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Posts Tagged ‘Intensity Frontier’

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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A talk about how a helicopter can advance high-energy physics was part of my initiation to my first collaboration meeting for the new muon g- minus 2 experiment at Fermilab.

A similar helicopter will carry the ring, just as the tank is carried here, from Brookhaven National Laboratory a portion of the way to Fermilab.

The meeting was a very exciting (and exhausting!) experience.

And let’s be honest any collaboration meeting with a talk devoted to helicopters is awesome. From the way we talk about this thing, it’s going to be our mascot. We need a helicopter because we are going to use the muon storage ring from the previous muon g-2 measurement at Brookhaven National Laboratory, which took a similar measurement to what we will look for. The helicopter will take the ring from Brookhaven, drop it on a barge that sends it to Illinois and then a helicopter will take it to Fermilab. I think it’s going to be very cool to see that happen.

This was our first meeting after receiving Stage 1 approval from Fermilab, meaning Lab management thinks this experiment it worth doing, although, there is no funding attached to it yet. The meeting took place in March over a Friday and Saturday and we needed every second of that time. There was much to discuss and it was all interesting, especially to me, as a newbie.

What is the muon g-2 experiment? Okay, some jargon, just to sound cool. The g-2 experiment’s goal is to measure the difference between the gryomagnetic ratio (spin/angular momentum) and the Bohr magneton.

Fermilab’s planned muon g-2 experiment will use the storage ring that was used in a previous muon g-2 experiment at Brookhaven National Laboratory.

And what does that mean? It’s basically measuring intrinsic properties (such as spin and angular momentum) of a particle. Experimentally, we are measuring the precession of the muon due to a magnetic field. You can imagine a top, just as it’s about to topple over. That motion is called precession. We measure the frequency of that (how many times the muon goes around before decaying, or in the case of the top, toppling over). Theorists can calculate the frequency of this very, very precisely and experimentalists can measure it very, very precisely.  Because of this level of preciseness, we are sensitive to physics beyond the Standard Model. The Standard Model is incorporates what we know now about particles and interactions, but does have some holes. The results from the new muon g minus 2 experiment will help us plug those holes by pointing to which theories beyond the Standard Model are most likely.

So that’s a brief summary about the physics for the muon g-2 experiment.

The muon g-2 collaboration at Fermilab during a March meeting.

On a more personal level, I’m involved with research and development for the tracking detector, which is used to find out where the decay positrons go, among other measurements. Our current plan is to use straws. They look pretty much like you would expect from the name. They are tubes made of a lightweight material that is usually coated with some sort of metal and a super thin wire runs through the center, and they are filled with a gas. When a charged particle passes through them, the gas ionizes and we collect the resulting signal. We aren’t sure what type of materials we are going to use for the straws, which is part of the fun. We are trying to figure out the best detector we can build on a reasonable budget.

–Mandy Rominsky

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This article first appeared in Fermilab Today on Oct. 7.

A muon collider is closer to reality after a successful high-pressure hydrogen gas-filled RF (HPRF) cavity beam test at Fermilab. The test, conducted in the MuCool Test Area (MTA) at Fermilab by the MuCool collaboration, shows the beginnings of a practical solution to a difficult obstacle.

From left: Ben Freemire, Katsuya Yonehara, Mukti Jana, Moses Chung and Giulia Collura standing behind the HPRF cavity (under the hood) and beam pipe section. Photo: Yagmur Torun, R&D

“This was years in the making,” said MTA coordinator Yagmur Torun. “This idea of using HPRF cavities for muon cooling was first proposed in the early 2000s.”

Muons, a heavier version of electrons, are elementary particles. They cannot break down into smaller components, like protons decaying into gluons and quarks. Muons have nearly 200 times the mass of electrons. Electrons would lose too much energy circling in an accelerator, while muons retain enough energy to reach collision speeds.

The problem is that the muons come into existence as a hot gas, which is much too large to fit through a conventional accelerator without beam cooling.

Muons also do not live long enough to complete the acceleration if standard beam cooling methods are used. With only 2.2 microseconds to accelerate and collide, every instance of muon action must be carefully controlled. Ionization cooling is the only practical method that is fast enough for muons and the MuCool R&D program at Fermilab is aimed at developing components for muon cooling.

For muon cooling, RF cavities are used to accelerate particles within a strong magnetic field. The magnets help contain and focus the beam of particles. However, there were significant problems with the RF cavities, as scientists found that the cavities did not work well inside the magnets.

“The cavity would break down, or start arcing. It was unusable,” said Torun, assistant professor at Illinois Institute of Technology with a joint appointment at Fermilab’s Accelerator Physics Center (APC). “There were various ways to attack the problem, but then Rolland Johnson suggested we fill the cavities with gas.”

Rolland Johnson, a physicist who worked at Fermilab for 30 years and founded Muons, Inc., introduced the novel concept of filling the RF cavities with hydrogen. The hydrogen gas would suppress the electrons stripped from the cavity surface, which had previously caused the breakdown of the cavity.

The beam pipe leading into the solenoid magnet, with the HPRF cavity installed in the MTA experimental hall. Photo: Yagmur Torun, R&D

Physicists currently use RF cavities to bunch charged particles and move them forward through an accelerator. A standing wave, set at a particular frequency, pushes the beam particles forward to the next cavity.

“In 2005, we tested the hydrogen gas in the RF cavity,” Katsuya Yonehara, Peoples Fellow at the APC and spokesperson for the HPRF beam test, said. “The results were promising. We saw the cavity would work in a magnetic field, but we had a remaining question—could a very intense muon beam cause the field in the cavity to collapse?”

In 2007, a beam line from the Fermilab Linac accelerator was installed in the MTA. It took four years of adjustments and upgrades before the beam line was ready for the test in July of this year.

“It worked,” Torun said. “The cavity didn’t break down. This is a big step in our search for a potential path for muon colliders and accelerators at Fermilab.”

In the next few months, there will be a more detailed study.

“We’re adjusting the cavity, and making improvements for studying its application to muon acceleration,” Yonehara said. “We’re seeing progress.”

—Ashley WennersHerron

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Fermilab distributed this press release Aug. 25.

This graph demonstrates that the new MINOS antineutrino result (blue) is more precise than last year’s result (red), as reflected by the smaller oval, and the new result is in better agreement with the mass range of the 2010 neutrino result (black), reflected by the overlap of the blue and red ovals. The ovals represent the 90 percent statistical confidence levels for each result. A 90 percent confidence level means that if scientists were to repeat the measurement many times, they would expect to obtain a result that lies within the contour 90 percent of the time. The points inside the ovals show the best, or most likely, value for each of the three measurements. The best value for the 2011 measurement of the squared mass difference for the antineutrinos is 2.62 x 10-3 eV2.

The physics community got a jolt last year when results showed for the first time that neutrinos and their antimatter counterparts, antineutrinos, might be the odd man out in the particle world and have different masses. This idea was something that went against most commonly accepted theories of how the subatomic world works.

A result released today (August 25) from the MINOS experiment at the Department of Energy’s Fermi National Accelerator Laboratory appears to quell concerns raised by a MINOS result in June 2010 and brings neutrino and antineutrino masses more closely in sync.

By bringing measurements of neutrinos and antineutrinos closer together, this new MINOS result allows physicists to lessen the potential ramifications of this specific neutrino imbalance. These ramifications include: a new way neutrinos interact with other particles, unseen interactions between neutrinos and matter in the earth and the need to rethink everything known about how the universe works at the tiniest levels.

“This more precise measurement shows us that these particles and their antimatter partners are very likely not as different as indicated earlier. Within our current range of vision it now seems more likely that the universe is behaving the way most people think it does,” said Rob Plunkett, Fermilab scientist and co-spokesman of MINOS. “This new, additional information on antineutrino parameters helps put limits on new physics, which will continue to be searched for by future planned experiments.”

University College London Physics Professor and MINOS co-spokesperson Jenny Thomas presented this new result – the world’s best measurement of muon neutrino and antineutrino mass comparisons — at the International Symposium on Lepton Photon Interactions at High Energies in Mumbai, India.

MINOS nearly doubled its data set since its June 2010 result from 100 antineutrino events to 197 events. While the new results are only about one standard deviation away from the previous results, the combination rules out concerns that the previous results could have been caused by detector or calculation errors. Instead, the combined results point to a statistical fluctuation that has lessened as more data is taken.

Physicists measured the differences between the squared masses between two types of neutrinos and compared them to the squared masses between two types of antineutrinos, a quantity called delta m squared. The 2010 result found, as a whole, that the range of mass difference in the neutrinos was about 40 percent less for antineutrinos, while the new result found a 16 percent difference.

“The previous results left a 2 percent chance that the neutrino and antineutrino masses were the same. This disagrees with what theories of how neutrinos operate predicted,” Thomas said. “So we have spent almost a year looking for some instrumental effect that could have caused the difference. It is comforting to know that statistics were the culprit.”

Because several neutrino experiments operating and planned across the globe rely on neutrino and antineutrino measurements being the same as part of their calculations, the new MINOS result hopefully removes a potential hurdle for them.

Fermilab’s accelerator complex is capable of producing intense beams of either muon antineutrinos or muon neutrinos to send to the two MINOS detectors, one at Fermilab and one in Minnesota. This capability allows the experimenters to measure the mass difference parameters. The measurement also relies on the unique characteristics of the MINOS far detector, particularly its magnetic field, which allows the detector to separate the positively and negatively charged muons resulting from interactions of antineutrinos and neutrinos, respectively.

The antineutrinos’ extremely rare interactions with matter allow most of them to pass through the Earth unperturbed. A small number, however, interact in the MINOS detector, located 735 km away from Fermilab in Soudan, Minnesota. During their journey, which lasts 2.5 milliseconds, the particles oscillate in a process governed by a difference between their mass states.

Further analysis will be needed by the upcoming Fermilab neutrino experiments NOvA and MINOS+ to close the mass difference even more. Both experiments will use an upgraded accelerator beam generated at Fermilab that will emit more than double the number of neutrinos. This upgraded beam is expected to start operating in 2013.

The MINOS experiment involves more than 140 scientists, engineers, technical specialists and students from 30 institutions, including universities and national laboratories, in five countries: Brazil, Greece, Poland, the United Kingdom and the United States. Funding comes from: the Department of Energy’s Office of Science and the National Science Foundation in the U.S., the Science and Technology Facilities

The 1,000-ton MINOS near detector sits 350 feet underground at Fermilab. The detector consists of 282 octagonal-shaped detector planes, each weighing more than a pickup truck. Scientists use the near detector to verify the intensity and purity of the muon neutrino beam leaving the Fermilab site. Photo: Peter Ginter.

Council in the U.K; the University of Minnesota in the U.S.; the University of Athens in Greece; and Brazil’s Foundation for Research Support of the State of São Paulo (FAPESP) and National Council of Scientific and Technological Development (CNPq).

Fermilab is a national laboratory supported by the Office of Science of the U.S. Department of Energy, operated under contract by Fermi Research Alliance, LLC.

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 http://science.energy.gov.

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Fermilab issued this press release today.

Alex Romanenko, sitting on the edge of a large cryogenic vessel, holds one of the superconducting RF cavities made of niobium. Photo: Fermilab (Click on image for larger version)

Alex Romanenko, a materials scientist at Fermi National Accelerator Laboratory, will receive $2.5 million from the Department of Energy’s Office of Science to expand his innovative research to develop superconducting accelerator components. These components could be applied in fields such as medicine, energy and discovery science.

Romanenko w as named a recipient of a DOE Early Career Research Program award for his research on the properties of superconducting radio-frequency cavities made of niobium metal. The prestigious award, which is given annually to the most promising researchers in the early stages of their careers, includes a $2.5 million award over five years to continue work in the specified area.

“Dr. Romanenko and his proposed research show great promise,” said Tim Hallman, associate director of the DOE’s Office of Science for Nuclear Physics. “We are pleased that he has been selected to receive an Early Career Research Program award to continue this work.”

Romanenko’s work could explain why some superconducting radio frequency cavities are highly efficient at accelerating charged particles to high speeds while others are not, as well as prescribe new ways to make cavities even more powerful. His research links t he performance of SRF cavities to the quality of the niobium metal used to make them. In particular, he investigates specific defects and impurities in niobium. Although scientists take painstaking measures to ensure that the niobium is completely pure and that the final SRF cavities are free from any contaminants, dust or debris, the cavities do not always perform the way that they should. Romanenko’s research is dedicated to finding out why that happens.

Romanenko began his research on SRF cavities as a graduate student at Cornell University, an institution known for its SRF research. He continued his award-winning work at Fermilab when he joined the laboratory in 2009 as a Peoples Fellow, a prestigious position given to scientists who have the potential to be leaders in their field. (More information at
http://www.fnal.gov/pub/today/archive_2011/today11-03-02.html )

Through his research, Romanenko found that a new, previously unexplored, type of defect near the cavity surface may result in surface differences that are responsible for a cavity’s inferior performance. What he found was surprising: the defect sites often contained niobium-hydrogen compounds, which might form when the cavities are prepared for operation. Specifically, he was able to pinpoint the problematic area to the first 40 nanometers of a cavity’s surface, a thickness equivalent to 120 layers of niobium atoms.  

“The technology of these cavities has developed so fast recently that it is ahead of the corresponding science,” Romanenko explained. “We know how to make them work to a certain level of performanc e, but do not necessarily understand the full physics behind why they do so. I hope to understand why cavities behave in certain ways first, improve on this and then apply what I learn to other materials.”

If Romanenko can isolate the specific nanostructural effects that cause problems in cavities, then Lance Cooley, Romanenko’s supervisor and head of the new Superconducting Materials Department in Fermilab’s Technical Division, is prepared to direct other scientists to develop ways to prevent or control them and transfer that knowledge to industry. This could someday make it possible to mass-produce nearly perfect niobium cavities as well as lay the groundwork for cavities made from other superconducting materials that can perform at higher temperatures and accelerating fields. Such high-performance cavities—strung together to create powerful, intense particle beams—would lead to accelerators that can be used in indust ry, in hospitals and at research institutions. These accelerators are needed, for example, to produce a range of radioisotopes for medical diagnostics and have the potential to treat nuclear waste, among other applications. (More information at http://www.acceleratorsamerica.org/applications/index.html)

Strung together like the pearls of a necklace and cooled to ultralow temperatures, SRF cavities can accelerate particles with high efficiency. Photo: Fermilab (Click on image for larger version)

“This award recognizes the high caliber of research that takes place at Fermilab,” Cooley said. “It is because of the laboratory’s existing world-class research program that Alex’s research is likely to succeed.”

The monetary award will cover part of Romanenko’s research efforts, fund a postdoctoral associate and a part-time technician, and pay for advanced analysis techniques used to examine surfaces in the next five years.

Fermilab is a national laboratory supported by the Office of Science of the U.S. Department of Energy, operated under contract by Fermi Research Alliance, LLC.

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 http://science.energy.gov

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This article first appeared in Fermilab Today July 20.

During the last week of June, roughly 100 physicists met in the thin air of Telluride, Colo., to contemplate the construction and physics goals of a muon collider. This new type of particle collider would be one of the most complex devices ever created by humans. It would employ a short-lived particle, the muon, which disintegrates in a mere 2 millionths of a second. That’s just long enough to use the particle as a probe to unveil the secrets of nature.

The muon collider plans and designs are still conceptual, and we won’t be building such a machine for at least 20 years. Undaunted, the scientists at Telluride trekked on to identify and solve the multifarious issues that revolve around three topics:

*creating a large number of muons and antimuons for the collider using the proposed Project X accelerator

*cooling these particles to form small packets that can be accelerated to an energy of up to 2 TeV

*making the muons and antimuons collide head on at 4 TeV in a complex and robust particle detector

For the detector design, the challenge is to differentiate between the particles coming from actual muon-antimuon collisions and the enormous background created by particles coming from muon decays. At the Telluride meeting, scientists reported a feasible solution: a detector that utilizes fast timing and clever geometry to deal with the ferocious backgrounds. Major, more detailed, studies need to be done before this type of detector becomes a reality.

Theorists provided a list of the “top six” key physics questions to explore 20 years from now, when a muon collider exists. The list includes:

*studying a very heavy, beyond-the-Standard Model Higgs boson, via WW scattering, which would be difficult to detect at the LHC

*probing in depth the collider production of dark matter particles

*studying a Z’-boson, should the LHC find evidence of such a particle. If it exists, a Z’ boson will act as an amplifier for new physics, and this would reduce the stringent technological requirements for muon cooling and background reduction.

The muon collider complex would fit on the Fermilab site and could be built in functional stages, beginning with the Project X proton accelerator. The next stage would be the construction of a large muon storage ring, or neutrino factory, followed by the construction of the muon collider itself. Staging distributes the costs over many years and many sub-projects and might be the way for the United States to once more host experiments at the Energy Frontier.

– Fermilab theorist Chris Hill

Related information:

Muon collider website

Muon collider program website

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Illustration: Fermilab/Diana Canzone

Two weeks ago, my Aunt and Grand mom (G-Mom) came from New Jersey to visit me at Fermilab.  The first thing they wanted to see was the house in Fermilab Village where my bride-to-be and I would be living for the rest of my graduate career.  G-Mom was impressed: “They hung pictures on the walls for you!”

Then it got complicated. G-Mom asked me what I do.

”I do nuclear physics with the MINERvA, a neutrino interactions experiment.  This detector has an array of nuclear targets that vary in size.  By looking at events that occur in nuclei of different size, we can discover things about those nuclei.” (See notation ** below)

Her follow-up question was: “How is it you find that interesting?”

I told her that what we do in nuclear/particle physics is try to solve mysteries and puzzles, and I like doing that.  Being an avid reader of mystery novels and voracious solver of cross-word puzzles, G-Mom was on-board with this reasoning.  So, I tried to explain the mysteries of nuclear physics that MINERvA will investigate in the style of a Sam Spade or Philip Marlowe private detective novel…

MINERvA, Intra-Nuclear Detective”

MINERvA was starting to lose her cool.  Of all the detectors in all the world, this proton walked into her’s.

After 23 hours of interrogating this proton about what he was doing at the time of the boson exchange, he wasn’t revealing sign one  The had detector picked up the proton in the vicinity of the incident.  His usual accomplice, the muon, was seen fleeing north, where he was apprehended by MINOS, the adjacent detector.  Even with the proton refusing to talk, the greenest rookie could spot a muon and a proton in the final state and tell you this was a case of charged-current quasi-elastic neutrino scattering.

It happens all the time at these energies.  A neutrino with a few GeV of kinetic energy flies deep into some back-alley nucleus and meets up with a neutron.  The deal goes down quickly: a W+ is exchanged; the neutron, fed its fix of charge, is now a proton; the neutrino flies away as a muon, thanked for its troubles with a charge of his own.  This is textbook quasi-elastic scattering.

But this was not a textbook case.  MINERvA had in her custody not one, but two protons!  Only after she drained the last drop of espresso would MINERvA allow her weary legs to drag her back to the interrogation room.  The questioning was fast and direct.

A diagram of "textbook" quasi-elastic scattering.

“Listen Proton, we know you and the muon came out of a carbon nucleus.  Was it quasi-elastic scattering?”

“Sure, but it wasn’t me.  It was the other proton.”

“The other proton told us the same thing.  Then what were you doing fleeing the nucleus?”

“I already told you: I watched the neutrino come in and scatter off a neutron.  Guy turns into a proton and runs right into me!”

“That’s what they all say.  We think both of you protons were directly involved in the scattering.”

“Oh, yeah? How are you going to prove it?  You don’t have jurisdiction inside the nucleus!

The proton was right.  Experiments are not able to see inside the nucleus.  It could not be proven that the protons were involved directly in the neutrino interaction.

But MINERvA was getting close to connecting the dots enough to figure out what this gang of particles was doing inside the nucleus. They couldn’t hide forever. Soon MINERvA would unravel their pattern and tell all the detectors in the world what was going on.

MINERvA collaboration. Credit: Fermilab/Reidar Hahn

** When an interaction happens inside of a large nucleus, the particles involved in the neutrino interaction (“primary particles”) must travel through a sea of protons and neutrons to get outside the nucleus, where they can be detected.  Primary particles may interact with the other protons and neutrons on their way out.  For example, a primary proton can knock out another proton from the nucleus.  Then the experiment will observe two protons coming out of the nucleus (“final state particles”).  The messiness of primary particles interacting on their way out of the nucleus is called Final State Interactions (FSI).  MINERvA will measure FSI in its wide range of nuclei, thus revealing clues about the mysterious inner-workings of the nucleus.

 

– Brian Tice

Related posts:

• MINERvA model for building research bridge with Latin American
• Meet MINERvA: a blend of particle and nuclear physics
• MINERvA Decathlon
MINERvA sees its first neutrinos!

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This article first appeared in symmetry breaking June 24.

The MINOS far detector is located in a cavern half a mile underground in the Soudan Underground Laboratory in Minnesota. The collaboration records about 1,000 neutrinos per year. A tiny fraction of them seem to be electron neutrinos. Photo: Peter Ginter

Step by step, physicists are moving closer to understanding the evolution of our universe.  Neutrinos — among the most abundant particles in the universe –  could have played a critical role in the unfolding of the universe right after the big bang. They are strong candidates for explaining why the big bang produced more matter than antimatter, leading to the universe as it exists today.

Scientists of the MINOS experiment at the Department of Energy’s Fermi National Accelerator Laboratory announced today the results from a search for a rare phenomenon, the transformation of muon neutrinos into electron neutrinos. If this type of neutrino transformation did not exist, neutrinos would not break the matter-antimatter symmetry, and a lot of scientists would be scratching their heads and wonder what else could have caused the dominance of matter of antimatter in our universe.

The MINOS result is consistent with and significantly constrains a measurement reported 10 days ago by the Japanese T2K experiment, which announced an indication of this type of transformation.

The observation of electron neutrino-like events allows MINOS scientists to extract information about a quantity called sin2 2θ13. If muon neutrinos don’t transform into electron neutrinos, sin2 2θ13 is zero. The new MINOS result constrains this quantity to a range between 0 and 0.12, improving on results it obtained with smaller data sets in 2009 and 2010. Credit: Fermilab

The Main Injector Neutrino Oscillation Search (MINOS) at Fermilab recorded a total of 62 electron neutrino-like events. If muon neutrinos do not transform into electron neutrinos, then MINOS should have seen only 49 events. The experiment should have seen 71 events if neutrinos transform as often as suggested by recent results from the Tokai-to-Kamioka (T2K) experiment in Japan. The two experiments use different methods and analysis techniques to look for this rare transformation.

To measure the transformation of muon neutrinos into other neutrinos, the MINOS experiment sends a muon neutrino beam 450 miles (735 kilometers) through the earth from the Main Injector accelerator at Fermilab to a 5,400-ton neutrino detector, located half a mile underground in the Soudan Underground Laboratory in northern Minnesota.  The experiment uses two almost identical detectors: the detector at Fermilab is used to check the purity of the muon neutrino beam, and the detector at Soudan looks for electron and muon neutrinos. The neutrinos’ trip from Fermilab to Soudan takes about one four hundredths of a second, giving the neutrinos enough time to change their identities.

For more than a decade, scientists have seen evidence that the three known types of neutrinos can morph into each other. Experiments have found that muon neutrinos disappear, with some of the best measurements provided by the MINOS experiment. Scientists think that a large fraction of these muon neutrinos transform into tau neutrinos, which so far have been very hard to detect, and they suspect that a tiny fraction transform into electron neutrinos.

The observation of electron neutrino-like events allows MINOS scientists to extract information about a quantity called sin2 2θ13. If muon neutrinos don’t transform into electron neutrinos, sin2 2θ13 is zero. The new MINOS result constrains this quantity to a range between 0 and 0.12, improving on results it obtained with smaller data sets in 2009 and 2010. Credit: Fermilab

The observation of electron neutrino-like events in the detector in Soudan allows MINOS scientists to extract information about a quantity called sin2 2 theta-13 (pronounced sine squared two theta one three). If muon neutrinos don’t transform into electron neutrinos, this quantity is zero. The range allowed by the latest MINOS measurement overlaps with but is narrower than the T2K range. MINOS constrains this quantity to a range between 0 and 0.12, improving on results it obtained with smaller data sets in 2009 and 2010. The T2K range for sin2 2 theta-13 is between 0.03 and 0.28.

“MINOS is expected to be more sensitive to the transformation with the amount of data that both experiments have,” said Fermilab physicist Robert Plunkett, co-spokesperson for the MINOS experiment. “It seems that nature has chosen a value for sin2 2 theta-13 that likely is in the lower part of the T2K allowed range. More work and more data are really needed to confirm both these measurements.”

The MINOS measurement is the latest step in a worldwide effort to learn more about neutrinos. MINOS will continue to collect data until February 2012. The T2K experiment was interrupted in March when the severe earth quake in Japan damaged the muon neutrino source for T2K. Scientists expect to resume operations of the experiment at the end of the year. Three nuclear-reactor based neutrino experiments, which use different techniques to measure sin2 2 theta-13, are in the process of starting up.

The MINOS far detector is located in a cavern half a mile underground in the Soudan Underground Laboratory in Minnesota. The collaboration records about 1,000 neutrinos per year. A tiny fraction of them seem to be electron neutrinos. Photo: Peter Ginter

“Science usually proceeds in small steps rather than sudden, big discoveries, and this certainly has been true for neutrino research,” said Jenny Thomas from University College London, co-spokesperson for the MINOS experiment. “If the transformation from muon neutrinos to electron neutrinos occurs at a large enough rate, future experiments  should find out whether nature has given us two light neutrinos and one heavy neutrino, or vice versa. This is really the next big thing in neutrino physics.”

A large value of sin2 2 theta-13 is welcome news for the worldwide neutrino physics community and a boon for the NOvA neutrino experiment, under construction at Fermilab. The experiment is designed to determine the neutrino mass hierarchy. It will find out whether there are one light and two heavy neutrinos, or whether there are two light neutrinos and a heavy one. Together with several nuclear physics experiments, such as EXO and Majorana, NOvA will help scientists determine what early-universe theories are the most viable ones.

To measure directly the matter-antimatter asymmetry hidden among the neutrino transformations, scientists have proposed the Long-Baseline Neutrino Experiment. It would send neutrinos on a 1,300-kilometer trip from Fermilab to a detector in South Dakota. This would give muon neutrinos more time to transform into other neutrinos than any other experiment. It would give scientists the best shot at observing whether neutrinos break the matter-antimatter symmetry and by how much. For more information about MINOS, NOvA and LBNE, visit the Fermilab neutrino website:
http://www.fnal.gov/pub/science/experiments/intensity/

The MINOS experiment involves more than 140 scientists, engineers, technical specialists and students from 30 institutions, including universities and national laboratories, in five countries: Brazil, Greece, Poland, the United Kingdom and the United States. Funding comes from: the Department of Energy Office of Science and the National Science Foundation in the U.S., the Science and Technology Facilities Council in the U.K; the University of Minnesota in the U.S.; the University of Athens in Greece; and Brazil’s Foundation for Research Support of the State of São Paulo (FAPESP) and National Council of Scientific and Technological Development (CNPq).

Kurt Riesselmann

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This column by Mike Lamm, head of Fermilab’s Magnet Systems Department and Mu2e Level 2 Manager for Solenoids, first appeared in Fermilab Today May 25.

For the past 18 months, the Technical Division magnet program has been working on the development of several complex magnets for Mu2e (pronounced mew-2-e), one of the flagship experiments of Fermilab’s Intensity Frontier program. A few weeks ago, we achieved an important milestone when our detailed, conceptual design for the Mu2e magnets passed a three-day Director’s Technical Design Review of the entire project.

The Mu2e experiment will provide a strong test for beyond the Standard Model theories. Mu2e will look for the predicted but not-yet-observed direct conversion of a muon into an electron, a process known as charged lepton flavor violation. We know that all quarks can change flavor, such as a charm quark turning into an up quark, and we have recently learned that leptons without charge can change flavor too, such as a muon neutrino transforming into an electron neutrino. Hence we suspect that charged leptons such as muons might be able to likewise change flavor by directly converting into an electron. If they do, it will be a very rare process, and its discovery will require a special beamline and particle detector.

The Mu2e experiment will smash an intense beam of protons from Fermilab’s Booster accelerator into a gold target to produce lots of low-energy muons. A magnet known as the production solenoid will slow and collect these particles (see graphic). A transport solenoid will guide the muons through the S-shaped chicane that weeds out unwanted particles. Then the muons will be captured in an aluminum target. If and when a muon converts to an electron within the target, an electron detector within a detector solenoid will identify the emerging electron.

The production solenoid and detector solenoid resemble the superconducting solenoid magnets currently used in Tevatron and LHC experiments, but with additional requirements. The production solenoid must achieve 5 Tesla, or 100,000 times the earth’s magnetic field–the highest central magnetic field of any solenoid in particle physics. Its coils will experience 170 tons of force during operation, or the weight of four fully loaded 18-wheeler trucks. The detector solenoid will be comparable in diameter to the massive ATLAS central solenoid at the LHC, but will be longer, with a total length of more than 11 meters. It will store about the same amount of energy as the ATLAS solenoid, but will feature a more uniform magnetic field.

The transport solenoid will be like nothing else ever built. Because of its complex S-shape its superconducting coils will experience strong forces and torques that will pull in opposite directions when the adjacent coils are forced to power down during an operational hiccup known as a quench. This made its design very challenging.

With the detailed, conceptual design of the Mu2e magnets approved and almost complete, we are moving one step closer to building this experiment, and one step closer to a better understanding of our universe.

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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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