Particle Physics Seminar

The Milagro Observatory collected data between the years 1999 and 2008. The original detector was a 60 by 80 m pond of up to 8m deep water instrumented with 723 PMTs that were arranged in two layers. The PMTs measured the Cherenkov light that relativistic particles of extensive air showers produce when they traverse the water. In 2004, 175 water tanks were added surrounding the pond and covering an area of 200 by 200 m. The addition of this array of water tanks approximately doubled the sensitivity of the detector. Milagro detected multiple sources of TeV gamma-rays, most are close to the Galactic plane and all are coincident with bright GeV pulsars. In addition, after accounting for the emission from these sources, there remains a significant excess emission in the Galactic plane which may be due to diffuse emission produced by cosmic rays interacting with matter and radiation in the galaxy or due to unresolved sources. Milagro also measured unexpected anisotropies in the cosmic ray arrival directions, which are difficult to explain with standard model astrophysics.
In my talk, I will summarize the results that are based on an analysis of the complete Milagro data set that has a peak sensitivity at energies of 10 TeV to 50 TeV. Building on the experience and success of Milagro a second generation water Cherenkov detector, the HAWC (High Altitude Water Cherenkov) TeV Gamma-Ray Observatory is being constructed at the Sierra Negra site in Mexico at 4100 m above sea level. This year, funding for the construction has been granted by NSF, DoE, and CONACyT with construction to be completed by 2014. However, gamma-ray observations will be collected during construction with an increasingly more sensitive detector. By 2012, the sensitivity of HAWC will exceed the capabilities of the Milagro Observatory. I will describe scientific motivation, the design as well as the construction schedule for HAWC.