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Posts Tagged ‘ICARUS’

This article appeared in Fermilab Today on Aug. 10, 2015.

The Fermilab Short-Baseline Neutrino program will use three detectors: SBND, MicroBooNE (shown here) and ICARUS. Photo: Reidar Hahn

The Fermilab Short-Baseline Neutrino program will use three detectors: SBND, MicroBooNE (shown here) and ICARUS. Photo: Reidar Hahn

In 1995, physicists working on the Liquid Scintillator Neutrino Detector, or LSND, at Los Alamos National Laboratory stumbled upon some curious results.

The experiment, whose goal was to investigate oscillations between the three different flavors of the elusive neutrino, saw evidence that there might be at least one additional flavor of neutrino lurking just out of reach. In 2002, an experiment at Fermilab called MiniBooNE started collecting data to explore this anomaly, but the results were inconclusive: some data seemed to refute the possibility of a fourth neutrino, but other data seemed to indicate particle interactions that couldn’t be explained with conventional three-neutrino models. The possibility of a mysterious, fourth neutrino remained alive.

“It’s a question that’s been first lingering with the anomalies from LSND and then MiniBooNE,” said Bonnie Fleming, co-spokesperson of a new neutrino experiment at Fermilab called MicroBooNE. “There’s now a worldwide campaign to address whether these short-baseline oscillations and hints from other experiments are indicating new physics.”

Scientists from Fermilab and more than 45 institutions around the world have teamed up to design a program to catch this hypothetical neutrino in the act. The program, called the Short-Baseline Neutrino (SBN) program, makes use of a trio of detectors positioned along one of Fermilab’s neutrino beams. Although there are other reactor and source-based experiments in the world that actively seek a fourth neutrino, also called a sterile neutrino, SBN is the only program that uses a particle accelerator to produce neutrinos and multiple neutrino detectors for this search.

“No one else is doing an experiment like this,” said Peter Wilson, coordinator for the SBN program. “There are no other experiments on this energy scale using the concept of a near detector and a far detector.”

Determining whether there are more than three neutrino flavors would affect how scientists interpret data from experiments like the planned Deep Underground Neutrino Experiment, which is expected to make transformative discoveries about neutrinos, and perhaps other aspects of the universe, in the future. Solving the mystery of the anomalies seen at LSND and MiniBooNE, however, will not be easy. Because the sterile neutrino would not interact through the weak nuclear force as the other three do (hence the name “sterile”), detecting this particle would be like chasing the shadow of a ghost.

It begins at the Fermilab Booster, where protons are accelerated to 8 GeV and smashed into a target, creating new particles. Charged particles are bent forward by a magnetic focusing device into a tunnel where most decay to produce muon neutrinos. The three detectors — named the Short-Baseline Near Detector, or SBND, MicroBooNE and ICARUS — will be spread out over a distance of 600 meters. SBND, 100 meters from the target, will take data close to the source to reduce systematic uncertainties by measuring the initial characteristics of the muon neutrino beam. Four hundred meters beyond the planned site for SBND is MicroBooNE, which is already installed. ICARUS will be located 110 meters past MicroBooNE. ICARUS is an existing detector from a previous experiment at the Italian INFN laboratory at Gran Sasso that is currently being refurbished at CERN. It will have a massive chamber holding 760 tons of liquid argon to beat down statistical uncertainties in the experiment.

All three of the detectors are time projection chambers, a type of detector that allows physicists to analyze particle collisions in three dimensions. For these particular TPCs, scientists use liquid argon because its relatively heavy mass ensures a higher rate of interactions.

MicroBooNE received its last fill of liquid argon in July and recently began taking data. Scientists are expecting to break ground on buildings for both ICARUS and SBND by this fall. In 2017, ICARUS will be fully refurbished and delivered to Fermilab. Scientists hope to complete building SBND that same year.

Since experimenters won’t be able to directly detect the sterile neutrino, they will search for clues in the trails of particles the three known neutrino flavors leave behind in the liquid argon after they interact. If the experiments, expected to begin running in 2018, see deviations in the expected neutrino oscillation pattern, scientists will know that they’re on the right track in their hunt for this fugitive particle. If not, they will be able to put the mystery of the sterile neutrino to rest.

“If we design a strong enough experiment, which I believe we have, then one of two things will happen when we start taking data,” said David Schmitz, co-spokesperson for SBND. “Either we will rule out the earlier hints, or we make, frankly, the most exciting discovery in particle physics in some time.”

Ali Sundermier

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This article appeared in symmetry on April 22, 2015.

The world’s largest liquid-argon neutrino detector will help with the search for sterile neutrinos at Fermilab. Photo: INFN

The world’s largest liquid-argon neutrino detector will help with the search for sterile neutrinos at Fermilab. Photo: INFN

Mysterious particles called neutrinos seem to come in three varieties. However, peculiar findings in experiments over the past two decades make scientists wonder if a fourth is lurking just out of sight.

To help solve this mystery, a group of scientists spearheaded by Nobel laureate Carlo Rubbia plans to bring ICARUS, the world’s largest liquid-argon neutrino detector, across the Atlantic Ocean to the United States. The detector is currently being refurbished at CERN, where it is the first beneficiary of a new test facility for neutrino detectors.

Neutrinos are some of the most abundant and yet also most mysterious particles in the universe. They have tiny masses, but no one is sure why—or where those masses come from. They interact so rarely that they can pass through the entire Earth as if it weren’t there. They oscillate from one type to another, so that even if you start out with one kind of neutrino, it might change to another kind by the time you detect it.

Many theories in particle physics predict the existence of a sterile neutrino, which would behave differently from the three known types of neutrino.

“Finding a fourth type of neutrinos would change the whole picture we’re trying to address with current and future experiments,” says Peter Wilson, a scientist at Fermi National Accelerator Laboratory.

The Program Advisory Committee at Fermilab recently endorsed a plan, managed by Wilson, to place a suite of three detectors in a neutrino beam at the laboratory to study neutrinos—and determine whether sterile neutrinos exist.

Over the last 20 years, experiments have seen clues pointing to the possible existence of sterile neutrinos. Their influence may have caused two different types of unexpected neutrino behavior seen at the Liquid Scintillator Neutrino Detector experiment at Los Alamos National Laboratory in New Mexico and the MiniBooNE experiment at Fermilab.

Both experiments saw indications that a surprisingly large number of neutrinos may be morphing from one kind to another a short distance from a neutrino source. The existence of a fourth type of neutrino could encourage this fast transition.

The new three-detector formation at Fermilab could provide the answer to this mystery.

In the suite of experiments, a 260-ton detector called Short Baseline Neutrino Detector will sit closest to the source of the beam, so close that it will be able to detect the neutrinos before they’ve had a chance to change from one type into another. This will give scientists a baseline to compare with results from the other two detectors. SBND is under construction by a team of scientists and engineers from universities in the United Kingdom, the United States and Switzerland, working with several national laboratories in Europe and the US.

The SBND detector will be filled with liquid argon, which gives off flashes of light when other particles pass through it.

“Liquid argon is an extremely exciting technology to make precision measurements with neutrinos,” says University of Manchester physicist Stefan Soldner-Rembold, who leads the UK project building a large section of the detector. “It’s the technology we’ll be using for the next 20 to 30 years of neutrino research.”

Farther from the beam will be the existing 170-ton MicroBooNE detector, which is complete and will begin operation at Fermilab this year. The MicroBooNE detector was designed to find out whether the excess of particles seen by MiniBooNE was caused by a new type of neutrino or a new type of background. Identifying either would have major implications for future neutrino experiments.

Finally, farthest from the beam would be a liquid-argon detector more than four times the size of MicroBooNE. The 760-ton detector was used in the ICARUS experiment, which studied neutrino oscillations at Gran Sasso Laboratory in Italy using a beam of neutrinos produced at CERN from 2010 to 2014.

Its original beam at CERN is not optimized for the next stage of the sterile neutrino search. “The Fermilab beamline is the only game in town for this type of experiment,” says physicist Steve Brice, deputy head of Fermilab’s Neutrino Division.

And the ICARUS detector “is the best detector in the world to detect this kind of particle,” says Alberto Scaramelli, the former technical director of Gran Sasso National Laboratory. “We should use it.”

Rubbia, who initiated construction of ICARUS and leads the ICARUS collaboration, proposed bringing the detector to Fermilab in August 2013. Since then, the ICARUS, MicroBooNE and SBND groups have banded together to create the current proposal. The updated plan received approval from the Fermilab Program Advisory Committee in February.

“The end product was really great because it went through the full scrutiny of three different collaborations,” says MicroBooNE co-leader Sam Zeller. “The detectors all have complementary strengths.”

In December, scientists shipped the ICARUS detector from the Gran Sasso laboratory to CERN, where it is currently undergoing upgrades. The three-detector short-baseline neutrino program at Fermilab is scheduled to begin operation in 2018.

Kathryn Jepsen

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