1. HAWC Science Survey of 2p sr up to 100 TeV energies Extended Sources
Probe knee in cosmic ray spectrum
Identify sources of Galactic cosmic rays
Extended Sources
The Galactic Plane and Molecular Clouds
Supernova Remnants and Pulsar Wind Nebula
Galaxy Clusters
Transient Sources
Active Galactic Nuclei (AGN)
Gamma Ray Bursts (GRBs)
Solar Energetic Particles
Fundamental Physics Measurements
Tests of Lorentz Invariance at High Energies
Indirect Detection of Dark Matter
Increase Scientific Return of Other Projects
Identifies new and flaring TeV sources for VERITAS and IceCube
Extends GLAST and VERITAS spectra to higher energies

2. High Altitude Water Cherenkov (HAWC)
From Milagro to HAWC
High Altitude Water Cherenkov (HAWC)
Increase Altitude to 4300 m from 2650 m
Increase Area to m2 from 4000 m2
Reuse Milagro PMTs and electronics
HAWC ~15x Sensitivity of Milagro
HAWC: Detect Crab in ~ 1 day
Milagro: Detects Crab in ~1/2 yr
HAWC Design:
Single layer of 900 PMTs (4 m depth vs Milagro’s 2 layers at 1.5 and 6 m) optically separated by curtains or in individual tanks e m g e m g
150 meters
4 meters

3. Higher Altitude is Closer to Shower Max.
Difference between 2600m (Milagro) and 4300m (HAWC):
~ 6x number of particles
HAWC’s median trigger energy ~1 TeV vs Milagro’s ~4 TeV

4. Gamma/Hadron Separation
Gammas
Protons
30 GeV
70 GeV
230 GeV
20 GeV
270 GeV
Size of HAWC
Size of Milagro deep layer
Energy Distribution at ground level
Larger Area implies better angular resolution + better cosmic ray background rejection

5. Lateral Distribution Protons have BROAD lateral distribution of muons
Gammas have NARROW lateral distribution of electrons

6. HAWC sensitivity calculation
Milagro MC is used to calculate HAWC sensitivity increase of 15x
Milagro Crab flux is within 10% of ACT flux
Milagro Cosmic Ray flux is within 30-50% of balloon flux and is used to correct the HAWC background calculation
B.O.T.E.C. (back of the envelope calculation) is similar
Energy Threshold 3x lower than Milagro (Approx. B gives 6x more particles, but density of PMTs is less)
Sensitivity increase depends on spectrum, but is ~3x
Area for Triggering is 5x larger than Milagro
Sensitivity increase is ~2x
Angular resolution improves because of increased lever arm, better core location, …
Sensitivity increase is 1.5-2x
Gamma/hadron rejection improves due to increased probability of detecting muon away from the core
Sensitivity increase is >1.5x ~6
~10
~15

7. HAWC Sensitivity calculation
Milagro MC is used to calculate the HAWC sensitivity increase of 15x
Milagro Crab flux is within 10% of ACT flux
Milagro Cosmic Ray flux is within 30-50% of balloon flux and is used to correct the HAWC background calculation
Milagro MC of gamma/hadron separation parameter for gamma rays, cosmic rays, and data

8. Gamma-Ray Sensitivity to Crab-like Source
VERITAS, HESS, MAGIC, Whipple sensitivity in 50 hours, (~0.2 sr/year)
GLAST sensitivity in year (4p sr)
HAWC, Milagro, sensitivity in 1 year (2p sr)
~ 6 TeV
GeV

9. Survey Sensitivity

10. HAWC Extended Source Sensitivity
Angular Resolution
Comparison of g-ray sensitivity between the IACT and HAWC 2 year sky surveys as a function of source angular diameter. The HESS detected Galactic sources are shown.

11. HAWC & Transients Flaring Blazars detectable by HAWC
at 5 Crab in 10 minutes
Orphan Flare
TeV
10 keV
Ecutoff=
GeV
GRBs out to z~0.3 (0.7) for 10-6 (10-5) ergs/cm2
Plus Solar Energetic
Particles and …
Full Moon
X-ray binary periods unobstructed by Moon or Sun

12. HAWC and GLAST Transient Sensitivity
GRB
<1 MeV
Flux
10-6
GLAST and HAWC sensitivity for a source of spectrum
dN/dE=KE-2
above 10 GeV
z=0 no E cutoff
z=0.1 Eexp~700GeV
z=0.3 Eexp~260GeV
z=0.5 Eexp~170GeV
10-8
10-10
AGN flares
1-15 x Crab
10-12

13. Site Location is Sierra Negra, Mexico
4100 m above sea level
Easy Access
2 hr drive from Puebla
4 hr drive from Mexico City
Existing Infrastructure
Few km from the US/Mexico Large Millimeter Telescope
Power, Internet, Roads
Sierra Negra Scientific Consortium of ~7 projects
Excellent Mexican Collaborators
~15 Faculty at 7 institutions have submitted proposal to CONACYT for HAWC
Experience in HEP, Auger, and astrophysics (including TeV)

14. LANL Design of Pond Top of Pond at 4098 m a.s.l.
Topographic Survey of Site
Excavate ~102,000 m3 reusing ~78,000 m3 with ~24,000 m3 excess

15. LANL Engineering Study of Pond Cover
Floating Cover with Access Ports for Installation and Repairs
Steel Building with Structural Supports in the Water
Individual Plastic Tanks of ~4m height and ~4m diameter in 30 x 30 array

16. HAWC Proposal and Budget
Joint Proposal to NSF and DoE High Energy Physics
Additional Collaborators – University of New Mexico, University of Utah and International Partners
Construction Budget
Milagro Construction Budget was $3.4M ($2.7M from NSF and $0.7M from DoE HEP)
Site Preparation & Water Acquisition
$0.6M
Pond or Tanks
$3.2M
PMT Refurbishment & Calibration System
$0.4M
Cabling, Electronics, Computers
$0.8M
Contingency 20%
$1.0M
Total
~$6 M
Add Milagro operating budget?

17. Conclusion
Milagro has demonstrated the power of the water Cherenkov technique
Detection of Crab Nebula and Mrk 421, known TeV sources
Discovery of new TeV sources
1st detection of TeV diffuse emission from the Galactic plane
Future: HAWC
Building on expertise with Milagro
Design improvements in Size, Altitude, Curtains . . .
15x Milagro sensitivity
Milagro /HAWC complementary to other particle astrophysics observatories
Put 8 in context

18. TeV g-rays: A New Window on the Sky
TeV gamma ray
Milagro
HESS
0.1 GeV
Milagro 10 TeV gamma-ray
TeV g-rays: A New Window on the Sky