They are smaller than molecules, atoms, and quarks. Created through nuclear fusion in stars, nuclear reactions and in highenergy particle collisions, neutrinos are nearly massless particles of energy that travel at almost the speed of light. They pass completely through all matter, rarely interacting with any other particle. Just like a ghost!
They are very unpredictable particles that change, or oscillate, from one form to another (muon to tau to electron), in no particular order. Yet they are powerful. “Despite being so small, neutrinos are numerous enough to affect the motions of stars and galaxies through their gravitational pull,” says Gregory Dooley, Ph.D, physics from MIT, who has studied galaxies and neutrinos. “In particular, neutrinos affected the distribution of matter in the early universe, which ultimately affects the motions, size, and number of galaxies today.”
Scientists are chasing these elusive particles in an effort to understand them, and by understanding them, hoping that we can better understand ourselves. Why we, as humans and even the universe itself, exist.
Sanford goes sub-Atomic
What is the origin of matter? What is dark matter and how do we know it’s really there? What are the properties of neutrinos? These are questions that the scientists at Sanford Lab are pondering. The Sanford Underground Research Facility (SURF) takes us into deep science and the exciting projects happening right here in South Dakota, projects at the very frontier of physics.
The Sanford Lab is located in the former Homestake mine in Lead, SD. Ironically, in order to study neutrinos, some of the smallest particles generated by the cosmos, we need to go deep underground. “Neutrinos are about 20 orders of magnitude smaller than an atom,” says Dr. Jaret Heise, director of science at the Sanford Lab. “That would translate to about 500,000 times lighter than the next lightest particle, the electron. And we still don’t know the mass, so it could be much lower still.”
South Dakota is at the epicenter of international research with scientists from 160 institutions around the world, collaborating on dozens of experiments, all with the goal of expanding our knowledge of how the universe works. But it isn’t just science that’s benefiting from the research, it’s also the economy.
“The Sanford Lab has had a tremendous impact on the economy of South Dakota, investing over $171 million in the state,” says Mike Headley, the executive director of the South Dakota Science and Technology Authority (SDSTA) which operates the SURF facility. “and 163 jobs have been created because the Sanford Lab is here.”
Q & A with scientist Jaret Heise
- What is a neutrino?
The neutrino is the most abundant matter particle in the Universe, first theorized by Wolfgang Pauli in the 1930s, and later detected in the 1950’s to explain observations of nuclear decays that appeared to violate the laws of physics. They are produced by nuclear fusion, the process that powers the sun (*see photo insert) and by the decay of radioactive elements. They can also be created at accelerator laboratories such as Fermilab located near Batavia, Illinois.
- What makes a neutrino unique?
These particles have no electric charge (unlike the electron or proton) and interact via a weak nuclear force. As far as we know, they are similar to electrons and quarks, meaning the neutrino cannot be broken up into smaller particles (in contrast to say neutrons and protons that are made of quarks).
Originally, the neutrino was assumed to have no mass, but knowing the neutrino oscillates from one type to another, it must also have at least some mass.
- Why are neutrinos called “ghost particles”?
Despite being surrounded by trillions and trillions of neutrinos, they interact so rarely that we hardly even know they exist (in the same way that people think of ghosts). These subatomic particles can travel vast distances without interacting with normal matter. In fact, trillions of neutrinos are passing right through you each second!
- What are some of the research projects going on at the Sanford lab?
Large Underground Xenon (LUX):
Recognized as the most sensitive dark matter experiment in the world, LUX published its findings in a January 2017 paper advancing the science of the types of possible Weakly Interacting Massive Particles (WIMPs) masses. The successor LUX-ZEPLIN (LZ) project will be the world’s most sensitive dark matter direct detection experiment for WIMPs over a large range of masses.
Majorana Demonstrator (MJD):
This experiment is investigating neutrinoless double beta decay. As part of their experiment, MJD produces the world’s purest copper at the Electroforming Lab, located 4,850 feet underground at the Ross Campus. The copper grows at 30 microns and takes 14 months to reach the desired thickness of about 0.5 inches. About 5500 lbs of electroformed copper was produced over a period of 4 years. Impurity levels are measured in parts per quadrillion, which means that for a 1-kg sample of the MJD copper expect to wait almost 4 months for one decay! Sending the copper to a machine shop on the surface would ruin it because cosmic rays will transform a small number of the copper atoms into radioactive Cobalt-60, so MJD Cu produced at Electroforming Lab is transported underground across the site to machine shop set up underground at the Davis Campus. MJD is currently completing the commissioning of their detector systems and moving to operations that are expected to continue through 2020.
- Why do scientists need to go deep underground to study particles that come from the universe?
Cosmic ray muons are energetic particles that rain down on Earth from outside our solar system. These muons create a background of noise that’s too loud for scientists to be able to hear the faint signals of rare processes they are studying. A muon is a type of particle similar to an electron, except heavier. On Earth’s surface, the flux of cosmic ray muons is roughly 2 or 3 passing through your hand every second. But by going deep underground, scientists can reduce the “noise” or number of muons passing through your hand to only about 1 every month. That creates a better environment for researching elusive particles like the neutrino.
- What do you hope to discover?
Generally, scientists at the facility hope to increase humanity’s knowledge of how the Universe works.
Studies of the neutrino will inform and test theories that help explain the extremely low mass and guide us to determine which of the three known types of neutrinos is heaviest and which is lightest (mass hierarchy).
The neutrino is the strangest particle we have ever seen. We also think that the solution to some of the most perplexing questions in physics today may be concealed in properties of the neutrino, such as an explanation of the matter-antimatter asymmetry that ultimately explains why we exist.
- Dark matter makes up 80% of the universe, but rarely interacts so how do we really know dark matter exists? The measured rotation of our galaxy should fling it apart given the high speed, but of course that’s not the case. Dark matter is holding our galaxy together. As we look out into the cosmos we see effects due to the bending of light due to deformations of space by the presence of matter (a process called gravitational lensing); some of the best evidence is from observations of the Bullet Cluster. The cluster contains a spectacular bullet-shaped cloud of hundred-million-degree gas and provides tantalizing evidence for the existence of dark matter.
- Is it possible to harness the power of neutrinos?
A likely use for the neutrino would be to leverage its ability to easily penetrate all materials and perhaps develop some type of new communications system.
- What’s next?
The Deep Underground Neutrino Experiment, DUNE, is a proposed international experiment designed to study the mysteries of neutrinos. It would be one of the largest international mega-science projects ever hosted in the U.S. DUNE aims to make definitive determinations of neutrino properties, the dynamics of the supernovae that produced the heavy elements necessary for life and the possibility of proton decay. DUNE research will be conducted using the Long-Baseline Neutrino Facility, LBNF, which combines capabilities at both Fermilab and the Sanford Underground Research Facility in South Dakota. All of the experiments done in the lab have the potential to win a Nobel Prize.
Mike Headley on Opportunities for Students at SURF
“These experiments at Sanford Lab enhance STEM education for K-12 schools throughout South Dakota,” says Mike Headley, executive director of the SDSTA. “Since last year, Our Education and Outreach department curriculum modules and assembly programs have reached more than 15,000 K-12 students in South Dakota. They also hold teacher workshops and host dozens of field trips.”
a. Up to six internships every summer are offered and the SDSTA hosts the Davis-Bahcall Scholars Program. Internships: http://www.sanfordlab.org/careers/dave-bozied-and-chris-bauer-internships
b.Davis-Bahcall: For students entering their first or second year of college. Davis-Bahcall Scholars will have the opportunity to spend four to five weeks of their summer exploring the world of modern scientific research at some of the nation’s leading laboratories and universities. They will spend two weeks at the Sanford Underground Research Facility, and travel to research laboratories within the United States and possibly in Italy (funding permitting). For more details and to apply visit: http://doe.sd.gov/secretary/DAVIS-BAHCALL.aspx
By Charlotte Hofer.