FNAL Art Image by Angela Gonzales
From The DOE’s Fermi National Accelerator Laboratory-an enduring source of strength for the US contribution to scientific research worldwide.
5.21.24
Shannon Brescher Shea, US Department of Energy
Neutrinos are by far the most abundant particles in the universe.
About 100 trillion neutrinos pass through your body every second without interacting with any of the particles in your body. You never notice them. The combination of that ghostly presence and the important role neutrinos play in the universe captivates physicists.
Neutrinos play a role in many fundamental aspects of our lives; they are produced in nuclear fusion processes that power the sun and stars, they are produced in radioactive decays that provide a source of heat inside our planet, and they are produced in nuclear reactors. Neutrinos are believed to be a vital ingredient in a star’s supernova process. These explosions spread heavy elements throughout space, elements that are needed to create the universe we live in. Neutrinos also provide a tool to study the structure of nucleons (protons and neutrinos), to learn how matter evolved from simple particles into more complex composites of particles, creating everything around us.
Before physicists can answer these questions and understand better the role neutrinos play in the evolution of our universe, they need to better understand how neutrinos interact with other particles. Experiments such as MINERvA are being conducted to precisely characterize different types of neutrino interactions, and to study the physical processes that govern these interactions.
MINERvA’s data will be of great use to neutrino experiments such as MINOS, NOvA and LBNF that study how neutrinos oscillate, or change types.
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Fermilab LBNF/DUNE Neutrino Experiment
A close-up of the charge readout planes for the DUNE vertical drift detector. Photo courtesy of DUNE collaboration.
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By offering a more detailed explanation of how neutrinos interact in a detector, these experiments can measure the details of neutrino oscillations with high precision.
Through the combination of data from low-energy and high-energy neutrino experiments, physicists can get a more complete picture of how neutrinos behave and their role in our universe.
Depictions of the Roman goddess of wisdom Minerva show her in flowing robes, wearing a noble war helmet and holding an owl. In contrast, the MINERvA experiment features a huge particle detector with the names of collaborating scientists scrawled on the front of it.
While quite different in appearance, this neutrino experiment provides deep wisdom to scientists just like its namesake represented. Among its many insights, scientists have used MINERvA to better understand the size and structure of protons, one of the building blocks of atoms.
MINERvA is a neutrino scattering experiment at the Department of Energy’s Fermilab. Neutrinos are tiny, electrically neutral particles that are incredibly abundant. The sun, other stars, and many different objects produce them as a result of atomic reactions. In fact, there are more neutrinos in the universe than any other particle that has mass.
Despite being ubiquitous, we never notice neutrinos because they hardly ever react with anything. Studying neutrinos is essential to understanding how our universe formed in the past and functions now.
To better understand this fundamental particle, scientists study how neutrinos interact with materials on the rare occasions that they actually do. MINERvA’s mission is to capture these interactions.
It uses a high-intensity neutrino beam to study how they interact with the nuclei of five different elements. By having the neutrinos hit targets made of different materials—water, helium, carbon, iron, lead, and plastic—scientists can compare the reactions. Charting out the different interactions will help scientists analyze the results of other experiments like the upcoming Deep Underground Neutrino Experiment.
In addition to this goal, scientists from the MINERvA collaboration figured out another clever use for their data—to investigate the proton’s size and structure.
Along with neutrons, protons make up the nuclei of the atoms that make up us and everything around us. They’re one of the building blocks of matter we interact with every day.
But studying subatomic particles is a lot trickier than studying larger objects. Subatomic particles are far too small to study with ordinary tools like microscopes. In addition, the “size” of a subatomic particle doesn’t quite have the same meaning as the size of an object you can measure with a ruler. Instead, scientists study the forces that hold the proton together.
In the past, scientists have studied the proton’s size using the electromagnetic force. Electromagnetism is one of the four fundamental forces of the universe. Magnetic fields, electrical fields, and even light fall under the electromagnetic force. It binds electrons to the nucleus (made of protons and neutrons) in the atom. It’s also partly responsible for the structure of the nucleus.
To represent the proton’s size, scientists have typically used the electric charge radius. That’s the average radius of the electric charge distributed in the proton. To measure this characteristic, scientists aim a beam of electrons at a single energy at a target. The electrons fly away from the protons in many different directions and energies, which gives scientists information about the internal structure of the protons.
Using this technique, scientists have been able to make a very precise measurement of the size of the average electric charge radius of the proton, and therefore the quarks that provide the electric charge.
Led by Tejin Cai (then a Ph.D. student at the University of Rochester), the MINERvA collaboration had a different approach. The idea was to use antineutrinos—the antimatter twin of neutrinos—to study protons.
Because neutrinos (and antineutrinos) don’t have a charge, they wouldn’t interact via the electromagnetic force. Instead, the neutrinos would interact via the weak force in the protons. The weak force and gravity are the only two ways neutrinos interact with anything.
Despite its name, the weak force is powerful. Another one of those four fundamental forces, it enables the process by which protons turn into neutrons or vice versa. These processes are what drive the sun and other stars’ nuclear reactions. Neutrinos offer a unique tool to study the weak force.
But the weak force only comes into play when particles are very, very close together. As neutrinos are soaring through space, they’re usually moving through the (comparatively) vast spaces between an atom’s electrons and nucleus.
Most of the time, neutrinos simply aren’t close enough to protons for them to interact via the weak force. To possibly get enough measurements, scientists need to shoot staggering numbers of neutrinos or antineutrinos at a target.
MINERvA’s powerful neutrino beam and diverse targets made that goal possible. In an ideal world, scientists would aim neutrinos at a target made of pure neutrons, or antineutrinos at a target made of pure protons. In this way, scientists could get the most specific measurements. Unfortunately, that’s not a very realistic experimental setup.
But MINERvA already had the next best thing—a lot of antineutrinos and a target made of polystyrene. The material that makes up Styrofoam, polystyrene is made of hydrogen bonded to carbon. Using this target, scientists would get measurements of how antineutrinos interact with both hydrogen and carbon.
To separate hydrogen from carbon, the scientists took an approach similar to taking a photo and then deleting the background to allow you to focus on just a few items. To determine those “background” neutrino-carbon interactions, the scientists looked at neutrons.
When antineutrinos interact with protons in carbon or protons by themselves in hydrogen, they produce neutrons. By tracking the neutrons, scientists could work backwards to identify and remove the carbon-antineutrino interactions from the hydrogen-antineutrino interactions.
Getting the needed number of interactions truly tested MINERvA’s capabilities. Over the course of three years, scientists recorded more than a million interactions of antineutrinos with other particles. A mere 5,000 of those were with hydrogen.
That data finally allowed the scientists to calculate the proton’s size using neutrinos. Instead of the electric charge radius, they calculated the proton’s weak charge radius. It was the first time that scientists have used neutrinos to make a statistically significant measurement of this characteristic.
Considering uncertainties, the result was very close to the previous measurements of the proton’s electric charge radius. Since it is fundamentally measuring the spatial distribution of quarks and gluons that make up the proton, the value was expected to be similar.
This new technique gives scientists another tool in their toolkit to study the proton’s structure. It’s a testament to the wisdom we can gain when scientists think creatively about using existing experiments to explore new areas of research.
See the full article here .
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The DOE’s Fermi National Accelerator Laboratory, located just outside Batavia, Illinois, near Chicago, is a United States Department of Energy national laboratory specializing in high-energy particle physics. Since 2007, Fermilab has been operated by the Fermi Research Alliance, a joint venture of the University of Chicago, and the Universities Research Association. Fermilab is a part of the Illinois Technology and Research Corridor.
Fermilab’s Tevatron was a landmark particle accelerator; until the startup in 2008 of the Large Hadron Collider(CH) near Geneva, Switzerland, it was the most powerful particle accelerator in the world, accelerating antiprotons to energies of 500 GeV, and producing proton-proton collisions with energies of up to 1.6 TeV, the first accelerator to reach one “tera-electron-volt” energy. At 3.9 miles (6.3 km), it was the world’s fourth-largest particle accelerator in circumference. One of its most important achievements was the 1995 discovery of the top quark, announced by research teams using the Tevatron’s CDF and DØ detectors. It was shut down in 2011.
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[Earlier than the LHC at CERN, The DOE’s Fermi National Accelerator Laboratory had sought the Higgs with the Tevatron Accelerator.
But the Tevatron could barely muster 2 TeV [Terraelectron volts], not enough energy to find the Higgs. CERN’s LHC is capable of 13 TeV.
Another possible attempt in the U.S. would have been the Super Conducting Supercollider.
Fermilab has gone on to become a world powerhouse in neutrino research with the LBNF/DUNE project which will send neutrinos 800 miles to SURF-The Sanford Underground Research Facility in Lead, South Dakota.
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In addition to high-energy collider physics, Fermilab hosts a series of fixed-target and neutrino experiments, such as The MicroBooNE (Micro Booster Neutrino Experiment),
NOνA (NuMI Off-Axis νe Appearance)
and Seaquest
Completed neutrino experiments include MINOS (Main Injector Neutrino Oscillation Search), MINOS+, MiniBooNE and SciBooNE (SciBar Booster Neutrino Experiment).
The MiniBooNE detector was a 40-foot (12 m) diameter sphere containing 800 tons of mineral oil lined with 1,520 phototube detectors. An estimated 1 million neutrino events were recorded each year.
SciBooNE sat in the same neutrino beam as MiniBooNE but had fine-grained tracking capabilities. The NOνA experiment uses, and the MINOS experiment used, Fermilab’s NuMI (Neutrinos at the Main Injector) beam, which is an intense beam of neutrinos that travels 455 miles (732 km) through the Earth to the Soudan Mine in Minnesota and the Ash River, Minnesota, site of the NOνA far detector.
The ICARUS neutrino experiment was moved from CERN to Fermilab.
In the public realm, Fermilab is home to a native prairie ecosystem restoration project and hosts many cultural events: public science lectures and symposia, classical and contemporary music concerts, folk dancing and arts galleries. The site is open from dawn to dusk to visitors who present valid photo identification.
Asteroid 11998 Fermilab is named in honor of the laboratory.
Weston, Illinois, was a community next to Batavia voted out of existence by its village board in 1966 to provide a site for Fermilab.
The laboratory was founded in 1969 as the National Accelerator Laboratory; it was renamed in honor of Enrico Fermi in 1974. The laboratory’s first director was Robert Rathbun Wilson, under whom the laboratory opened ahead of time and under budget. Many of the sculptures on the site are of his creation. He is the namesake of the site’s high-rise laboratory building, whose unique shape has become the symbol for Fermilab and which is the center of activity on the campus.
After Wilson stepped down in 1978 to protest the lack of funding for the lab, Leon M. Lederman took on the job. It was under his guidance that the original accelerator was replaced with the Tevatron, an accelerator capable of colliding protons and antiprotons at a combined energy of 1.96 TeV. Lederman stepped down in 1989. The science education center at the site was named in his honor.
The later directors include:
John Peoples, 1989 to 1996
Michael S. Witherell, July 1999 to June 2005
Piermaria Oddone, July 2005 to July 2013
Nigel Lockyer, September 2013 to the present
Fermilab continues to participate in the work at the Large Hadron Collider (LHC); it serves as a Tier 1 site in the Worldwide LHC Computing Grid and hosts 1000 U.S. scientists who work on the CMS project.
With the newly completed assembly, the PIP-II team concludes a long process that began in earnest in 2018 with the development of the cryomodule’s design, led by Fermilab. The lab’s earlier development of the lower-frequency SSR1 cryomodule heavily influenced this design.
In this final section of the linac, these superconducting cryomodules will power beams of protons to the final energy of 800 million electronvolts, or MeV, before the protons exit the linac. From there, the proton beam will transfer to the upgraded Booster and Main Injector accelerators, where it will gain more energy before being turned into a beam of neutrinos. These neutrinos will then be sent on a 1,300-kilometer journey through Earth to the Deep Underground Neutrino Experiment and the Long Baseline Neutrino Facility in Lead, South Dakota.
Completed just before work began on the HB650 cryomodule, the SSR1 cryomodules will make up a different part of the new linac.
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