities for Henderson DUSEL

Jeffrey Wilkes Dept of Physics, U. of Washington

for

Kregg PhilpottINT, U. of Washington

Henderson DUSEL Capstone Workshop 2006May 6, 2006 - 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

mapsImage from http://www.unine.ch

dl

l=d sec()

dl

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 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

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 4.6093e-8 cm-2 s-1

● Equivalent Calculated depth of 2.7635 kmwe(for points directly under summit of Harrison Mt.)

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

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

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

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

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, kreggp@u.washington.edu