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  • richardmitnick 9:15 am on May 15, 2015 Permalink | Reply
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    From FNAL: “Summer, winter and muons” 

    FNAL Home

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    May 15, 2015
    Maury Goodman, Argonne National Laboratory

    These tracks show a six-muon event in the MINOS far detector.

    The MINOS detectors at Fermilab and in Soudan, Minnesota, were built to study neutrino oscillations over a vast distance. But it turns out that they are also powerful cosmic ray muon detectors.

    FNAL Minos Far Detector.

    When a cosmic ray strikes an atom in the Earth’s atmosphere, it sets off a cascade of particle decay, creating kaons or pions, which in turn decay into muons.

    MINOS previously made the first deep measurement of the ratio of positive to negative muons arising from cosmic ray showers, and that number is related to the ratio of positive to negative cosmic shower kaons. That, in turn, has implications for the predicted rates of neutrino detection in neutrino telescopes such as IceCube.

    MINOS also measured how the cosmic ray muon rate changed with the seasons of the year. It is well known that this rate fluctuates a few percent, being higher in summer when the higher temperatures lower the atmospheric density, which allows for more pion and kaon decay. MINOS was able to correlate this with temperature and demonstrate sensitivity to the ratio of pions to kaons. This ratio happens to be important for calculations of neutrino rates from targets in beams, such as for MINOS itself.

    Now MINOS has made a new measurement of the seasonal variations of underground multiple-muon events. These events come from cosmic ray showers in which two or more muons penetrate the Earth and appear as parallel tracks in the detector.

    The answer was unexpected. Instead of being higher in the summer, the seasonal variation of multiple muons differed. In the near detector, about 300 feet below the surface, the rate was at a maximum in the winter. See the figure below showing the rate of multiple muons throughout the year (top) and single muons (bottom). (Day zero is Jan. 1.)

    In the far detector, about a half mile below the surface, the multiple muons that were within about 13 feet of each other had a maximum rate in the winter, while the events in which muons were separated by 20 or more feet had a summer maximum.

    The difference in depth between the near and far detectors affects the minimum muon energy needed to penetrate the rock and reach the detector. Sophisticated simulations of cosmic ray air showers exist but do not currently include seasonal effects.

    The understanding of this unexpected result will require new simulations or new data. It would be a wonderful coincidence if, once again, the reason turned out to be useful for the neutrino community.

    Multiple-muon events — events in which two or more muons simultaneously penetrate the Earth — seen by the MINOS near detector take a dip in the summer (top). By contrast, single-muon events detected by the MINOS near detector rise in the summer (bottom).

    See the full article here.

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  • richardmitnick 11:48 am on March 3, 2015 Permalink | Reply
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    From FNAL: “Detecting something with nothing” 

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

    Tuesday, March 3, 2015
    Lauren Biron

    From left: Jason Bono (Rice University), Dan Ambrose (University of Minnesota) and Richie Bonventre (Lawrence Berkeley National Laboratory) work on the Mu2e straw chamber tracker unit at Lab 3. Photo: Reidar Hahn

    Researchers are one step closer to finding new physics with the completion of a harp-shaped prototype detector element for the Mu2e experiment.

    FNAL Mu2e experiment

    Mu2e will look for the conversion of a muon to only an electron (with no other particles emitted) — something predicted but never before seen. This experiment will help scientists better understand how these heavy cousins of the electron decay. A successful sighting would bring us nearer to a unifying theory of the four forces of nature.

    The experiment will be 10,000 times as sensitive as other experiments looking for this conversion, and a crucial part is the detector that will track the whizzing electrons. Researchers want to find one whose sole signature is its energy of 105 MeV, indicating that it is the product of the elusive muon decay.

    In order to measure the electron, scientists track the helical path it takes through the detector. But there’s a catch. Every interaction with detector material skews the path of the electron slightly, disturbing the measurement. The challenge for Mu2e designers is thus to make a detector with as little material as possible, says Mu2e scientist Vadim Rusu.

    “You want to detect the electron with nothing — and this is as close to nothing as we can get,” he said.

    So how to detect the invisible using as little as possible? That’s where the Mu2e tracker design comes in. Panels made of thin straws of metalized Mylar, each only 15 microns thick, will sit inside a cylindrical magnet. Rusu says that these are the thinnest straws that people have ever used in a particle physics experiment.

    These straws, filled with a combination of argon and carbon dioxide gas and threaded with a thin wire, will wait in vacuum for the electrons. Circuit boards placed on both ends of the straws will gather the electrical signal produced when electrons hit the gas inside the straw. Scientists will measure the arrival times at each end of the wire to help accurately plot the electron’s overall trajectory.

    “This is another tricky thing that very few have attempted in the past,” Rusu said.

    The group working on the Mu2e tracker electronics have also created the tiny, low-power circuit boards that will sit at the end of each straw. With limited space to run cooling lines, necessary features that whisk away heat that would otherwise sit in the vacuum, the electronics needed to be as cool and small as possible.

    “We actually spent a lot of time designing very low-power electronics,” Rusu said.

    This first prototype, which researchers began putting together in October, gives scientists a chance to work out kinks, improve design and assembly procedures, and develop the necessary components.

    One lesson already learned? Machining curved metal with elongated holes that can properly hold the straws is difficult and expensive. The solution? Using 3-D printing to make a high-tech, transparent plastic version instead.

    Researchers also came up with a system to properly stretch the straws into place. While running a current through the straw, they use a magnet to pluck the straw — just like strumming a guitar string — and measure the vibration. This lets them set the proper tension that will keep the straw straight throughout the lifetime of the experiment.

    Although the first prototype of the tracker is complete, scientists are already hard at work on a second version (using the 3D-printed plastic), which should be ready in June or July. The prototype will then be tested for leaks and to see if the electronics pick up and transmit signals properly.

    A recent review of Mu2e went well, and Rusu expects work on the tracker construction to begin in 2016.

    See the full article here.

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  • richardmitnick 7:06 pm on February 19, 2015 Permalink | Reply
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    From BNL: “Searching for Signs of a Force from the ‘Dark Side’ in Particle Collisions at RHIC” 

    Brookhaven Lab

    February 19, 2015
    Karen McNulty Walsh

    Data from the Relativistic Heavy Ion Collider (RHIC) and other experiments nearly rule out role of ‘dark photons’ as an explanation for the ‘g-2’ anomaly

    Dark photon hunters at RHIC’s PHENIX detector: Stony Brook University postdocs Deepali Sharma and Yorito Yamaguchi with Brookhaven physicist/PHENIX co-spokesperson David Morrison and PHENIX collaborator Yasuyuki Akiba, vice chief scientist at the RIKEN Nishina Center in Japan and experimental group leader of the RIKEN BNL Research Center at Brookhaven Lab.

    BNL Phenix


    Scientists searching for signs of elusive “dark photons” as an explanation for an anomaly in a groundbreaking physics experiment have nearly ruled out their role. Though the postulated particles could still exist as carriers of a force affecting dark matter, it is increasingly unlikely these particles from the “dark sector” can explain the discrepancy scientists have seen between a precision measurement of the behavior of muons (cousins of more familiar electrons) and calculations based on the reigning theory of particle interactions.

    “In physics, ruling out possible explanations is an essential part of discovery.”
    — Berndt Mueller, Brookhaven’s Associate Laboratory Director for Nuclear and Particle Physics

    “We were hunting for a ‘bump’ in a very narrow range of data that could indicate dark photons interacting with muons—but we do not see a signal of this dark photon,” said Yasuyuki Akiba, one of the physicists involved in the search.

    The results, accepted for publication as a rapid communication in Physical Review C, leave open the possibility that something even more unusual might explain the anomalous experimental results, the only known deviation from a prediction of the long-standing, thoroughly tested Standard Model.

    The Standard Model of elementary particles (more complete depiction), including the Higgs boson, the three generations of matter fields, and the gauge bosons, as well as their properties and interactions, and the effect of spontaneous electroweak symmetry breaking by the Higgs field.

    Alternatively, they could indicate a problem with the muon experiment—an idea that scientists will soon get a chance to test—or that dark photons have properties not detectable by the current experiment.

    “Either way we have learned something interesting,” said physicist Berndt Mueller, Associate Laboratory Director for Nuclear and Particle Physics at the U.S. Department of Energy’s Brookhaven National Laboratory, home to both the measurements of muon behavior and the new search for dark photons. “In physics, ruling out possible explanations is an essential part of discovery. In this case, we had a serendipitous opportunity to test a possible explanation for one experimental observation with data from a quite different quest.”
    A tale of two experiments

    The former experiment, known as the muon g-2 experiment, made precision measurements of how the spins of these subatomic particles “wobble” like tiny tops as they circulate within a powerful magnetic field. The results (announced in 2001, 2002, and 2004) deviated significantly from theoretical predictions, indicating there might be some kind of particle beyond those described by the existing Standard Model that were exerting some force on the muons. The second experiment, the PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC), a particle collider operating as a DOE Office of Science user facility at Brookhaven Lab since 2000, picks up signals of particles as they emerge from energetic particle collisions aimed at exploring the fundamental building blocks of matter. As the search for explanations of the g-2 results heated up, physicists at PHENIX realized they had an untapped dataset that might offer insight into one possible source, dark photons.

    The “g-2” experiment at Brookhaven Lab discovered an anomaly in the way subatomic particles called muons wobble in a magnetic field. Scientists have been searching for explanations for this anomaly, including a possible role for dark photons. The g-2 muon storage ring later traveled from Brookhaven to Fermilab, where a followup experiment will refine the g-2 measurements.

    One person who’s been working on this search is PHENIX collaborator Yorito Yamaguchi, who started the analysis as a postdoctoral fellow at the Center for Nuclear Study at the University of Tokyo, and continued in his current position as a postdoc working with longtime PHENIX collaborator Abhay Deshpande in the RHIC Spin Physics Group at Stony Brook University (SBU).

    “We know that dark matter is filling our universe,” Yamaguchi said, referring to the mysterious invisible substance that together with dark energy comprises some 95 percent of the cosmos. According to physicists, there must be force carrier particles that mediate the interactions of dark matter particles, analogous to the photons and other force carriers that mediate interactions among the particles of the Standard Model. The lightest of these “dark side” force carrier particles is called the dark photon.

    “If dark photons exist, they can mix in with ordinary photons, essentially switching back and forth with ordinary photons, and make a contribution to other particles’ interactions,” Yamaguchi explained—including the degree of wobble of the subatomic muon in a magnetic field.

    PHENIX collaborator Yasuyuki Akiba, vice chief scientist at the RIKEN Nishina Center in Japan and experimental group leader of the RIKEN BNL Research Center at Brookhaven, likens the unseen effect to the way the outermost planets in our solar system affect the movement of the other planets through the force of gravity.

    “Uranus and Neptune were discovered because of these interactions,” Akiba said. “Astronomers noticed small deviations in the known planets’ motions from expectations based on calculation, and then calculated there must be another planet causing these effects. The calculations told them where to look.”

    Detecting the “unseeable”

    To figure out where to look for dark photons that might explain the g-2 anomaly, the PHENIX scientists turned to theorists’ calculations on the effects such unseen particles might have on the value of g-2, one of the factors in the equation describing the magnetic wobble of the muon.

    “The dark photon can add to the muon g-2 prediction, but the amount depends on its mass and how it mixes with ordinary photons,” Akiba said. There is a range of possible dark photon masses and mixing parameters the physicists can explore to see if there are signs of such interactions, and experiments around the world have been searching—so far with negative results that have gradually ruled out the places such dark photons could be hiding. “So we are like astronomers looking in the remaining region that could possibly explain the muon g-2 experiment results,” Akiba said.

    What the PHENIX physicists were actually looking for was a bump in the production of pairs of electrons and their positively charged counterparts, known as positrons. Such electron-positron pairs are produced very occasionally from photons emerging from pion decays in RHIC collisions. “It’s a small effect, but easy to see,” said Brookhaven theoretical physicist William Marciano. Those regular, or background, pairs are produced with a well-known, smooth distribution, he said.

    But if one of the photons mixes with a dark photon, which then decays to an electron-positron pair, the distribution is not smooth. Instead it occurs at the specific mass of the dark photon—the peak the scientists were searching for—rather than a continuum of values.

    “If PHENIX sees a million pion decays they might have a handful of dark photons,” Marciano said. “They have a very good spectrometer to measure the electron-positron pair and reconstruct the mass very precisely.”

    Yamaguchi and Akiba started by looking at the electron-positron pair data they already had in hand—from 2006 proton-proton and 2008 deuteron-gold collisions at RHIC—which Yamaguchi had previously analyzed as part of his Ph.D. thesis. “But we knew that there was yet another electron pair dataset from the 2009 proton-proton run at RHIC,” Akiba said. “So we talked to Deepali Sharma, another postdoc who was working on her own electron pair analysis for that dataset as part of Stony Brook’s Heavy Ion Physics Group.”

    Putting all the data together, they did not see a bump.

    “At a confidence level of 85 percent, the combined analysis suggests that dark photons cannot explain the g-2 anomaly. Furthermore, most of the range where such dark photons could exist is ruled out with 90 percent confidence,” Yamaguchi said. “Still physicists like to have a confidence level of 97 percent or greater for a result to begin to look definitive. We’re not quite there yet.”
    The final word?

    Coincidentally, another experiment searching for evidence of dark photons that could explain g-2, the BaBar experiment at DOE’s SLAC National Accelerator Laboratory, recently published a very similar result. “They covered a very wide region, including the one we studied, and they don’t have any signal that explains g-2 either,” Yamaguchi said, adding that the two independent experiments make the result ruling out dark photons even more concrete. With 100 times more pion decay data already in hand from the 2014 RHIC run, the PHENIX team hopes to further increase the certainty of their result.

    If they rule out the entire range of values that could explain g-2, “either you say that’s the end of the dark photon for g-2, or you have to give the dark photon some properties that experiments like PHENIX would not be able to detect,” Marciano said. For instance, “maybe the dark photon doesn’t primarily decay into an electron-positron pair…”

    What about other explanations for g-2? Physicists have long-suggested the existence of so-called supersymmetric partners of the existing Standard Model particles that might trigger as-yet-undescribed particle interactions. Experiments at the Large Hadron Collider have been searching for signs of these predicted supersymmetric particles, but so far no such signals have turned up. “They’ve eliminated large chunks of parameter space, but they can’t say the idea of supersymmetry has been eliminated completely,” Marciano said.

    Could there have been a problem with the muon g-2 experiment? Physicists will soon get a chance to repeat the measurements thanks to a monumental undertaking to transport the muon g-2 storage ring from Brookhaven to DOE’s Fermi National Accelerator Laboratory in 2013. At Fermilab, scientists are reconstructing the experiment to make use of a much more intense and pure beam of muons than was available at Brookhaven. With a four-fold increase in the measurement’s precision, the new experiment, set to start in 2016, will be more sensitive to virtual or hidden particles and forces than any previous experiment of its kind. The results will reveal whether the anomaly still stands, and, if so, set off a new quest for explanations.

    Ten years after it ceased taking data at Brookhaven, the muon g-2 storage ring embarked on a cross-country journey from the woods of Long Island to the plains near Chicago.

    And what about the existence of dark photons? Theoretical physicists say there are still good reasons these mysterious particles should exist—to explain a variety of unrelated astrophysical observations.

    “Dark photons that could explain some of these phenomena, such as a possible excess of positrons coming from outer space, don’t need the same properties as you need to explain the g-2 anomaly,” Marciano said. But there are other possible explanations for these phenomena as well, he said, so the search for signs of darkness in the astrophysical arena may not be as clear-cut as it was for g-2.

    What is clear is that the quest for understanding the subatomic particle soup that makes up the cosmos is far from over. But the process of science—which includes the interplay of theory and experiments that put predictions to the test, repetition, increasing precision, and being alert to unforeseen connections—will continue to bring the subatomic world into ever-sharper focus.

    The muon g-2 experiment at Brookhaven was funded by the DOE Office of Science, the U.S. National Science Foundation, the German Bundesminister fur Bildung und Forschung, and the Russian Ministry of Science, and through the U.S.-Japan Agreement in High Energy Physics. Research at RHIC is funded primarily by the DOE Office of Science and also by these agencies and organizations.

    See the full article here.

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    One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world.Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.

  • richardmitnick 2:09 pm on December 2, 2014 Permalink | Reply
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    From Symmetry: “Muon versus the volcano” 


    December 02, 2014
    Glenn Roberts Jr.

    Particles produced by cosmic rays enter volcanoes and live to tell the tale.

    Exploring the innards of Mount Vesuvius, the active volcano that once destroyed the ancient town of Pompeii, sounds like a risky endeavor. Unless you’re a muon.

    Scientists from institutions in Italy, France, Japan and the United States are using muons, the big brothers of electrons, to study the structure of Mount Vesuvius and other volcanoes in Italy, France, Japan and the Caribbean.

    Muons are particles produced in the constant shower of cosmic rays that interact with Earth’s atmosphere. If you hold out your hand, a muon will pass through it about once per second—and it will keep on going. The highest-energy muons can travel more than a mile through solid rock.

    “[Studying volcanoes with muons] should help in giving information on how an eruption would develop,” says scientist Giulio Saracino of INFN, Italy’s National Institute for Nuclear Physics, who is a member of the MU-RAY experiment at Mount Vesuvius. Researchers say the measurements could be used in conjunction with other methods to identify areas of greatest risk based on concentrations of lower-density rock susceptible to fracture in an eruption.

    In May 2013 MU-RAY scientists took a 1-square-meter prototype of a muon detector to a research station at the foot of Mount Vesuvius for a technical run. The detector is an advanced version of technology used in physics experiments at Fermi National Accelerator Laboratory and Gran Sasso National Laboratory. A handful of researchers, assisted by local high school students in the delivery and setup of equipment, completed the installation in about three workdays.

    Courtesy of: MU-RAY collaboration

    Vesuvius is considered the most dangerous volcano on the planet, owing to its well-documented history of incredibly explosive eruptions and the half a million people living in its high-risk “red zone.”

    “If you live in Naples, you feel the presence of Mount Vesuvius as a sleeping giant that could suddenly awaken with tremendous effects,” says MU-RAY scientist Paolo Strolin, also of INFN. “A better understanding of its dangers is worth any challenge.”

    Geologists and volcanologists have amassed an array of tools to study aspects of volcanoes: satellites, seismic readers, laser surveying kits and equipment to monitor gases, gravity fluctuations and electrical and electromagnetic signals.

    Nobel Laureate Luis Alvarez of the University of California, Berkeley, pioneered the muon radiography technique used on volcanoes in the late 1960s when he used it to look for hidden chambers in the Great Pyramid of Chephren in Egypt. In 2007, scientists used it to image the interior of an active volcano, Japan’s Mount Asama, for the first time.

    “This is quite unique compared to other survey methods,” says Valentin Niess of CNRS, the French National Center for Scientific Research, and a member of the TOMUVOL collaboration, a group of about 30 scientists studying the long-dormant Puy de Dôme in France.

    Volcano researchers hope using muons will pay off by helping to identify areas prone to particular risk from eruptions, says TOMUVOL scientist Cristina Cârloganu of CNRS: “That could significantly reduce the volcanic hazards.”

    See the full article here.

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    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 8:45 pm on August 5, 2014 Permalink | Reply
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    From SLAC: “Rebooted Muon Experiment Tests Detector Design at SLAC” 

    SLAC Lab

    August 5, 2014
    Last year, a monster magnet set out from Brookhaven National Lab on an epic, 35-day trek by land and sea to its new home at Fermilab, where it will serve as the heart of a search for evidence of new subatomic particles. Last month, with much less fanfare, researchers came to the End Station Test Beam (ESTB) facility at the Department of Energy’s SLAC National Accelerator Laboratory to test the eyes and nerves of the same experiment: a cutting-edge design for a new detector.

    Muon g-2 magnet to be transported to Fermilab.

    The goal of the experiment, called Muon g-2 (pronounced gee-minus-two), is to precisely measure a property of muons by studying the way their spins precess, or wobble like a slowing top, in the grip of a powerful magnet. Researchers can track this spin by observing the muon’s decay into electrons, their lighter, longer-lived siblings.

    In the experiment’s original incarnation at Brookhaven, researchers discovered the spin rate is a tiny bit different from what theory says it should be – a difference that could indicate the influence of unknown virtual particles that pop into existence from the vacuum, affect the muons, and disappear once more.

    However, the researchers at Brookhaven weren’t able to measure the property precisely enough to know for sure. That prompted the relocation of the experiment – including the headline-grabbing move of the giant ring magnet – to Fermilab, with its more powerful muon beam.

    More Muons = More Data

    To take advantage of more muons, and thus more data, a team led by University of Washington physicist David Hertzog developed a new detector design for the experiment, a novel combination of lead-fluoride crystals and silicon photomultiplier chips that they hope will capture more information about the escaping electrons.

    Hertzog and his colleagues brought some of the crystals and silicon chips to SLAC’s ESTB facility, where electrons from the linear accelerator could stand in for the results of muon decays – but controlled and easily tracked muon decays, unlike what the detectors will face during the actual experiment.

    “These detectors will need to catch a tremendous number of muon decays, pinpointing their times and the energies of the electrons,” Hertzog said. “The electrons at ESTB can be delivered one at a time and with known energies, so we can see how the crystals and silicon photomultipliers respond.”

    The tests at ESTB have been much more low-key than the magnet’s 3200-mile trek, but Hertzog said his team can also look back at a successful venture.

    “This experiment has been really enjoyable,” Hertzog said. “We’ve got good data and our system seems to be working well.”

    See the full article here.

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  • richardmitnick 2:55 pm on June 19, 2014 Permalink | Reply
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    From Fermilab- “Frontier Science Result: DZero Shedding light on forward muons 

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

    Thursday, June 19, 2014
    Mark Williams

    The DZero experiment, like all such general-purpose particle detectors, is built from a number of distinct subsystems, each designed to perform a specific task. One such component is the muon system, which forms the outermost layer of the detector. Its job is to identify muons from proton-antiproton collisions and measure their trajectories and timing information for use in both the trigger and the subsequent event reconstruction.

    Fermilab DZero

    In fact, the muon system is itself divided into two complementary parts: three muon tracking layers and three interleaved layers of muon scintillators. The tracking layers provide precise information about the location of muons as they leave the detector, which is used to build the trajectories. The scintillators measure the times that the muons pass through, with excellent precision of less than 1 nanosecond. Together, this is all the information necessary to fully reconstruct muons in the event. A recent limited-authorship publication describes the performance of the muon scintillator counters in the forward region, demonstrating both the excellent performance and the methods used to monitor the system.

    Each layer of forward muon scintillator counters forms an overlapping (“fish-scaled”) set of aluminum-covered plastic plates, which produce a burst of visible light photons when a muon passes through. This light is then fed into photon counters and converted to an electric current. Because the detection medium is light-based, the information is available very soon after the initial proton-antiproton collision and is hence used to make a decision about whether or not to save (trigger) the event for later use. Triggering is essential to select the roughly 100 events per second that can be saved to tape, out of the several million proton-antiproton collisions in this time.

    The timing information is also essential for identifying muons from cosmic-ray sources, which must be removed from the data sample. If a cosmic muon passes directly through the detector, it can look much like a pair of muons originating from the center. However, it will hit the top of the detector around 30 nanoseconds before the bottom, while a genuine muon pair produced in the collision will arrive at the muon system concurrently. By using appropriate timing windows, cosmic-ray muons can be almost completely eliminated from the data without significant reduction of signal efficiency.

    Scientists measured the performance of the forward muon scintillators regularly using a variety of independent methods. The efficiency of the light collection components was tested on a daily basis using built-in LED sources. The scintillating plastic plates were tested with radioactive beta ray (electron) sources. The overall performance of the full system was also tested using reconstructed muons identified by the muon tracking system. All methods show consistent results: a very slow reduction in the signal sizes over time, expected due to the effects of radiation aging. This slow change was anticipated during the detector design and had no effect on the muon identification efficiency.

    Overall, the detector performed very well during its entire life, with typically over 99.9 percent of counters working during data collection, and its excellent design provided extended spatial coverage and outstanding trigger capabilities.

    See the full article here.

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  • richardmitnick 10:36 am on June 13, 2014 Permalink | Reply
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    From Fermilab: “Physics in a Nutshell – Spinning muons” 

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

    Friday, June 13, 2014
    Fermilab Don Lincoln
    This article was written by Don Lincoln

    If you take an electrical charge and set it in motion, you create a magnet. This is true in both the world of ordinary experience and the quantum world, although the details there are a bit trickier. The simplest quantum system is a single, moving charged particle — say an electron or a muon. While I could select either type of particle for this article, for reasons that will become clear, I concentrate on the muon.

    Subatomic particles like the muon have both electrical charge and quantum mechanical spin. Quantum mechanical spin differs a bit from ordinary spin, but it has the same consequence: the spinning muon acts like a magnet. The magnet has a specific strength, determined by the charge of the muon and the fact that it is a spin-1/2 particle. Together, the spin and strength produce an effect that scientists call the magnetic moment.

    The prediction of the magnetic moment of the muon (and electron) was first given by Paul Dirac. The measurement involves something called the g factor, and the value of g was predicted to be 2. The way scientists search for deviations from predictions is to measure the quantity (g-2)/2. If the particle had the exact magnetic moment predicted by Dirac, this quantity would be exactly zero. Early measurements of the muon’s g factor showed that it differed from predictions by 0.1 percent.

    Such a small difference between theory and measurement could be due to measurement or calculation error. However, the predictions and measurements are now very precise. For muons, the measured value of (g-2)/2 is 0.0011659209, where the measurement uncertainty is only in the last “9.” That means that all the other numbers are meaningful: The measurement is accurate to one part in ten billion. This is equivalent to measuring the circumference of the Earth at the equator to a precision of just under a quarter inch.

    So what causes this 0.1 percent difference? There are many names for it, and two such names are virtual particles and quantum foam. In short, empty space isn’t empty space. At the subatomic level, particles are popping in and out of existence like the bubbles in foam. These particles are found in a more concentrated way near particles such as muons. You can think of these virtual particles as bees swarming surrounding a particularly aromatic flower (the muon). These virtual particles alter the strength of the muon’s magnetic field.

    Scientists can calculate the effect of these virtual particles, and they agree very well with data to high precision. However, the theory and experiment don’t agree perfectly. Given the precision of the prediction and the measurement, it is possible that this discrepancy might be the signature of physics beyond the Standard Model. The Fermilab Muon g-2 experiment will study the magnetic moment of muons with greater precision than has been possible in the past. If the discrepancy remains and the uncertainty decreases, it may be that research involving spinning muons might yield the measurement that turns a possible crack in the Standard Model into a broken dam through which a new theory rushes and changes everything.

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

    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.

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  • richardmitnick 12:34 pm on December 10, 2013 Permalink | Reply
    Tags: , , , , Muon studies, ,   

    From Fermilab: “Mu2e superconducting cable prototype successful” 

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


    Tuesday, Dec. 10, 2013
    Leah Hesla

    Last month, members of the Technical Division conducted final tests on the first batch of prototype superconducting cable for the proposed Mu2e experiment. The cable met every prescribed benchmark, carrying over 6,800 amps of electrical current — well above its design current — at 4.2 Kelvin in a magnetic field of 5 Tesla.

    This aluminum-clad niobium-titanium superconductor is a critical component of one of Mu2e’s three magnets, the transport solenoid. As the name implies, the transport solenoid will help transport a beam of muons from its production source to the detector, where scientists will study the particle interactions.

    “This prototype conductor is an important part of our transport solenoid magnet program,” said Giorgio Ambrosio, who is in charge of the transport solenoid design and development. “We know that no superconducting magnet is better than its conductor.”

    Having met this milestone ahead of schedule, members of the Superconducting Materials and Magnet Systems departments will march ahead with the other three superconducting cable prototypes for Mu2e: one for the production solenoid and two for the detector solenoid. They plan to complete the cable prototyping stage in a few months’ time.

    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.

    ScienceSprings is powered by MAINGEAR computers

  • richardmitnick 2:32 pm on October 23, 2013 Permalink | Reply
    Tags: , , , Muon studies,   

    From Fermilab: “A step closer to demonstrating muon ionization cooling” 

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

    Wednesday, Oct. 23, 2013
    Mark Palmer

    This month, scientists of the Muon Accelerator Program celebrated the arrival of a U.S.-supplied magnet and six tons of RF hardware at the Muon Ionization Cooling Experiment (MICE), located at Rutherford Appleton Laboratory in the UK. The experiment’s goal is to demonstrate the feasibility of shrinking the size of a muon beam with a process called ionization cooling. Creating compact muon beams is a crucial step toward future muon accelerators and [muon] colliders*.

    Alan Bross works in the MuCool Test Area

    In ionization cooling, muons are cooled by sending them through absorber materials made of light nuclei (such as hydrogen) and then are reaccelerated using RF cavities. This process can be repeated many times and reduces the transverse momentum of each muon relative to its longitudinal momentum.

    In 2015, MICE scientists will begin key experiments that will characterize the interactions of muon beams with various absorbers. The muon trajectories will be carefully measured using scintillating fiber tracking detectors embedded in spectrometer solenoid magnets located at the beginning and end of the cooling beamline. A subsequent experimental configuration, expected to be in operation later in the decade, will employ a full “cooling cell” with suitable absorbers, focusing solenoid magnets and multiple RF cavities to characterize the evolution of the beam’s emittance as the beam travels through a whole sequence of devices.

    In support of these R&D efforts, the DOE-funded U.S. Muon Accelerator Program is providing two spectrometer solenoid magnets and two coupling coil magnets, as well as RF and detector hardware for the experiment. The NSF has provided additional support for U.S. participation in the experiment.

    *A.K.A. “Higgs factories”

    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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