Main Injector Neutrino Oscillation Search - FAQs:

Q: What is the purpose of the Laboratory? The MINOS Laboratory (the tour site) houses the MINOS Far Detector and was completed in 2003. The goal of this effort is to measure the mass of particles called neutrinos, which are smaller than the nuclei of atoms. The neutrinos studied here will be generated about 450 miles away at Fermi National Accelerator Laboratory, just west of Chicago, and sent through the earth to the MINOS Far Detector. The older part of the laboratory next-door houses the CDMS II dark-matter detection experiment.

Q: Why are the laboratories located deep underground? The MINOS Far Detector consists of a large quantity of very sensitive energy detectors. Since the beginning of time, natural radiation called cosmic rays have come down onto the surface of the earth from the sky. If the MINOS Detector were located on the surface of the earth, these cosmic rays would confuse the detector and mask the effects we are seeking. In the MINOS Laboratory, almost 1/2 mile underground, we use the earth itself as a shield to vastly decrease the number of cosmic rays. CDMS II is even more sensitive to cosmic rays, so the deep underground site is a necessity.

Q: What is a neutrino? What is "dark matter"? A neutrino is a sub-atomic particle without electric charge that experiences only very weak interactions with ordinary matter. It is very similar to an electron, but without its electric charge. Neutrinos are produced in beta decay, when a neutron decays into a proton and an electron, and in similar processes, such as the fusion that powers our sun and most other stars. Neutrinos come in at least three varieties�one is associated with the electron, one with a much heavier particle called the muon and the final variety with an even heavier particle called the tau. As for "dark matter": no one really knows! It may be very heavy so-far undiscovered elementary particles. What we DO know is that there is a lot of it - perhaps 90% of the matter in the universe is of this type.

Q: Who is working on the projects? The MINOS Collaboration is an international effort of scientists, support staff and students from universities and laboratories in the United States, the United Kingdom, Greece, Popland, and Brazil. The MINOS institutions (Fall 2009) are Argonne, Athens, Benedictine, Brookhaven, Caltech , Cambridge, Campinas, Fermilab, Goias, Harvard, Holy Cross, IIT, Indiana, Iowa State, Minnesota-Twin Cities, Minnesota-Duluth, Otterbein, Oxford, Pittsburgh, Rutherford, Sao Paulo, South Carolina, Stanford, Sussex, Texas A&M, Texas-Austin, Tufts, UCL, Warsaw, and William & Mary. The CDMS collaboration includes groups from Case Western Reserve University, Fermilab, Lawrence Berkeley National Laboratory, the National Institute of Standards and Technology, Princeton, Santa Clara, Stanford, California at Berkeley and Santa Barbara, and the University of Colorado at Denver.

Q: How much do the projects cost? The overall cost of the MINOS project over a period of years is about $174 million. The MINOS Far Detector will cost about $32 million when it is completed. The MINOS Laboratory cost approximately $7 million to excavate and finish to an empty room and a similar amount to install all of the steel support structures and electrical, communications and other support systems. The cost of the CDMS II project is about $16 million.

Q: Who funds the projects? Most of the financial support for MINOS comes from the U.S. Department of Energy (DOE), as part of its program to support fundamental research in energy-related sciences. Additional support is provided by science funding agency of the UK. Other sources include the National Science Foundation (NSF), the universities and institutes participating in MINOS, and the State of Minnesota. CDMS II is also funded by a combination of NSF and DOE support.

Q: How big is the new MINOS Laboratory? The MINOS Laboratory is 270 feet long, approximately 50 feet wide and 40 feet high. About 50,000 tons of rock was excavated to make this cavity. All of the rock was taken up the elevator, 6 tons at a time. Most of the rock was piled on the surface southeast of the headframe; some of it was used to build the parking lot west of the engine house.

Q: How big is the MINOS detector? The MINOS Far Detector consists of two super-modules. Each one is an octagon (neutrino stop sign!), 8 m or 27 feet across, and 15 meters or 48 feet long.

Q: What does MINOS mean? MINOS stands for Main Injector Neutrino Oscillation Search. The "Main Injector" is the principal accelerator at Fermilab responsible for producing the neutrino beam. The term "oscillation search" refers to the technique that the MINOS project is using to determine whether neutrinos have mass and, if so, how much that mass might be for each type of neutrino. In Greek mythology, Minos was the King of Crete who built the labyrinth and was the son of Zeus and Europa.

Q: What is the MINOS detector made of? The detector consists of alternating planes of iron and plastic scintillator strips. Scintillator is a special plastic with embedded chemicals that produce pulses of light when the plastic is traversed by a high-speed, electrically-charged particle. A special wavelength-shifting optical fiber is glued along the center line of each 1.5 inch wide strip. Chemicals in the fiber convert ultraviolet scintillation light into visible light that travels down the fiber to the edge of the detector. At the detector edge, the light is transmitted from the wavelength-shifting fibers to clear optical fibers that transmit the light to photomultiplier tubes. These are extremely sensitive light detectors that generate an electrical pulse for each microscopic flash of light they see. These electrical pulses are collected, recorded and analyzed by custom integrated circuits (produced in Norway). The data are then further analyzed and archived by a network of computers scattered around the laboratory. In total, the MINOS Far Detector will weigh about 6,000 tons with iron as most of the mass. The iron is magnetized by an electrical current passed through the middle of the detector, in order to provide information about the momentum and charge of particle tracks observed in the detector.

Q: Where do the neutrinos come from? Most of the neutrinos that the MINOS Far Detector will observe will be produced at the Fermi National Accelerator Laboratory. The Fermilab Main Injector will produce an intense beam of protons with an energy of 120 billion electron volts. This beam will be directed at a special graphite target. Many of the beam protons will interact in the target and some will produce other sub-atomic particles called π mesons. The π mesons will travel down an 675 m (2,200 foot) vacuum pipe. While traveling down the vacuum pipe, most of the π mesons will decay and produce neutrinos and other particles called μ mesons. Some of the μ mesons will also decay and also produce neutrinos. A 10 m (33 foot) thick iron absorber at the end of the vacuum pipe followed by a 240 m (800 foot) rock berm will absorb all particles in the beam other than neutrinos. The neutrinos will mostly continue straight through the iron and the earth and begin their 735 km (about 450 mile) journey to Soudan.

Q: What/where is Fermilab? Fermilab (officially the Fermi National Accelerator Laboratory) was established in Batavia IL (40m west of Chicago) in 1970 to house the highest-energy particle accelerator ("atom smasher") in the world. It is the home of major physics experiments in the US, including two that hope to soon discover the postulated elementary particle (the "Higgs boson") that explains why particles such as neutrinos have mass (if we discover that they really do!). It is operated by a consortium of more than 90 universities (including almost all mentioned here).

Q: How does the MINOS Far Detector know that a neutrino passed through? Most of the time, the detector does not know that a neutrino passed through. Neutrinos interact very weakly with ordinary matter, which is why most of them will travel almost 450 miles through the earth from Fermilab to Soudan without a tunnel. However, the number of neutrinos shot from Fermilab to Soudan is very large, so large that about once every 2 hours a neutrino will interact in the detector and produce one or more charged particles that will produce light in the plastic scintillator detectors. In addition to neutrinos produced at Fermilab, the MINOS Far Detector will also measure neutrinos produced naturally from cosmic radiation.

Q: How does detecting neutrinos traveling from Fermilab to Soudan measure neutrino mass? Neutrinos come in 3 varieties, one each associated with the electron, the mu and the tau. Our understanding of quantum mechanics, the part of physics that describes the behavior of these particles, indicates that if neutrinos have mass, it is possible for a neutrino to spontaneously change from one type to another, that is, to "oscillate" its variety. The oscillation probability depends on their energy and the mass differences among the three different neutrino varieties. Thus, strictly speaking, MINOS does not measure neutrino mass. Rather, it measures neutrino oscillation probability as a function of neutrino energy and thus neutrino mass differences.

Q: How can you tell the neutrinos have changed from one type to another? Generally, the type of neutrino that interacted in the detector can be deduced from the pattern of the energy deposition. An electron-type neutrino is likely to produce a short, wide shower of hits. A narrow, long energy deposition pattern indicates a muon-type neutrino. Tau-type neutrinos are very difficult to observe directly, but a large number of these will be obvious statistically as "too many of the wrong kind of events". The MINOS Near Detector, a smaller version of the Far Detector, is installed at Fermilab to measure the relative number of each neutrino type in the beam as it leaves Fermilab. The Far Detector makes a similar measurement at Soudan. A difference in these two measurements is the signature of neutrino oscillations and thus neutrino mass.

Q: Why is it important to do this experiment? Measuring neutrino mass and the oscillation probabilities among the different neutrino varieties will add considerably to our knowledge of the fundamental interactions in the universe. These interactions controlled the formation of the universe in a massive explosion or "Big Bang" some 14 billion years ago. They continue to control how our universe develops at all scales from the sub-atomic microscopic level to the huge distances studied in astrophysics. There are good reasons to believe that our universe is filled with invisible neutrinos traveling in all directions, some produced by fusion or other processes in stars and even some left over from the Big Bang. Neutrinos with mass could greatly affect the development of the universe through gravitational interactions. They could be another portion of the "dark matter" that we believe significantly affects the development of the universe.

Q: How long did it take to construct the MINOS Laboratory? Excavation of the MINOS Far Detector Laboratory began in the summer of 1999. The excavation was complete and the ceiling, walls and floor finished with concrete in November 2000. The lab outfitting: steel fabrication and installation and installation of electrical, communications and other systems was completed in July 2001. The first MINOS Far Detector plane was placed at the end of July, 2001, and the detector was taking data in August of 2003. The CDMS II experimental buildings were finished (in the next-door laboratory) in the spring of 2002.

Q: How was all this big equipment brought 1/2 mile underground to the laboratory? Installation of the MINOS Far Detector resembles the proverbial problem of building a boat in a bottle. Everything you see came down the same mine shaft that you used to travel underground. The hoisting system at Soudan is capable of handling pieces of equipment as large as about 4 feet by 6 feet by 33 feet in length with weights up to 6 tons. Everything used in the laboratory was carefully designed to fit within these limits. The steel was transported in bundles of 4m-wide strips, 8m long. Two bundles are welded together to make the 8m-wide octagons. The detector planes were brought underground in strips, packed in special, reusable shipping boxes. The strips were welded to the steel in the open area directly under the Visitors' Gallery. Then, a special hoisting fixture called a "strongback" was used to swivel the assembled plane from a horizontal to a vertical position and to move it to the proper position in the detector

Q: Why was it necessary to build a second lab? The MINOS Far Detector is too big to fit in the Soudan 2 Lab, even if everything else were removed. The Soudan 2 Lab is also oriented almost directly north-south, because of the stress pattern in the local rock. The MINOS Lab was built to point directly to Fermilab. The orientation of the MINOS Lab long axis is 23° east of south. The new construction also freed up space for CDMS II, and perhaps future experiments.

Q: Are there other labs like this in the world? During the past 50 years, more than a dozen underground mines and tunnels have been used for physics experiments. Many of these sites housed small installations and are no longer active. The major underground laboratory sites in use today include the Homestake Gold Mine in Lead, SD; the Creighton Mine in Sudbury, Canada; the Boulby Mine in northeastern England; the Gran Sasso Tunnel in Italy; the Frejus Tunnel between France and Italy, the Baksan Laboratory in Russia; and the Kamioka Laboratory in Japan.

Q: What is the relationship between the MINOS Laboratory and the Soudan Underground Mine State Park? The site at Soudan was donated to the people of Minnesota by U.S. Steel in 1962. The State of Minnesota has operated the Soudan site as a State Park through the Department of Natural Resources (DNR) since that time. DNR personnel under the direction of Park Manager Jim Essig operate and maintain all of the hoisting, pumping, electrical, communications and other systems that serve the Soudan site. They also escort approximately 40,000 visitors each year underground to tour the last working areas of the Soudan iron mine. The University of Minnesota leases the underground laboratory from the State and operates it under a contract with the U.S. Department of Energy. University personnel staff the laboratory itself under the direction of Lab Manager Jerry Meier.