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  • richardmitnick 12:36 pm on November 28, 2018 Permalink | Reply
    Tags: , , , FNAL MiniBooNE, Hints of a ‘sterile’ neutrino, ,   

    From FNAL via COSMOS Magazine: “Hints of a ‘sterile’ neutrino” 

    FNAL II photo

    FNAL Art Image
    FNAL Art Image by Angela Gonzales

    From Fermi National Accelerator Lab , an enduring source of strength for the US contribution to scientific research world wide.
    via

    Cosmos Magazine bloc

    COSMOS Magazine

    Curious result could point to flaws in the Standard Model of particle physics.

    Standard Model of Elementary Particles


    Something missing? The Standard Model admits three types of neutrino. New evidences suggest a fourth might also exist. generalfmv/Getty Images

    Scientists may have caught a glimpse of a new breed of particle from an unseen side of the universe.

    Researchers conducting an exercise known as the Mini Booster Neutrino Experiment (MiniBooNE) at Fermilab near Chicago in the US have painstakingly compiled measurements of neutrinos over the last 15 years.

    FNAL/MiniBooNE

    The experiment has yielded only the three types of neutrinos described in the Standard model: electron neutrinos, muon neutrinos and tau neutrinos. But now the scientists have published a paper in the journal Physical Review Letters, reporting a possible trace of a fourth.

    Neutrinos are subatomic particles less than a million times lighter than electrons. They are one of the three components of matter, along with electrons and quarks, which make up the nuclei in atoms. Each component has two heavier counterparts, which decay after fractions of seconds: this array of particles in threes is known as the Standard Model.

    A fourth particle that bucks the threefold pattern could be big news says MiniBooNE spokesman Rex Tayloe, from Indiana University in the United States.

    “If that is the correct explanation of the signal, it is an important and far-reaching result as it opens up the field of particle physics to a new set of particles – beyond the current Standard Model,” he says.

    Neutrinos are already the most mysterious particle in the Standard Model. They are preposterously numerous – 100 million neutrinos pass through the human body every second, barely interacting.

    And because they interact so weakly, only a tiny number are ever detected. Their mass is still uncertain. It is so small that for a long time it was thought to be zero.

    Unlike quarks and electrons, which decay from unstable, heavy forms into lighter, stable ones, neutrinos continually change form, slipping between the three forms as they as they torpedo through space at close to the speed of light.

    It is this shape-changing that MiniBooNE has been studying, using a 541-metre beam of neutrinos. The scientists create them by smashing high-energy protons into a target of the metal beryllium, which creates unstable particles called pions that quickly decay, creating neutrinos.

    The process creates a type called muon neutrinos, which are directed to MiniBooNE’s detector, a 12.2-metre sphere filled with 818 tonnes of pure mineral oil, lined with 1520 photomultipliers that catch tiny flashes of light caused by the occasional neutrino interaction.

    The Standard Model predicts a small percentage of muon neutrinos will change into electron neutrinos in the half-kilometre flight. But MiniBooNE found more of these than expected.

    One possible explanation for this rapid oscillation is a fourth neutrino form – but because it has never been detected it must not even interact in the incredibly weak way that the other three forms do. The scientists term it a sterile neutrino.

    The hint of a new, invisible particle raises scientists’ hopes for a whole new family that could help solve puzzles of dark matter, dark energy and the imbalance of matter and antimatter in the universe.

    But the isuue is far from resolved. While MiniBooNE’s result is line with an experiment in the nineties at Los Alamos in New Mexico in the US, other experiments have failed to confirm the same effect, which has physicists scratching their heads.

    Solutions could be found by new larger experiments that are coming online, such as DUNE, which tracks neutrinos over a 1300-kilometre path under the US.

    SURF DUNE LBNF Caverns at Sanford Lab


    FNAL LBNF/DUNE from FNAL to SURF, Lead, South Dakota, USA

    There is also the huge Japanese detector Hyper-Kamiokande, and a larger scale version of MiniBooNE.

    Hyper-Kamiokande, a neutrino physics laboratory located underground in the Mozumi Mine of the Kamioka Mining and Smelting Co. near the Kamioka section of the city of Hida in Gifu Prefecture, Japan.

    It’s possible the new data will overturn the sterile neutrino theory as a systematic error of some sort. But even if so, given their history, the mysterious particles are still likely to have some surprises in store.

    See the full article here .


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  • richardmitnick 2:02 pm on September 25, 2018 Permalink | Reply
    Tags: , , , FNAL MiniBooNE, , , , LSND, , , ,   

    From Symmetry: “How not to be fooled in physics” 

    Symmetry Mag
    From Symmetry

    09/25/18
    Laura Dattaro

    1
    Illustration by Sandbox Studio, Chicago with Ana Kova

    Particle physicists and astrophysicists employ a variety of tools to avoid erroneous results.

    In the 1990s, an experiment conducted in Los Alamos, about 35 miles northwest of the capital of New Mexico, appeared to find something odd.

    Scientists designed the Liquid Scintillator Neutrino Detector experiment at the US Department of Energy’s Los Alamos National Laboratory to count neutrinos, ghostly particles that come in three types and rarely interact with other matter.

    LSND experiment at Los Alamos National Laboratory and Virginia Tech

    LSND was looking for evidence of neutrino oscillation, or neutrinos changing from one type to another.

    Several previous experiments had seen indications of such oscillations, which show that neutrinos have small masses not incorporated into the Standard Model, the ruling theory of particle physics. LSND scientists wanted to double-check these earlier measurements.

    By studying a nearly pure source of one type of neutrinos—muon neutrinos—LSND did find evidence of oscillation to a different type of neutrinos, electron neutrinos. However, they found many more electron neutrinos in their detector than predicted, creating a new puzzle.

    This excess could have been a sign that neutrinos oscillate between not three but four different types, suggesting the existence of a possible new type of neutrino, called a sterile neutrino, which theorists had suggested as a possible way to incorporate tiny neutrino masses into the Standard Model.

    Or there could be another explanation. The question is: What? And how can scientists guard against being fooled in physics?

    Brand new thing

    Many physicists are looking for results that go beyond the Standard Model. They come up with experiments to test its predictions; if what they find doesn’t match up, they have potentially discovered something new.

    “Do we see what we expected from the calculations if all we have there is the Standard Model?” says Paris Sphicas, a researcher at CERN.

    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.


    Standard Model of Particle Physics from Symmetry Magazine

    “If the answer is yes, then it means we have nothing new. If the answer is no, then you have the next question, which is, ‘Is this within the uncertainties of our estimates? Could this be a result of a mistake in our estimates?’ And so on and so on.”

    A long list of possible factors can trick scientists into thinking they’ve made a discovery. A big part of scientific research is identifying them and finding ways to test what’s really going on.

    “The community standard for discovery is a high bar, and it ought to be,” says Yale University neutrino physicist Bonnie Fleming. “It takes time to really convince ourselves we’ve really found something.”

    In the case of the LSND anomaly, scientists wonder whether unaccounted-for background events tipped the scales or if some sort of mechanical problem caused an error in the measurement.

    Scientists have designed follow-up experiments to see if they can reproduce the result. An experiment called MiniBooNE, hosted by Fermi National Accelerator Laboratory, recently reported seeing signs of a similar excess. Other experiments, such as the MINOS experiment, also at Fermilab, have not seen it, complicating the search.

    FNAL/MiniBooNE

    FNAL Minos map


    FNAL/MINOS


    FNAL MINOS Far Detector in the Soudan Mine in northern Minnesota

    “[LSND and MiniBooNE] are clearly measuring an excess of events over what they expect,” says MINOS co-spokesperson Jenny Thomas, a physicist at University College London. “Are those important signal events, or are they a background they haven’t estimated properly? That’s what they are up against.”

    Managing expectations

    Much of the work in understanding a signal involves preparatory work before one is even seen.

    In designing an experiment, researchers need to understand what physics processes can produce or mimic the signal being sought, events that are often referred to as “background.”

    Physicists can predict backgrounds through simulations of experiments. Some types of detector backgrounds can be identified through “null tests,” such as pointing a telescope at a blank wall. Other backgrounds can be identified through tests with the data itself, such as so-called “jack-knife tests,” which involve splitting data into subsets—say, data from Monday and data from Tuesday—which by design must produce the same results. Any inconsistencies would warn scientists about a signal that appears in just one subset.

    Researchers looking at a specific signal work to develop a deep understanding of what other physics processes could produce the same signature in their detector. MiniBooNE, for example, studies a beam primarily made of muon neutrinos to measure how often those neutrinos oscillate to other flavors. But it will occasionally pick up stray electron neutrinos, which look like muon neutrinos that have transformed. Beyond that, other physics processes can mimic the signal of an electron neutrino event.

    “We know we’re going to be faked by those, so we have to do the best job to estimate how many of them there are,” Fleming says. “Whatever excess we find has to be in addition to those.”

    Even more variable than a particle beam: human beings. While science strives to be an objective measurement of facts, the process itself is conducted by a collection of people whose actions can be colored by biases, personal stories and emotion. A preconceived notion that an experiment will (or won’t) produce a certain result, for example, could influence a researcher’s work in subtle ways.

    “I think there’s a stereotype that scientists are somehow dispassionate, cold, calculating observers of reality,” says Brian Keating, an astrophysicist at University of California San Diego and author of the book Losing the Nobel Prize, which chronicles how the desire to make a prize-winning discovery can steer a scientist away from best practices. “In reality, the truth is we actually participate in it, and there are sociological elements at work that influence a human being. Scientists, despite the stereotypes, are very much human beings.”

    Staying cognizant of this fact and incorporating methods for removing bias are especially important if a particular claim upends long-standing knowledge—such as, for example, our understanding of neutrinos. In these cases, scientists know to adhere to the adage: Extraordinary claims require extraordinary evidence.

    “If you’re walking outside your house and you see a car, you probably think, ‘That’s a car,’” says Jonah Kanner, a research scientist at Caltech. “But if you see a dragon, you might think, ‘Is that really a dragon? Am I sure that’s a dragon?’ You’d want a higher level of evidence.”


    Dragon or discovery?

    Physicists have been burned by dragons before. In 1969, for example, a scientist named Joe Weber announced that he had detected gravitational waves: ripples in the fabric of space-time first predicted by Albert Einstein in 1916. Such a detection, which many had thought was impossible to make, would have proved a key tenet of relativity. Weber rocketed to momentary fame, until other physicists found they could not replicate his results.

    The false discovery rocked the gravitational wave community, which, over the decades, became increasingly cautious about making such announcements.

    So in 2009, as the Laser Interferometer Gravitational Wave Observatory, or LIGO, came online for its next science run, the scientific collaboration came up with a way to make sure collaboration members stayed skeptical of their results. They developed a method of adding a false or simulated signal into the detector data stream without alerting the majority of the 800 or so researchers on the team. They called it a blind injection. The rest of the members knew an injection was possible, but not guaranteed.

    “We’d been not detecting signals for 30 years,” Kanner, a member of the LIGO collaboration, says. “How clear or obvious would the signature have to be for everyone to believe it?… It forced us to push our algorithms and our statistics and our procedures, but also to test the sociology and see if we could get a group of people to agree on this.”

    In late 2010, the team got the alert they had been waiting for: The computers detected a signal. For six months, hundreds of scientists analyzed the results, eventually concluding that the signal looked like gravitational waves. They wrote a paper detailing the evidence, and more than 400 team members voted on its approval. Then a senior member told them it had all been faked.

    Picking out and spending so much time examining such an artificial signal may seem like a waste of time, but the test worked just as intended. The exercise forced the scientists to work through all of the ways they would need to scrutinize a real result before one ever came through. It forced the collaboration to develop new tests and approaches to demonstrating the consistency of a possible signal in advance of a real event.

    “It was designed to keep us honest in a sense,” Kanner says. “Everyone to some extent goes in with some guess or expectation about what’s going to come out of that experiment. Part of the idea of the blind injection was to try and tip the scales on that bias, where our beliefs about whether we thought nature should produce an event would be less important.”

    All of the hard work paid off: In September 2015, when an authentic signal hit the LIGO detectors, scientists knew what to do. In 2016, the collaboration announced the first confirmed direct detection of gravitational waves. One year later, the discovery won the Nobel Prize.


    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

    Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger

    ESA/eLISA the future of gravitational wave research

    1
    Skymap showing how adding Virgo to LIGO helps in reducing the size of the source-likely region in the sky. (Credit: Giuseppe Greco (Virgo Urbino group)

    No easy answers

    While blind injections worked for the gravitational waves community, each area of physics presents its own unique challenges.

    Neutrino physicists have an extremely small sample size with which to work, because their particles interact so rarely. That’s why experiments such as the NOvA experiment and the upcoming Deep Underground Neutrino experiment use such enormous detectors.

    FNAL/NOvA experiment map


    FNAL NOvA detector in northern Minnesota


    FNAL NOvA Near Detector

    Astronomers have even fewer samples: They have just one universe to study, and no way to conduct controlled experiments. That’s why they conduct decades-long surveys, to collect as much data as possible.

    Researchers working at the Large Hadron Collider have no shortage of interactions to study—an estimated 600 million events are detected every second.

    LHC

    CERN map


    CERN LHC Tunnel

    CERN LHC particles

    But due to the enormous size, cost and complexity of the technology, scientists have built only one LHC. That’s why inside the collider sit multiple different detectors, which can check one another’s work by measuring the same things in a variety of ways with detectors of different designs.

    CERN ATLAS


    CERN/CMS Detector



    CERN ALICE detector


    CERN LHCb chamber, LHC

    While there are many central tenets to checking a result—knowing your experiment and background well, running simulations and checking that they agree with your data, testing alternative explanations of a suspected result—there’s no comprehensive checklist that every physicist performs. Strategies vary from experiment to experiment, among fields and over time.

    Scientists must do everything they can to test a result, because in the end, it will need to stand up to the scrutiny of their peers. Fellow physicists will question the new result, subject it to their own analyses, try out alternative interpretations, and, ultimately, try to repeat the measurement in a different way. Especially if they’re dealing with dragons.

    See the full article here .


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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 8:39 am on September 18, 2018 Permalink | Reply
    Tags: , , , FNAL MiniBooNE, , , Super-Kamioka Neutrino Detection Experiment at Kamioka Observatory Tokyo Japan   

    From COSMOS Magazine: “Hints of a fourth type of neutrino create more confusion” 

    Cosmos Magazine bloc

    From COSMOS Magazine

    18 September 2018
    Katie Mack

    Anomalous experimental results hint at the possibility of a fourth kind of neutrino, but more data only makes the situation more confusing.

    1
    Inside the Super-Kamioka Neutrino Detection Experiment at Kamioka Observatory, Tokyo, Japan. Credit: Kamioka Observatory, ICRR (Institute for Cosmic Ray Research), The University of Tokyo

    It was a balmy summer in 1998 when I first became aware of the confounding weirdness of neutrinos. I have vivid memories of that day, as an embarrassingly young student researcher, walking along a river in Japan, listening to a graduate student tell me about her own research project: an attempt to solve a frustrating neutrino–related mystery. We were both visiting a giant detector experiment called Super-Kamiokande, in the heady days right after it released data that forever altered the Standard Model of Particle Physics.

    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.


    Standard Model of Particle Physics from Symmetry Magazine

    What Super-K found was that neutrinos – ghostly, elusive particles that are produced in the hearts of stars and can pass through the whole Earth with only a miniscule chance of interacting with anything – have mass.

    A particle having mass might not sound like a big deal, but the original version of the otherwise fantastically successful Standard Model described neutrinos as massless – just like photons, the particles that carry light and other electromagnetic waves. Unlike photons, however, neutrinos come in three ‘flavours’: electron, muon, and tau.

    Super-K’s discovery was that neutrinos could change from one flavour to another as they travelled, in a process called oscillation. This can only happen if the three flavours have different masses from one another, which means they can’t be massless.

    The finding suggested there must be a fourth neutrino, one invisible in experiments.

    This discovery was a big deal, but it wasn’t the mystery the grad student was working to solve. A few years before, an experiment called the Liquid Scintillator Neutrino Detector (LSND), based in the US, had seen tantalising evidence that neutrinos were oscillating in a way that made no sense at all with the results of other experiments, including Super-K. The LSND finding indirectly suggested there had to be a fourth neutrino in the picture that the other neutrinos were sometimes oscillating into. This fourth neutrino would be invisible in experiments, lacking the kind of interactions that made the others detectable, which gave it the name ‘sterile neutrino’. And it would have to be much more massive than the other three.

    As I learned that day by the river, the result had persisted, unexplained, for years. Most people assumed something had gone wrong with the experiment, but no one knew what.

    In 2007, the plot thickened. An experiment called MiniBooNE, designed primarily to figure out what the heck happened with LSND, didn’t find the distribution of neutrinos it should have seen to confirm the LSND result.

    FNAL/MiniBooNE

    But some extra neutrinos did show up in MiniBooNE in a different energy range. They were inconsistent with LSND and every other experiment, perhaps suggesting the existence of even more flavours of neutrino.

    Meanwhile, experiments looking at neutrinos produced by nuclear reactors were seeing numbers that also couldn’t easily be explained without a sterile neutrino, though some physicists wrote these off as possibly due to calibration errors.

    And now the plot has grown even thicker.

    In May, MiniBooNE announced new results that seem more consistent with LSND, but even less palatable in the context of other experiments. MiniBooNE works by creating a beam of muon neutrinos and shooting them through the dirt at an underground detector 450 m away. The detector, meanwhile, is monitoring the arrival of electron neutrinos, in case any muon neutrinos are shape-shifting. More of these electron neutrinos turn up than standard neutrino models predict, which implies that some muon neutrinos transform by oscillating into sterile neutrinos too. (Technically, all neutrinos would be swapping around with all others, but this beam only makes sense if there’s an extra, massive one in the mix.)

    But there are several reasons this explanation is facing resistance. One is that experiments just looking for muon neutrinos disappearing (becoming sterile neutrinos or anything else) don’t find a consistent picture. Secondly, if sterile neutrinos at the proposed mass exist, they should have been around in the very early universe, and measurements we have from the cosmic microwave background of the number of neutrino types kicking around then strongly suggest it was just the normal three.

    So, as usual, there’s more work to be done. A MiniBooNE follow-up called MicroBooNE is currently taking data and might make the picture clearer, and other experiments are on the way.

    FNAL/MicroBooNE

    It seems very likely that something strange is happening in the neutrino sector. It just remains to be seen exactly what, and how, over the next 20 years of constant neutrino bombardment, it will change our understanding of everything else.

    See the full article here .


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  • richardmitnick 10:09 am on August 6, 2018 Permalink | Reply
    Tags: , FNAL MiniBooNE, Las Cruces Sun News, ,   

    From Fermilab via Las Cruces Sun News: “NMSU physicist may have evidence of the elusive sterile neutrino” 

    FNAL II photo

    FNAL Art Image
    FNAL Art Image by Angela Gonzales

    From Fermilab , an enduring source of strength for the US contribution to scientific research world wide.

    via

    2

    Las Cruces Sun News

    July 21, 2018 [Just now in social media]
    Billy Huntsman

    A New Mexico State University professor is part of an international research team that recently released the results of an experiment that may support a theory for a fourth fundamental particle – the mysterious sterile neutrino that passes through matter without interacting with it….

    Robert Cooper, assistant professor in NMSU’s Department of Physics, is one of a group of scientists from 17 universities and labs, which conducted their experiments collectively known as MiniBooNE at the Fermi National Accelerator Laboratory near Chicago.

    FNAL/MiniBooNE

    3
    MiniBooNE’s oil tank is 12 meters in diameter and lined with 1,520 photodetectors. Ryan Patterson / Princeton / Fermilab.

    “We are presenting very compelling evidence that could support the sterile neutrino hypothesis,” Cooper said. “It will take other types of experiments that look at this phenomenon from a slightly different ‘angle’ to claim discovery.”

    But they are not jumping to conclusions. Cooper emphasized the research team is not claiming the discovery of a fourth neutrino.

    3
    Robert Cooper, in the Department of Physics at New Mexico State University, is part of a research team whose research may support evidence for a fourth fundamental particle: the sterile neutrino. (Photo: NMSU photo by Billy Huntsman)

    “Besides the sterile neutrino theory, another explanation could be that there is a new or underestimated source of background events,” Cooper said. “Clearly, sterile neutrinos could rewrite our understanding of neutrino and particle physics, but either way, something new is occurring.”

    MiniBooNE has been conducting experiments for over 20 years. The anomaly that resulted in the sterile-neutrino hypothesis was first detected in the 1990s at Los Alamos National Laboratory.

    “Not much was done differently this time around,” Cooper said. “The detector was run twice as long, and as a result, MiniBooNE doubled the number of neutrino events. Some have argued that the excess of electron events could have been due to an ‘unlucky’ statistical fluctuation. The increased number of events has improved our ‘statistical sensitivity’ and shows that this result is significant and very unlikely to be due to a statistical accident.”

    MiniBooNE specifically researches neutrino oscillations. Currently there are three kinds, or flavors, of neutrinos known: an electron neutrino, a muon neutrino, and a tau neutrino. Neutrino oscillation is the phenomenon in which neutrinos change into different flavors.

    “MiniBooNE was designed to search for electron neutrinos,” Cooper said. “It identifies electron neutrinos by searching for interactions that produce electrons in the final state. We use the Booster Neutrino Beamline at Fermilab to produce a pure beam of muon neutrinos to search for these.”

    “An electron neutrino can produce an electron when it interacts with matter, and the muon neutrino can produce a muon when it interacts with matter,” Cooper said. “At the neutrino energies we produce in our experiments, more than 800 million electron volts, and the distance scales of our experiment – half a kilometer – we expect to see almost no electrons in the final state.”

    But at the conclusion of their experiments, the researchers saw an excess of final-state electrons beyond what they expected.

    “We have measurements and models that constrain this number to a small amount,” Cooper said. “Another source of ‘false’ electrons is gamma rays. Our detector does an extraordinary job of distinguishing background gamma ray events from electrons, but some may slip through the cracks of our analysis. Just like contamination, we have multiple measurements of these backgrounds and extensive simulation and modeling. Therefore, our excess of electron events seems significant, validated, and real.”

    The existence of a sterile fourth neutrino would mean a total rethinking of particle physics would be necessary.

    “Our understanding of particle physics, cosmology, and possibly dark matter would be affected,” Cooper said. “Discovering new particles is a very big deal. Supposing sterile neutrinos exist, this would have deep consequences about the types of future experiments we perform to explore the boundaries of our particle physics knowledge.”

    Sterile neutrinos could answer a number of questions about dark matter, which physicists theorize makes up most of the universe and about which very little is known.

    Cooper said there could even be two or more types of sterile neutrinos.

    A formal discovery will require more work and the MiniBooNE team is continuing its research.

    “I’m working on multiple new efforts to validate this possible discovery,” Cooper said. “All that being said, we have very significant evidence, but it is not absolute proof yet.”

    The preprint article has been submitted to a peer-reviewed journal and is available at: https://arxiv.org/abs/1805.12028 Observation of a Significant Excess of Electron-Like Events in the MiniBooNE Short-Baseline Neutrino Experiment.

    See the full article here .


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    Dark Energy Camera [DECam], built at FNAL

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  • richardmitnick 2:56 pm on June 22, 2018 Permalink | Reply
    Tags: , , FNAL MiniBooNE, , ,   

    From Scientific American: “Evidence Builds for a New Kind of Neutrino” 

    Scientific American

    From Scientific American

    June 7, 2018
    Clara Moskowitz

    FNAL/MiniBooNE

    Physicists have caught ghostly particles called neutrinos misbehaving at an Illinois experiment, suggesting an extra species of neutrino exists. If borne out, the findings would be nothing short of revolutionary, introducing a new fundamental particle to the lexicon of physics that might even help explain the mystery of dark matter.

    Undeterred by the fact that no one agrees on what the observations actually mean, experts gathered at a neutrino conference this week in Germany are already excitedly discussing these and other far-reaching implications.

    Neutrinos are confusing to begin with. Formed long ago in the universe’s first moments and today in the hearts of stars and the cores of nuclear reactors, the miniscule particles travel at nearly the speed of light, and scarcely interact with anything else; billions pass harmlessly through your body each day, and a typical neutrino could traverse a layer of lead a light-year thick unscathed. Ever since their discovery in the mid–20th century, neutrinos were predicted to weigh nothing at all, but experiments in the 1990s showed they do have some mass—although physicists still do not know exactly how much. Stranger still, they come in three known varieties, or flavors—electron neutrinos, muon neutrinos and tau neutrinos—and, most bizarrely, can transform from one flavor to another. Because of these oddities and others, many physicists have been betting on neutrinos to open the door to the next frontier in physics.

    Now some think the door has cracked ajar. The discovery comes from 15 years’ worth of data gathered by the Mini Booster Neutrino Experiment (MiniBooNE) at Fermi National Accelerator Laboratory in Batavia, Ill. MiniBooNE detects and characterizes neutrinos by the flashes of light they occasionally create when they strike atomic nuclei in a giant vat filled with 800 tons of pure mineral oil. Its design is similar to that of an earlier project, the Liquid Scintillator Neutrino Detector (LSND) at Los Alamos National Laboratory in New Mexico. In the 1990s LSND observed a curious anomaly, a greater-than-expected number of electron neutrinos in a beam of particles that started out as muon neutrinos; MiniBooNE has now seen the same thing, in a neutrino beam generated by one of Fermilab’s particle accelerators.

    Because muon neutrinos could not have transformed directly into electron flavor over the short distance of the LSND experiment, theorists at the time proposed that some of the particles were oscillating into a fourth flavor—a “sterile neutrino”—and then turning into electron neutrinos, producing the mysterious excess. Although the possibility was tantalizing, many physicists assumed the findings were a fluke, caused by some mundane error particular to LSND. But now that MiniBooNE has observed the very same pattern, scientists are being forced to reckon with potentially more profound causes for the phenomenon. “Now you have to really say you have two experiments seeing the same physics effect, so there must be something fundamental going on,” says MiniBooNE co-spokesperson Richard Van de Water of Los Alamos. “People can’t ignore this anymore.”

    The MiniBooNE team submitted its findings on May 30 to the preprint server arXiv, and is presenting them this week at the XXVIII International Conference on Neutrino Physics and Astrophysics in Heidelberg, Germany.

    A Fourth Flavor

    Sterile neutrinos are an exciting prospect, but outside experts say it is too early to conclude such particles are behind the observations. “If it is sterile neutrinos, it’d be revolutionary,” says Mark Thomson, a neutrino physicist and chief executive of the U.K.’s Science and Technology Facilities Council who was not part of the research. “But that’s a big ‘if.’”

    This new flavor would be called “sterile” because the particles would not feel any of the forces of nature, save for gravity, which would effectively block off communication with the rest of the particle world. Even so, they would still have mass, potentially making them an attractive explanation for the mysterious “dark matter” that seems to contribute additional mass to galaxies and galaxy clusters. “If there is a sterile neutrino, it’s not just some extra particle hanging out there, but maybe some messenger to the universe’s ‘dark sector,’” Van de Water says. “That’s why this is really exciting.” Yet the sterile neutrinos that might be showing up at MiniBooNE seem to be too light to account for dark matter themselves—rather they might be the first vanguard of a whole group of sterile neutrinos of various masses. “Once there is one [sterile neutrino], it begs the question: How many?” says Kevork Abazajian, a theoretical physicist at the University of California, Irvine. “They could participate in oscillations and be dark matter.”

    The findings are hard to interpret, however, because if neutrinos are transforming into sterile neutrinos in MiniBooNE, then scientists would expect to measure not just the appearance of extra electron neutrinos, but a corresponding disappearance of the muon neutrinos they started out as, balanced like two sides of an equation. Yet MiniBooNE and other experiments do not see such a disappearance. “That’s a problem, but it’s not a huge problem,” says theoretical physicist André de Gouvêa of Fermilab. “The reason this is not slam-dunk evidence against the sterile neutrino hypothesis is that [detecting] disappearance is very hard. You have to know exactly how much you had at the beginning, and that’s a challenge.”

    Another Mystery?

    Or perhaps MiniBooNE has discovered something big, but not sterile neutrinos. Maybe some other new aspect of the universe is responsible for the unexpected pattern of particles in the experiment’s beam. “Right now people are thinking about whether there are other new phenomena out there that could resolve this ambiguity,” de Gouvêa says. “Maybe the neutrinos have some new force that we haven’t thought about, or maybe the neutrinos decay in some funny way. It kind of feels like we haven’t hit the right hypothesis yet.”

    Unusually, this is one mystery physicists will not have to wait too long to solve. Another experiment at Fermilab called MicroBooNE was designed to follow MiniBooNE and will be able to study the excess more closely.

    FNAL/MicrobooNE

    One drawback of MiniBooNE is that it cannot be sure the flashes of light it sees are truly coming from neutrinos—it is possible that some unknown process is producing an excess of photons that mimic the neutrino signal. MicroBooNE, which should deliver its first data later this year, can distinguish between neutrino signals and impostors. If the signal turns out to be an excess of ordinary photons, rather than electron neutrinos, then all bets are off. “We don’t know what would do that in terms of physics, but if it is due to photons, we know that this sterile neutrino interpretation is not correct,” de Gouvêa says.

    In addition to MicroBooNE, Fermilab is building two other detectors to sit on the same beam of neutrinos and work in concert to study the neutrino oscillations going on there. Known collectively as the Short-Baseline Neutrino Program, the new system should be up and running by 2020 and could deliver definitive data in the early part of that decade, says Steve Brice, head of Fermilab’s Neutrino Division.

    FNAL Short baseline neutrino detector

    Until then physicists will continue to debate the mysteries of neutrinos—a field that is growing in size and excitement every year. The meeting happening now in Heidelberg, for example, is the largest neutrino conference ever. “It’s been a steady ramp-up over the last decade,” Brice says. “It’s an area that’s hard to study, but it’s proving to be a very fruitful field for physics.”

    See the full article here .


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  • richardmitnick 3:57 pm on June 4, 2018 Permalink | Reply
    Tags: , FNAL MiniBooNE, , , ,   

    From physicsworld.com: “Evidence for sterile neutrinos claimed by Fermilab experiment” 

    physicsworld
    From physicsworld.com

    04 Jun 2018
    Edwin Cartlidge

    Physicists working on the Mini Booster Neutrino Experiment (MiniBooNE) at Fermilab in the US have released new results that they argue provide strong evidence for the existence of a new type of particle known as a sterile neutrino. The researchers say that their data are fully consistent with a previous hint of sterile neutrinos that emerged more than 20 years ago from the Liquid Scintillator Neutrino Detector (LSND) at the Los Alamos National Laboratory in New Mexico, although other groups have failed to reproduce the findings.

    FNAL/MiniBooNE

    Sterile neutrinos, if they exist, would be even more elusive than standard neutrinos, which themselves are chargeless and nearly massless. The Standard Model of particle physics tells us that neutrinos come in three flavours – electron, muon and tau – and that they “oscillate” from one flavour to another as they travel through space. But some extensions of the Standard Model predict that these known neutrinos can also oscillate into and out of sterile neutrinos, which might not interact at all with any other ordinary matter.

    MiniBooNE monitors the tiny flashes of light that are produced occasionally when electron neutrinos interact with atomic nuclei in about 800 tonnes of pure mineral oil contained in a spherical tank located underground on the Fermilab site near Chicago.

    MiniBooNE receptors

    Those neutrinos are generated after protons from the lab’s Booster accelerator are fired into a beryllium target to create muon neutrinos, which then oscillate to electron neutrinos as they travel several hundred metres through the Earth to the detector.

    Statistically speaking

    In a preprint uploaded recently to the arXiv server, the MiniBooNE collaboration reports having detected far more electron neutrinos than would be expected from purely Standard Model oscillations after collecting data for 15 years. According to collaboration member William Louis of Los Alamos, the measurement suggests that some of the muon neutrinos oscillate into sterile neutrinos that in turn transform into electron neutrinos. That interpretation, he says, is bolstered by the fact that the variation of electron-neutrino excess with neutrino energy – a parameter of neutrino oscillations – seen in MiniBooNE matches that recorded at Liquid Scintillator Neutrino Detector. He and his colleagues conclude that the combined excess from the two experiments has a statistical significance of 6.1σ, which is well above the 5σ that is normally considered a discovery in particle physics.

    Although MiniBooNE is quite similar to LSND – in using mineral oil to observe neutrinos from an accelerator-based source – and indeed has inherited personnel from the earlier project, its researchers are nevertheless confident that there are no common sources of error. “We think that is very unlikely,” says Louis. “The two experiments have very different energies and backgrounds, and therefore very different possible systematic errors”.

    Not a done deal

    However, the existence of sterile neutrinos is not yet a done deal. While some groups operating experiments that exploit neutrinos from nuclear reactors or radioactive sources have also gathered (somewhat weaker) evidence for the hypothetical particles, other groups have looked and found nothing. These include the IceCube collaboration, which operates a detector at the South Pole, and the now completed Main Injector Neutrino Oscillation Search (MINOS) at Fermilab.

    U Wisconsin ICECUBE neutrino detector at the South Pole

    U Wisconsin ICECUBE neutrino detector at the South Pole

    Lunar Icecube

    IceCube DeepCore annotated

    IceCube PINGU annotated


    DM-Ice II at IceCube annotated

    FNAL MINOS experiment

    FNAL Minos map

    FNAL MINOS near detector

    FNAL MINOS Far Detector in the Soudan Mine in northern Minnesota

    Indeed, some physicists outside the MiniBooNE collaboration have told Physics World that they remain unconvinced by the latest results.

    To try and settle the issue, numerous other dedicated experiments are either operating or under development. For their part, Louis and colleagues are currently setting up another three detectors at Fermilab – one of which is now running – to monitor the neutrino flux closer to the beryllium target than MiniBooNE and also further away. The idea, he says, is to show beyond doubt that the electron neutrino excess really is due to oscillations, given that the measured oscillation rate should vary with distance from the source as well as with energy. Results are expected “over the next three to five years,” he says.

    See the full article here .


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    We engage with policymakers and the general public to develop awareness and understanding of the value of physics and, through IOP Publishing, we are world leaders in professional scientific communications.
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  • richardmitnick 2:32 pm on April 9, 2018 Permalink | Reply
    Tags: , FNAL MiniBooNE, Muon neutrinos,   

    From FNAL: “Neutrino experiment at Fermilab delivers an unprecedented measurement” 

    FNAL II photo

    FNAL Art Image
    FNAL Art Image by Angela Gonzales

    Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

    measurement

    April 6, 2018
    Kurt Riesselmann

    1
    This interior view of the MiniBooNE detector tank shows the array of photodetectors used to pick up the light particles that are created when a neutrino interacts with a nucleus inside the tank. Photo: Reidar Hahn

    FNAL/MiniBooNE

    MiniBooNE scientists demonstrate a new way to probe the nucleus with muon neutrinos.

    Tiny particles known as neutrinos are an excellent tool to study the inner workings of atomic nuclei. Unlike electrons or protons, neutrinos have no electric charge, and they interact with an atom’s core only via the weak nuclear force. This makes them a unique tool for probing the building blocks of matter. But the challenge is that neutrinos are hard to produce and detect, and it is very difficult to determine the energy that a neutrino has when it hits an atom.

    This week a group of scientists working on the MiniBooNE experiment at the Department of Energy’s Fermilab reported a breakthrough: They were able to identify exactly-known-energy muon neutrinos hitting the atoms at the heart of their particle detector. The result eliminates a major source of uncertainty when testing theoretical models of neutrino interactions and neutrino oscillations.

    “The issue of neutrino energy is so important,” said Joshua Spitz, Norman M. Leff assistant professor at the University of Michigan and co-leader of the team that made the discovery, along with Joseph Grange at Argonne National Laboratory. “It is extraordinarily rare to know the energy of a neutrino and how much energy it transfers to the target atom. For neutrino-based studies of nuclei, this is the first time it has been achieved.”

    To learn more about nuclei, physicists shoot particles at atoms and measure how they collide and scatter. If the energy of a particle is sufficiently large, a nucleus hit by the particle can break apart and reveal information about the subatomic forces that bind the nucleus together.

    But to get the most accurate measurements, scientists need to know the exact energy of the particle breaking up the atom. That, however, is almost never possible when doing experiments with neutrinos.

    Like other muon neutrino experiments, MiniBooNE uses a beam that comprises muon neutrinos with a range of energies. Since neutrinos have no electric charge, scientists have no “filter” that allows them to select neutrinos with a specific energy.

    MiniBooNE scientists, however, came up with a clever way to identify the energy of a subset of the muon neutrinos hitting their detector. They realized that their experiment receives some muon neutrinos that have the exact energy of 236 million electronvolts (MeV). These neutrinos stem from the decay of kaons at rest about 86 meters from the MiniBooNE detector emerging from the aluminum core of the particle absorber of the NuMI beamline, which was built for other experiments at Fermilab.

    Energetic kaons decay into muon neutrinos with a range of energies. The trick is to identify muon neutrinos that emerge from the decay of kaons at rest. Conservation of energy and momentum then require that all muon neutrinos emerging from the kaon-at-rest decay have to have exactly the energy of 236 MeV.

    “It is not often in neutrino physics that you know the energy of the incoming neutrino,” said MiniBooNE co-spokesperson Richard Van De Water of Los Alamos National Laboratory. “With the first observation by MiniBooNE of monoenergetic muon neutrinos from kaon decay, we can study the charged current interactions with a known probe that enable theorists to improve their cross section models. This is important work for the future short- and long-baseline neutrino programs at Fermilab.”

    This analysis was conducted with data collected from 2009 to 2011.

    “The result is notable,” said Rex Tayloe, co-spokesperson of the MiniBooNE collaboration and professor of physics at Indiana University Bloomington. “We were able to extract this result because of the well-understood MiniBooNE detector and our previous careful studies of neutrino interactions over 15 years of data collection.”

    Spitz and his colleagues already are working on the next monoenergetic neutrino result. A second neutrino detector located near MiniBooNE, called MicroBooNE, also receives muon neutrinos from the NuMI absorber, 102 meters away. Since MicroBooNE uses liquid-argon technology to record neutrino interactions, Spitz is optimistic that the MicroBooNE data will provide even more information.

    “MicroBooNE will provide more precise measurements of this known-energy neutrino,” he said. “The results will be extremely valuable for future neutrino oscillation experiments.”

    The MiniBooNE result was published in the April 6, 2018, issue of Physical Review Letters. This research was supported by the U.S. Department of Energy Office of Science.

    See the full article here .

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    Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics. Fermilab is America’s premier laboratory for particle physics and accelerator research, funded by the U.S. Department of Energy. Thousands of scientists from universities and laboratories around the world
    collaborate at Fermilab on experiments at the frontiers of discovery.


    FNAL/MINERvA

    FNAL DAMIC

    FNAL Muon g-2 studio

    FNAL Short-Baseline Near Detector under construction

    FNAL Mu2e solenoid

    Dark Energy Camera [DECam], built at FNAL

    FNAL DUNE Argon tank at SURF

    FNAL/MicrobooNE

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    FNAL LBNF/DUNE from FNAL to SURF, Lead, South Dakota, USA

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  • richardmitnick 1:52 pm on May 3, 2016 Permalink | Reply
    Tags: , FNAL MiniBooNE,   

    From FNAL: “Preparing for the sterile neutrino search: Fermilab breaks ground on Short-Baseline Near Detector building” 

    FNAL II photo

    Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

    May 3, 2016
    Rashmi Shivni

    1
    Fermilab broke ground on the Short-Baseline Neutrino Detector building on April 27. From left: Josh Kenney, FESS; Steve Dixon, AD; David Schmitz, University of Chicago; Ting Miao, ND; Ornella Palamara, ND; Peter Wilson, ND; Catherine James, ND. Photo: Reidar Hahn

    FNAL Short-Baseline Near Detector
    FNAL Short-Baseline Near Detector

    On April 27, Fermilab broke ground on the building that will house the future Short-Baseline Near Detector.

    The particle detector, SBND, is one of three that, together, scientists will use to search for the sterile neutrino, a hypothesized particle whose existence, if confirmed, could not only help us better understand the types of neutrino we already know about, but also provide clues about how the universe formed.

    Members of the Fermilab Neutrino and Particle Physics divisions, working together with international collaborators, are currently refining the design of the detector itself. It will take about eight months to complete the SBND building.

    The three detectors make up the laboratory’s Short-Baseline Neutrino Program, which will use a powerful neutrino beam generated by the Fermilab accelerator complex. The beam will pass first through SBND and then through the MicroBooNE detector, which is already installed and taking data, having observed its first neutrino interactions in October. Finally, the beam will travel through ICARUS, the largest of the three detectors. ICARUS, which was used in a previous experiment at the Italian Gran Sasso laboratory, is currently at the CERN laboratory in Switzerland receiving upgrades before its big move to Fermilab in 2017.

    FNAL/Microboone
    FNAL/MicrobooNE

    FNAL/ICARUS
    FNAL/ICARUS

    INFN Gran Sasso ICARUS
    INFN Gran Sasso ICARUS, previous home of ICARUS

    “The entire Short-Baseline Neutrino Program is looking for oscillations, or the transformations, of muon neutrinos into electron neutrinos,” said Peter Wilson, SBN program coordinator. “Sterile neutrinos might have a role in this oscillation process.”

    The beam coming out of the accelerator comprises primarily muon neutrinos; the detectors will measure their transformation into electron neutrinos.

    All three detectors have specific functions in detecting the transformation. As the detector closest to the beam source, SBND will take an initial measurement of the beam’s composition – how much the beam contains each of the different neutrino types.

    “The intermediary and far detectors are used to search for sterile neutrinos in two different ways,” said Ornella Palamara, co-spokesperson for the SBND experiment. “Either there’s an appearance of an excess of electron neutrinos or there’s a disappearance of the number of muon neutrinos compared to the number we start with.”

    If there are more electron neutrinos than predicted, then muon neutrinos may have oscillated first into sterile neutrinos and then to electron neutrinos. If the data show a smaller number of muon neutrinos than predicted, the muon neutrinos may have transformed only into sterile neutrinos, which cannot be seen in the far detectors.

    Scientists first picked up on experimental hints of a sterile neutrino at Los Alamos National Laboratory’s LSND experiment in 1995. When the Fermilab experiment MiniBooNE followed up, scientists could not confirm the sterile neutrino’s existence, but neither could they rule it out.

    “That’s the power of this program,” Palamara said. “We’re building off previous measurements, but we have more sensitive tools to measure the neutrinos.”

    Part of the sensitivity of SBND lies in its liquid-argon time projection chamber, the active part of the detector, which will contain 112 tons of liquid argon. Neutrinos will interact with the nuclei of the argon atoms, and scientists on SBND will study the resulting particles to better understand the neutrinos that caused the interaction. Their findings will likely have application in future accelerator-based neutrino programs, such as the international Deep Underground Neutrino Experiment hosted by Fermilab.

    The Short-Baseline Neutrino Program will begin taking data in 2018.

    “The SBND groundbreaking is a noteworthy milestone, but it’s part of a much larger program,” Wilson said. “Many people are working on it, and everyone is excited to get the chance to understand new physics.”

    See the full article here .

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    Fermilab Campus

    Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics. Fermilab is America’s premier laboratory for particle physics and accelerator research, funded by the U.S. Department of Energy. Thousands of scientists from universities and laboratories around the world
    collaborate at Fermilab on experiments at the frontiers of discovery.

     
  • richardmitnick 4:42 pm on August 12, 2015 Permalink | Reply
    Tags: , FNAL MiniBooNE, ,   

    From FNAL: “MicroBooNE sees first cosmic muons” 

    FNAL II photo

    Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

    Aug. 12, 2015
    Ali Sundermier

    1
    This image shows the first cosmic ray event recorded in the MicroBooNE TPC on Aug. 6. Image: MicroBooNE

    A school bus-sized detector packed with 170 tons of liquid argon has seen its first particle footprints.

    On Aug. 6, MicroBooNE , a liquid-argon time projection chamber, or LArTPC, recorded images of the tracks of cosmic muons, particles that shower down on Earth when cosmic rays collide with nuclei in our atmosphere.

    Temp 1
    MicroBooNE

    “This is the first detector of this size and scale we’ve ever launched in the U.S. for use in a neutrino beam, so it’s a very important milestone for the future of neutrino physics,” said Sam Zeller, co-spokesperson for the MicroBooNE collaboration.

    Picking up cosmic muons is just one brief stop during MicroBooNE’s expedition into particle physics. The centerpiece of the three detectors planned for Fermilab’s Short-Baseline Neutrino program, or SBN, MicroBooNE will pursue the much more elusive neutrino, taking data about this weakly interacting particle for about three years. When beam starts up in October, it will travel 470 meters and then traverse the liquid argon in MicroBooNE, where neutrino interactions will result in tracks that the detector can convert into precise three-dimensional images. Scientists will use these images to investigate anomalies seen in an earlier experiment called MiniBooNE, with the aim to determine whether the excess of low-energy events that MiniBooNE saw was due to a new source of background photons or if there could be additional types of neutrinos beyond the three established flavors.

    One of MicroBooNE’s goals is to measure how often a neutrino that interacts with an argon atom will produce certain types of particles. A second goal is to conduct R&D for future large-scale LArTPCs. MicroBooNE will carry signals up to two and a half meters across the detector, the longest drift ever for a LArTPC in a neutrino beam. This requires a very high voltage and very pure liquid argon. It is also the first time a detector will operate with its electronics submerged in liquid argon on such a large scale. All of these characteristics will be important for future experiments such as the Deep Underground Neutrino Experiment, or DUNE, which plans to use similar technology to probe neutrinos.

    “The entire particle physics community worldwide has identified neutrino physics as one of the key lines of research that could help us understand better how to go beyond what we know now,” said Matt Toups, run coordinator and co-commissioner for MicroBooNE with Fermilab Scientist Bruce Baller. “Those questions that are driving the field, we hope to answer with a very large LArTPC detector.”

    Another benefit of the experiment, Zeller said, is training the next generation of LArTPC experts for future programs and experiments. MicroBooNE is a collaborative effort of 25 institutions, with 55 students and postdocs working tirelessly to perfect the technology. Collaborators are keeping their eyes on the road toward the future of neutrino physics and liquid-argon technology.

    “It’s been a long haul,” said Bonnie Fleming, MicroBooNE co-spokesperson. “Eight and a half years ago liquid argon was a total underdog. I used to joke that no one would sit next to me at the lunch table. And it’s a world of difference now. The field has chosen liquid argon as its future technology, and all eyes are on us to see if our detector will work.”

    See the full article here.

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    Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics. Fermilab is America’s premier laboratory for particle physics and accelerator research, funded by the U.S. Department of Energy. Thousands of scientists from universities and laboratories around the world
    collaborate at Fermilab on experiments at the frontiers of discovery.

     
  • richardmitnick 12:45 pm on October 9, 2014 Permalink | Reply
    Tags: , FNAL MiniBooNE,   

    From FNAL: “Physics in a Nutshell – Neutrinos meet liquid argon” 


    Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

    Thursday, Oct. 9, 2014
    Tia Miceli

    Fermilab’s flagship effort is its neutrino program, which is ramping up to be the strongest in the world. This means creating the world’s best neutrino detectors. To that end, scientists at Fermilab are pursuing one hot technology that is lighting up neutrino physics, detection based on cryogenic liquid argon.

    tube
    Like neon, argon is used to make colorful lighted signs. Particle physicists are now putting argon to a far more exciting use: detecting neutrinos. Image: P Slawinski

    At first, argon seems to be a pretty boring element. As a noble gas, it does not react chemically. Making up one percent of our atmosphere, it is its third most common component, surpassed only by nitrogen and oxygen. But don’t let its mundane properties fool you. When we cool it down to extremely cold temperatures, it turns into a liquid with incredible properties for cutting-edge neutrino detectors.

    For particle physics, perhaps liquid argon’s most important feature is that it acts as both a target and detector for neutrinos, although it isn’t the only material that can be used this way. The Super-Kamiokande experiment in Japan used water stored in a deep-underground tank as large as Wilson Hall to detect neutrinos. Here at Fermilab, the MiniBooNE experiment used a giant sphere of oil that operated much the same way as Super-Kamiokande’s tank.

    sk
    Super-Kamiokande experiment

    mb
    The MiniBooNE experiment records a neutrino event, in this 2002 image from Fermilab. The ring of light, registered by some of more than one thousand light sensors inside the detector, indicates the collision of a muon neutrino with an atomic nuclei. Credit: Fermilab

    But with 40 protons and neutrons, liquid argon is denser than water or oil, so liquid-argon detectors see more neutrino collisions per unit volume than their oil- or water-based predecessors. That means faster measurements and consequently faster discoveries.

    Another advantage of liquid argon is that, when a neutrino interacts with it and subsequently generates charged particles, it produces two separate kinds of signals; oil- or water-based detectors produce only one. One type of signal, unique to liquid argon, results from its ability to record the charged particles’ trajectories.

    Charged particles are created in the liquid argon after a neutrino flies in and collides with an argon nucleus. The charged debris travels through the argon and easily knocks off electrons from the neighboring atoms along its path. The electronic traces in the liquid argon are pushed by an applied electric field toward an array of wires (similar to a guitar’s) on the side of the detector. The wires collect data on the particle trajectories, producing a signal.

    The second signal type is one shared with oil- and water-based detection: a flash of light. When a charged particle bumps into an argon atom’s electron, the electron transitions to a higher energy. As the electron transitions back to its original state, the excess energy is emitted as light.

    It turns out that argon is also relatively cheap. Companies liquefy air and heat it slowly. Since each of air’s components has a unique boiling temperature, they can be separated. The boiled-off argon is moved to a separate chamber where it is again condensed. The commercially available liquid argon that we buy is still not pure enough for our experiments, so once the liquid argon arrives at the lab, we filter out the remaining impurities by a factor of 10,000.

    Using a common and innocuous gas, Fermilab is establishing itself to be the world’s premier neutrino physics research center. Stay tuned to discover what secrets this technology will unlock!

    See the full article here.

    Fermilab Campus

    Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics.

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