Nine sources of extremely high-energy gamma rays have been identified in a new catalog compiled by researchers with the High-Altitude Water Cherenkov (HAWC) Gamma-Ray Observatory, including nine University of Maryland physicists. All nine sources produce gamma rays with energies over 56 trillion electron volts (TeV)—more than eight times the energy of the most powerful proton beams produced at particle accelerators on Earth—and three emit gamma rays extending to 100 TeV and beyond, making these the highest-energy sources ever observed in our galaxy. The catalog helps to explain where the particles originate and how they are produced with such extreme energies.The High-Altitude Water Cherenkov (HAWC) Gamma-Ray Observatory was used to create a map of the galactic plane indicating the highest energy gamma ray sources yet discovered. (Credit: Jordan Goodman/University of Maryland)

“The very high-energy gamma rays we detect are produced by interactions of even higher energy charged particles near their source,” said Jordan Goodman, a Distinguished University Professor of Physics at UMD and U.S. lead investigator and spokesperson for the HAWC collaboration.  “Charged particles are bent in the magnetic fields of our galaxy and don’t point back to their origin. Gamma rays, like light, travel in straight lines allowing us to use them to map the sources of the high-energy emission. HAWC, which is a wide field-of-view instrument, views the overhead sky 24/7 giving us a deep exposure to look for the rare high energy gamma ray events.”

The catalog of high-energy sources was published online in the journal Physical Review Letters on Jan. 15, 2020.  Higher-energy astrophysical particles have previously been detected, but this is the first time specific galactic sources have been pinpointed for such high-energy particles. All of the sources have extremely energetic pulsars nearby. The number of sources detected may indicate that ultra-high-energy emission is a generic feature of powerful particle winds coming from pulsars embedded in interstellar gas clouds known as nebulae, and that more detections will be forthcoming.

The HAWC Gamma-Ray Observatory consists of an array of water-filled tanks sitting high on the slopes of the Sierra Negra volcano in Puebla, Mexico, where the atmosphere is thin and offers better conditions for observing gamma rays. When gamma rays strike molecules in the atmosphere they produce showers of energetic particles. Nothing can travel faster than the speed of light in a vacuum, but in water light moves a little slower. As a result, some particles in cosmic ray showers travel faster than light in the water inside the HAWC detector tanks. The faster-than-light particles, in turn, produce characteristic flashes of light called Cherenkov radiation. Using recordings of the Cherenkov flashes in the HAWC water tanks, researchers reconstruct the sources of particle showers and learn about the particles that caused them.

The HAWC collaborators plan to continue searching for the sources of high-energy cosmic rays. By combining their data with measurements from other types of observatories, such as neutrino, X-ray, radio and optical telescopes, they hope to elucidate the astrophysical mechanisms that produce the cosmic rays that continuously rain down on our planet.

“There are still many unanswered questions about cosmic-ray origins and acceleration,” said Kelly Malone, an astrophysicist in the Neutron Science and Technology group at Los Alamos National Laboratory and a member of the HAWC scientific collaboration. “High energy gamma rays are produced near cosmic-ray sites and can be used to probe cosmic-ray acceleration. However, there is some ambiguity in using gamma rays to study this, as high-energy gamma rays can also be produced via other mechanisms, such as lower-energy photons scattering off of electrons, which commonly occurs near pulsars.”

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In addition to Goodman, other UMD co-authors from the Department of Physics included Visiting Professor Robert Ellsworth; Principal Engineer Michael Schneider; Research Scientist Andrew James Smith; Graduate Students Kristi Engel and Elijah Job Tabachnick; and Postdoctoral Associates Colas Rivière, Chad Brisbois and Israel Martinez-Castellanos.

Text for this news item was adapted with permission from a press release written by Los Alamos National Laboratory. 

The paper “Multiple Galactic Sources with Emission Above 56 TeV Detected by HAWC,” A.U. Abeysekara, et al. was published in Physical Review Letters on January 15, 2020.

The National Science Foundation, the U.S. Department of Energy and Los Alamos National Laboratory provided funding for the United States’ participation in the HAWC project. The Consejo Nacional de Ciencia y Tecnología (CONACyT) is the primary funder for Mexican participation. The content of this article does not necessarily reflect the views of these organizations.  

Media Relations Contact: Bailey Bedford, 301-405-9401,   

UMD physicists have observed, for the first time, interference between particles of light created using a trapped ion and a collection of neutral atoms. Their results could be an essential step toward the realization of a distributed network of quantum computers capable of processing information in novel ways.

As part of the University of Maryland’s Education Abroad program, eligible students are welcome to apply for the the Physics in Florence semester, held at the International Studies Institute (ISI). Prof. Luis Orozco has been responsible for the program, which enrolled 12 students in the Fall of 2019. The curriculum includes three physics classes, an Italian language course, and an elective such as studio art, art history, history and political science, Italian language and literature, international business, and interdisciplinary studies in the humanities.  

One of this fall’s highlights was a visit to the Biblioteca Nazionale, located near the ISI.  Orozco and the students were able to see several of Galileo's original documents, including his log of experiments with inclined planes, his drawings of Jupiter's moons, and his watercolor of the moon's phases.

Another trip was to Geneva, where the students visited CERN. At the Compact Muon Solenoid (CMS) experiment, UMD postdoc Markus Seidel gave the students a tour of the detector, and graduate student Nathan Evetts of the University of British Columbia explained the workings of the Antiproton Ring. 

David Reitze, director of the U.S. gravitational observatory (LIGO), helped arrange a visit to the European Gravitational Observatory (EGO) near Pisa. Valerio Boschi hosted the students and explained the Virgo instrument and its interaction with the two LIGO interferometers in Louisiana and Washington state. After Boschi provided an extensive tour, EGO director Stavros Katsanevas met the students and discussed the current and future physics goals of EGO. 

Near the end of the term, students visited the Galileo Museum, in the Palazzo Castellani near their ISI classes.  The museum houses intriguing scientific instruments, including those of the Medici and the Grand Dukes of Tuscany. Examples include sextants, astrolabes, solar clocks, globes of various orientations, thermometers, telescopes, vacuum pumps and a Ptolemaic mechanical model showing the universe rotating around the earth.  Maps from the 16th century show remarkable accuracy, particularly for the east coast of North America and both sides of South America. Explorers Amerigo Vespucci and Giovanni da Verrazano were both natives of Florence.

At the center of the museum, the Galileo room highlights his contributions to mechanics with a reproduction of one of the inclined plane machines that he used to measure the relationship between time and distance under acceleration. There are also good references to his astronomical observations, with one of the original lenses of his telescope in place.

On a painted table of chemical affinities, the class spotted a symbol that looks like an h bar (ℏ, or Planck’s constant). Having learned about Planck’s constant in class, the students wondered about the symbol’s origin. Orozco found that it was originally a sickle, and that it had stood for lead in alchemy and for Saturn in astrology. Why had Planck called it h? Orozco found that it may reference Hilfsgröße, which is the concept of a “helpful quantity.” This helpful quantity has opened a new world of understanding, much as Galileo did when he found that the distance traveled in fixed time intervals on his inclined plane is proportional to odd numbers (1,3,5,7, etc.)—a classical and early lesson in physics.

Trips to the Biblioteca Nazionale,CERN, EGO and the Galileo Museum are shown in these photos by Adam Dirccam, Anthony Giuffre, Stefano Baldassarri, Sean Markey and Cameron Moneypenny.

A major unsolved puzzle in particle physics and cosmology is the apparent asymmetry in the abundance of matter and antimatter in the universe. One condition for such an asymmetry to arise is the breaking of charge-parity (CP) symmetry in laws of interactions amongst particles, resulting in differences in reactions involving partiPhoebe Hamilton, Will Parker, Hassan Jawahery, Yipeng Sun, Manuel Franco Sevilla and Zishuo Yang. cles and antiparticles. CP violation has been observed in particles containing the strange and bottom quarks--kaons and B mesons--and the results conform to the predictions of the Standard Model at the current level of experimental accuracy. However, CP violation in the Standard Model is not sufficient to explain the matter-antimatter asymmetry in the universe. A key goal of the LHCb experiment is to search for additional sources of CP violation beyond the Standard Model. The Standard Model predicts negligible CP violation in decays of particles containing the charm quark, thus any significant effect in charm mesons could be due to new sources of CP violation. Using the data recorded in 2011-2018, the LHCb experiment has observed CP violation in decays of D mesons – mesons made of a charm quark and anti-up quark.
(see https://arxiv.org/abs/1903.08726 and https://home.cern/news/press-release/physics/lhcb-sees-new-flavour-matter-antimatter-asymmetry.) This work was rated a Physics World Breakthrough of the Year finalist for 2019.

Theorists are hard at work to explain the observed CP violation, which is very small but larger than most of the existing predictions within the Standard Model. Failing any Standard Model explanation, this result could open the door to exploring new sources of CP violation beyond the Standard Model.

The LHCb collaboration is now preparing to complete and install the new upgraded detector elements that will significantly enhance the precision of the spectrometer, thus allowing more precise measurements of CP violation and other very rare effects that may arise from particles and interactions that are not present in the Standard Model. The new upgraded detector elements would enable the experiment to operate at higher intensities of the large hadron collider (LHC) and read out the entire detector--millions of sensor signals--at beam collisions that occur every 25 nanoseconds. Over the past six years, the Maryland team in LHCb has been deeply engaged in the design and construction of a charge particle detector, based on silicon sensors, focusing on the development of the electronics that would enable the readout and transfer of the sensor signals. The team is now preparing to complete the construction of the nearly 600 main electronics boards and 2000 auxiliary boards, which will be shipped to CERN for installation in the LHCb experiment starting in Spring of 2020. The experiment is expected to resume operation in 2021.