HAWC Gamma Ray Observatory Begins Operations

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Published: Wednesday, August 21 2013 09:43

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The High-Altitude Water Cherenkov (HAWC) Gamma Ray Observatory formally began operations on August 1. This is the culmination of four years of work by a persevering team of scientists and technicians from Mexico and the United States. Researchers from the University of Maryland, including Jordan Goodman, Andrew Smith, Brian Baughman, Jim Braun and Josh Wood, are playing a very prominent role in the construction of HAWC and will help lead in the analysis of data from the observatory.

“HAWC will be the world’s premier wide-field TeV gamma-ray observatory with between 10 and 15 times the sensitivity of previous generation wide-field detectors,” said Goodman, UMD professor and principal investigator for the project.

HAWC is located at an altitude of 4100 meters (13,500’) on the slope of the volcanoes Sierra Negra and Pico de Orizaba at the border between the states of Puebla and Veracruz. The observatory, which is still under construction, uses an array of Cherenkov detectors to observe high-energy cosmic rays and gamma rays. Currently 111 out of 300 Cherenkov detectors are deployed and taking data. Each Cherenkov detector consists of 180,000 liters (40,000 gallons) of extra-pure water stored inside an enormous tank (5 meters high and 7.3 meters in diameter) with four highly sensitive light sensors fixed to the bottom of the tank.

The HAWC array, operating with 111 Cherenkov detectors since August 1 and growing each week, will be sensitive to of high-energy particles and radiation between 100 GeV and 100 TeV, energy equivalent to billion times the energy of visible light.

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In 2009, HAWC was identified as the Mexican astronomical project with the highest expected impact on high-energy astrophysics and in the US was endorsed by a joint NSF – DOE panel. Shortly thereafter a test array with three Cherenkov detectors was installed at the volcano Sierra Negra and successfully observed cosmic rays and gamma rays. Following these early tests, a prototype array of seven Cherenkov detectors was built in 2009 to test the tank design, simulate real data-taking, and study the logistics of deploying a large-scale observatory in this remote location. In 2012, the first 30 of 300 HAWC detectors were deployed, and since that time have been operated nearly continuously. The 30-detector stage of HAWC permitted calibration of the observatory via the observation of the shadow of the moon as it blocked cosmic rays.

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The Most Energetic Particles in the Known Universe

Gamma rays (electromagnetic radiation of very-high frequency) and cosmic rays (subatomic particles of very-high energy) are products of the most energetic and cataclysmic events in the known universe. These phenomena include the collisions of two neutron stars, the explosions of supernovae, binary systems of stars with stellar accretion, and active galactic nuclei which host black holes millions of times more massive than the Sun.

When high-energy cosmic rays and gamma rays reach the Earth, they interact with air molecules in the upper atmosphere. Gamma rays, for example, are converted into pairs of charged matter and anti-matter particles (mainly electrons and positrons). These particles rapidly interact with other air molecules, producing additional gamma rays of reduced energy which then create further charged particle pairs. This chain reaction proceeds until a large cascade of particles and radiation reaches ground level, where it can be recorded in the HAWC detectors.

When the charged particle cascade from an extra-terrestrial gamma ray passes through a Cherenkov detector, its particles are traveling faster than the speed of light in water. The resulting effect is similar to the shock wave produced in the atmosphere by a supersonic airplane (a "sonic boom"), but instead of producing sound the particles produce a visible cone of blue light. The flash of light, called Cherenkov radiation, is measured by the light sensor fixed to the bottom of each detector in HAWC. By combining the light signal observed in many tanks with fast electronics and high precision computing equipment, it is possible for scientists to determine the time of arrival, energy, and direction of the original extraterrestrial gamma ray or cosmic ray."

For more information see http://www.hawc-observatory.org/

Finding Unconventional Superconductors by Visual Inspection

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Published: Wednesday, February 13 2013 00:00

Researchers, including Steve Anlage, have discovered a new and simple experimental test to see if a superconductor is ‘unconventional’ and unusual. Many of the high temperature superconductors discovered over the past 30 years are thought to be unconventional in nature. One strategy for discovering new higher temperature superconductors is to create even more exotic unconventional superconductors. The experiment creates a clear graphical image of the properties of the superconductor in different directions, as shown below. An anisotropic image is a clear sign of the unconventional nature of the superconducting state. This image shows the four nodal directions of the d-wave superconductor YBa2Cu3O7- as enhanced response (tall, white areas). The technique can now be applied to newly discovered superconductors to test them for unconventional properties, and will help guide the search for even higher temperature superconductors. The results appeared in a spring issue of Physical Review Letters.

JQI and CNAM Researchers Uncover New Exotic Insulator

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Published: Friday, December 14 2012 00:00

Topological insulators have recently emerged as a new and exciting form of quantum matter, in which topologies of the system (rather than symmetries) dictate the physical properties much like the situation found for the quantum Hall effect. To date, the majority of research has focused on non-interacting electron materials such as the bismuth-dichalcogenides, where the nearly free-electron model is sufficient to explain the non-trivial electronic structures that give rise to the observed topological states. An extension of this approach to strongly-correlated electron systems is challenging owing to the difficulty in determining the correct band structure by calculation, and remains as the next grand challenge in condensed matter physics.

A pioneering advance in this direction was made in 2009 by the team of Victor Galitski, who showed that a particularly simple type of heavy-electron material called a Kondo insulator, in which a filled band of heavy quasiparticles gives rise to a narrow band insulator, can host a three-dimensional topological insulating phase analogous to the non-interacting systems such as Bi2Se3. They developed a topological classification scheme for the emergent band structures of these systems, and predicted that at least one compound, samarium hexaboride, may be an ideal candidate.

Recently, this work and experiments performed in the Center for Nanophysics and Advanced Materials by the teams of Johnpierre Paglione and Richard Greene were highlighted in Nature [vol. 492, 165 (2012)] and Scientific American [December 12, 2012]. The experiments, using a technique called point-contact spectroscopy, explored the nature of the Kondo insulator SmB6 and found that the material indeed hosts an unusual metallic surface state as predicted by Dzero and co-workers, even though the bulk of the material becomes insulating upon cooling. Confirmed by other groups studying the properties of the surface state transport, this observation paves the way for the discovery of a new class of strongly-correlated topological insulator materials.

December 14, 2012

LHC to Announce Latest Results at International Conference of High Energy Physics

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Published: Tuesday, September 11 2012 15:50

Scientist from the Large Hadron Collider (LHC) at CERN announced new results in the search for the Higgs boson on July 4, at the International Conference of High Energy Physics, in Melbourne, Australia. The webcast is available at: http://webcast.web.cern.ch/webcast/ University of Maryland researchers are members of the CMS (Compact Muon Solenoid) collaboration, one of two large experiments at the LHC. They have made and continue to make significant contributions to nearly every aspect of CMS from the construction and operation of the detector to physics analysis. For more about UMD at the LHC click here."

The Compact Muon Solenoid

Topological Matter in Optical Lattices

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Published: Friday, December 09 2011 09:20

Atoms trapped by laser light have become excellent platforms for simulating solid state systems. These systems are also a playground for exploring quantum matter and even uncovering new phenomena not yet seen in nature. Researchers at the Joint Quantum Institute* have shown that an optical lattice system exhibits a never-before-seen quantum state called a topological semimetal. The semimetal, which debuts in this week’s Advance Online Publication for the journal Nature Physics (DOI:10.1038/NPHYS2134}, can undergo a new type of phase transition to a topological insulator. Topological insulators are one of the hottest topics in condensed matter research because of their dual-personality. They are insulators throughout the bulk of the material but are conductors along the edges. Read More