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Posts Tagged ‘Miniboone’

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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Antineutrino data from MiniBooNE show the region of oscillation parameter space that is allowed at 90 percent confidence level (solid blue curve)." These results were consistent with findings from LSND, and were among the findings discussed at the Short-Baseline Neutrino Workshop that took place at Fermilab last week. Click on image to see larger version.

This article first appeared in Fermilab Today May 19.

When exciting results are popping up all over the place, it calls for bringing the best minds together from around the world to discuss the findings and make plans for the future. That’s precisely what happened at the Short-Baseline Neutrino Workshop 2011, which took place May 12-14 at Fermilab. More than 100 people from 44 institutions attended.

Neutrinos are a million times lighter than an electron and are electrically neutral, which allows them to pass through matter unaffected, making them difficult to detect. Neutrinos exist in three flavors: muon, electron and tau, and have the ability to transform from one flavor into another, a process known as oscillation.

The purpose of various short-baseline neutrino experiments is to explore questions about neutrinos that travel over a relatively short distance.

Recently, a number of tantalizing results have sprung up from both short and long baseline experiments, which seem to suggest that neutrino oscillations occur under circumstances that were previously believed to not allow them, said Bill Louis, physicist at Los Alamos National Laboratory and workshop co-organizer.

“Even if just one of these results is correct, it may possibly have a profound impact on our understanding of particle and nuclear physics,” Louis said.

Learning more about this area of physics is a key part of Fermilab’s future.

A few months after the Tevatron shuts down, there will be an 11-month period during which scientists will improve on proton sources to better serve experiments at the Intensity Frontier, including neutrino, kaon and muon programs, said Fermilab Deputy Director Young-Kee Kim. Once the complex comes back online, Fermilab plans to resume operation of neutrino beams using both 120 GeV and 8 GeV protons on the neutrino-production targets.

The MiniBooNE detector, shown above, was one project at the recent Short-Baseline Neutrino Workshop that presented interesting results. Photo: MiniBooNE collaboration.

Antineutrino data from MiniBooNE show the region of oscillation parameter space that is allowed at 90 percent confidence level (solid blue curve).” These results were consistent with findings from LSND, and were among the findings discussed at the Short-Baseline Neutrino Workshop that took place at Fermilab last week.
In their lectures, Steve Holmes, project manager for the proposed Project X, and Chris Polly, acting project manager for the future muon g-2 experiment at Fermilab, touched on the topic of the proposed beamlines. Kim further discussed future plans and solicited attendee feedback.

The ensuing discussions yielded a consensus amongst workshop attendees: The beamlines have tremendous potential, but measures will need to be taken to minimize background signals caused by cosmic radiation. Some possibilities include reusing or repurposing already existing equipment, or building additional components, which could result in a high-intensity neutrino beam that would be suitable for future experiments.

Workshop speakers also touched on what can be done in the interim between now and Project X. Among these speakers were: Geoffrey Mills (LANL), who discussed the potential of BooNE, the two-detector version of MiniBooNE; Roxanne Guenette (Yale University), who presented an overview of liquid argon detector applications in the MiniBooNE beamline; and Ryan Patterson (CalTech) and John Cooper (Fermilab), who spoke on what could be accomplished with a third NOvA detector.

See a full list of presenters online.

Louis was most impressed by the quality and diversity of the talks that touched on both experimental and theoretical issues and covered the gamut of neutrino topics.

“The talks were uniformly excellent,” Louis said. “It was just great hearing all of the different possibilities and plans for future neutrino experiments.”

— Christine Herman

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This article ran in Fermilab Today May 20.

A new analysis using combined MiniBooNE and SciBooNE data looked for disappearing muon neutrinos building on a MiniBooNE study from 2009.

A new analysis using combined MiniBooNE and SciBooNE data looked for disappearing muon neutrinos building on a MiniBooNE study from 2009.

Kendall Mahn, TRIUMF; and Yasuhiro Nakajima, Kyoto University; were among the experimenters who performed this analysis.
When it comes to neutrinos, it’s best to expect the unexpected.

Previous Results of the Week have showcased a surprising difference between MiniBooNE electron neutrino appearance and electron antineutrino appearance results. In this special result, we present an analysis done by combining MiniBooNE and SciBooNE data to improve our understanding of a MiniBooNE analysis from 2009.

Previously, MiniBooNE looked for an excess of electron neutrino events in a muon neutrino beam over a short distance (0.5 km). Experimenters then conducted the same search using antineutrinos. While the tests were the same, the results were surprisingly different. The neutrino data is consistent with background, but the antineutrino data shows an excess of events consistent with the controversial 1990 results from the Liquid Scintillator Neutrino Detector experiment at Los Alamos National Laboratory.

If this observed difference is due to new physics, the new physics must be rather exotic. The most common explanation for these results uses the idea of sterile neutrinos, which physicists believe are neutrinos that do not have charged partners. Collaborators believe that as the muon neutrino travels, it will sometimes convert into a sterile neutrino, which then would convert into an electron neutrino. We expect that the sterile neutrino is only detectable from this reaction.

If sterile neutrinos exist, then the muon neutrinos should disappear, that is, some of the muon neutrinos will have converted to undetectable sterile neutrinos and the rate of muon neutrinos will be lower than we expect. Let’s say the muon neutrinos constitute a pie before baking. Disappearance is characterized by a missing slice of this pie, as some of the muon neutrinos have changed into sterile neutrinos, which we can’t see.

A previous search for the disappearance of muon neutrinos and muon antineutrinos two years ago compared MiniBooNE data to the predicted number of events at the detector. This is like counting the ingredients and examining the empty pie tin before baking, and then estimating the total pie weight and size after baking without looking at it directly.

Of course, this method is limited by our understanding of the initial number of neutrinos that reach MiniBooNE and the specifics of how they interact, that is, how well we know the ingredients beforehand .

Now, MiniBooNE has teamed up with the SciBooNE experiment to perform an improved analysis on the disappearance of muon neutrinos. SciBooNE, a dedicated cross section experiment shares the same neutrino target and flux as MiniBooNE, but was located in the same neutrino beam closer to the neutrino source. By adding the SciBooNE data to our analysis, we are able to measure the neutrino rate before the muon neutrinos disappear. This is like weighing the pie and inspecting it before baking, and is less dependent on our initial predictions.

The first joint venture of these two experiments observes no muon neutrino disappearance at 90 percent confidence level, which constrains models that require large amounts of disappearance. Our next step will be to look at muon antineutrino disappearance with both experiments, an important step to understanding the nature of new physics, if it exists.

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— Kendall Mahn and Yasuhiro Nakajima

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