Sunday, July 26, 2015


The Universe is a mysterious place. Although much is known about the physics processes that guide it, there are many more unanswered questions. WIPAC addresses contemporary astroparticle physics topics through several experiments, studying phenomena like neutrinos, cosmic rays, gamma rays, dark matter, weakly interacting massive particles (WIMPs), and gamma-ray bursts.


Jul 2015
A Combined Maximum-Likelihood Analysis of the High-Energy Astrophysical Neutrino Flux Measured with IceCube
Jun 2015
Detection of a Type IIn Supernova in Optical Follow-up Observations of IceCube Neutrino Events
Observation of Small-scale Anisotropy in the Arrival Direction Distribution of TeV Cosmic Rays with HAWC
First Constraints on the Ultra-High Energy Neutrino Flux from a Prototype Station of the Askaryan Radio Array
Image courtesy of NSF/IceCube
Image courtesy of NSF/IceCube


Nearly massless and without electrical charge, neutrinos are fermions that can travel from the edges of the Universe on an uninterrupted trajectory, making them excellent cosmic messengers. These same qualities also make them elusive and hard to detect.
Both the IceCube Neutrino Observatory and the Askaryan Radio Array (ARA) are neutrino detectors, searching for evidence of these tiny particles at different energies and in different ways. IceCube observes the radiation that is emitted when a neutrino interacts with an atom in the ice and detects neutrinos with energies in excess of 0.1 TeV. A subdetector within IceCube known as DeepCore has the capability to see neutrinos with energies as low as approximately 10 GeV.
Ultrahigh-energy (PeV and above) neutrinos are the focus of ARA, which uses radio waves to detect GZK or cosmogenic neutrinos.
Image courtesy of NSF/J. Yang
Image courtesy of NSF/J. Yang

Cosmic Rays

The Earth's atmosphere is constantly being bombarded by cosmic rays, subatomic particles of cosmic origin with energies up to one hundred million times higher than can be created in man-made accelerators. Despite their plentiful nature, little is known about exactly how cosmic rays are generated but their production is believed to include the release of neutrinos.
The theoretical issue of designing a blueprint for such a powerful cosmic accelerator challenged the physics community for decades. Two leading ideas emerged to explain the production of cosmic rays: the massive black holes at the centers of active galaxies and the exploding fireballs discovered by astronomers known as gamma-ray bursts.
Production of cosmic rays is inevitably accompanied by neutrinos, and in early 2012 the IceCube Collaboration published results in the journal Nature describing a search for the emission of neutrinos from gamma-ray bursts. In data taken during the detector’s construction, no neutrinos were observed from 300 GRBs between May 2008 and April 2010, a result that contradicts 15 years of predictions and challenges one of the two leading theories for the origin of the highest energy cosmic rays.
As the IceCube Neutrino Observatory grows in size and theoretical understanding develops, researchers hope to better comprehend the mystery of cosmic ray production.
Image courtesy of NASA
Image courtesy of NASA

Gamma Rays

High-energy electromagnetic radiation known as gamma rays comes from many sources. They occur naturally as part of radioactive decay, but the highest energy gamma rays come from astronomical sources.
The High-Altitude Water Cherenkov (HAWC) Observatory is a second-generation TeV gamma-ray detector. Building on the success of the Milagro experiment, HAWC is designed to measure spectra of galactic sources up to and beyond 100 TeV, map galactic diffuse gamma-ray emission, and study transient phenomena.
Image courtesy of NASA
Image courtesy of NASA

Dark Matter

It is estimated that nearly one quarter of the Universe consists of dark matter. It is clear that dark matter exists, but it has yet to be directly observed and many of its aspects remain unclear.
According to some theoretical models, an observable signature of dark matter is the rate of dark matter-nucleon interactions taking place in an Earth-bound experiment. A direct detection method involves the search for weakly interacting massive particles (WIMPs), theoretically favored candidates for dark matter. Researchers search for WIMPs through observation of WIMP-nucleon elastic scattering.
WIPAC enters the international dark matter search with the IceCube Neutrino Observatory and DM-Ice, a sodium iodide (NaI) scintillation detector array at the South Pole that searches for a modulation in the detected event rate. IceCube searches for neutrinos from the annihilation of dark matter particles gravitationally trapped at the center of the Sun and Earth. IceCube is competitive with specific direct detection methods for dark matter when the WIMP mass is large enough.

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