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  • richardmitnick 11:20 am on July 28, 2015 Permalink | Reply
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    From Symmetry: “Is this the only universe?” 

    Symmetry

    July 28, 2015
    Laura Dattaro

    1
    Artwork by Sandbox Studio, Chicago with Ana Kova

    Human history has been a journey toward insignificance.

    As we’ve gained more knowledge, we’ve had our planet downgraded from the center of the universe to a chunk of rock orbiting an average star in a galaxy that is one among billions.

    So it only makes sense that many physicists now believe that even our universe might be just a small piece of a greater whole. In fact, there may be infinitely many universes, bubbling into existence and growing exponentially. It’s a theory known as the multiverse.

    One of the best pieces of evidence for the multiverse was first discovered in 1998, when physicists realized that the universe was expanding at ever increasing speed. They dubbed the force behind this acceleration dark energy. The value of its energy density, also known as the cosmological constant, is bizarrely tiny: 120 orders of magnitude smaller than theory says it should be.

    For decades, physicists have sought an explanation for this disparity. The best one they’ve come up with so far, says Yasunori Nomura, a theoretical physicist at the University of California, Berkeley, is that it’s only small in our universe. There may be other universes where the number takes a different value, and it is only here that the rate of expansion is just right to form galaxies and stars and planets where people like us can observe it. “Only if this vacuum energy stayed to a very special value will we exist,” Nomura says. “There are no good other theories to understand why we observe this specific value.”

    For further evidence of a multiverse, just look to string theory, which posits that the fundamental laws of physics have their own phases, just like matter can exist as a solid, liquid or gas. If that’s correct, there should be other universes where the laws are in different phases from our own—which would affect seemingly fundamental values that we observe here in our universe, like the cosmological constant. “In that situation you’ll have a patchwork of regions, some in this phase, some in others,” says Matthew Kleban, a theoretical physicist at New York University.

    These regions could take the form of bubbles, with new universes popping into existence all the time. One of these bubbles could collide with our own, leaving traces that, if discovered, would prove other universes are out there. We haven’t seen one of these collisions yet, but physicists are hopeful that we might in the not so distant future.

    If we can’t find evidence of a collision, Kleban says, it may be possible to experimentally induce a phase change—an ultra-high-energy version of coaxing water into vapor by boiling it on the stove. You could effectively prove our universe is not the only one if you could produce phase-transitioned energy, though you would run the risk of it expanding out of control and destroying the Earth. “If those phases do exist—if they can be brought into being by some kind of experiment—then they certainly exist somewhere in the universe,” Kleban says.

    No one is yet trying to do this.

    There might be a (relatively) simpler way. Einstein’s general theory of relativity implies that our universe may have a “shape.” It could be either positively curved, like a sphere, or negatively curved, like a saddle. A negatively curved universe would be strong evidence of a multiverse, Nomura says. And a positively curved universe would show that there’s something wrong with our current theory of the multiverse, while not necessarily proving there’s only one. (Proving that is a next-to-impossible task. If there are other universes out there that don’t interact with ours in any sense, we can’t prove whether they exist.)

    In recent years, physicists have discovered that the universe appears almost entirely flat. But there’s still a possibility that it’s slightly curved in one direction or the other, and Nomura predicts that within the next few decades, measurements of the universe’s shape could be precise enough to detect a slight curvature. That would give physicists new evidence about the nature of the multiverse. “In fact, this evidence will be reasonably strong since we do not know any other theory which may naturally lead to a nonzero curvature at a level observable in the universe,” Nomura says.

    If the curvature turned out to be positive, theorists would face some very difficult questions. They would still be left without an explanation for why the expansion rate of the universe is what it is. The phases within string theory would also need re-examining. “We will face difficult problems,” Nomura says. “Our theory of dark energy is gone if it’s the wrong curvature.”

    But with the right curvature, a curved universe could reframe how physicists look at values that, at present, appear to be fundamental. If there were different universes with different phases of laws, we might not need to seek fundamental explanations for some of the properties our universe exhibits.

    And it would, of course, mean we are tinier still than we ever imagined. “It’s like another step in this kind of existential crisis,” Kleban says. “It would have a huge impact on people’s imaginations.”

    See the full article here.

    Please help promote STEM in your local schools.

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 5:43 pm on July 27, 2015 Permalink | Reply
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    From Symmetry: “W bosons remain left-handed” 

    Symmetry

    July 27, 2015
    Sarah Charley

    1
    LHCb. Courtesy of CERN

    A new result from the LHCb collaboration weakens previous hints at the existence of a new type of W boson.

    A measurement released today by the LHCb collaboration dumped some cold water on previous results that suggested an expanded cast of characters mediating the weak force.

    The weak force is one of the four fundamental forces, along with the electromagnetic, gravitational and strong forces. The weak force acts on quarks, fundamental building blocks of nature, through particles called W and Z bosons.

    2
    The Feynman diagram for beta decay of a neutron into a proton, electron, and electron antineutrino via an intermediate heavy W boson

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    A Feynman diagram showing the exchange of a pair of W bosons. This is one of the leading terms contributing to neutral Kaon oscillation

    Just like a pair of gloves, particles can in principle be left-handed or right-handed. The new result from LHCb presents evidence that the W bosons that mediate the weak force are all left-handed; they interact only with left-handed quarks.

    This weakens earlier hints from the Belle and BaBar experiments of the existence of right-handed W bosons.

    The LHCb experiment at the Large Hadron Collider examined the decays of a heavy and unstable particle called Lambda-b—a baryon consisting of an up quark, down quark and bottom quark.

    CERN LHC Map
    CERN LHC Grand Tunnel
    CERN LHC particles
    LHC

    Weak decays can change a bottom quark into either a charm quark, about 1 percent of the time, or into a lighter up quark. The LHCb experiment measured how often the bottom quark in this particle transformed into an up quark, resulting in a proton, muon and neutrino in the final state.

    “We found no evidence for a new right-handed W boson,” says Marina Artuso, a Professor of Physics at Syracuse University and a scientist working on the LHCb experiment.

    If the scientists on LHCb had seen bottom quarks turning into up quarks more often than predicted, it could have meant that a new interaction with right-handed W bosons had been uncovered, Artuso says. “But our measured value agreed with our model’s value, indicating that the right-handed universe may not be there.”

    Earlier experiments by the Belle and BaBar collaborations studied transformations of bottom quarks into up quarks in two different ways: in studies of a single, specific type of transformation, and in studies that ideally included all the different ways the transformation occurs.

    If nothing were interfering with the process (like, say, a right-handed W boson), then these two types of studies would give the same value of the bottom-to-up transformation parameter. However, that wasn’t the case.

    The difference, however, was small enough that it could have come from calculations used in interpreting the result. Today’s LHCb result makes it seem like right-handed W bosons might not exist after all, at least not in a way that is revealed in these measurements.

    Michael Roney, spokesperson for the BaBar experiment, says, “This result not only provides a new, precise measurement of this important Standard Model parameter, but it also rules out one of the interesting theoretical explanations for the discrepancy… which still leaves us with this puzzle to solve.”

    See the full article here.

    Please help promote STEM in your local schools.

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 1:25 pm on July 23, 2015 Permalink | Reply
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    From Symmetry: “A new first for T2K” 

    Symmetry

    July 23, 2015
    Kathryn Jepsen

    1
    Courtesy of Kamioka Observatory, ICRR (Institute for Cosmic Ray Research), The University of Tokyo

    The Japan-based neutrino experiment has seen its first three candidate electron antineutrinos

    Scientists on the T2K neutrino experiment in Japan announced today that they have spotted their first possible electron antineutrinos.

    When the T2K experiment first began taking data in January 2010, it studied a beam of neutrinos traveling 295 kilometers from the J-PARC facility in Tokai, on the east coast, to the Super-Kamiokande detector in Kamioka in western Japan. Neutrinos rarely interact with matter, so they can stream straight through the earth from source to detector.

    From May 2014 to June 2015, scientists used a different beamline configuration to produce predominantly the antimatter partners of neutrinos, antineutrinos. After scientists eliminated signals that could have come from other particles, three candidate electron antineutrino events remained.

    T2K scientists hope to determine if there is a difference in the behavior of neutrinos and antineutrinos.

    “That is the holy grail of neutrino physics,” says Chang Kee Jung of State University of New York at Stony Brook, who until recently served as international co-spokesperson for the experiment.

    If scientists caught neutrinos and their antiparticles acting differently, it could help explain how matter came to dominate over antimatter after the big bang. The big bang should have produced equal amounts of each, which would have annihilated one another completely, leaving nothing to form our universe. And yet, here we are; scientists are looking for a way to explain that.

    “In the current paradigm of particle physics, this is the best bet,” Jung says.

    Scientists have previously seen differences in the ways that other matter and antimatter particles behave, but the differences have never been enough to explain our universe. Whether neutrinos and antineutrinos act differently is still an open question.

    Neutrinos come in three types: electron neutrinos, muon neutrinos and tau neutrinos. As they travel, they morph from one type to another. T2K scientists want to know if there’s a difference between the oscillations of muon neutrinos and muon antineutrinos. A possible upgrade to the Super-Kamiokande detector could help with future data-taking.

    One other currently operating experiment can look for this matter-antimatter difference: the [FNAL] NOvA experiment, which studies a beam that originates at Fermilab near Chicago with a detector near the Canadian border in Minnesota.

    FNAL NOvA experiment
    FNAL NOvA

    “This result shows the principle of the experiment is going to work,” says Indiana University physicist Mark Messier, co-spokesperson for the NOvA experiment. “With more data, we will be on the path to answering the big questions.”

    It might take T2K and NOvA data combined to get scientists closer to the answer, Jung says, and it will likely take until the construction of the even larger DUNE neutrino experiment in South Dakota to get a final verdict.

    See the full article here.

    Please help promote STEM in your local schools.

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 11:54 am on July 22, 2015 Permalink | Reply
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    From Symmetry: “Underground plans” 

    Symmetry

    July 22, 2015
    Liz Kruesi

    1
    Courtesy of Kamioka Observatory, ICRR (Institute for Cosmic Ray Research), The University of Tokyo

    The Super-Kamiokande collaboration has approved a project to improve the sensitivity of the Super-K neutrino detector.

    Super-Kamiokande, buried under about 1 kilometer of mountain rock in Kamioka, Japan, is one of the largest neutrino detectors on Earth. Its tank is full of 50,000 tons (about 13 million gallons) of ultrapure water, which it uses to search for signs of notoriously difficult-to-catch particles.

    Recently members of the Super-K collaboration gave the go-ahead to a plan to make the detector a thousand times more sensitive with the help of a chemical compound called gadolinium sulfate.

    Neutrinos are made in a variety of natural processes. They are also produced in nuclear reactors, and scientists can create beams of neutrinos in particle accelerators. These particles are electrically neutral, have little mass and interact only weakly with matter—characteristics that make them extremely difficult to detect even though trillions fly through any given detector each second.

    Super-K catches about 30 neutrinos that interact with the hydrogen and oxygen in the water molecules in its tank each day. It keeps its water ultrapure with a filtration system that removes bacteria, ions and gases.

    Scientists take extra precautions both to keep the ultrapure water clean and to avoid contact with the highly corrosive substance.

    “Somebody once dropped a hammer into the tank,” says experimentalist Mark Vagins of the University of Tokyo’s Kavli Institute for the Physics and Mathematics of the Universe. “It was chrome-plated to look nice and shiny. Eventually we found the chrome and not the hammer.”

    When a neutrino interacts in the Super-K detector, it creates other particles that travel through the water faster than the speed of light, creating a blue flash. The tank is lined with about 13,000 phototube detectors that can see the light.

    Looking for relic neutrinos

    On average, several massive stars explode as supernovae every second somewhere in the universe. If theory is correct, all supernovae to have exploded throughout the universe’s 13.8 billion years have thrown out trillions upon trillions of neutrinos. That means the cosmos would glow in a faint background of relic neutrinos—if scientists could just find a way to see even a fraction of those ghostlike particles.

    For about half of the year, the Super-K detector is used in the T2K experiment, which produces a beam of neutrinos in Tokai, Japan, some 183 miles (295 kilometers) away, and aims it at Super-K. During the trip to the detector, some of the neutrinos change from one type of neutrino to another. T2K studies that change, which could give scientists hints as to why our universe holds so much more matter than antimatter.

    But a T2K beam doesn’t run continuously during that half year. Instead, researchers send a beam pulse every few seconds, and each pulse lasts just a few microseconds long. Super-K still detects neutrinos from natural processes while scientists are running T2K.

    In 2002, at a neutrino meeting in Munich, Germany, experimentalist Vagins and theorist John Beacom of The Ohio State University began thinking of how they could better use Super-K to spy the universe’s relic supernova neutrinos.

    “For at least a few hours we were standing there in the Munich subway station somewhere deep underground, hatching our underground plans,” Beacom says.

    To pick out the few signals that come from neutrino events, you have to battle a constant clatter of background noise of other particles. Other incoming cosmic particles such as muons (the electron’s heavier cousin) or even electrons emitted from naturally occurring radioactive substances in rock can produce signals that look like the ones scientists hope to find from neutrinos. No one wants to claim a discovery that later turns out to be a signal from a nearby rock.

    Super-K already guards against some of this background noise by being buried underground. But some unwanted particles can get through, and so scientists need ways to separate the signals they want from deceiving background signals.

    Vagins and Beacom settled on an idea—and a name for the next stage of the experiment: Gadolinium Antineutrino Detector Zealously Outperforming Old Kamiokande, Super! (GADZOOKS!). They proposed to add 100 tons of the compound gadolinium sulfate—Gd2(SO4)3—to Super-K’s ultrapure water.

    When a neutrino interacts with a molecule, it releases a charged lepton (a muon, electron, tau or one of their antiparticles) along with a neutron. Neutrons are thousands of times more likely to interact with the gadolinium sulfate than with another water molecule. So when a neutrino traverses Super-K and interacts with a molecule, its muon, electron, or antiparticle (Super-K can’t see tau particles) will generate a first pulse of light, and the neutron will create a second pulse of light: “two pulses, like a knock-knock,” Beacom says.

    By contrast, a background muon or electron will make only one light pulse.

    To extract only the neutrino interactions, scientists will use GADZOOKS! to focus on the two-signal events and throw out the single-signal events, reducing the background noise considerably.

    The prototype

    But you can’t just add 100 tons of a chemical compound to a huge detector without doing some tests first. So Vagins and colleagues built a scaled-down version, which they called Evaluating Gadolinium’s Action on Detector Systems (EGADS). At 0.4 percent the size of Super-K, it uses 240 of the same phototubes and 200 tons (52,000 gallons) of ultrapure water.

    Over the past several years, Vagins’ team has worked extensively to show the benefits of their idea. One aspect of their efforts has been to build a filtration system that removes everything from the ultrapure water except for the gadolinium sulfate. They presented their results at a collaboration meeting in late June.

    On June 27, the Super-K team officially approved the proposal to add gadolinium sulfate but renamed the project SuperK-Gd. The next steps are to drain Super-K to check for leaks and fix them, replace any burned out phototubes, and then refill the tank.

    But this process must be coordinated with T2K, says Masayuki Nakahata, the Super-K collaboration spokesperson.

    Once the tank is refilled with ultrapure water, scientists will add in the 100 tons of gadolinium sulfate. Once the compound is added, the current filtration system could remove it any time researchers would like, Vagins says.

    “But I believe that once we get this into Super-K and we see the power of it, it’s going to become indispensable,” he says. “It’s going to be the kind of thing that people wouldn’t want to give up the extra physics once they’re used to it.”

    See the full article here.

    Please help promote STEM in your local schools.

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 2:09 pm on July 15, 2015 Permalink | Reply
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    From Symmetry: “Miraculous WIMPs” 

    Symmetry

    July 15, 2015
    Manuel Gnida

    1
    Artwork by Sandbox Studio, Chicago with Ana Kova

    What are WIMPs, and what makes them such popular dark matter candidates?

    Invisible dark matter accounts for 85 percent of all matter in the universe, affecting the motion of galaxies, bending the path of light and influencing the structure of the entire cosmos. Yet we don’t know much for certain about its nature.

    Most dark matter experiments are searching for a type of particles called WIMPs, or weakly interacting massive particles.

    “Weakly interacting” means that WIMPs barely ever “talk” to regular matter. They don’t often bump into other matter and also don’t emit light—properties that could explain why researchers haven’t been able to detect them yet.

    Created in the early universe, they would be heavy (“massive”) and slow-moving enough to gravitationally clump together and form structures observed in today’s universe.

    Scientists predict that dark matter is made of particles. But that assumption is based on what they know about the nature of regular matter, which makes up only about 4 percent of the universe.

    WIMPs advanced in popularity in the late 1970s and early 1980s when scientists realized that particles that naturally pop out in models of Supersymmetry could potentially explain the seemingly unrelated cosmic mystery of dark matter.

    Supersymmetry, developed to fill gaps in our understanding of known particles and forces, postulates that each fundamental particle has a yet-to-be-discovered superpartner. It turns out that the lightest one of the bunch has properties that make it a top contender for dark matter.

    Supersymmetry standard model
    Standard Model of Supersymmetry

    “The lightest supersymmetric WIMP is stable and is not allowed to decay into other particles,” says theoretical physicist Tim Tait of the University of California, Irvine. “Once created in the big bang, many of these WIMPs would therefore still be around today and could have gone unnoticed because they rarely produce a detectable signal.”

    When researchers use the properties of the lightest supersymmetric particle to calculate how many of them would still be around today, they end up with a number that matches closely the amount of dark matter experimentally observed—a link referred to as the “WIMP miracle.” Many researchers believe it could be more than coincidence.

    “But WIMPs are also popular because we know how to look for them,” says dark matter hunter Thomas Shutt of Stanford University and SLAC National Accelerator Laboratory. “After years of developments, we finally know how to build detectors that have a chance of catching a glimpse of them.”

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    Shutt is co-founder of the LUX experiment and one of the key figures in the development of the next-generation LUX-ZEPLIN experiment. He is one member of the group of scientists trying to detect WIMPs as they traverse large, underground detectors.

    Lux Dark Matter 2
    LUX

    Lux Zeplin project
    LUX-ZEPLIN

    Other scientists hope to create them in powerful particle collisions at CERN’s Large Hadron Collider.

    CERN LHC Map
    CERN LHC Grand Tunnel
    CERN LHC particles
    LHC at CERN

    “Most supersymmetric theories estimate the mass of the lightest WIMP to be somewhere above 100 gigaelectronvolts, which is well within LHC’s energy regime,” Tait says. “I myself and others are very excited about the recent LHC restart. There is a lot of hope to create dark matter in the lab.”

    3

    A third way of searching for WIMPs is to look for revealing signals reaching Earth from space. Although individual WIMPs are stable, they decay into other particles when two of them collide and annihilate each other. This process should leave behind detectable amounts of radiation. Researchers therefore point their instruments at astronomical objects rich in dark matter such as dwarf satellite galaxies orbiting our Milky Way or the center of the Milky Way itself.

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    “Dark matter interacts with regular matter through gravitation, impacting structure formation in the universe,” says Risa Wechsler, a researcher at Stanford and SLAC. “If dark matter is made of WIMPs, our predictions of the distribution of dark matter based on this assumption must also match our observations.”

    Wechsler and others calculate, for example, how many dwarf galaxies our Milky Way should have and participate in research efforts under way to determine if everything predicted can also be found experimentally.

    So how would researchers know for sure that dark matter is made of WIMPs? “We would need to see conclusive evidence for WIMPs in more than one experiment, ideally using all three ways of detection,” Wechsler says.

    In the light of today’s mature detection methods, dark matter hunters should be able to find WIMPs in the next five to 10 years, Shutt, Tait and Wechsler say. Time will tell if scientists have the right idea about the nature of dark matter.

    See the full article here.

    Please help promote STEM in your local schools.

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 1:56 pm on July 9, 2015 Permalink | Reply
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    From Symmetry: “More data, no problem” 

    Symmetry

    July 09, 2015
    Katie Elyce Jones

    Scientists are ready to handle the increased data of the current run of the Large Hadron Collider.

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    Photo by Reidar Hahn, Fermilab

    Physicist Alexx Perloff, a graduate student at Texas A&M University on the CMS experiment, is using data from the first run of the Large Hadron Collider for his thesis, which he plans to complete this year.

    CERN LHC Map
    CERN LHC Grand Tunnel
    CERN LHC particles
    LHC

    CERN CMS Detector
    CMS

    When all is said and done, it will have taken Perloff a year and a half to conduct the computing necessary to analyze all the information he needs—not unusual for a thesis.

    But had he used the computing tools LHC scientists are using now, he estimates he could have finished his particular kind of analysis in about three weeks. Although Perloff represents only one scientist working on the LHC, his experience shows the great leaps scientists have made in LHC computing by democratizing their data, becoming more responsive to popular demand and improving their analysis software.

    A deluge of data

    Scientists estimate the current run of the LHC could create up to 10 times more data than the first one. CERN already routinely stores 6 gigabytes (or 6 billion units of digital information) per second, up from 1 gigabyte per second in the first run.

    The second run of the LHC is more data-intensive because the accelerator itself is more intense: The collision energy is 60 percent greater, resulting in “pile-up” or more collisions per proton bunch. Proton bunches are also injected into the ring closer together, resulting in more collisions per second.

    On top of that, the experiments have upgraded their triggers, which automatically choose which of the millions of particle events per second to record. The CMS trigger will now record more than twice as much data per second as it did in the previous run.

    Had CMS and ATLAS scientists relied only on adding more computers to make up for the data hike, they would likely have needed about four to six times more computing power in CPUs and storage than they used in the first run of the LHC.

    CERN ATLAS New
    ATLAS

    To avoid such a costly expansion, they found smarter ways to share and analyze the data.

    Flattening the hierarchy

    Over a decade ago, network connections were less reliable than they are today, so the Worldwide LHC Computing Grid was designed to have different levels, or tiers, that controlled data flow.

    All data recorded by the detectors goes through the CERN Data Centre, known as Tier-0, where it is initially processed, then to a handful of Tier-1 centers in different regions across the globe.

    CERN DATA Center
    One view of the Cern Data Centre

    During the last run, the Tier-1 centers served Tier-2 centers, which were mostly the smaller university computing centers where the bulk of physicists do their analyses.

    “The experience for a user on Run I was more restrictive,” says Oliver Gutsche, assistant head of the Scientific Computing Division for Science Workflows and Operations at Fermilab, the US Tier-1 center for CMS*. “You had to plan well ahead.”

    Now that the network has proved reliable, a new model “flattens” the hierarchy, enabling a user at any ATLAS or CMS Tier-2 center to access data from any of their centers in the world. This was initiated in Run I and is now fully in place for Run II.

    Through a separate upgrade known as data federation, users can also open a file from another computing center through the network, enabling them to view the file without going through the process of transferring it from center to center.

    Another significant upgrade affects the network stateside. Through its Energy Sciences Network, or ESnet, the US Department of Energy increased the bandwidth of the transatlantic network that connects the US CMS and ATLAS Tier-1 centers to Europe. A high-speed network, ESnet transfers data 15,000 times faster than the average home network provider.

    Dealing with the rush

    One of the thrilling things about being a scientist on the LHC is that when something exciting shows up in the detector, everyone wants to talk about it. The downside is everyone also wants to look at it.

    “When data is more interesting, it creates high demand and a bottleneck,” says David Lange, CMS software and computing co-coordinator and a scientist at Lawrence Livermore National Laboratory. “By making better use of our resources, we can make more data available to more people at any time.”

    To avoid bottlenecks, ATLAS and CMS are now making data accessible by popularity.

    “For CMS, this is an automated system that makes more copies when popularity rises and reduces copies when popularity declines,” Gutsche says.

    Improving the algorithms

    One of the greatest recent gains in computing efficiency for the LHC relied on the physicists who dig into the data. By working closely with physicists, software engineers edited the algorithms that describe the physics playing out in the LHC, thereby significantly improving processing time for reconstruction and simulation jobs.

    “A huge amount of effort was put in, primarily by physicists, to understand how the physics could be analyzed while making the computing more efficient,” says Richard Mount, senior research scientist at SLAC National Accelerator Laboratory who was ATLAS computing coordinator during the recent LHC upgrades.

    CMS tripled the speed of event reconstruction and halved simulation time. Similarly, ATLAS quadrupled reconstruction speed.

    Algorithms that determine data acquisition on the upgraded triggers were also improved to better capture rare physics events and filter out the background noise of routine (and therefore uninteresting) events.

    “More data” has been the drumbeat of physicists since the end of the first run, and now that it’s finally here, LHC scientists and students like Perloff can pick up where they left off in the search for new physics—anytime, anywhere.

    *While not noted in the article, I believe that Brookhaven National Laboratory is the Tier 1 site for Atlas in the United States.

    See the full article here.

    Please help promote STEM in your local schools.

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 2:06 pm on July 7, 2015 Permalink | Reply
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    From Symmetry: “What is dark energy?” 

    Symmetry

    1
    From NASA/ WFIRST*

    July 07, 2015
    Diana Kwon

    It’s everywhere. It will determine the fate of our universe. And we still have no idea what it is.

    Looking up at the night sky reveals a small piece of the cosmos—patches of stars speckled across a dark, black void. Though the universe appears stationary to the naked eye, it is expanding at an increasing rate, with the distance between galaxies doubling every 10 billion years. Scientists attribute this phenomenon to dark energy, which makes up 70 percent of our universe—and will determine its eventual fate.

    A changing universe

    In the early 1900s, when Albert Einstein formulated the theory of general relativity, scientists believed in a static universe. This posed a problem for Einstein. According to his calculations, space was dynamic—either contracting or expanding. To resolve this discrepancy in his equations, he added the cosmological constant (usually denoted by the Greek capital letter lambda: Λ), a factor to counter the force of gravity. But when news broke that the universe was expanding, Einstein dropped the term, reportedly calling it his biggest blunder.

    Fast-forward to 1998. Scientists observing supernovae, the extremely bright, explosive deaths of stars, made an unexpected discovery. By comparing the observed to expected brightness of these explosions, they found that the universe’s expansion was accelerating.

    Why this was happening was a mystery. Michael Turner, a theoretical cosmologist at the University of Chicago, coined the term “dark energy” to describe the unknown cause of this accelerating expansion.

    For almost two decades, physicists have been developing theories about what dark energy could be. Some propose dark energy is static, others say it changes over time. Some even suggest that it might not exist.

    “We’re at the very beginning of a very profound puzzle,” Turner says.

    Filling the void

    Dark energy is an additional “thing” in the universe besides regular and dark matter. Two leading theories describe what it might be: a cosmological constant or something called quintessence.

    The cosmological constant is considered a strong contender. Named after Einstein’s correction, it suggests that dark energy is the energy associated with the vacuum of space and has remained unchanged over the 14 billion years of the universe’s history.

    Unchanging and uniformly distributed through space, it will continue to drive cosmic acceleration at a constant pace until the universe becomes a cold, lonely place where galaxies become too far apart to see.

    Scientists favor the cosmological constant for its simplicity and because existing experimental evidence points to it. Despite its popularity, a major conceptual problem exists—it’s way smaller than it should be.

    “The simplest quantum mechanical estimate would give you a number that’s enormous compared to the actual size of the cosmological constant if it’s dark energy,” describes Aaron Roodman, an experimental physicist at SLAC National Accelerator Laboratory. “How you end up with something that’s non-zero and really tiny is very mysterious.”

    Some physicists suggest that the value is zero and that dark energy is something other than a cosmological constant. One possibility is that a field generates the energy driving cosmic acceleration; this is called quintessence, or the “fifth stuff.” Unlike the cosmological constant, it does not remain unchanging over time.

    This model has subsets that differently predict how exactly dark energy changes. One example is called phantom dark energy, where not only is expansion accelerating, but the acceleration is also increasing over time. This leads to a scenario called the Big Rip, where expansion becomes infinitely fast, tearing galaxies, atoms and the fabric of space-time itself apart.

    A new take on gravity

    It’s also possible that dark energy doesn’t exist and something strange is going on with gravity.

    Modifying gravity allows for all sorts of weird possibilities. One theory incorporates a higher dimension that gravity can extend to but we can’t directly access. This dimension can influence ours, and interactions can produce effects like cosmic acceleration.

    Revising gravity is no easy task. Einstein’s theory of general relatively has proven to be incredibly accurate, and attempts to rewrite his equations have been largely unsuccessful. Trying to fit cosmic acceleration into these equations makes them unable to explain well understood phenomena, such as how the moon revolves around the earth.

    Scientists have extensively tested Einstein’s theory, but they are just beginning to investigate it at the enormous intergalactic scales of dark energy’s effects. If scientists find inconsistencies, they will have uncovered signs of new physics.

    “If the only way we could interpret the discrepancy was that something strange is going on with gravity, we’d be pointed in a whole new direction in fundamental physics,” says astrophysicist Josh Frieman, director of the Dark Energy Survey, an experiment aimed at finding the cause of cosmic acceleration.

    Because modified gravity models fall into uncharted territory, they make the fate of the universe more difficult to predict. To do so, scientists will first need to better understand how it works.

    Surveying the skies

    In the quest to understand dark energy, the initial tasks are to determine whether it actually exists and to test whether it fits with the idea of the cosmological constant.

    To do this, scientists are studying the history of the universe’s expansion as well as the growth of galaxies and other structures. Gravity and the cosmological constant make very specific predictions about what they should see, so finding discrepancies can help rule out some of these theories.

    However, eliminating possibilities doesn’t necessarily mean an answer is near.

    “We need more experimental data. We need another clue. Nothing that exists is very compelling,” Turner says. “But the next clue could come in weeks, months or years with the currently running and future experiments.”
    The verdict

    If you ask a physicist to bet on which theory they thought was most likely, most will put their money on the cosmological constant.

    But many, including Scott Dodelson, a Fermilab astrophysicist studying dark energy, think it’s conceivable that none of these theories are correct.

    “It’s possible that we’re very wrong in the way we’re thinking about this and that we need to rethink our interpretations of the observations completely,” Dodelson says.

    The ultimate fate of our universe is a question humans have been pondering since the earliest civilizations. The answer might not be around the corner, but we’re certainly closer than we’ve ever been before.

    *This is not the image presented with the article.
    See the full article here.

    Please help promote STEM in your local schools.

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 11:19 am on July 3, 2015 Permalink | Reply
    Tags: , , Symmetry Magazine   

    From Symmetry: “How do you solve a puzzle like neutrinos?” 

    Symmetry

    June 30, 2015
    Lauren Biron

    When it comes to studying particles that zip through matter as though it weren’t even there, you use every method you can think of.

    1
    Artwork by Sandbox Studio, Chicago with Ana Kova

    Sam Zeller sounds borderline embarrassed by scientists’ lack of understanding of neutrinos—particularly how much mass they have.

    “I think it’s a pretty sad thing that we don’t know,” she says. “We know the masses of all the particles except for neutrinos.” And that’s true even for the Higgs, which scientists only discovered in 2012.

    Ghostly neutrinos, staggeringly abundant and ridiculously aloof, have held onto their secrets long past when they were theorized in the 1930s and detected in the 1950s. Scientists have learned a few things about them:

    They come in three flavors associated with three other fundamental particles (the electron, muon and tau).
    They change, or oscillate, from one type to another.
    They rarely interact with anything, and trillions upon trillions stream through us every minute.
    They have a very small mass.

    But right now, there are still more questions than answers.

    Zeller, one of thousands of neutrino researchers around the world and co-spokesperson for the neutrino experiment MicroBooNE based at Fermilab, says the questions about neutrinos don’t stop at mass.

    FNAL MicroBooNE
    MicroBooNE

    She writes down a shopping list of things physicists want to find out:

    Is one type of neutrino much heavier than the other two, or much lighter?
    What is the absolute mass of the neutrino?
    Are there more than three types of neutrinos?
    Do neutrinos and antineutrinos behave differently?
    Is the neutrino its own antiparticle?
    Is our picture of neutrinos correct?

    No single experiment can answer all of these questions. Instead, there are dozens of experiments looking at neutrinos from different sources, each contributing a piece to the puzzle. Some neutrinos stream unimpeded from far away, born in supernovae, the sun, the atmosphere or cosmic sources. Others originate closer to home, in the Earth, nuclear reactors, radioactive decays or particle accelerators. Their different birthplaces imbue them with different flavors and energies—a range so great, it spans at least 16 orders of magnitude. Armed with the knowledge of where and how to look, scientists are entering an exhilarating experimental time.

    “That’s why neutrino physics is so exciting right now,” Zeller says. “It’s not as if we’re shooting in the dark or we don’t know what we’re doing. Worldwide, we’re embarking on a program to answer these questions. That path will make use of these many different sources, and in the end you put it all together and hope the story makes sense.”

    2

    Neutrinos from nuclear reactors

    The first confirmation that neutrinos were more than just a theory came from nuclear reactors, where neutrinos are produced in a process called beta decay. A team of scientists led by Clyde Cowan and Frederick Reines found neutrinos spewing in a steady stream from reactors at the Hanford Site in Washington and the Savannah River Plant in South Carolina between 1953 and 1959.

    Reactors have been useful for neutrino physics ever since, particularly because they produce only one kind of neutrino: electron antineutrinos. When studying the way particles change from one type to another, it’s invaluable to know exactly what you’re starting with.

    Reactor experiments such as KamLAND, which studied particles from 53 nuclear reactors in Japan, echoed results from projects examining solar and atmospheric neutrinos. All of them found that neutrinos changed flavor over time.

    KamLAND
    KamLAND

    “Once we know that neutrinos are oscillating, that gives us the strongest evidence that neutrinos are massive,” says Dan Dwyer, a scientist at Lawrence Berkeley National Laboratory and researcher on the international Daya Bay Reactor Neutrino Experiment based in China.

    Daya Bay
    Daya Bay

    Such projects now look for the way neutrinos change and for hints about their relative masses.

    Because reactor experiments allow for precision, they’re also ideal to hunt for a fourth type of particle—the yet unobserved sterile neutrino, thought to interact only through gravity.

    3

    Neutrinos from accelerators

    Reactor neutrinos aren’t the only way to look for additional neutrinos. That’s where the powerhouse of neutrino research—the accelerator—comes in.

    Scientists can use a beam of easier-to-control particles such as protons to create a beam of neutrinos.

    First, they accelerate the protons and smash them into a target. The energy released in this collision converts to mass in the form of a flood of new massive particles. Those particles decay into less massive particles, including neutrinos.

    Before the massive particles decay, scientists use magnets to focus them into a beam. Afterward, they use blocking material to skim off unwanted bits while the neutrinos—which can pass through a light-year of lead without even noticing it’s there—flow freely through.

    Neutrino beams from accelerators are typically made of muon neutrinos and antineutrinos, but the experiments that use accelerators split into two main groups: short-baseline experiments, which look at oscillations over smaller distances, and long-baseline experiments, which study neutrinos that have traveled over hundreds of miles.

    Both types of experiments look at how neutrinos oscillate. At short distances, neutrinos are less likely to have changed flavors, though the influence of undiscovered new particles or forces might affect that rate. At long distances, neutrinos are more likely to have changed after traveling for a few milliseconds at nearly the speed of light. Oscillation patterns can give scientists clues as to the masses of the different types of neutrinos.

    Oscillation studies over long distances, like Japan’s T2K experiment or the United States’ NOvA experiment and proposed DUNE experiment, can help researchers find how neutrinos relate to antineutrinos. One method is to search for charge parity violation.

    T2K
    T2K

    FNAL DUNE
    DUNE

    This complicated-sounding term essentially asks whether matter and antimatter can pull off “the old switcheroo”—that is, whether the universe treats matter and antimatter particles identically. If the oscillations of neutrinos are fundamentally different from the oscillations of antineutrinos, then CP is broken.

    Scientists already know that CP is violated for one major building block of the universe: the quarks. Does the same happen for the other major family, the leptons? Neutrinos might hold the key.

    4

    Studying neutrinos without neutrinos

    It’s odd that one of the most important questions regarding neutrinos can be answered only by looking for a process apparently lacking in neutrinos.

    In neutrinoless double beta decay, a particle would decay into electrons and neutrinos, but the neutrinos would annihilate one another within the nucleus.

    “If you see it, it tells you that neutrinos are different in a fundamental way,” says Boris Kayser, a theorist at Fermilab.

    Neutrinoless double beta decay would occur only if neutrinos and their antiparticles were one and the same. No other fundamental particle of matter has this property.

    “Neutrinos are very special,” Kayser says. “It could be that they violate rules that other particles don’t violate.”

    Several experiments worldwide are under way to search for this process, with future generations planned.

    A different experiment, KATRIN, hopes to find the masses of the neutrinos by looking at particular electrons. As a radioactive kind of hydrogen decays, it spits out an antineutrino and a partner electron. Scientists will use the world’s largest spectrometer to measure the energy of these electrons to learn about the neutrino.

    KATRIN Experiment
    KATRIN

    6

    Geoneutrinos

    Unperturbed by magnetism or mass in their paths, neutrinos are perhaps the ultimate messengers of the universe. Once found, the particles point back to their origins, places scientists can’t otherwise see. Investigating these neutrinos provides insight into the particles themselves and is a useful way to probe the unknown.

    Take the Earth as an example. Scientists can use detectors to capture geoneutrinos, typically low-energy electron antineutrinos, to learn about the composition of our planet without trying to drill miles below the surface. Because we’ve learned that neutrinos are born of particle decay, the number of geoneutrinos tells researchers how much potassium, thorium and uranium lurk below, heating our world.

    7

    Solar neutrinos

    Neutrinos are also created in processes in the sun. But when Ray Davis built a solar neutrino detector filled with dry cleaning fluid, his experiment picked up only a third of the predicted neutrinos.

    This solar neutrino problem hinted that we didn’t understand our sun; in reality, we didn’t understand neutrinos. Solar neutrino experiments after Davis’ showed that neutrinos from the sun were changing flavor, and a reactor experiment later confirmed that the flavor change was caused by neutrino oscillation.

    Modern solar neutrino experiments such as Italy’s Borexino provide insight into the core of the sun and help put limits on sterile neutrinos.

    Others, like Japan’s Super-Kamiokande detector, can look at how solar neutrinos change when traveling through the earth versus neutrinos oscillating primarily in the vacuum of space.

    Super-Kamiokande experiment Japan
    Super-Kamiokande

    “The reason that’s important is that if the neutrino interacts with matter in new, unknown ways, which is possible, then this effect would be changed,” says Josh Klein, professor of physics at the University of Pennsylvania. “It’s a very sensitive measure of new physics.”

    8

    Cosmic neutrinos

    Cosmic neutrinos illuminate powerful phenomena occurring within our galaxy and beyond. Massive extragalactic neutrino hunting experiments, such as the IceCube experiment that sprawls across a cubic kilometer of ice in Antarctica, can find neutrinos that have oscillated over much longer distances than we can test with accelerators.

    ICECUBE neutrino detector
    IceCube neutrino detector interior
    IceCube

    “We see neutrinos [with energies] from below 10 [billion electronvolts] to above a thousand [trillion electronvolts],” says Francis Halzen, physicist at the University of Wisconsin, Madison, and leader of IceCube. “Nobody has ever built something that covers this energy range of particles.”

    Giant neutrino detectors like this one can look for sterile neutrinos and gather information on oscillations and mass hierarchy.

    They’re also useful for understanding dark matter and supernovae, analyzing atmospheric neutrinos that form when cosmic rays hit our atmosphere and telling other astronomers where to point their telescopes if neutrinos from a supernova burst hit. Physicists learn properties of neutrinos, but the neutrinos in turn unlock secrets of the universe.

    “Whenever we have made a picture of the universe in a different wavelength region of light, we have always seen things we didn’t expect,” Halzen says. “We’re doing now what astronomers have been doing for decades: looking at the sky in different ways.”

    Neutrinos matter for matter

    At the end of the day, why go to all this trouble for such a tiny particle? In addition to helping scientists probe the interior of the Earth or the far-off corners of the cosmos, neutrinos could hold the key to why matter exists today.

    Scientists know that antimatter and matter are produced in equal parts and should ultimately have annihilated one another, leaving a dark and empty universe. But here we stand, matter in all its glory.

    Sometime early in the universe’s history, an imbalance arose and shifted the scales toward a matter-dominated universe. If physicists find that neutrinos have certain characteristics—including CP violation—it could help explain why the universe turned out the way it did.

    “They’re the most abundant massive particle in the universe,” Zeller says. “If you find out something weird about neutrinos, it’s bound to tell you something about how the universe evolved or how it came to be the way we observe today.”

    See the full article here.

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 3:18 pm on June 24, 2015 Permalink | Reply
    Tags: , , , , Symmetry Magazine   

    From Symmetry: “Seeing in gamma rays” 

    Symmetry

    June 24, 2015
    Glenn Roberts Jr.

    1
    Courtesy of Fermi LAT collaboration

    The Fermi Gamma-ray Space Telescope creates maps of the gamma-ray sky.

    Maps from the Fermi Gamma-ray Space Telescope literally show the universe in a different light.

    NASA Fermi Telescope
    Fermi

    Fermi’s Large Area Telescope (LAT) has been watching the universe at a broad range of gamma-ray energies for more than seven years.

    Gamma rays are the highest-energy form of light in the cosmos. They come from jets of high-energy particles accelerated near supermassive black holes at the centers of galaxies, shock waves around exploded stars, and the intense magnetic fields of fast-spinning collapsed stars. On Earth, gamma rays are produced by nuclear reactors, lightning and the decay of radioactive elements.

    From low-Earth orbit, the Fermi Gamma-ray Space Telescope scans the entire sky for gamma rays every three hours. It captures new and recurring sources of gamma rays at different energies, and it can be diverted from its usual course to fix on explosive events known as gamma-ray bursts.

    Combining data collected over years, the LAT collaboration periodically creates gamma-ray maps of the universe. These colored maps plot the universe’s most extreme events and high-energy objects.

    The all-sky maps typically portray the universe as an ellipse that shows the entire sky at once, as viewed from Earth. On the maps, the brightest gamma-ray light is shown in yellow and progressively dimmer gamma-ray light is shown in red, blue, and black. These are false colors, though; gamma-rays are invisible.

    The maps are oriented with the center of the Milky Way at their center and the plane of our galaxy oriented horizontally across the middle. The plane of the Milky Way is bright in gamma rays. Above and below the bright band, much of the gamma-ray light comes from outside of our galaxy.

    “What you see in gamma rays is not so predictable,” says Elliott Bloom, a SLAC National Accelerator Laboratory professor and member of the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC) who is part of a scientific collaboration supporting Fermi’s principal instrument, the Large Area Telescope.

    Teams of researchers have identified mysterious, massive “bubbles” blooming 30,000 light-years outward from our galaxy’s center, for example, with most features appearing only at gamma-ray wavelengths.

    Scientists create several versions of the Fermi sky maps. Some of them focus only on a specific energy range, says Eric Charles, another member of the Fermi collaboration who is also a KIPAC scientist.

    “You learn a lot by correlating things in different energy ‘bins,’” he says. “If you look at another map and see completely different things, then there may be these different processes. What becomes useful is at different wavelengths you can make comparisons and correlate things.”

    But sometimes what you need is the big picture, says Seth Digel, a SLAC senior staff scientist and a member of KIPAC and the Fermi team. “There are some aspects you can only study with maps, such as looking at the extended gamma-ray emissions—not just the point sources, but regions of the sky that are glowing in gamma rays for different reasons.”

    See the full article here.

    Please help promote STEM in your local schools.

    STEM Icon

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 7:42 am on June 10, 2015 Permalink | Reply
    Tags: , Hyper-K, , Symmetry Magazine   

    From Symmetry: “Japan’s next big neutrino project” 

    Symmetry

    June 09, 2015
    Glenn Roberts Jr.

    1
    Artwork by Sandbox Studio, Chicago

    The proposed Hyper-K experiment would dwarf its predecessor.

    In 1998, the Super-K detector in Japan revealed that ubiquitous, almost massless particles called neutrinos have the ability to morph from one type to another. That landmark finding has become one of the most heavily cited scientific results in particle physics.

    Super-Kamiokande experiment Japan
    Super-K

    Now scientists have proposed to build a successor to the still-operating Super-K: Hyper-K, a detector with an active volume 25 times its size.

    Part microscope and part telescope, the proposed Hyper-K experiment could fill in some of the blanks in our understanding of our universe. It could help explain why the universe favors matter over antimatter. It could provide new details about the fluctuating “flavors” or types of neutrinos. It could help elucidate whether there is any difference between neutrinos and their anti-particles.

    It could also provide a better understanding of dark matter and exploding stars and could reveal whether protons—a main ingredient in all atoms—have an expiration date.

    The proposed experiment would be complementary to DUNE, a planned long-baseline neutrino experiment in the United States that will use different technology.

    FNAL DUNE
    FNAL DUNE

    The “K” in Super-K and Hyper-K stands for a play on the word Kamioka, the name of a mountainous area about 200 miles west of Tokyo that houses multiple particle physics experiments.

    “The uniqueness of Hyper-K is its size and resolution,” says Tsuyoshi Nakaya of Kyoto University, who leads the Hyper-K steering committee and has been a part of Super-K since 1999.

    The central component in the Hyper-K project would be a massive cylindrical tank measuring about 248 meters long and 54 meters high, filled with 1.1 million tons of highly purified water. An alternate Hyper-K design calls for an egg-shaped tank.

    2
    Courtesy of: © Hyper-Kamiokande Collaboration

    Hyper-K would consist of an array of photo-detectors that would measure flashes of light produced in particle events and processes occurring in the tank. The mountain above Hyper-K would help to shield the detectors from the “noise” of other particles such as cosmic rays.

    Hyper-K would study a beam of neutrinos produced at the Japan Proton Accelerator Research Complex about 180 miles away in Tokai, and it would be able to detect neutrinos produced even farther away in Earth’s atmosphere and beyond. Hyper-K could also detect particles produced in the decay of a proton, something scientists have yet to see.

    “The discovery of proton decays would be revolutionary,” says Masato Shiozawa, Hyper-K project leader who works at the Institute for Cosmic Ray Research in Japan.

    Hyper-K has already won international support from institutions in 13 countries, with the largest groups coming from Japan, the United Kingdom, the United States, Switzerland and Canada. In January the ICCR announced a cooperative agreement to pursue Hyper-K with the Institute of Particle and Nuclear Studies in Japan’s High Energy Accelerator Research Organization.

    About 200 researchers are already working on the design of Hyper-K, and the collaboration is still welcoming new members. They hope to begin construction in 2018.

    See the full article here.

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.


     
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