At Black Hills State University, the Physics program is investigating the nature of dark matter and neutrinos. Key questions in 21st century physics that have been identified by many national institutes including: the National Research Board, the National Science and Technology Council, the High Energy Physics Advisory Panel (HEPAP), and more.
BHSU, led by Dr. Kara Keeter, is establishing a nuclear and particle astrophysics program at Black Hills State University that studies the very smallest particles in the universe in order to understand structures as large as stars, supernovae, and even galaxies. Two elusive particles, neutrinos and dark matter, are the current subject of intense debate and interest. In fact, national advisory committees list investigating the nature of dark matter and neutrinos among the highest priority questions in particle physics today. Below are some details about BHSU's Physics programs efforts in dark matter research and Neutrino research.
Dark Matter Research:
BHSU is involved in two collaborations to build detectors to search for dark matter in the form of WIMPs (Weakly Interacting Massive Particles). These two collaborations are:
- DARKSIDE (Depleted Argon Dark Matter Detector)
- MAX (Multi-ton Liquid Argon and Xenon Dark Matter Detectors)
WIMPS? What are WIMPS?
Cold dark matter experiments are a primary focus area of major funding organizations such as the NSF, DOE and NASA*. Astrophysical evidence for cold dark matter is now compelling, but its nature remains a fundamental mystery. Particularly intriguing is the possibility that dark matter is made of Weakly Interacting Massive Particles (WIMPs) that interact only via the gravitational force and the weak nuclear force. These WIMPs may be observed by detecting their collisions with ordinary nuclei as the Earth's motion intercepts their path around the galaxy.
The Dark Matter Scientific Advisory Group has identified detectors based on noble liquids as one of the most promising technologies for detecting dark matter WIMPs. Liquid argon is an especially promising medium for WIMP detection due to its efficient conversion of energy from WIMP-induced nuclear recoils into both ionization and scintillation, allowing a very effective separation of nuclear recoil events from β/γ background radiation.
DARKSIDE and MAX Explained:
DARKSIDE and MAX are international collaborations to build dark matter detectors. The DARKSIDE Collaboration is designing a small detector that will use liquid argon from underground sources so that it is depleted in 39Ar. This is important because 39Ar is radioactive and would be a source of undesirable background. This isotope of argon is produced when cosmic rays strike natural atmospheric argon atoms.
The MAX Collaboration is designing a much larger detector that will use the DARKSIDE detector as a prototype. The MAX detector will actually be two detectors, one using liquid argon and one using liquid xenon, that will share resources and common costs such as basic engineering design. MAX will be able to provide:
- Confirmation of discovery in twin targets
- Confirmation of A2 dependence of cross section
- Measurement of the mass of the WIMP by comparison of recoil spectra in different targets
- Indication on spin-dependent or spin-independent nature of interactions
It is critical to the success of these searches that the argon or xenon be free of impurities that would distort or quench the signal. BHSU is designing and building a custom trace gas analyzer based on cavity ring-down spectroscopy (CRDS) that will exceed the currently available sensitivities by an order of magnitude. We are working with Dr. Kevin Lehmann of UVa, who holds several patents. The BHSU system will be in demand by all neutrino and dark matter experiments using noble liquids.
Find out what BHSU students and staff are researching on neutrinos. These particles come to Earth from space, and are so hard to “see” that it is necessary to place the detectors deep underground, to shield from background “noise” found on surface. The Sanford Underground Research Facility (SURF) at Homestake acts as a perfect location for this type of research.
BHSU is involved in two experiments to look for neutrinoless double beta decays:
- MAJORANA (Ge-based Neutrinoless Double Beta Decay Detector)
- SNO+ (Nd-based Neutrinoless Double Beta Decay Detector)
Both of these collaborations are international in scope. MAJORANA is part of the Initial Suite of Experiments to be deployed in SURF, while the SNO+ detector is housed within the infrastructure of the Sudbury Neutrino Observatory in a mine near Sudbury, Ontario.
Neutrinoless Double Beta Decays Explained:
Although it has been determined that neutrinos have mass, there are still questions regarding the nature of neutrinos: whether they are Majorana particles or Dirac particles; what is the mass scale; etc. One experimental approach to answer these questions is to look for neutrinoless double beta decay reactions. Certain isotopes may undergo decay reactions involving the simultaneous emission of two beta particles (electrons). According to the Standard Model of Particle Physics, two neutrinos (or antineutrinos) should also be emitted. However, if the neutrino can serve as its own antiparticle (i.e., if it is a Majorana particle) then it should be possible to have a double beta decay in which no neutrinos are emitted.
By carefully measuring the cross section of double beta decay reactions in ultra-sensitive experiments, neutrinoless double beta decay may be observed, violating the conservation of lepton number and proving that neutrinos are Majorana particles.