1. HAWC Science  Survey of 2  sr (half the sky) up to 100 TeV energies 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. From Milagro to HAWC High Altitude Water Cherenkov (HAWC) Increase Altitude to 4100 m from 2650 m Increase Area to 22000 m 2 from 4000 m 2 Reuse Milagro PMTs and electronics HAWC ~15x Sensitivity of Milagro HAWC: Detect Crab in ~ 1 day (5  ) Milagro: Detects Crab in ~1/2 yr e   150 meters 4 meters e  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

3. 4100m 2600m Difference between 2600m (Milagro) and 4100m (HAWC): ~ 5x number of particles HAWC’s median trigger energy ~1 TeV vs Milagro’s ~4 TeV Higher Altitude is Closer to Shower Max.

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

5. 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 ~10 ~6 ~15

6. 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 Milagro

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

8. Angular Resolution HAWC Angular Resolution

9. Flaring Blazars detectable by HAWC at 5 Crab in 10 minutes HAWC & Transients Orphan Flare Full Moon X-ray binary periods unobstructed by Moon or Sun GRBs out to z~0.3 (0.7) for 10 -6 (10 -5 ) ergs/cm 2 Plus Solar Energetic Particles and … TeV 10 keV E cutoff = 700 260 170 GeV

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

11. 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)

12. HAWC Baseline Design  Fiducial volume: 150m x 150m x 4m  4,100 m elevation  5m PMT spacing under 4m of water  ~35mCrab sensitivity over the northern sky (5  in 2 year) 170m 150m 6m roof 8” Hamamatsu R5912 PMTs columns Polypropylene-nylon liner ~115Ml Filtered water Curtains

13. LANL Design of Pond Top of Pond at 4098 m a.s.l. Topographic Survey of Site

14. Steel Building with Structural Supports in the Water LANL Engineering Study: Pond Cover Floating Cover with Access Ports for Installation and Repairs Individual Plastic Tanks of ~4-5m height and ~4-5m diameter in 30 x 30 array

15. Tanks Simplifies construction, deployment. Modular design. Auger Tanks were manufactured in Mexico by Rotoblas Can purchase special 4m tanks off the shelf. Possibly special order 5m tanks, fabricated locally in Mexico.

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

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 1 st 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

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

19. Survey Sensitivity

20. Gamma/Hadron Separation Gammas Protons 30 GeV70 GeV230 GeV 20 GeV70 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