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Posts Tagged ‘NOvA’

A measurement to watch

Monday, October 12th, 2015

This article appeared in symmetry on Oct. 7, 2015.

Finding a small discrepancy in measurements of the properties of neutrinos could show us how they fit into the bigger picture.

Finding a small discrepancy in measurements of the properties of neutrinos could show us how they fit into the bigger picture.

Physics, perhaps more so than any other science, relies on measuring the same thing in multiple ways. Different experiments let scientists narrow in on right answers that satisfy all parties—a scientific system of checks and balances.

That’s why it’s exciting when a difference, even a minute one, appears. It can teach physicists something about their current model – or physics that extends beyond it. It’s possible that just such a discrepancy exists between a certain measurement of neutrinos coming out of accelerator experiments and reactor-based experiments.

Neutrinos are minuscule, neutral particles that don’t interact with much of anything. They can happily pass through a light-year of lead without a peep. Trillions pass through you every second. In fact, they are the most abundant massive particle in the universe—and something scientists are, naturally, quite keen to understand.

The ghostly particles come in three flavors: electron, muon and tau. They transition between these three flavors as they travel. This means that a muon neutrino leaving an accelerator at Fermi National Accelerator Laboratory in Illinois can show up as an electron neutrino in an underground detector in South Dakota.

Not complicated enough for you? These neutrino flavors are made of mixtures of three different “mass states” of neutrinos, masses 1, 2 and 3.

At the end of the day, neutrinos are weird. They hang out in the quantum realm, a land of probabilities and mixing matrices and other shenanigans. But here’s what you should know. There are lots of different things we can measure about neutrinos—and one of them is a parameter called theta13 (pronounced theta one three). Theta13 relates deeply to how neutrinos mix together, and it’s here that scientists have seen the faintest hint of disagreement from different experiments.

Accelerators vs. reactors

There are lots of different ways to learn about neutrinos and things like theta13. Two of the most popular involve particle accelerators and nuclear reactors.

The best measurements of theta13 come from nuclear reactor experiments such as Double Chooz, RENO and Daya Bay Reactor Neutrino Experiment based in China (which released the best measurement to date a few weeks ago).

Detectors located near nuclear reactors provide such wonderful readings of theta13 because reactors produce an extremely pure fountain of electron antineutrinos, and theta13 is closely tied to how electron neutrinos mix. Researchers can calculate theta13 based on the number of electron antineutrinos that disappear as they travel from a near detector to the far detector, transforming into other types.

Accelerators, on the other hand, typically start with a beam of muon neutrinos. And while that beam is fairly pure, it can have a bit of contamination in the form of electron neutrinos. Far detectors can look for both muon neutrinos that have disappeared and electron neutrinos that have appeared, but that variety comes with a price.

“Both the power and the curse of long-baseline neutrino oscillation is that it’s sensitive to all of neutrino oscillation, not just theta13,” says Dan Dwyer, a scientist at Lawrence Berkeley National Laboratory and researcher on Daya Bay.

With that in mind, we come to the source of the disagreement. The results coming out of accelerator-based experiments, such as the United States-based NOvA and Japan-based T2K, see just a few more electron neutrinos than researchers would predict based on what the reactor experiments are saying.

“The theta13 value that fits the beam experiments, that really describes how much electron neutrino you get, is somewhat larger than what Daya Bay, RENO and Double Chooz measure,” says Kate Scholberg, professor of physics at Duke University and researcher on T2K. “So there’s a little bit of tension.”

Many grains of salt

Data coming out of the accelerator experiments is still very young compared to the strong readings from reactor experiments, and it is complicated by the nature of the beam. No one is jumping on the discrepancy yet because it can be explained in different ways. Most importantly, the accelerator experiments just don’t have enough information.

“We have to wait for T2K and NOvA to get sufficient statistics, and that’s going to take a while,” says Stephen Parke, head of the Theoretical Physics Department at Fermilab. Parke, Scholberg and Dwyer all estimated that about five more years of data collection will be required before researchers are able to start saying anything substantial.

“There’s been a lot of pressure on Daya Bay to try to eke out as precise a measurement as we possibly can,” Dwyer says. “Every bit of increased precision we provide further improves the ability of NOvA and T2K and eventually [proposed neutrino experiment] DUNE to measure the other parameters.”

Finding meaning in neutrinos

If the accelerator experiments gather more data and if a clear discrepancy emerges—a big if—what does it mean?

Turns out there are lots of reasons to love theta13. It’s one of the fundamental parameters that can define our universe. From a practical standpoint, it helps design future experiments to better understand neutrinos. And it could help physicists learn something new.

“We don’t expect things not to agree, but we kind of hope that they won’t,” says André de Gouvêa, professor of physics at Northwestern University. “It means that we’re missing something.”

That something could be CP violation, evidence that neutrinos and antineutrinos behave differently. CP violation has never been seen in neutrinos before, but if researchers observed it with accelerator experiments, it could help explain why our universe is made of matter rather than equal parts of matter and antimatter.

Figuring out if CP violation is occurring means nailing down all of the different neutrino mixing parameters, which in turn means building more powerful, next-generation experiments such as Hyper-K in Japan, JUNO in China and the Deep Underground Neutrino Experiment in the United States. DUNE will build on oscillation experiments like NOvA but will be able to better separate background noise from neutrino events, see a broader energy spectrum of neutrinos and find other neutrino characteristics.

DUNE, which will be built in a repurposed gold mine in South Dakota and detect neutrinos passed 800 miles through the Earth from Fermilab in Illinois, will be one of the best ways to see CP violation and rely on expertise gained from smaller neutrino experiments.

“Developing these types of experiments is very complicated,” de Gouvêa says. One of the major challenges of physics experiments is making sure you are measuring what you think you are measuring. “That’s part of the reason why we have a significant number of neutrino oscillation experiments.”

Ultimately, the neutrino puzzle is still missing many pieces. A variety of experiments are ramping up to fill in the gaps, making it an exciting time to be a neutrino physicist.

“We have to untangle the mysteries of the neutrino, and it’s not easy,” Parke says. “The neutrino doesn’t give up her secrets very easily.”

Lauren Biron

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How to make a neutrino beam

Friday, December 12th, 2014

This article appeared in Fermilab Today on Dec. 11, 2014.

Ingredients for a neutrino beam: speedy protons, target, magnetic horn, decay pipe, absorbers. Image adapted from Fermilab

Ingredients for a neutrino beam: speedy protons, target, magnetic horn, decay pipe, absorbers. Image adapted from Fermilab

Fermilab is in the middle of expanding its neutrino program and is developing new detectors to study these ghostly particles. With its exquisite particle accelerator complex, Fermilab is capable of creating very intense beams of neutrinos.

Our neutrino recipe starts with a tank of hydrogen. The hydrogen atoms are fed an extra electron to make them negatively charged, allowing them to be accelerated. Once the charged atoms are accelerated, all of the electrons are ripped off, leaving a beam of positive protons. The protons are extracted into either the Booster Neutrino Beamline (BNB) or are further accelerated and extracted into the Neutrino Main Injector beamline (NuMI). Fermilab is the only laboratory with two neutrino beams. Our two beams have different energies, which allows us to study different properties of the neutrinos.

In the BNB, these protons smash into a target to break up the strong bonds of the quarks inside the proton. These collisions are so violent that they produce new quarks from their excess energy. These quarks immediately form together again into lighter composite short-lived particles called pions and kaons.

Since the pions and kaons emerge at different directions and speeds, they need to be herded together. As a bugle tunes your breath into musical notes, a horn of a different type rounds up and focuses the pions and kaons. The BNB horn looks roughly like the bell of a six-foot long bugle. It produces an electric field that in turn generates a funnel-like magnetic field, which directs all of the dispersed pions and kaons of positive electric charge straight ahead. Particles with negative charges get defocused. By switching the direction of the electric field, we can focus the negatively charged particles while defocusing the positive charges.

The focused particles in the BNB beam travel through a 50-meter long tunnel. This is where the magic happens. In this empty tunnel, the pions and kaons decay in flight into neutrinos, electrons and muons. At the end of the decay tunnel is a wall of steel and concrete to stop and absorb any particle that is not a neutrino. Because neutrinos interact so rarely, they easily whiz through the absorbers and on towards the experiments. And that’s the basic formula to make a beam of neutrinos!

A single neutrino beamline can support many experiments because the neutrinos interact too rarely to get “used up.” The BNB feeds neutrinos to MicroBooNE, and most of them go on through to the other side towards the MiniBooNE detector. Similarly, most of those go on through the other side as well and continue traveling to infinity and beyond. Detectors located in this beam measure neutrino oscillations and their interactions.

The NuMI beamline is designed similarly, but uses a different target material, two focusing horns, and a 675-meter decay pipe. The spacing between the two NuMI horns is adjustable, allowing fine-tuning of the neutrino beam energy. The NuMI beamline has higher-energy neutrinos than the BNB and thus studies different properties of neutrino oscillations.

The NuMI beamline feeds neutrinos to the MINERvA experiment and on through to the MINOS near detector. The NuMI beamline then continues about 450 miles through Earth on toward the MINOS far detector in the Soudan mine in Minnesota. By the time the beam reaches the far detector, it is about 20 miles in diameter! By having a near and far detector, we are able to observe neutrino flavor oscillations by measuring how much of the beam is electron neutrino flavor and muon neutrino flavor at each of these two detectors.

The last of the big Fermilab neutrino experiments is NOvA. Its near detector is off to the side of the NuMI beam and measures neutrinos only with a specific range of direction and energy. The NOvA far detector is positioned to measure the neutrinos with the same properties at a greater distance, about 500 miles away in Ash River, Minnesota. By placing the NOvA detectors 3 degrees to the side of the beam’s center, NOvA will get to make more precise oscillation measurements for a range of neutrino energies.

As more experiments are designed with more demanding requirements, Fermilab may expect to see more neutrino beamline R&D and the construction of new beamlines.

Tia Miceli

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This Fermilab press release came out on Oct. 6, 2014.

With construction completed, the NOvA experiment has begun its probe into the mysteries of ghostly particles that may hold the key to understanding the universe. Image: Fermilab/Sandbox Studio

With construction completed, the NOvA experiment has begun its probe into the mysteries of ghostly particles that may hold the key to understanding the universe. Image: Fermilab/Sandbox Studio

It’s the most powerful accelerator-based neutrino experiment ever built in the United States, and the longest-distance one in the world. It’s called NOvA, and after nearly five years of construction, scientists are now using the two massive detectors – placed 500 miles apart – to study one of nature’s most elusive subatomic particles.

Scientists believe that a better understanding of neutrinos, one of the most abundant and difficult-to-study particles, may lead to a clearer picture of the origins of matter and the inner workings of the universe. Using the world’s most powerful beam of neutrinos, generated at the U.S. Department of Energy’s Fermi National Accelerator Laboratory near Chicago, the NOvA experiment can precisely record the telltale traces of those rare instances when one of these ghostly particles interacts with matter.

Construction on NOvA’s two massive neutrino detectors began in 2009. In September, the Department of Energy officially proclaimed construction of the experiment completed, on schedule and under budget.

“Congratulations to the NOvA collaboration for successfully completing the construction phase of this important and exciting experiment,” said James Siegrist, DOE associate director of science for high energy physics. “With every neutrino interaction recorded, we learn more about these particles and their role in shaping our universe.”

NOvA’s particle detectors were both constructed in the path of the neutrino beam sent from Fermilab in Batavia, Illinois, to northern Minnesota. The 300-ton near detector, installed underground at the laboratory, observes the neutrinos as they embark on their near-light-speed journey through the Earth, with no tunnel needed. The 14,000-ton far detector — constructed in Ash River, Minnesota, near the Canadian border – spots those neutrinos after their 500-mile trip and allows scientists to analyze how they change over that long distance.

For the next six years, Fermilab will send tens of thousands of billions of neutrinos every second in a beam aimed at both detectors, and scientists expect to catch only a few each day in the far detector, so rarely do neutrinos interact with matter.

From this data, scientists hope to learn more about how and why neutrinos change between one type and another. The three types, called flavors, are the muon, electron and tau neutrino. Over longer distances, neutrinos can flip between these flavors. NOvA is specifically designed to study muon neutrinos changing into electron neutrinos. Unraveling this mystery may help scientists understand why the universe is composed of matter and why that matter was not annihilated by antimatter after the big bang.

Scientists will also probe the still-unknown masses of the three types of neutrinos in an attempt to determine which is the heaviest.

“Neutrino research is one of the cornerstones of Fermilab’s future and an important part of the worldwide particle physics program,” said Fermilab Director Nigel Lockyer. “We’re proud of the NOvA team for completing the construction of this world-class experiment, and we’re looking forward to seeing the first results in 2015.”

The far detector in Minnesota is believed to be the largest free-standing plastic structure in the world, at 200 feet long, 50 feet high and 50 feet wide. Both detectors are constructed from PVC and filled with a scintillating liquid that gives off light when a neutrino interacts with it. Fiber optic cables transmit that light to a data acquisition system, which creates 3-D pictures of those interactions for scientists to analyze.

The NOvA far detector in Ash River saw its first long-distance neutrinos in November 2013. The far detector is operated by the University of Minnesota under an agreement with Fermilab, and students at the university were employed to manufacture the component parts of both detectors.

“Building the NOvA detectors was a wide-ranging effort that involved hundreds of people in several countries,” said Gary Feldman, co-spokesperson of the NOvA experiment. “To see the construction completed and the operations phase beginning is a victory for all of us and a testament to the hard work of the entire collaboration.”

The NOvA collaboration comprises 208 scientists from 38 institutions in the United States, Brazil, the Czech Republic, Greece, India, Russia and the United Kingdom. The experiment receives funding from the U.S. Department of Energy, the National Science Foundation and other funding agencies.

For more information, visit the experiment’s website: http://www-nova.fnal.gov.

Note: NOvA stands for NuMI Off-Axis Electron Neutrino Appearance. NuMI is itself an acronym, standing for Neutrinos from the Main Injector, Fermilab’s flagship accelerator.

Fermilab is America’s premier national laboratory for particle physics and accelerator research. A U.S. Department of Energy Office of Science laboratory, Fermilab is located near Chicago, Illinois, and operated under contract by the Fermi Research Alliance, LLC. Visit Fermilab’s website at www.fnal.gov and follow us on Twitter at @FermilabToday.

The DOE Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

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Fermilab released this press release on Feb. 11, 2014.

Workers at the NOvA hall in northern Minnesota assemble the final block of the far detector in early February 2014, with the nearly completed detector in the background. Each block of the detector measures about 50 feet by 50 feet by 6 feet and is made up of 384 plastic PVC modules, assembled flat on a massive pivoting machine. Photo courtesy of NOvA collaboration

Workers at the NOvA hall in northern Minnesota assemble the final block of the far detector in early February 2014, with the nearly completed detector in the background. Each block of the detector measures about 50 feet by 50 feet by 6 feet and is made up of 384 plastic PVC modules, assembled flat on a massive pivoting machine. Photo courtesy of NOvA collaboration

Scientists on the world’s longest-distance neutrino experiment announced today that they have seen their first neutrinos.

The NOvA experiment consists of two huge particle detectors placed 500 miles apart, and its job is to explore the properties of an intense beam of ghostly particles called neutrinos. Neutrinos are abundant in nature, but they very rarely interact with other matter. Studying them could yield crucial information about the early moments of the universe.

“NOvA represents a new generation of neutrino experiments,” said Fermilab Director Nigel Lockyer. “We are proud to reach this important milestone on our way to learning more about these fundamental particles.”

Scientists generate a beam of the particles for the NOvA experiment using one of the world’s largest accelerators, located at the Department of Energy’s Fermi National Accelerator Laboratory near Chicago. They aim this beam in the direction of the two particle detectors, one near the source at Fermilab and the other in Ash River, Minn., near the Canadian border. The detector in Ash River is operated by the University of Minnesota under a cooperative agreement with the Department of Energy’s Office of Science.

Billions of those particles are sent through the earth every two seconds, aimed at the massive detectors. Once the experiment is fully operational, scientists will catch a precious few each day.

Neutrinos are curious particles. They come in three types, called flavors, and change between them as they travel. The two detectors of the NOvA experiment are placed so far apart to give the neutrinos the time to oscillate from one flavor to another while traveling at nearly the speed of light. Even though only a fraction of the experiment’s larger detector, called the far detector, is fully built, filled with scintillator and wired with electronics at this point, the experiment has already used it to record signals from its first neutrinos.

“That the first neutrinos have been detected even before the NOvA far detector installation is complete is a real tribute to everyone involved. That includes the staff at Fermilab, Ash River Lab and the University of Minnesota module facility, the NOvA scientists, and all of the professionals and students building this detector,” said University of Minnesota physicist Marvin Marshak, Ash River Laboratory director. “This early result suggests that the NOvA collaboration will make important contributions to our knowledge of these particles in the not so distant future.”

Once completed, NOvA’s near and far detectors will weigh 300 and 14,000 tons, respectively. Crews will put into place the last module of the far detector early this spring and will finish outfitting both detectors with electronics in the summer.

“The first neutrinos mean we’re on our way,” said Harvard physicist Gary Feldman, who has been a co-leader of the experiment from the beginning. “We started meeting more than 10 years ago to discuss how to design this experiment, so we are eager to get under way.”

The NOvA collaboration is made up of 208 scientists from 38 institutions in the United States, Brazil, the Czech Republic, Greece, India, Russia and the United Kingdom. The experiment receives funding from the U.S. Department of Energy, the National Science Foundation and other funding agencies.

The NOvA experiment is scheduled to run for six years. Because neutrinos interact with matter so rarely, scientists expect to catch just about 5,000 neutrinos or antineutrinos during that time. Scientists can study the timing, direction and energy of the particles that interact in their detectors to determine whether they came from Fermilab or elsewhere.

Fermilab creates a beam of neutrinos by smashing protons into a graphite target, which releases a variety of particles. Scientists use magnets to steer the charged particles that emerge from the energy of the collision into a beam. Some of those particles decay into neutrinos, and the scientists filter the non-neutrinos from the beam.

Fermilab started sending a beam of neutrinos through the detectors in September, after 16 months of work by about 300 people to upgrade the lab’s accelerator complex.

“It is great to see the first neutrinos from the upgraded complex,” said Fermilab physicist Paul Derwent, who led the accelerator upgrade project. “It is the culmination of a lot of hard work to get the program up and running again.”

Different types of neutrinos have different masses, but scientists do not know how these masses compare to one another. A goal of the NOvA experiment is to determine the order of the neutrino masses, known as the mass hierarchy, which will help scientists narrow their list of possible theories about how neutrinos work.

“Seeing neutrinos in the first modules of the detector in Minnesota is a major milestone,” said Fermilab physicist Rick Tesarek, deputy project leader for NOvA. “Now we can start doing physics.”

Note: NOvA stands for NuMI Off-Axis Electron Neutrino Appearance. NuMI is itself an acronym, standing for Neutrinos from the Main Injector, Fermilab’s flagship accelerator.

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This article appeared in symmetry on January 30, 2014.

A video from Fermilab highlights some of the many steps needed to build the largest neutrino experiment in the United States.

A video from Fermilab highlights some of the many steps needed to build the largest neutrino experiment in the United States.

Coordinating the construction of an international particle physics experiment is never an easy task.

This is indeed the case for NOvA, a US-based physics experiment that studies a beam of hard-to-catch particles sent an unprecedented 500 miles through the Earth toward a 14,000-ton particle detector. Building the experiment has required harmonizing the efforts of several dozen laboratories, universities and companies from the United States, Brazil, the Czech Republic, Greece, India, Japan, Russia and the United Kingdom.

“It sinks in,” says John Perko, a construction technician at the NOvA facility in Ash River, Minnesota, in a new video about the process of building the NOvA detector. “It makes you feel that the whole world’s watching.”

The scientists on the NOvA collaboration have come together to study neutrinos, particles that are abundant in nature but that physicists still don’t quite understand. They are mysteriously lightweight, leading physicists to wonder if something other than the Higgs boson gives them their masses. Neutrinos come in three types, and they morph from one to another. Scientists think they might hold clues to what caused the imbalance between matter and antimatter in our universe.

To study these elusive particles, scientists on the NOvA collaboration designed a set of two detectors—a 300-ton one located near the source of the neutrino beam and a 14,000-ton one located in Ash River, Minnesota.

Fermilab recently posted a video highlighting some of the many steps required to build these detectors, from extruding 50-foot-long plastic tubes at a company in Manitowoc, Wisconsin, to assembling them into modules at a facility staffed by students at the University of Minnesota, to putting together the world’s largest free-standing plastic structure.

“I’m familiar with all the neutrino projects that are going on, and getting to actually be a part of one of those projects is pretty exciting,” University of Minnesota physics student Nicole Olsen says in the video.

Workers are scheduled to finish building the detectors this spring, and they plan to finish outfitting them with electronics in the summer. They have already begun to take data with portions of the experiment, and their capabilities will only improve as they get closer to completing construction.

Kathryn Jepsen

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Fermilab planning a busy 2012

Tuesday, January 3rd, 2012

This column by Fermilab Director Pier Oddone first appeared in Fermilab Today Jan. 3 .

We have a mountain of exciting work coming our way!

In accelerator operations, we need to give enough neutrinos to MINERvA to complete their low-energy run, enough anti-neutrinos to MiniBooNE to complete their run and enough neutrinos to MINOS to enable their independent neutrino velocity measurement that will follow up on last year’s OPERA results. We need to provide test beams to several technology development projects and overcome setbacks due to an aging infrastructure to deliver beam to the SeaQuest nuclear physics experiment. And we need to do all of this in the first few months of the year before a year-long shutdown starts. During the shutdown, we will modify the accelerator complex for the NOvA era and begin the campaign to double the number of protons from the Booster to deliver simultaneous beams to various experiments.

In parallel with accelerator modifications, we will push forward on many new experiments. The NOvA detector is in full construction mode, and we face challenges in the very large number of detector elements and large mechanical systems. Any project of this scale requires a huge effort to achieve the full promise of its design. We have the resources in our FY2012 budget to make a lot of progress toward MicroBooNE, Mu2e and LBNE. We will continue to work with DOE to advance Muon g-2. All these experiments are at an important stage in their development and need to be firmly established this year.

At the Cosmic Frontier, we will commission and start operation of the Dark Energy Survey at the Blanco Telescope in Chile, where the camera has arrived and is being tested. In the dark matter arena we will commission and operate the 60 kg COUPP detector at Canada’s SNOLAB and continue the run of the CDMS 15 kg detector in the Soudan Mine while carrying out R&D on future projects. We continue to have a major role in the operation of the Pierre Auger cosmic-ray observatory. In addition we should complete the first phase of the Fermilab Holometer, which will study the properties of space-time at the Planck scale.

At the Energy Frontier, we play a major role in the LHC detector operations and analysis. It should be a fabulously exciting year at the LHC as we push on the hints that we already see in the data.

Beyond construction and operation of facilities we continue our R&D efforts on the superconducting RF technology necessary for Project X and other future accelerators. We will be building the Illinois Accelerator Research Center and moving forward to connect our advanced accelerator program with industry and universities. Our rich program on theory, computation and detector technology will continue to support our laboratory and the particle physics community.

If we accomplish all that is ahead of us for 2012, it will be a year to remember and celebrate when we hit New Year’s Day 2013!

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httpv://www.youtube.com/watch?v=YtuMqjCiymQ&list=UUD5B6VoXv41fJ-IW8Wrhz9A&index=3&feature=plcp

It could be the largest structure ever to be built from plastic. Its footprint of 1,052 square meters will cover an area about the size of a quarter of a football field. Its height will rise past the top of a five-story apartment building. And with 368,640 tubes of white PVC, the structure will have about as many components as some of the largest LEGO structures built in the world.

The NOvA detector will comprise 368,640 PVC tubes that will be filled with mineral oil. A company in Wisconsin extrudes the tubes, which look like extra-long downspouts, in panels of 16. Credit: Rich Talaga, Argonne

But this huge structure, to be constructed in Ash River, Minn., won’t serve as a plastic replica. It will be the skeleton of a fully functional particle detector. Wired with fiber optic cables and filled with 500 truckloads of mineral oil, the 15,000-ton NOvA detector will enable scientists to discover how the masses of the three types of neutrinos—the lightest, tiniest particles known to mankind—stack up.

Last week, the preparations for the assembly of this white PVC behemoth passed a pivotal test. In an assembly building at Fermilab, 40 miles west of Chicago, scientists, engineers and technicians from Fermilab, Argonne National Laboratory and the University of Minnesota successfully operated for the first time the NOvA pivoter, the hydraulic system developed by Fermilab to move and rotate huge, 200-ton plastic blocks for the assembly of the NOvA detector. (See this 3-minute video with a time lapse of the pivoter test and a fly-through animation of the NOvA detector hall.)

“This is a big deal,” said Fermilab physicist Pat Lukens, who manages the assembly of the detector. “Now the focus will shift to Ash River. We will assemble 500 truckloads of plastic modules.”

But this is no ordinary plastic. Argonne’s Rich Talaga and other NOvA collaborators spent many years finding the right ingredients to produce the strongest and most reflective PVC for the 16-meter-long tubes that hold and support the weight of the mineral oil.

“Ordinary plastic tends to deform under pressure,” said Talaga, who worked closely with Fermilab’s Anna Pla-Dalmau. “Think of a plastic coat hanger. It changes shape when you put a sweater on it. We had to find a plastic that has to be strong for 20 years and doesn’t get weaker and rupture.”

Using a machine developed and tested at Argonne National Laboratory, technicians apply special no-drip glue to a NOvA panel to create blocks that are 16 meters by 16 meters square and weigh 200 tons. Credit: Rich Talaga, Argonne

For Extrutech Plastics in Manitowoc, Wisc., a company that makes PVC wall and ceiling panels and other plastic products, the purchase order for the NOvA tubes was the largest ever. The company has begun the production of the PVC panels, which look like 16 extra-long downspouts with a four-by-six-centimeter cross section attached side-by-side. The panels, which must meet the tight specifications for the thickness and uniformity of the NOvA plastic, are shipped to a warehouse rented by the University of Minnesota. There, students and technicians outfit each tube with a fiber optic cable that will capture the faint light that a neutrino creates when it breaks up an atom in the mineral oil. Avalanche photodiodes attached to each fiber will record and amplify the signal, which is then digitized and transmitted to the central data acquisition system.

To make sure that no light gets lost, Talaga and his group used a special PVC formulation that includes large amounts of titanium-dioxide to create a strong plastic that is white and highly reflective.

“The oil doesn’t absorb much light,” said Talaga. “The light created by a neutrino interaction is either absorbed by the walls of the tubes or by the fiber optic cable inside each tube. By making the walls highly reflective, the light bounces back eight, nine or ten times without significant absorption and you see a stronger signal in the fiber.”

To transform the roughly 24,000 plastic panels into one giant particle detector, technicians will place 24 panels next to each other to make a layer of tubes, 16 meters by 16 meters square. After an application of special no-drip glue, the next layer will be placed on top, with the tubes lying perpendicularly to the layer below. Gluing and lifting of the 1,000-pound panels will be done with machines developed and tested at Argonne, where the first set of machines was used to build the test block used on the pivoter at Fermilab.

The Argonne group just finished the installation of the first gluing machine at Ash River. The full-size pivoter, six times as wide as the one tested at Fermilab, is under construction and will be ready for operation early next year. Bill Miller, of the University of Minnesota, who participated in the pivoter test at Fermilab, will lead the assembly of the detector in Ash River. He will supervise local staff, hired by the University of Minnesota for the task.

“We plan to assemble the first block in Ash River this spring,” said Lukens, who’s overseen the development of the NOvA assembly plans for three years. “It will take 18 months to assemble the entire detector.”

Scientists from 28 institutions are working on the NOvA experiment. When operational, the experiment will examine the world’s highest-intensity, longest-distance neutrino beam, generated at the Fermilab.

Engineers at Fermilab designed and tested a hydraulic system that will move and rotate the huge, 200-ton plastic blocks for the assembly of the NOvA detector. Credit: Reidar Hahn, Fermilab

Accelerators will produce a beam of muon neutrinos that will travel straight through the earth to the NOvA detector in northern Minnesota. During their split-second trip to Ash River, some of these neutrinos will turn into electron neutrinos and tau neutrinos. By measuring the composition of the neutrino beam with a small, 222-ton detector at Fermilab and a large detector in Ash River, scientists expect to discover the neutrino mass hierarchy, determining whether there are two light neutrinos and one heavy one, or two heavy ones and a light one.

For photos of the construction of the NOvA detector building in Ash River, see the photo gallery in the October 2011 issue of symmetry magazine.

— Kurt Riesselmann

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The March earthquake and subsequent tsunami in Japan killed 20,352 people. Finding ways to reduce the death toll from such natural disasters has captured the interest of scientists in many fields.

There exists several ways to predict an earthquake such as the detection of radon gas emission or electromagnetic changes. However short-term predictions (hours todays) are, in general, unlikely.

At least for now.

Neutrino physics aims to answer some fundamental questions in physics, such as neutrino mass, and matter-antimatter asymmetry, but some think it could also answer fundamental questions about the Earth’s most volatile activities.

Using giant neutrino detectors physicists may be able to predict earthquakes and/or volcano eruptions by detecting geoneutrinos.

Geoneutrinos were first found by the Kamioka Liquid-scintillator Anti-Neutrino Detector (KamLAND) experiment in 2005 and recently by the Borexino Collaboration at the Gran Sasso National Laboratory of the Italian Institute of Nuclear Physics. Geoneutrinos are electron antineutrinos – the antimatter counterparts of electron neutrinos. Geoneutrinos are produced by the radioactive decay of uranium, thorium and potassium in Earth’s crust and mantle.

Geoneutrinos provide us another way to better understand the Earth’s interior besides the usual way of seismology by analyzing the vibrations produced by earthquakes and sensed by thousands of instrument stations worldwide. Geoneutrinos can provide crude information about chemistry, that is to say, how much uranium and how much thorium there is. This will help us to better understand deep-Earth processes which will affect events on the surface such as earthquakes and volcanoes.

A group of Chinese physicists proposed another method for earthquake prediction via neutrino tomography. The idea is to use antineutrinos emitted from nuclear reactors as a probe. As the antineutrinos traverse through a region prone to earthquakes, observable variations in the matter effect on the antineutrino oscillation would provide a tomography of the vicinity of the region. Although they concluded that it is a difficult task with the present technology, “there is hope that a medium-term earthquake forecast would be feasible” with the development of geology, and new detection technology.

Can the NOvA detector being built at Fermilab and in northern Minnesota detect geoneutrinos and make a prediction about earthquakes? The answer is probably no. While the 1,000 ton KamLAND detector sits in an old mine with 2,700 meters, or a little less than 1 ½ miles, of shielding to reduce cosmic ray interference, the 14-kiloton NOvA far detector in Minnesota has only three meters, or about 10 feet, of shielding.

The 222-ton NOvA near detector at Fermilab has 105 meters, or 344 feet, of shielding and will detect a much lower cosmic- ray rate, but it is not big enough to detector the geoneutrinos.

With more and more advanced technologies and geoneutrino-detecting facilities, we may expect that we can have a detailed understanding of Earth’s interior and the source of its internal heat in the near future. Someday, we may be able to predict the occurrence of events such as earthquakes, tsunami and volcano eruptions using our neutrino detectors.

– Xinchun Tian

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Neutrinos could tell us why matter formed in the early universe.

The Japan-based experiment T2K Tuesday gave scores of U.S. particle hunters a license to ready their detectors and take aim at the biggest question in the universe: How everything we see came to exist.

“It’s our hunting license,” said Fermilab physicist and University of Rochester professor Kevin McFarland, who works on T2K and neutrino experiments at Fermilab.

The observation by T2K affects what the Fermilab neutrino experiments NOvA and the proposed Long Baseline Neutrino Experiment, LBNE, can expect to discover and how quickly. It also makes the experiment McFarland serves as co-spokesman on, MINERvA, more important than ever in the international neutrino-research field.

Physicists working with T2K recorded six muon neutrinos changing into electron neutrinos across a long distance, a transformation called theta 13 in physics circles. Physicists had predicted that they should observe only 1.5 of these transformations as background events rather than the six they did observe, so the probability of the existence of an electron neutrino appearance is estimated to be 99.3 percent. While the T2K observation doesn’t rise to the level of “discovery” in the science community, it is far enough beyond the expected statistical error bar to make people shout for joy and start revising plans for their own particle hunts.

“Because neutrino science is so hard, scientist don’t get a lot of exciting days,” McFarland said the day of the T2K announcement. “But this is a very exciting day.”

The T2K observation also was statistically large enough that it quells a long-standing fear that this transformation would be statistically too small, much less than one percent, to observe. At that level, modern technology wouldn’t be able to use the observation as a stepping stone to move to the next research phase in figure out how matter came to dominate antimatter in the universe.

The quarry:

Something, possibly neutrinos, tipped the scales to have more matter than antimatter in the universe allowing for life. Credit: symmetry magazine

Physics predicts that the three types of neutrino particles can change back and forth into one another across long distances. Previous solar and reactor neutrino experiments had observed two types doing just that, but the third switch – muon neutrino into electron neutrino – had remained elusive.

T2K’s recording of this transformation, the first of its kind, means that physicists will have the tools to track down the next two potential discoveries on the path to the ultimate trophy. After the Big Bang, equal amounts of matter and antimatter should have annihilated each other leaving nothing but free-floating energy. But we’re here and antimatter isn’t, so that didn’t happen. Something tipped the scales in matter’s favor, allowing particles to join together and form planets, plants and people. Physicists think neutrinos could be that tipping-point particle.

Following the tracks:

The first step in finding out if they are right is T2K’s observation. Plugging this observation into the research equation, physicists on NOvA, an experiment under construction in Minnesota, will be able to tease out the details of what is called the neutrino mass hierarchy. The pattern of this hierarchy essentially will tell physicist if neutrinos behave like other particles, in a pattern of light, heavy and very heavy, or neutrinos behave oddly in a pattern of light, heavy and heavy.

This pattern of masses is important to know because it provides a clue to help physicists understand what causes neutrinos to have masses that are so much lighter than other particles and why neutrinos aren’t massless as predicted by the Standard Model, the playbook for how the world works at the subatomic level.

Physicists think the origins of neutrino masses are closely tied to subatomic processes that took place right after the big bang. Determining which neutrino types are heaviest and lightest—the neutrino mass ordering—is a first step toward revealing these processes. Credit: symmetry magazine

NOvA is ideally situated to do discern this pattern because its particle beam will travel three times as farther than T2K’s, allowing researchers see how the material in the Earth alters the change from muon to electron neutrinos. T2K’s observation of half a dozen muon neutrino to electron neutrino changes points to the relatively high rate of the change, so NOvA should have a lot of data to work with to speed up the discovery of the mass hierarchy.

Step three is combining what NOvA learns about the mass hierarchy with more precise data from the LBNE experiment to look for differences in the neutrino and antineutrino probabilities of changing from muon to electron neutrino types. After accounting for the effect of the earth and the mass hierarchy, any remaining difference would point to a fundamental difference between matter and antimatter neutrinos. Differences between matter and anti-matter are nearly non-existent in nature and these differences are precious clues about why matter dominated antimatter to survive in today’s universe.

The three types of neutrinos mix across long distances enabling physicists to see them to change type if the distance is long enough. Credit: symmetry magazine

LBNE, proposed for South Dakota, sits even farther away from the Fermilab neutrino source, making it well-suited to make this comparison of antineutrinos, which are rarer and harder to detect than neutrinos. T2K’s observation of a large change signal means LBNE will have better statistics to create precise comparisons.
The level of precision could mean the difference between getting an answer or not, depending on how subtle the difference is between neutrinos and antineutrinos.

Bringing out the rifle scope:

Short-baseline experiments can’t compete in the hunt for why matter dominated antimatter, which requires tracking neutrinos across great distances, but they can provide the precision measurements that work like a rifle scope for the particle hunters. MINERvA at Fermilab and the neutrino reactor experiments Daya Bay in China and Double Chooz in France will provide the data to allow NOvA and LBNE to zoom in on the minute details of mass hierarchy and how neutrinos change types.

The reactor-based experiments with detectors near to neutrino spewing reactors were designed to be experts at finding the neutrino change T2K found. Ideally, they will find a cleaner neutrino transformation signal, without the data complications, such as the effects of Earth material on the transformation that come with T2K and NOvA being multi-purpose experiments. Cleaner reactor experiment measurements provide a baseline for the measurements of NOvA and LBNE.

MINERvA will provide data to help NOvA and LBNE map the type and amount of background events that can obscure their search. This will enable physicists to put the trophy deer-like potential discovery in their analysis cross-hairs and discount the imposter trees and hunters dressed in brown that cloud the view of their data. While MINERvA was built for this job and currently aids neutrino experiments across the globe, including T2K, with this variable-removing research information, T2K’s observation makes MINERvA’s unique skill more important. The large T2K signal means a lot of data and the ability to do precision analysis if MINERvA can tell researchers what variables to discount.

“There is always an exchange of data, and one experiment builds on another,” McFarland says.

Previously data from the MINOS experiment at Fermilab told T2K how to tune the energy of its particle beam. Now T2K is returning the favor with an observation that will help Fermilab experiments.

“Experiments building on one another,” he says, “that is what makes it exciting.”

Related information:

Symmetry breaking: Japan’s T2K experiment observes electrion neutrino appearance

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The NOvA Far Detector (red) and surface building 'placed' inside Soldier Field stadium in Chicago, for a sense of scale of the detector size. The Far Detector measures 51.2 feet wide by 51.2 feet high by 206.7 feet long, or 15.6 meters wide, 15.6 meters high and 63 meters long.

Let me set the scene for you. The NFL season has been cancelled so in an effort to raise money the Chicago Bears have rented out their Soldier Field stadium. The DOE obtained the lease and entrusted a host of physicists to build a particle detector inside the 61,500 seater.

 None of this is true of course (well the coming NFL season may be in a lockout) but it gives you a sense of scale of the NOvA experiment if you compare the size of one of its detectors, the Far Detector, to the football stadium.

The NOvA (NuMI Off-axis electron-neutrino [νe]Appearance) experiment is a neutrino oscillation experiment designed to search for muon-neutrino to electron-neutrino oscillations and is the flagship project for the Fermi National Accelerator Laboratory (Fermilab) Intensity Frontier initiative. NOvA is a two-detector experiment with the smallest of the two a 200 ton Near Detector at Fermilab and the second a 15 kiloton Far Detector situated 503 miles, or 810 kilometers away in Ash River, Minnesota.

The experiment proceeds with an intense beam of muon neutrinos from the NuMI (Neutrinos at the Main Injector) beam at Fermilab. The neutrinos are then directed to travel along a trajectory such that they can be observed by the Near and Far Detectors. The neutrinos that reach Ash River, on the Canadian border, are compared to the neutrinos detected by the Near Detector. We know that neutrinos ”oscillate” or change type as they travel which is why NOvA is searching for the number of neutrinos that have oscillated from muon neutrinos to electron neutrinos, hence electron neutrino appearance: essentially measuring how many electron neutrinos have appeared compared to what is detected at the Near Detector.

So what is so great about knowing that, you may ask. Well, in neutrino physics our understanding of neutrino oscillations is governed by the PMNS matrix – a mathematical description of the probability of the different neutrinos changing from one type to another.

There are six different parameters that are derived from the PMNS matrix. Firstly, you have the three mixing angles theta-13, theta-23 and theta-12. These are essentially the proportions of each of the three known types of neutrinos that combine to form each type like Neapolitan ice cream. For example, electron neutrinos make up the largest share of the mixing angle for the electron neutrino. Second, you have a CP-violating phase which is the breaking of particle-antiparticle (charge conjugation – C) and mirror (parity – P) symmetries . Lastly, you have any two of three mass-squared differences which measure the difference between the masses of the neutrino types. The true nature of these parameters is beyond the scope of this introductory blog but, in short, NOvA aims to make the first measurement of the mixing angle theta-13 and push the search for electron neutrino appearance beyond the current scientific community’s limits by more than an order of magnitude. For a non-zero theta-13, it is possible for NOvA to observe CP violation in neutrinos, which will help us understand why the universe has a matter-antimatter asymmetry, and to establish the neutrino mass ordering or ”hierarchy” of neutrino types from lightest to heaviest.

Before NOvA can make any physics measurements it needs two fully assembled and calibrated detectors, which basically means that we understand what our detector is telling us!

The detectors are totally active, segmented and deploy the technology of liquid scintillator (mineral oil plus 5 percent pseudocumene) contained in highly reflective, rigid PVC extrusion cells to detect neutrino interactions.

The charged particles produced by a neutrino interaction inside the detector cause the liquid scintillator to produce light that is captured by optical fibers and carried to light-sensitive detectors at one end of each cell. The Far Detector will consist of about 400,000 1.6 inch by 2.4 inch by 52.5 feet, or 4 centimeter by 6 centimeter by 16 meter, cells that require approximately 3.2 gallons, or 12 million liters, of scintillator and 8,078 miles, or 13,000 kilometers, of .07-centimeter, or 0.7-millimeter, optical fiber. That is roughly equivalent to having enough fiber to feed through the Earth from Fermilab, near Chicago, to Sydney, Australia! The Near Detector will have the same design but will only be about 1/200th as massive.

The Far Detector is under construction and will begin taking data in early 2013. Due to the segmented nature of the detectors, data can be collected as soon as a section of readout has been installed.

Event display of the first NuMI neutrino event observed by NOvA's NDOS detector. The colored squares are a representation of time and location of the hits recorded by the detector cells. Click on image to see a larger version.

The Near Detector eventually will sit underground at Fermilab in the NuMI beamline but a portion of it has been built as a prototype on the surface. This prototype detector, named NDOS, began running at Fermilab in November and registered its first neutrinos from the NuMI beam in December 2010. The full installation of NDOS was completed in March 2011, at which point the detector entered an ongoing commissioning phase. NDOS is fundamental to understanding the fabrication and assembly procedures to be used in the construction of the Near and Far Detectors as well as inferring detector response and fine-tuning data acquisition systems and event reconstruction algorithms.

This is only the beginning for NOvA and future blog entries will aim to expand on some of the details brushed over here (in particular the underlying physics) as well as provide an insight into the daily activities of NOvA physicists. Who knows, maybe sometime soon NOvA will be putting neutrino physics firmly in the spotlight! For now I leave you with a picture of an event topology display showing the first NuMI beam neutrino event observed by NOvA’s NDOS.

NOvA really is a super experiment!!

— Gavin S. Davies

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