High-Energy Astrophysics

Particle astrophysics lies at the intersection of physics and astronomy, exploring elementary particles that have cosmic origins. Within this field, CCAPP is at the forefront of one of the most exciting areas of exploration: ultra-high energy (UHE) cosmic rays, gamma rays and neutrinos. These rare particles cross paths with Earth at energies one thousand times greater than that of the Large Hadron Collider, the laboratory currently accelerating protons to the highest terrestrial energies.

In 2013, IceCube reported the first observation of UHE neutrinos with extra-solar origin. The details of this signal have begun providing clues about the origins of UHE cosmic rays, fundamental particle physics at high energy, and fundamental tests of dark matter. While we know neutrinos are produced by phenomena such as fusion reactions in the sun, supernovae and possibly active galaxy nuclei, the particles only interact with matter via the weak nuclear force and they are electrically neutral. They are therefore difficult to record and require ambitious detectors involving many scientists from around the world working in tandem.

Astroparticle theorists and experimentalists at CCAPP are investigating the nature and origins of UHE particles using IceCube, ARA, ANITA, AUGER and Fermi—some of the most ambitious and cutting-edge detection instruments in the world. To get the fullest understanding of these elusive particles, CCAPP scientists use a multimessenger approach—compiling information from different types of observations for each event to illuminate the high-energy astrophysical universe.

ARA and ANITA focus on UHE neutrino detection via the Askaryan effect, which requires vast volumes of ice; they therefore operate in Antarctica, as does IceCube. The Pierre Auger Observatory measures particle cascades detectable both in muon radiation at the Earth’s surface and in UV fluorescence from the portion of the shower in the sky. The Fermi Large Area Telescope—named for the original theorist who postulated the existence of neutrinos—is a satellite that records high-energy gamma rays as they pass through the detector mass, producing pairs of electrons and positrons.

The Fermi collaboration has posted discoveries of numerous strange, gamma ray-emitting astrophysical objects within our galaxy. Most recently, CCAPP researchers have focused on the galactic center as an area to search for dark matter. The galactic center has also produced the so-called “Fermi bubbles”—vast, symmetric regions emanating from the center of the Milky Way that radiate gamma rays.

CCAPP hosts several theoretical efforts that take advantage of new IceCube, Fermi, ANITA and ARA data in order to probe fundamental particle physics. IceCube data, for example, has been used to understand and constrain the ability of the three neutrino flavors to oscillate—that is, to randomly change flavor via quantum mechanics. Other experimental efforts in the astroparticle group are driving towards solving the mystery of the origin of cosmic rays and other problems involving cosmology and dark matter.

The greatest strength of CCAPP astroparticle physics is the ability for researchers of different sub-fields to collaborate freely. The high-energy astrophysical universe contains promising avenues of research, and CCAPP professors, graduate students and postdoctoral fellows are poised to illuminate this field together, working in collaboration.