This is a collaborative award to support the scientists who will work on the construction, commissioning and initial analysis of data from the High Altitude Water Cherenkov (HAWC) gamma-ray observatory being built at the Sierra Negra in Mexico. The HAWC collaboration consists of 14 US and 11 Mexican institutions. The observations of HAWC will probe the most extreme environments in the Universe, providing a unique view of non-thermal processes in the Galaxy and beyond. The key science goals of HAWC are to: (a) Measure the spectrum of Galactic sources to the highest energies; (b) Map the Galactic diffuse gamma-ray emission from 1 TeV to 100 TeV, measuring the cosmic-ray flux and spectrum across the Galaxy; (c) Study transient emission from active galactic nuclei (AGN); (d) Monitor the sky for 100 GeV emission from gamma-ray bursts; and (e) Search for new TeV physics with HAWC's unbiased sky survey. HAWC measurements have the potential to shed light on the fundamental symmetries of nature, including the search for Lorentz violation at extreme energies, the search for the dark matter in the universe, and the direct detection of massive relic particles. HAWC is a water Cherenkov air-shower detector consisting of 300 large water tanks. The tanks will be densely packed to cover an area of about 20,000 square meters. The goal is to begin taking data while the array is under construction and to have the full detector online within approximately three years.
Broader Impacts: HAWC is an all-sky instrument that will serve as a TeV "finder" telescope for Imaging Atmospheric Cherenkov Telescopes (IACTs) and IceCube and will have the sensitivity to extend the measurement of satellite-discovered sources to TeV. HAWC will build on the strong outreach record of Milagro to bring this exciting field of research to students and the general public. Since HAWC is a joint US-Mexican project, this will be an excellent opportunity to attract talented Hispanic students to the field of Particle Astrophysics and to Physics in general. The project has developed an outreach video about HAWC and web materials about HAWC and Particle Astrophysics in both Spanish and English.
The PI worked in a collaboration of 16 US and 12 Mexican institutions to start construction and data-taking of a detector of gamma and cosmic rays coming from both galactic and extragalactic sources. The sensitivity of the experiment will extend to TeV energies. The gamma ray directions will point back to their sources, which are frequently compact objects. TeV gamma rays are markers of the most extreme environments in the known universe: supernova explosions, active galactic nuclei, and gamma-ray bursts. Gamma rays are thought to be correlated with the acceleration sites of charged cosmic rays, whose origins have been a mystery for nearly 100 years. The experimental method is to detect extensive air showers created by the interactions of the primary particles with nuclei of the atmosphere. The secondary shower particles are observed by detecting the Cherenkov light produced by them as they traverse a transparent medium – water. The light detectors are photomultiplier tubes (PMT’s) which are placed at the bottom of large tanks of clear water. The array of tanks is located on the flanks of the Sierra Negra volcano near Puebla, Mexico at an altitude of 4100 meters. Signals from the PMT detections of the secondary shower particles are digitized and used to reconstruct both the arrival direction and the energy of the primary particle. The experiment is designed to have a total of 300 water tanks, with 4 PMT’s in each tank. To date about 120 tanks have been installed at the site, and are taking data. The readout of signals and the reconstruction of directions and energies is already functioning. One of the technical challenges is to frequently calibrate each PMT i.e. determine its response to a known amount of incident light. This is done in several ways. One is the use of a laser coupled to optical fibers which are connected to a light distributor in each tank. Another is to use the fact that in proton and nuclei – induced showers there are many muons which have know properties with respect to Cherenkov light production. The PI has worked on the study of data taken in the current detector as well as data from a prototype in order to develop algorithms to use the muon signals for this type of calibration. Another activity of the PI has been to develop a simulation of the PMT signals, as well as a simulation of the response of the coaxial cables used to transmit them, and a simulation of the response of the analog end of the electronics. These simulations have provided useful guidelines for the cable choice and the analysis of the signals. The project so far is on track to obtain very interesting results.
