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  • richardmitnick 4:37 pm on February 6, 2018 Permalink | Reply
    Tags: , Fermilab’s Muon g-2 experiment officially starts up, , , Muon g-2, , ,   

    From FNAL: “Fermilab’s Muon g-2 experiment officially starts up” 

    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.

    February 6, 2018
    Bruno Martin

    FNAL Muon g-2 studio


    Fermilab’s Muon g-2 experiment has officially begun taking data. Pictured here is the centerpiece of the experiment, a 50-foot-wide electromagnet ring, which generates a uniform magnetic field so scientists can make measurements of particles called muons with immense precision. Photo: Reidar Hahn

    The Muon g-2 experiment at Fermilab, which has been six years in the making, is officially up and running after reaching its final construction milestone. The U.S. Department of Energy on Jan. 16 granted the last of five approval stages to the project, Critical Decision 4 (CD-4), formally allowing its transition into operations.

    “We laid down the plans for Muon g-2 early on and have stuck to that through four years of construction,” said Fermilab’s Chris Polly, the experiment’s co-spokesperson and former project manager. “We’ve come out on schedule and under budget, which sets a good precedent for all the other projects.”

    The experiment will send particles called muons — heavier cousins of the electron — around a 50-foot-wide muon storage ring that was relocated from Brookhaven National Laboratory in New York state in 2013. The uniform magnetic field inside the ring exerts a torque that affects the muons’ own spins, causing them to wobble. In the early 2000s, scientists at Brookhaven found the value of this wobble, called magnetic precession, to be different from the “g-2” value predicted by theory.

    At Fermilab, the Muon g-2 experiment aims to confirm or refute this intriguing discrepancy with theory by repeating the measurements with a fourfold improvement in accuracy, up to 140 parts per billion. That’s like measuring the length of a football field with a margin of error that is only one-tenth the thickness of a human hair. If the experimental deviation from theory turns out to be real, it would mean that undiscovered forces or particles beyond the Standard Model — the theoretical framework that describes how the universe works — are appearing and disappearing from the vacuum to disturb the muons’ magnetic moment.

    And if it isn’t?

    “Well, if we find the measurement is consistent with theory, it will allow us to narrow our search for new physics, since it will rule out some current models that would no longer be viable,” Polly said.

    For example, Polly added, there are theories positing the existence of supersymmetric particles — superheavy partners to those in the Standard Model — and new categories of particles that could be the constituents of the mysterious dark matter, which makes up 80 percent of the universe’s mass. Some of these theories would no longer be valid.

    “That’s the value of a null result,” Polly said. “It helps us make sure that the theories that we would use to try to understand these other bigger questions are consistent.”

    All that’s left now is to finish fine-tuning the instruments so the experiment can start its several-year run of data collection.

    “For most of the team, this was the first project we’ve worked on,” said Fermilab physicist Mary Convery, who served as the experiment’s deputy project manager. “To see it through from design to construction and now to operations has been very rewarding.”

    Muon g-2 operations got a head start in June 2017, when the team fired up the particle beam to start calibrating the detectors and tweaking components that required additional work.

    “Since the accelerator turned back on in November, we have been commissioning the beamlines, the storage ring and the rest of the experiment,” said University of Washington physicist David Hertzog, Muon g-2 co-spokesperson.

    As early as next month, Muon g-2 will be ready to start collecting physics-quality data at Fermilab and explore the nature of the previously measured g-2 discrepancy.

    “We’ve set ourselves the goal of collecting three times the amount of data that they had in Brookhaven’s three-year run during this first spring season,” Hertzog said. “But this is just the very beginning: The experiment will run with higher intensity next year. The ultimate goal is to collect 21 times the Brookhaven statistics.”

    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 2:44 pm on January 30, 2018 Permalink | Reply
    Tags: , , Muon g-2, ,   

    From FNAL: “Muon machine makes milestone magnetic map” 

    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.

    January 29, 2018
    Tom Barratt

    1
    David Flay holds one of the probes that Muon g-2 scientists will use to map the magnetic field inside the experiment’s storage ring. Photo: Reidar Hahn.

    Muons are mysterious, and scientists are diving deep into the particle to get a handle on a property that might render it — and the universe — a little less mysterious.

    Like electrons – muons’ lighter siblings – they are particles with a sort of natural internal magnet. They also have an angular momentum called spin, kind of like a spinning top. The combination of the spin and internal magnet of a particle is called the gyromagnetic ratio, dubbed “g,” but previous attempts at measuring it for muons have thrown up intriguing surprises.

    The goal of the Muon g-2 experiment at Fermilab is to measure it more precisely than ever before.

    FNAL Muon g-2 studio

    To reach these remarkable levels of precision, scientists have to keep very careful tabs on a few parts of the experiment, one of which is how strong its magnetic field is. The team has been measuring and tweaking the magnetic field for months and is now very close to achieving a stable field before experiments can properly begin.

    “We’re in the experiment’s commissioning period right now, where we’re basically learning how our systems behave and making sure everything works properly before we transition into stable running,” said David Flay, a University of Massachusetts scientist working on the calibration of the magnetic field for Muon g-2.

    Muon mystery

    Muon g-2 is following up on an intriguing result seen at Brookhaven National Laboratory in New York in the early 2000s, when the experiment made observations of muons that didn’t match with theoretical predictions. The experiment’s 15-meter-diameter circular magnet, called a storage ring, was shipped to Illinois across land and sea in 2013, and the measurement is now being conducted at Fermilab with four times the precision.

    When Brookhaven carried out the experiment, the result was surprising: The muon value of g differed significantly from what calculations said it should be, and no one is quite sure why. It’s possible the experiment itself was flawed and the result was false, but it also opens the door to the possibility of exotic new particles and theories. With its four-fold increase in precision, Muon g-2 will shed more light on the situation.

    To measure g, beams of muons circulating inside the experiment’s storage ring are subjected to an intense magnetic field – about 30,000 times the strength of Earth’s natural field. This causes the muons to rotate around the magnetic field, or precess, in a particular way. By measuring this precession, it is possible to precisely extract the value of g.

    The strength of magnetic field to which the muons are exposed directly affects how they precess, so it’s absolutely crucial to make extremely precise measurements of the field strength and maintain its uniformity throughout the ring – not an easy task.

    If Muon g-2 backs up Brookhaven’s result, it would be huge news. The Standard Model would need rethinking and it would open up a whole new chapter of particle physics.

    A leading theory to explain the intriguing results are new kinds of virtual particles, quantum phenomena that flit in and out of existence, even in an otherwise empty vacuum. All known particles do this, but their total effect doesn’t quite account for Brookhaven’s results. Scientists are therefore predicting one or more new, undiscovered kinds, whose additional ephemeral presence could be providing the strange muon observations.

    “The biggest challenge so far has been dealing with the unexpected,” said Joe Grange, scientist at Argonne National Laboratory working on Muon g-2’s magnetic field. “When a mystery pops up that needs to be solved relatively quickly, things can get hectic. But it’s also one of the more fun parts of our work.”

    Probing the field

    The magnetic field strength measurements are made using small, sensitive electronic devices called probes. Three types of probes – fixed, trolley and plunging – work together to build up a 3-D map of the magnetic field inside the experiment. The field can drift over time, and things like temperature changes in the experiment’s building can subtly affect the ring’s shape, so roughly 400 fixed probes are positioned just above and below the storage ring to keep a constant eye on the field inside. Because these probes are always watching, the scientists know when and by how much to tweak the field to keep it uniform.

    For these measurements, and every few days when the experiments is paused and the muon beam is stopped, a 0.5-meter-long, curved cylindrical trolley on rails containing 17 probes is sent around the ring to take a precise field map in the region where the muons are stored. Each orbit takes a couple of hours. The trolley probes are themselves calibrated by a plunging probe, which can move in and out of its own chamber at a specific location in the ring when needed.

    The fixed probes have been installed and working since fall 2016, while the 17 trolley probes have recently been removed, upgraded and reinstalled.

    “The probes are inside the ring where we can’t see them,” Flay said. “So matching up their positions to get an accurate calibration between them is not an easy thing to do.”

    The team developed some innovative solutions to tackle this problem, including a barcode-style system inside the ring, which the trolley scans to relay where it is as it moves around.

    Global g-2

    Muon g-2 is an international collaboration hosted by Fermilab. Together with scientists from Fermilab, Argonne, and Brookhaven, several universities across the U.S. work with international collaborators from countries as wide-ranging as South Korea, Italy and the UK. In total, around 30 institutions and 150 people work on the experiment.

    “It’s the detailed efforts of the Argonne, University of Washington, University of Massachusetts and University of Michigan teams that have produced these reliable, quality tools that give us a complete picture of the magnetic field,” said Brendan Kiburg, Fermilab scientist working on Muon g-2. “It has taken years of meticulous work.”

    The team is working to finish the main field strength measurement part of the commissioning process by early 2018, before going on to analyze exactly how the muons experience the generated field. The experiment is planned to begin in full in February 2018.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

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    FNAL Icon

    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 1:13 pm on January 25, 2018 Permalink | Reply
    Tags: , , Muon g-2, , ,   

    From Science: “Renewed measurements of muon’s magnetism could open door to new physics” 

    ScienceMag
    Science Magazine

    Jan. 25, 2018
    Adrian Cho

    1
    The magnetism of muons is measured as the short-lived particles circulate in a 700-ton ring. FNAL.

    Next week, physicists will pick up an old quest for new physics. A team of 190 researchers at Fermi National Accelerator Laboratory (Fermilab) in Batavia, Illinois, will begin measuring to exquisite precision the magnetism of a fleeting particle called the muon. They hope to firm up tantalizing hints from an earlier incarnation of the experiment, which suggested that the particle is ever so slightly more magnetic than predicted by the prevailing standard model of particle physics. That would give researchers something they have desired for decades: proof of physics beyond the standard model.

    “Physics could use a little shot of love from nature right now,” says David Hertzog, a physicist at the University of Washington in Seattle and co-spokesperson for the experiment, which is known as Muon g-2 (pronounced “gee minus two”). Physicists are feeling increasingly stymied because the world’s biggest atom smasher, the Large Hadron Collider (LHC) near Geneva, Switzerland, has yet to blast out particles beyond those in the standard model. However, g-2 could provide indirect evidence of particles too heavy to be produced by the LHC.

    The muon is a heavier, unstable cousin of the electron. Because it is charged, it will circle in a magnetic field. Each muon is also magnetized like a miniature bar magnet. Place a muon in a magnetic field perpendicular to the orientation of its magnetization, and its magnetic polarity will turn, or precess, just like a twirling compass needle.

    At first glance, theory predicts that in a magnetic field a muon’s magnetism should precess at the same rate as the particle itself circulates, so that if it starts out polarized in the direction it’s flying, it will remain locked that way throughout its orbit. Thanks to quantum uncertainty, however, the muon continually emits and reabsorbs other particles. That haze of particles popping in and out of existence increases the muon’s magnetism and make it precess slightly faster than it circulates.

    Because the muon can emit and reabsorb any particle, its magnetism tallies all possible particles—even new ones too massive for the LHC to make. Other charged particles could also sample this unseen zoo, says Aida El-Khadra, a theorist at the University of Illinois in Urbana. But, she adds, “The muon hits the sweet spot of being light enough to be long-lived and heavy enough to be sensitive to new physics.”

    From 1997 to 2001, researchers on the original g-2 experiment at Brookhaven National Laboratory in Upton, New York, tested this promise by shooting the particles by the thousands into a ring-shaped vacuum chamber 45 meters in diameter, sandwiched between superconducting magnets.

    Over hundreds of microseconds, the positively charged muons decay into positrons, which tend to be spat out in the direction of the muons’ polarization. Physicists can track the muons’ precession by watching for positrons with detectors lining the edge of the ring.

    The g-2 team first reported a slight excess in the muon’s magnetism in 2001. That result quickly faded as theorists found a simple math mistake in the standard model prediction (Science, 21 December 2001, p. 2449). Still, by the time the team reported on the last of its Brookhaven data in 2004, the discrepancy had re-emerged. Since then, the result has grown, as theorists improved their standard model calculations. They had struggled to account for the process in which the muon emits and reabsorbs particles called hadrons, says Michel Davier, a theorist at the University of Paris-South in Orsay, France. By using data from electron-positron colliders, he says, the theorists managed to reduce this largest uncertainty.

    Physicists measure the strength of signals in multiples of the experimental uncertainty, σ, and the discrepancy now stands at 3.5 σ—short of the 5 σ needed to claim a discovery, but interesting enough to warrant trying again.

    In 2013, the g-2 team lugged the experiment on a 5000-kilometer odyssey from Brookhaven to Fermilab, taking the ring by barge around the U.S. eastern seaboard and up the Mississippi River. Since then, they have made the magnetic field three times more uniform, and at Fermilab, they can generate far purer muon beams. “It’s really a whole new experiment,” says Lee Roberts, a g-2 physicist at Boston University. “Everything is better.”

    Over 3 years, the team aims to collect 21 times more data than during its time at Brookhaven, Roberts says. By next year, Hertzog says, the team hopes to have enough data for a first result, which could push the discrepancy above 5 σ.

    Will the muon end up being a portal to new physics? JoAnne Hewett, a theorist at SLAC National Accelerator Laboratory in Menlo Park, California, hesitates to wager. “In my physics lifetime, every 3-σ deviation from the standard model has gone away,” she says. “If it weren’t for that baggage, I’d be cautiously optimistic.”

    The magnetism of muons is measured as the short-lived particles circulate in a 700-ton ring.

    See the full article here .

    Please help promote STEM in your local schools.

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