This award will assist in funding an upgrade to the Central Laser "test beam" Facility (CLF) located near the center of the Pierre Auger Observatory (PAO). The PAO uses the atmosphere as a giant calorimeter to measure the highest energy particles known to exist. At these extreme energies (1-100 EeV; 1 EeV = 10^18 eV; 1 eV is the energy an electron or proton gains when it is accelerated by a voltage of one Volt), particle test beams, traditionally used to characterize accelerator based detectors, simply do not exist. However, light scattered out of a pulsed Ultra-Violet (UV) laser beam directed into the atmosphere will generate tracks that can be recorded by the same fluorescence detectors that record tracks from extensive air showers. There is an approximate effective optical equivalence between a 5 milliJoule UV laser track and a 100 EeV air shower.
The proposed CLF upgrade will add a Raman LIDAR receiver and a robotic photometric calibration system, and make related improvements. It will target three specific areas: 1. Use the "super test beam" to crosscheck the end-to-end photometric calibration of the fluorescence detector which sets the energy scale for the observatory. 2. Within a few minutes of the detection of air-showers of particular interest, the Raman receiver will make an independent precision measurement of the aerosol optical depth profile and water vapor profile. Events of interest include very high energy candidates detected in hybrid mode, air showers from the region near the radio galaxy Centaurus A, and exotic candidates with shower profiles that may not fit the standard shape. Aerosol optical depth is the largest time varying correction applied to air shower reconstruction. 3. Systematically compare the aerosol optical depth profiles measured by the Raman LIDAR receiver and by the side-scatter method currently used to fill the observatory's aerosol profile database. This comparison is especially important to the elongation rate analysis of hybrid data that suggests the particle composition may transition to heavier primaries above 10 EeV.
CSM undergraduates are naturally involved in the research, as they are required to complete a senior design project as part of their curriculum. Raman LIDAR is a standard aerosol profile measurement technique that will enhance the usefulness of the atmospheric data base collected by non-traditional methods. This will enable more direct comparisons with other data sets in the atmospheric science community.
This grant provided key funding of equipment and material to for a transformative upgrade of the central laser facility (CLF) (http://astroserve.mines.edu/lasers) which is located near the middle of the Pierre Auger Cosmic Ray Observatory (www.auger.org). The Pierre Auger Observatory was constructed and is operated by an international collaboration of scientists and engineers from 16 countries. It is located in the Mendoza province of Argentina and views the southern hemisphere of the sky including the center of our galaxy. The detectors that comprise the Observatory cover an area of 3000 km2. The Pierre Auger Observatory is the largest high energy comic ray detector in the world. The funding in this particular grant was used for equipment and shipping costs of the CLF upgrade. More than half of the total equipment cost for the CLF upgrade was provided by international partners in Italy and Spain. The Auger observatory measures the highest energy particles known to exist. Given the historical name of "cosmic rays", the kinetic energy of one of these particles can exceed 1020 eV. This about the same amount of kinetic energy of a baseball pitch. The difference is that all this kinetic energy is carried by a single subatomic particle. Practically everything we know about the universe beyond the solar system is based on measurements of photons. Optical telescopes that measure light (visible photons) are one example. Other examples are the photon measurements by radio telescopes, infrared telescopes, X-ray detectors, and gamma-ray detectors. In contrast, cosmic rays are not photons and their energies extend a million times higher than the energies of photons measured by the largest gamma-ray detectors. So these cosmic rays carry unique information about some of the most extreme objects and processes in our universe. Their energies are also beyond the reach of the largest manmade accelerators including the Large Hadron Collider at CERN. In contrast to experiments at manmade accelerators, there are no "test beams" that can be used to benchmark the performance of high energy cosmic ray observatories. At the Pierre Auger Observatory a cost effective alternative is provided by lasers that direct calibrated pulses of ultraviolet light in to the atmosphere. The scattered laser light makes tracks in the 4 optical detectors that are located along the edges of the observatory footprint on the ground. The tracks have properties that are similar to the tracks produced by the interaction of high energy cosmic rays in the atmosphere. (One difference is that the cosmic ray tracks go down and the laser light tracks go up.) However, unlike cosmic rays, Pierre Auger CLF can be pointed in specified directions, fired at precise specified times and at precise specified energies. The CLF is operated and programmed remotely. Major items in the CLF upgrade include (* funded by this grant): *Replace leaky equipment shelter with a newer 40' modified shipping container. The original shelter leaked water and dust which reduced the precision of the beam calibration. The materials and most of the equipment were shipped to the observatory in modified 40' shipping container. *2000 liter passive water reservoir to reduce temperature fluctuations inside the facility. *Computer controlled sliding shutter to protect a UV transmitting window used by the Raman LIDAR receiver. *2 propane heaters (2 for redundancy) *Extending the concrete pad for facility *Shipping costs from Golden Colorado to the Observatory. UV solid state laser Raman LIDAR receiver including optics, detectors, cables, controls, computers. The Raman LIDAR provides an independent measurement of how much light scatters out of the laser beam as it travels through the atmosphere. Automated beam calibration system for energy and polarization. Optical tables At the end of the reporting period for this grant, the modifications to the shipping container had been finished. The equipment and material had been procurred. The laser and robotic calibration system had been tested. The containter with equipment and material had been packed and shipped to the Pierre Auger Observatory for installation.
