What is it?
Physics is concerned with the most fundamental aspects of matter, energy, space and time and how they interact to make the physical universe work. All natural sciences depend upon physics for the foundations of their knowledge. There are many branches of physics ranging from the most basic of topics like mechanics, electricity, light, heat and sound. Some specialties include atomic physics, nuclear physics and elementary particle physics. Physics is the foundation of all the physical sciences, such as chemistry, material science and geology and is important for many other fields of human endeavor such as biology, medicine and computing. The more we learn about physics, the better we understand our place in the universe9.
Astrophysics is the branch of physics that studies objects on the largest scale. It is a part of astronomy primarily concerned with the physical properties and structures of stars, stellar systems and interstellar material. It applies the laws of physics to astronomical bodies in order for us to understand how these bodies formed, how they interact with other bodies and how they cease to be10.
Dark matter makes up approximately 25% of the matter in the Universe. Scientist know more about what properties dark matter doesn’t have than what properties it does have because there is very little visible matter that makes up for the 25% of matter unaccounted for. This is why dark matter is called “dark” – it isn’t part of visible planets and stars. Dark matter is also not made up of baryons, which are what make up dark clouds. It has also been determined that dark matter is not antimatter. Lastly, black holes the size of galaxies are not made up of dark matter. Dark matter is commonly believed to be made up of particles like axions or Weakly Interacting Massive Particles (WIMPs)6.
Cosmology is the study of the universe on a large scale and focuses on understanding the origin, evolution, and future of the universe. The prevailing theory of how the universe came to be is the Big Bang Theory1.
Neutron oscillation refers to the conversion of neutrons into anti-neutrons. This phenomenon is studied in reactor facilities and relates to neutrino oscillations28.
Solar Neutrinos are produced by the nuclear reactions that power the Sun. The main contribution comes from a proton-proton chain reaction. The highest flux of solar neutrinos come directly from the proton-proton interaction with the largest fraction of neutrinos passing through the Earth being solar neutrinos. The first solar neutrino experiment was in the Homestake Mine where a radiochemical method was developed to separate and detect radioactive atoms that formed by capturing solar neutrinos15.
Geoneutrinos are neutrinos produced by radioactive decays deep inside the Earth. The first detection of geoneutrinos was in 2005 by the KamLAND experiment in Japan where scientists detected electron antineutrinos (antimatter counterparts to neutrinos) from the radioactive decay of uranium-238 and thorium-232. The experiment detects about one geoneutrino per month. This has been a very important discovery for science as it provides a means of learning more about the Earth's interior, what it's made of, and how subatomic processes like radioactive decay can even impact major events at the surface 16.
Gravity waves are ripples generated from matter in motion that propagate in spacetime. Like waves generated by a stone tossed into a pond, these ripples travel out from a source26.
Neutrinoless Double Beta Decay
Neutrinoless double beta decay is predicted to exist, but has not yet been seen. In this exchange, two neutrinos annihilate each other, or one nucleon absorbs the neutrino emitted by another nucleon of the nucleus. In order for this to occur, the neutrino must be its own antiparticle, or Majorona particle. A measurement of the neutrinoless double beta decay half life would allow for measurement of the neutrino mass27.
Because of the nature and size of the detectors and other devices used in underground experiements, much of the assembly, construction, and manufacture of this technology occurs underground, offering researchers the opportunity to study these processes.
Low Background Counting
Low background counting is a term used to describe underground laboratories that are shielded from natural radioactivity and cosmic rays. These facilities include clean rooms and other features that make them condusive to interdisciplinary science 14.
Neutrino Properties: Neutrinos have no charge and an extremely small mass. They are difficult to stop or to detect and are able to pass through ordinary matter almost undisturbed 13.
Long-baseline v Oscillation
Where c = charge conjugation and P = parity, CP Violation refers to a violation of CP symmetry, a concept that says that matter and antimatter should be exact opposites in every way, including how they behave23 24.
The MNSP Matrix, developed and name for Maki, Nakagawa, Sakata, and Pontecorvo, describes neutrino oscillation between three "flavors" of neutrinos. The MNSP matrix Uli is as follows:(1)
where cij = cosθij, and sij = sinθij and l,i represent neutrino flavors25.
Nucleon Decay is the decay of neutrons or protons via standard radioactivity. Protons and neutrons form the nucleus of the atom and are referred to collectively as nucleons. The term nucleon decay is often used interchangeably with proton decay. The study of this decay ties in with our understanding of the universe and its expansion.
Atmospheric Neutrinos: Atmospheric neutrinos are the waste products of hadrons (protons, neutrons and other subatomic particles). They are produced in the collision of primary cosmic rays (most often protons) with nuclei in the upper atmosphere. These decay into munon and munon neutrinos, the former then decaying into more neutrinos. This is what deep, underground neutrino detectors are trying to measure 1718.
Experiments at DUSEL
|Credit: The LUX Collaboration
This diagram illustrates how a former Homestake gold mine warehouse has been
converted into the LUX surface laboratory, where a sensitive dark-matter detector will be
tested before installation 4,850 feet underground.
Image courtesy of Sanford Underground Science and Engineering Laboratory.
The Large Underground Xenon detector (LUX) project began in October 2006 and is focused on finding dark matter particles, which are also called weakly interacting massive particles (WIMPs). These particles have never been detected before due to the fact that they go through most materials and substances. The LUX project uses a detector filled with 300 kilograms of liquid xenon that will be kept at 165 degrees below zero on the Fahrenheit scale. Liquid xenon is three times denser than water 5. When the WIMPs interact with the detector’s liquid xenon, they will generate electrical charges in the xenon as well as a flash of light. Details regarding these two signals will determine a signature that will verify the discovery of dark matter 8. The detector was initially staged and assembled at Case Western University before it was moved to an above-ground surface lab with clean room at Sanford Lab that has been built within a former Homestake Mine warehouse 52.
The LUX detector will ultimately be housed in the Davis Cavern, where Dr. Raymond Davis Jr. conducted his Noble Prize winning neutrino experiments in the 1960s. The David Laboratory that has been built in the Davis Cavern is separated by the Yates drift by airlocks and kept as a class 100,000 clean room (meaning that 100,000 particles that are 0.5 µm or larger are permitted per cubic foot of air). There are plans to build clean rooms within the Davis Cavern that will reduce this clean level to better than 1,000 4. In the Davis Laboratory, the LUX will be shielded from cosmic interference such as cosmic rays, uranium, and thorium 8. The LUX Detector is the largest project planned for the 4,850 foot level of the S/DUSEL.
|Credit: Bill Harlan/Sanford Underground Laboratory
Scientists work in the new LUX surface laboratory at the Sanford Underground
Laboratory at Homestake. The plywood sheet covers the "detector pit" — a three-story
hole where the LUX dark-matter detector will be installed and tested before installation
4,850 feet underground. The class-enclosure in back is a clean room. Left to right:
Sanford Lab Science Liaison Jaret Heise, Sanford Lab Science Supervisor Tom
Trancynger, Texas A&M graduate student Ty Stiegler and Case Western Reserve
graduate student Patrick Phelps.
Image courtesy of Sanford Underground Science and Engineering Laboratory.
The surface facility is also shielded with a 1 meter of water, which reduces the event rate due to gammas and neutrons in the detector from 10 kHz to 100 Hz. The tank is considerably smaller than the tank in the Davis Laboratory. The surface facility is also affected by High-energy cosmic muons that are expected at a rate of 50 Hz in the detector. The shield of water does not guard against these muons, but turning the detector on for a short period can reduce the effect of muon activity when they move through the detector volume 3.
The Majorana Collaboration, named after physicist Elliot Majorana who studied particles that are their own anti-particle in the 1930s, includes scientists from 15 universities across the globe, including Canada, Japan, and Russia. Scientists plan to use germanium crystals that are extremely rare, purified, and enriched to find an equally rare form of nuclear decay. It is a process that is only possible if neutrinos have their own mass and are their own anti-particle. The rate of nuclear decay in the experiment is directly related to the magnitude of neutrino mass. Detecting the double beta decay of the germanium means looking for ionized atoms in the germanium crystals. Electrons in these ionized atoms drift, which makes an electronic pulse, which indicated double beta decay 8.
Like the LUX Detector, the Majorana Collaboration experiment will need to be shielded from cosmic interference. Such interference could make signals that would mask the electronic pulse that indicates double beta decay. Members of the Majorana Collaboration will electroform copper underground to use as the inside liner for the detector so that it will be as pure as possible 8. The germanium crystals will be built underground by physicists. Building them underground helps in keeping the crystals pure of any cosmic interference that could hamper the experiment due to its sensitivity 7.
Who's Doing It?
- What is the universe made of?
- How did the universe evolve?
- What is dark matter?
- What are neutrinos?
- Are protons unstable?
Calder, Nigel. Einstein’s Universe: The Layperson’s Guide. London: Penguin, 2005.
Nonfiction (1st floor – Main Collection): 530.11 CAL
Davies, P. C. W. About Time: Einstein’s Unfinished Revolution. New York: Simon & Schuster, 1995.
Nonfiction (1st floor – Main Collection): 530:11 D257a
Feynman, Richard Phillips. The Very Best of the Feynman Lectures. New York: Basic Books, 2005.
Books on CD (1st floor – AV Collection): 530 FEY
Gates, Evalyn. Einstein’s Telescope: The Hunt for Dark Matter and Dark Energy in the Universe. New York: W. W. Norton, 2009.
New Items (1st floor): 523.1126 GAT
Hawking, Stephen and Roger Penrose. The Nature of Space and Time. Princeton, NJ: Princeton UP, 2000.
Nonfiction (1st floor – Main Collection): 530.11 HAW
Kaku, Michio. Hyperspace: A Scientific Odyssey through Parallel Universes, Time Warps, and the Tenth Dimension. New York: Anchor Books, 1995.
Nonfiction (1st floor – Main Collection): 530.142 KAK
Keel, W. C. The Sky at Einstein’s Feet. Berlin: Praxis, 2006.
Nonfiction (1st floor – Main Collection): 523.01 KEE
Trinh, Xuan Thuan. Chaos and Harmony: Perspectives on Scientific Revolutions of the Twentieth Century. Trans. Axel Reisinger. Philadelpha: Templeton FP, 2006.
Nonfiction (1st floor – Main Collection): 523.01 TRI
White, Michael and John Gribbin. Stephen Hawking: A Life in Science. New York: Dutton, 1992.
Biography (1st floor – Main Collection): B H392w
Corredoria, M. Lopez and C. Castro Perelman, eds. Against the Tide: a Critical Review by Scientists of How Physics and Astronomy Get Done. Boca Raton, FL: Universal Publishers, 2008.
Nonfiction (1st floor – Main Collection): 530.072 AGA
Maguelijo, João. Faster than the Speed of Light: The Story of Scientific Speculation. Cambridge, MA: Perseus, 2003.
Nonfiction (1st floor – Main Collection): 535.1 M2131
- LUX Homepage (Information, Resources, Talks, etc.)
- Information and Resources on the Majorana Collaboration via Pacific Northwest National Laboratory
- "Atom Smashers" on Independent Lens, produced by PBS.
- Digging for Dark Matter: The Large Underground Xenon (LUX) Detector by Ian O'Neill on Universe Today.
- Astronomy Without A Telescope – Astronomy On Ice by Steve Nerlich on Universe Today.
- Early Results from Large Dark Matter Detector Cast Doubt on Earlier Claims by John Matson on Scientific American.
- Dark matter 'no result' comes under fire by Jon Cartwright on Physics World.
- Dark Matter - The Biggest Mystery in the Universe by Richard Panek in the Smithsonian Magazine.
- Physics for the 21st Century, Dark Matter unit developed by Rick Gaitskell, professor of physics and head of the particle astrophysics group, Brown University and produced by the Science Media Group at the Harvard-Smithsonian Center for Astrophysics.
- Quest for Dark Energy May Fade to Black by Dennis Overbye in the New York Times.
- Tevatron faces final curtain by Eugenie Samuel Reich in nature news on nature.com.
- Radioactivity challenges dark-matter detector by Eugenie Samuel Reich in nature news on nature.com.