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  • richardmitnick 3:18 pm on June 24, 2015 Permalink | Reply
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    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.

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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.

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 12:33 pm on June 4, 2015 Permalink | Reply
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    From Symmetry: “The universe at your fingertips” 

    Symmetry

    June 04, 2015
    Manuel Gnida

    1
    Courtesy of DECam Legacy Survey

    Raw images from the DECam Legacy Survey’s new image archive will appear online the day after they are taken.

    When it was time to celebrate the 20th anniversary of the Star Wars trilogy, director George Lucas was prompted by technological leaps in the filmmaking industry to produce a digitally remastered special edition.

    Today scientists of the DECam Legacy Survey released their own version of a special edition. They published the first in a series of catalogs that offer an update to images of the night sky originally taken with the 15-year-old camera of the Sloan Digital Sky Survey [SDSS].

    SDSS Telescope
    SDSS telescope at Apache Point, NM, USA

    In the spirit of the new information age, the survey will share frequent updates on its public website. With its Sky Viewer, users can explore the contents of the universe, whose busyness might surprise anyone accustomed to bland skies polluted by city lights.

    Site visitors can choose whether they want to look at false-color images or theoretical models of the sky, or see the difference between the two. The website also contains a map of dust emissions in the Milky Way based on data first reported in one of the most cited journal articles of all astrophysics.

    Similar exploration tools exist for the image archives of SDSS and the Hubble telescope. However, these data became publicly available only after a period of restricted use by a limited group of researchers.

    “The Legacy Survey is unique in that it doesn’t have any proprietary restrictions,” says David Schlegel of Lawrence Berkeley National Laboratory, who initiated the new project together with Arjun Dey, a staff astronomer at the National Optical Astronomy Observatory. “Raw images will appear the day after they were taken, and we plan on releasing processed versions every three to six months.”

    The Legacy Survey’s image archive will eventually cover one third of the sky. Hopes are that it will serve scientists around the world in a multitude of studies, from explorations of the structure of our Milky Way galaxy to analyses of our universe’s mysterious dark energy that accelerates the cosmic expansion.

    Today’s data release is the outcome of the survey’s first observations with the 520-megapixel Dark Energy Camera, or DECam, which is mounted on the Blanco telescope in Chile.

    Dark Energy Camera
    DECam, built at FNAL

    CTIO Victor M Blanco 4m Telescope
    CTIO Victor M Blanco 4m Telescope interior
    CTIO Victor M Blanco 4 meter telescope in Chile

    Additional snapshots will be also taken with cameras of the Bok and Mayall telescopes in Arizona. The experiments began last fall and will take place on a total of over 500 nights spread out over three years.

    Bok Telescope U Arizona Stewrad Observatory
    U Arizona Steward Observatory Bok Telescope

    NOAO Mayall 4 m telescope exterior
    NOAO Mayall Telescope

    Processing mixed-quality data from three different telescopes collected under varying observation conditions will be a big challenge for the scientists.

    “Given the large area of the sky we want to cover and the limited experimental time we have been assigned, we can only take three images of each part of the sky,” says Legacy Survey member Dustin Lang of Carnegie Mellon University, who developed new image processing techniques that describe the observations with theoretical models. “We need to make the most of our data, no matter whether the observation conditions are good or bad on a given night.”

    Researchers want to link the images of stars, galaxies and other cosmic objects to complementary information they collect with spectroscopy, the analysis of light emissions. This includes, for instance, redshifts that measure how fast objects are moving relative to us, information crucial for dark energy studies.

    After three years are up, the Legacy Survey should live up to its name. The information it gathers will live on as a guide for a new surveyor, the Dark Energy Spectroscopic Instrument, whose redshift measurements will chart the expansion history of the universe over the last 10 billion years of cosmic time.

    See the full article here.

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 4:08 pm on May 26, 2015 Permalink | Reply
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    From Symmetry: “A goldmine of scientific research” 

    Symmetry

    May 26, 2015
    Amelia Williamson Smith

    1
    Photo by Anna Davis

    The underground home of the LUX dark matter experiment has a rich scientific history.

    There’s more than gold in the Black Hills of South Dakota. For longer than five decades, the Homestake mine has hosted scientists searching for particles impossible to detect on Earth’s surface.

    It all began with the Davis Cavern.

    In the early 1960s, Ray Davis, a nuclear chemist at Brookhaven National Laboratory designed an experiment to detect particles produced in fusion reactions in the sun. The experiment would earn him a share of the Nobel Prize in Physics in 2002.

    Davis was searching for neutrinos, fundamental particles that had been discovered only a few years before. Neutrinos are very difficult to detect; they can pass through the entire Earth without bumping into another particle. But they are constantly streaming through us. So, with a big enough detector, Davis knew he could catch at least a few.

    Davis’ experiment had to be done deep underground; without the shielding of layers of rock and earth it would be flooded by the shower of cosmic rays also constantly raining from space.

    Davis put his first small prototype detector in a limestone mine near Akron, Ohio. But it was only about half a mile underground, not deep enough.

    “The only reason for mining deep into the earth was for something valuable like gold,” says Kenneth Lande, professor of physics at the University of Pennsylvania, who worked on the experiment with Davis. “And so a gold mine became the obvious place to look.”

    But there was no precedent for hosting a particle physics experiment in such a place. “There was no case where a physics group would appear at a working mine and say, ‘Can we move in please?’”

    Davis approached the Homestake Mining Company anyway, and the company agreed to excavate a cavern for the experiment.

    BNL funded the experiment. In 1965, it was installed in a cavern 4850 feet below the surface.

    The detector consisted of a 100,000-gallon tank of chlorine atoms. Davis had predicted that as solar neutrinos passed through the tank, one would occasionally collide with a chlorine atom, changing it to an argon atom. After letting the detector run for a couple of months at a time, Davis’ team would flush out the tank and count the argon atoms to determine how many neutrino interactions had occurred.

    “The detector had approximately 1031 atoms in it. One argon atom was produced every two days,” Lande says. “To design something that could do that kind of extraction was mind-boggling.”

    2
    Ray Davis. Courtesy of: Brookhaven National Laboratory

    A different kind of laboratory

    During the early years of the Davis experiment, around 2000 miners worked at the mine, along with engineers and geologists. The small group of scientists working on the Davis experiment would travel down into the mine with them.

    To go down the shaft to the 4850-foot level, they would get into what was called the “cage,” a 4.4-foot by 12.5-foot metal conveyance that held 36 people. The ride down, lit only by the glow of a couple of headlamps, took about five minutes, says Tom Regan, former operations safety manager and now safety consultant, who worked as a student laborer in the mine during the early years of the Davis experiment.

    Once they reached the 4850-foot level, the scientists walked across a rock dump. “It was guarded so a person couldn’t fall down the hole,” Regan says. “But you had to sometimes wait for a production train of rock or even loads of supplies or men or materials.”

    The Davis Cavern was 24 feet long, 24 feet wide, and 30 feet high. A small room off to the side held the group’s control system. “We were basically out of touch with the rest of the world when we were underground,” Lande says. “There was no difference between day and night, heat and cold, and snow and sunshine.”

    The miners and locals from Lead, South Dakota—the community surrounding the mine—were welcoming of the scientists and interested in their work, Lande says. “We’d go out to dinner at the local restaurant and we’d hear this hot conversation in the next booth, and they would be discussing black holes and neutron stars. So science became the talk of the small town.”

    4
    Davis Cavern, during the solar neutrino experiment. Photo by: Anna Davis

    The solar neutrino problem

    As the experiment began taking data, Davis’ group found they were detecting only about one-third the number of neutrinos predicted—a discrepancy that became known as the “solar neutrino problem.”

    Davis described the situation in his Nobel Prize biographical sketch: “My opinion in the early years was that something was wrong with the standard solar model; many physicists thought there was something wrong with my experiment.”

    However, every test of the experiment confirmed the results, and no problems were found with the model of the sun. Davis’ group began to suspect it was instead a problem with the neutrinos.

    This suspicion was confirmed in 2001, when the Sudbury Neutrino Observatory experiment [SNO] in Canada determined that as solar neutrinos travel through space, they oscillate, or change, between three flavors—electron, muon and tau. By the time neutrinos from the sun reach the Earth, they are an equal mixture of the three types.

    Sudbury Neutrino Observatory
    SNO

    The Davis experiment was sensitive only to electron neutrinos, so it was able to detect only one-third of the neutrinos from the sun. The solar neutrino problem was solved.

    5
    Davis Cavern, during a more recent expansion. Photo by: Matthew Kapust, Sanford Underground Research Facility

    A different kind of gold

    The Davis experiment ran for almost 40 years, until the mine closed in 2003.

    But the days of science in the Davis Cavern weren’t over. In 2006, the mining company donated Homestake to the state of South Dakota. It was renamed the Sanford Underground Research Facility.

    In 2009, many former Homestake miners became technicians on a $15.2 million project to renovate the experimental area. They completed the new 30,000-square-foot Davis Campus in 2012.

    Although scientists still ride in the cage to get down to the 4850-foot level of the mine, once they arrive it looks completely different.

    “It’s a very interesting contrast,” says Stanford University professor Thomas Shutt of SLAC National Accelerator Laboratory. “Going into the mine, it’s all mining carts, rust and rock, and then you get down to the Davis Campus, and it’s a really state-of-the-art facility.”

    The campus now contains block buildings with doors and windows. It has its own heating and air conditioning system, ventilation system, humidifiers and dust filters.

    The original Davis Cavern has been expanded and now houses the Large Underground Xenon experiment, the most sensitive detector yet searching for what many consider the most promising candidate for a type of dark matter particle.

    LUX Dark matter
    LUX

    Shielded from distracting background particles this far underground, scientists hope LUX will detect the rare interaction of dark matter particles with the nucleus of xenon atoms in the 368-kilogram tank.

    Another cavern nearby was excavated as part of the Davis Campus renovation project and now holds the Majorana Demonstrator experiment, which will soon start to examine whether neutrinos are their own antimatter partners.

    Majorano Demonstrator Experiment
    Majorano Demonstrator Experiment

    LUX began taking data in 2013. It is currently on its second run and will continue through spring 2016.

    After its current run, LUX will be replaced by the LUX-ZEPLIN, or LZ, experiment, which will be 50 times bigger in usable mass and several hundred times more sensitive than the current LUX results.

    LZ project
    LZ

    Science in the mine is still the talk of the town in Lead, says Carmen Carmona, an assistant project scientist at the University of California, Santa Barbara, who works on LUX. “When you go out on the streets and talk to people—especially the families of the miners from the gold mine days—they want to know how it is working underground now and how the experiment is going.”

    The spirit of cooperation between the mining community, the science community and the public community lives on, Regan says.

    “It’s been kind of a legacy to provide the beneficial space and be good neighbors and good hosts,” Regan says. “Our goal is for them to succeed, so we do everything we can to help and provide the best and safest place for them to do their good science.”

    6
    In 2010, Sanford Lab enlarged the Davis Cavern to support the Large Underground Xenon experiment. Matthew Kapust, Sanford Underground Research Facility

    7
    This cavern is being outfitted for the Compact Accelerator System Performing Astrophysical Research. CASPAR will use a low-powered accelerator to study what happens when stars die. Matthew Kapust, Sanford Underground Research Facility

    8
    Davis Cavern undergoes outfitting for the LUX experiment. Matthew Kapust, Sanford Underground Research Facility

    9
    Each day scientists working at the the Davis Campus pass this area, known as the Big X. The entrance to the Davis Campus is to the left; Yates Shaft is to the right. Matthew Kapust, Sanford Underground Research Facility

    10
    LUX researchers install the detector at the 4850 level. Matthew Kapust, Sanford Underground Research Facility

    11
    The Majorana Demonstrator experiment requires a very strict level of cleanliness. Researcher work in full clean room garb and assemble their detectors inside nitrogen-filled glove boxes. Matthew Kapust, Sanford Underground Research Facility

    12
    The LUX detector was built in a clean room on the surface and then brought underground. Matthew Kapust, Sanford Underground Research Facility

    See the full article here.

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 3:23 pm on May 20, 2015 Permalink | Reply
    Tags: , Caltech SPIDER, , FNAL DAMIC, Project 8, Symmetry Magazine   

    From Symmetry: “Small teams, big dreams” 

    Symmetry

    May 20, 2015
    Diana Kwon

    1
    Artwork by Sandbox Studio, Chicago with Ana Kova

    A small group of determined scientists can make big contributions to physics.

    Particle physics is the realm of billion-dollar machines and teams of thousands of scientists, all working together to explore the smallest components of the universe. But not all physics experiments are huge, as the scientists of FNAL DAMIC , Project 8, SPIDER and ATRAP can attest. Each of their groups could fit in a single Greyhound bus, with seats to spare. Don’t let their size fool you; their numbers may be small, but their ambitions are not.

    FNAL DAMIC
    FNAL DAMIC

    Project 8
    DOE Project 8

    Caltech SPIDER
    Caltech SPIDER

    CERN ATRAP New
    CERN ATRAP

    Smaller machines

    Small detectors play an important role in searching for difficult-to-find particles.

    Take dark matter, for example. Because no one knows what exactly dark matter is or what the mass of a dark matter particle might be, detection experiments need to cover all the bases.

    DAMIC is an experiment that aims to observe dark matter particles that larger detectors can’t see.

    The standard strategy used in most experiments is scaling up the size of the detector to increase the number of potential targets for dark matter particles to hit. DAMIC takes another approach: eliminating all sources of background noise to allow the detector to see potential dark matter particle interactions of lower and lower energies.

    The detector sits in a dust-free room 2 kilometers below ground at SNOLAB in Sudbury, Canada.

    SNOLAB
    SNOLAB

    To eliminate as much noise as possible, it is held in 10 tons of lead at around minus 240 degrees Fahrenheit. Its small size allows scientists to shield it more easily than they could a larger instrument.

    DAMIC is currently the smallest dark matter detection experiment—both in the size of apparatus and the number of people on the team. While many dark matter detectors use more than a hundred thousand grams of active material, the current version of DAMIC runs on a mere five grams and the full detector will have 100 grams. Its team is made up of around ten scientists and students.

    “What’s really nice is that even though this is a small experiment, it has the potential of making a huge contribution and having a big impact,” says DAMIC member Javier Tiffenberg, a postdoctoral fellow at Fermilab.

    Top to bottom engagement

    In collaborations larger than 100 people, specialized teams usually work on different parts of an experiment. In smaller groups, all members work together and engage in everything from machine construction to data analysis.

    The 20 or so members of the Project 8 experiment are developing a new technique to measure the mass of neutrinos. On this experiment, moving quickly between designing, testing and analyzing an apparatus is of great importance, says Martin Fertl, a postdoctoral researcher at the University of Washington. Immediate access to hardware and analysis tools helps these projects move forward quickly and allows changes to be implemented with ease.

    “A single person can install a new piece of hardware and within a day or so, test the equipment, take new data, analyze that data and then decide whether or not the system requires any additional modification,” he says.

    Project 8 aims to determine the mass of neutrinos indirectly using tritium. Tritium decays to Helium-3, releasing an electron and a neutrino. Scientists can measure the energy emitted by these electrons to help them determine the neutrino mass.

    “It was satisfying for us all when the first data came out and we were seeing electrons,” says UW postdoc Matthew Sternberg. “We basically all took a crack at the data to see what we could pull off of it.”

    A fertile training ground

    Small collaborations can be especially beneficial to fledging scientists entering the field.

    Space-based projects carry a high cost and risk that can prevent students from being very involved. Balloon-borne experiments, however, are the next best thing. By getting above the atmosphere, balloons provide many of the same benefits for a fraction of the price.

    In the roughly 30-member collaboration of the balloon-borne SPIDER experiment, graduate students played a role in designing, engineering, building and launching the instrument, and are now working on analysis.

    “It’s great training for graduate students who end up working on large satellite experiments,” says Sasha Rahlin, a graduate student at Princeton University.

    SPIDER is composed of six large cameras tethered to a balloon and was launched 110,000 feet above Antarctica to orbit the Earth for about 20 days in search of information about the early universe. Using measurements from this flight, researchers are looking for fluctuations in the polarization of cosmic background radiation, the light leftover from the big bang.

    “When the balloon went up, all of us were in the control room watching each sub-system turn on and do exactly what it was supposed to,” Rahlin says. “There was a huge moment of ‘Wow, this actually works.’ And every component from start to finish had grad student blood, sweat and tears.”

    Around 20 people went down to McMurdo Station in Antarctica to launch SPIDER with the help of a team from NASA that launches balloon experiments in several locations around the world. According to Zigmund Kermish, a postdoctoral fellow at Princeton University, being a small group sometimes means having to optimize time and manpower to get tasks done.

    “It’s been really inspiring to see what we do with limited resources,” said Kermish. “It’s amazing what motivated graduated students can make happen.”

    Big ambitions

    Scientists on small collaborations are working toward big scientific goals. The ATRAP experiment is no exception; it will help answer some fundamental questions about why our universe exists.

    Four members of the collaboration are located at CERN, where the apparatus is located, while only 15 people are involved overall.

    ATRAP creates antihydrogen by confining positrons and antiprotons in a trap, cooling them to near absolute zero until they can combine to form atoms. ATRAP holds these atoms while physicists make precise measurements of their properties to compare with hydrogen atoms, their matter counterparts.

    This can help determine whether nature treats matter and antimatter alike, says Eric Tardiff, a Harvard University postdoc at CERN. If researchers find evidence for violation of this symmetry, they will have a potential explanation for one of physics’ largest mysteries—why the universe contains unequal amounts of antimatter and matter particles. “No experiment has explained [this asymmetry] yet,” he says.

    Think small

    Small experiments play an important role in particle physics. They help train researchers early in their career by giving them experience across many parts of the scientific process. And despite their size, they hold enormous potential to make game-changing scientific discoveries. As Margaret Mead once said, “Never doubt that a small group of thoughtful, committed citizens can change the world.”

    See the full article here.

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 7:15 pm on May 19, 2015 Permalink | Reply
    Tags: , , Symmetry Magazine   

    From Symmetry: “Looking to the heavens for neutrino masses” 

    Symmetry

    May 19, 2015
    Matthew R. Francis

    1
    Artwork by Sandbox Studio, Chicago

    Neutrinos may be the lightest of all the particles with mass, weighing in at a tiny fraction of the mass of an electron. And yet, because they are so abundant, they played a significant role in the evolution and growth of the biggest things in the universe: galaxy clusters, made up of hundreds or thousands of galaxies bound together by mutual gravity.

    Thanks to this deep connection, scientists are using these giants to study the tiny particles that helped form them. In doing so, they may find out more about the fundamental forces that govern the universe.

    Curiously light

    When neutrinos were first discovered, scientists didn’t know right away if they had any mass. They thought they might be like photons, which carry energy but are intrinsically weightless.

    But then they discovered that neutrinos came in three different types [flavors] and that they can switch from one type to another, something only particles with mass could do.

    Scientists know that the masses of neutrinos are extremely light, so light that they wonder whether they come from a source other than the Higgs field, which gives mass to the other fundamental particles we know. But scientists have yet to pin down the exact size of these masses.

    It’s hard to measure the mass of such a tiny particle with precision.

    In fact, it’s hard to measure anything about neutrinos. They are electrically neutral, so they are immune to the effects of magnetic fields and related methods physicists use to detect particles. They barely interact with other particles at all: Only a more-or-less direct hit with an atomic nucleus can stop a neutrino, and that doesn’t happen often.

    Roughly a trillion neutrinos pass through your body each second from the sun alone, and almost none of those end up striking any of your atoms. Even the densest matter is nearly transparent to neutrinos. However, by creating beams of neutrinos and by building large, sensitive targets to catch neutrinos from nuclear reactors and the sun, scientists have been able to detect a small portion of the particles as they pass through.

    In experiments so far, scientists have estimated that the total mass of the three types of neutrinos together is roughly between 0.06 electronvolts and 0.2 electronvolts. For comparison, an electron’s mass is 511 thousand electronvolts and a proton weighs in at 938 million electronvolts.

    Because the Standard Model—the theory describing particles and the interactions governing them—predicts massless neutrinos, finding the exact neutrino mass value will help physicists modify their models, yielding new insights into the fundamental forces of nature.

    2
    Standard Model of Particle Physics. The diagram shows the elementary particles of the Standard Model (the Higgs boson, the three generations of quarks and leptons, and the gauge bosons), including their names, masses, spins, charges, chiralities, and interactions with the strong, weak and electromagnetic forces. It also depicts the crucial role of the Higgs boson in electroweak symmetry breaking, and shows how the properties of the various particles differ in the (high-energy) symmetric phase (top) and the (low-energy) broken-symmetry phase (bottom).

    Studying galaxy clusters could provide a more precise answer.

    Footprints of a neutrino

    One way to study galaxy clusters is to measure the cosmic microwave background [CMB], the light traveling to us from 380,000 years after the big bang.

    Cosmic Background Radiation Planck
    CMB per ESA Planck

    ESA Planck
    ESA/Planck

    During its 13.8-billion-year journey, this light passed through and near all the galaxies and galaxy clusters that formed. For the most part, these obstacles didn’t have a big effect, but taken cumulatively, they filtered the CMB light in a unique way, given the galaxies’ number, size and distribution.

    The filtering affected the polarization—the orientation of the electric part of light—and originated in the gravitational field of galaxies. As CMB light traveled through the gravitational field, its path curved and its polarization twisted very slightly, an effect known as gravitational lensing. (This is a less dramatic version of lensing familiar from the beautiful Hubble Space Telescope images.)

    NASA Hubble Telescope
    NASA/ESA Hubble

    The effect is similar to the one that got everyone excited in 2014, when researchers with the BICEP2 telescope announced they had measured the polarization of CMB light due to primordial gravitational waves, which subsequent study showed to be more ambiguous.

    BICEP 2BICEP 2 interior
    BICEP

    That ambiguity won’t be a problem here, says Oxford University cosmologist Erminia Calabrese, who studies the CMB on the Atacama Cosmology Telescope [ACT] Polarization project.

    Princeton Atacama Technology Telescope
    ACT

    “There is one pattern of CMB polarization that is generated only by the deflection of the CMB radiation.” That means we won’t easily mistake gravitational lensing for anything else.

    Small and mighty

    Manoj Kaplinghat, a physicist at the University of California at Irvine, was one of the first to work out how neutrino mass could be estimated from CMB data alone. Neutrinos move very quickly relative to stuff like atoms and the invisible dark matter that binds galaxies together. That means they don’t clump up like other forms of matter, but their small mass still contributes to the gravitational field.

    Enough neutrinos, even fairly low-mass ones, can deprive a newborn galaxy of a noticeable amount of mass as they stream away, possibly throttling the growth of galaxies that can form in the early universe. It’s nearly as simple as that: Heavier neutrinos mean galaxies must grow more slowly, while lighter neutrinos mean faster galaxy growth.

    Kaplinghat and colleagues realized the polarization of the CMB provides a measure the total amount of gravity from galaxies in the form of gravitational lensing, which working backward will constrain the mass of neutrinos. “When you put all that together, what you realize is you can do a lot of cool neutrino physics,” he says.

    Of course the CMB doesn’t provide a direct measurement of the neutrino mass. From the point of view of cosmology, the three types of neutrinos are indistinguishable. As a result, what CMB polarization gives us is the total mass of all three types together.

    However, other projects are working on the other end of this puzzle. Experiments such as the Main Injector Neutrino Oscillation Search, managed by Fermilab, have determined the differences in mass between the different neutrino types.

    Depending on which neutrino is heaviest, we know how the masses of the other two types of neutrinos relate. If we can figure out the total mass, we can figure out the masses of each one. Together, cosmological and terrestrial measurements will get us the individual neutrino masses that neither is able to alone.

    The space-based Planck observatory and POLARBEAR project in northern Chile have yielded preliminary results in this search already.

    POLARBEAR McGill Telescope
    POLARBEAR telescope

    And scientists at ACTPol, located at high elevation in Chile’s Atacama Desert, are working on this as well. They will determine the neutrino mass as well as the best estimates we have, down to the lowest possible values allowed, once the experiments are running at their highest precision, Calabrese says.

    Progress is necessarily slow: The gravitational lensing pattern comes from seeing small patterns emerging from light captured across a large swath of the sky, much like the image in an Impressionist painting arises from abstract brushstrokes that look like very little by themselves.

    In more scientific terms, it’s a cumulative, statistical effect, and the more data we have, the better chance we have to measure the lensing effect—and the mass of a neutrino.

    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 12:54 pm on May 12, 2015 Permalink | Reply
    Tags: ANITA, , COSI, , SPIDER, Symmetry Magazine   

    From Symmetry: “High adventure physics” 

    Symmetry

    May 12, 2015
    Angela Anderson

    1
    Photo by Harm Schoorlemmer, ANITA

    Three groups of hardy scientists recently met up in Antarctica to launch experiments into the big blue via balloon.

    UC Berkeley grad student Carolyn Kierans recently watched her 5000-pound astrophysics experiment ascend 110,000 feet over Antarctica on the end of a helium-filled balloon the size of a football field.

    She had been up since 3 a.m. with the team that prepped and transported the telescope known as COSI—Compton Spectrometer and Imager—across the ice shelf on an oversized vehicle called “The Boss.” They waited hours at the launch site in a thick fog for the winds to die down before getting the go-ahead to fill the balloon.

    Then the sky opened up, and they were cleared for launch.

    “I was with the crew at the launch pad, in the middle of nowhere, when the clouds disappeared and I could finally see the balloon hundreds of feet up,” she recalls. “I had to stop and say, ‘Wait, I’m doing my PhD in physics right now?’”

    Kierans was among three groups of hardy physicists who met up at Antarctica’s McMurdo Station last fall to fly their curious-looking instruments during NASA’s most recent Antarctic Scientific Balloon Campaign.

    2
    Fully assembled and flight ready, COSI gets some final adjustments from Carolyn Kierans during testing. Photo by: Laura Gerwin

    For Antarctica’s three summer months, December through February, conditions are right to conduct studies in the upper atmosphere via scientific balloon. The sun never sets during those months, so the balloons are spared nighttime temperatures that would cause significant changes in altitude. And seasonal wind patterns take the balloons on a circular route almost entirely over land.

    To allow the balloons enough time to collect data and safely land before conditions change, all launches must take place within a few weeks in December. Near the end of 2014, three teams of physicists arrived at the end of the Earth to try to launch, one after the other, within that small window.

    Each team was driven by a different scientific pursuit: COSI set out to capture images of gamma rays for clues to the life and death of stars; ANITA (Antarctic Impulsive Transient Antenna) sought rare signs of ultra-high-energy neutrinos; and SPIDER was probing the cosmic microwave background [CMB] for evidence of cosmic inflation.

    Cosmic Microwave Background  Planck
    CMB per ESA/Planck

    Months of intense preparation, naps on the floor of a barn, competition for launch times during narrow windows of opportunity, and numerous aborted attempts did not dampen spirits. The teams shared meals, supplies, hikes and live music jams with locals at one of two town bars—united by the common pursuit of physics on high.

    “The community was like a gigantic family with the same goal of getting those balloons up,” Kierans says.

    None could be sure of a successful launch. Nor could they know exactly when or where their balloon would land once it took flight or how they would navigate the icy landscape to retrieve their precious data.

    ‘The crinkling of Mylar’

    Balloon-based physics experiments take many months of preparation. The teams first met up during the summer at the Columbia Scientific Balloon Facility in Palestine, Texas, where they assembled payloads and tested science and flight systems. Then they disassembled their experiments, shipped them in boxes and put them back together at McMurdo starting in October to be launch-ready by early December. Each group had 10 to 20 team members on the continent during peak work efforts.

    “We had about eight weeks to get everything back together and perform all the calibrations—it’s an exhausting and stressful period—and a very long time to be away from family,” recalls William Jones, assistant professor of physics at Princeton University and SPIDER lead.

    A successful launch depends on the optimal functioning of gear and instruments—and the cooperation of the weather.

    First in line was the ANITA experiment. ANITA hunts for the highest energy particles ever observed. Scientists have known about ultra-high-energy neutrinos since the 1960s, but they still don’t know exactly where they come from or how they get their energy.

    “Nothing on Earth can produce such particles right now,” says Harm Schoorlemmer, a postdoctoral fellow at the University of Hawaii from the ANITA team. “They are five to seven orders of magnitude higher in energy than particles we can accelerate in machines like the LHC at CERN.”

    Neutrinos travel through the universe barely interacting with anything—until they hit the dense Earth. ANITA’s 48 antennas on a 25-foot-tall gondola fly pointed down to capture radio waves in the Antarctic ice—signs of ultra-high-energy neutrino reactions.

    “The ice sheet has the advantage that it is transparent for radio waves,” says Christian Miki, University of Hawaii staff scientist and ANITA on-ice lead. “By flying high—about 120,000 feet up—ANITA can capture a diameter of 600 kilometers all at once.”

    Numerous ANITA launch attempts were scrubbed due to weather. It took several hours from hangar to launch at the Long Duration Balloon Facility, and Antarctic weather is known for radical shifts within the hour, Miki says.

    3
    ANITA hangs from the The Boss on its way to the launch pad. Photo by: Harm Schoorlemmer, ANITA

    The day before the actual launch, the payload had been brought out of the hanger and checks were being performed when the team noticed an Emperor penguin hanging out on the edge of the launch pad. “We thought this was either good luck—getting a blessing from the Antarctic gods—or bad luck as penguins are flightless birds,” Miki recalls.

    Apparently graced, the ANITA team rolled out on December 18 for the real deal. The 4944-pound experiment was loaded onto the The Boss and taken to the launch site. Hours passed as they waited for optimal conditions; all the instruments were checked and double-checked. Finally, they got the go-ahead from NASA.

    “It’s hard to grasp the scales involved,” Schoorlemmer says. “The balloon is 800 to 900 feet above The Boss before the line is cut—buildings are about 35 to 40 feet tall. It takes one and a half hours to fill the balloon with helium, and then everything goes quiet. All we could hear is the crinkling of the Mylar and people going ‘Ooh, ooh.’”

    Hunting gamma rays

    Next up was COSI, a wide-field gamma-ray telescope that studies radiation blasted toward Earth by the most energetic or extreme environments in the universe, such as gamma-ray bursts, pulsars and nuclear decay from supernova remnants. Because gamma rays don’t make it through the Earth’s atmosphere, the telescope must rise above it. Pointed out to space, it can survey 25 percent of the sky at one time for sources of gamma-ray emissions and help detect where these high-energy photons come from. Researchers hope to use its images to learn more about the life and death of stars or the mysterious source of positrons in our galaxy.

    Testing gamma ray telescopes like COSI on balloons can help scientists develop technologies that can eventually be used on satellites. The recent COSI launch was the first to use a new ultra-long-duration balloon design in hopes of getting 100 days worth of data.

    COSI was launch-ready at the same time as ANITA but waited for it to go up before preparing to do the same. They also experienced several attempts called off due to weather.

    4
    COSI’s super pressure balloon is finally released from the spool and takes flight. Photo by: Jeffrey Filippini, SPIDER

    “For nine days in a row, we showed up and did all the prep work,” only to abandon the efforts, Kierans says. On one attempt they got as far as laying out the balloon, which was theoretically the point of no return, before the weather turned against them. They somehow managed to put the 1.5-millimeter-thick, 5000-pound balloon back into the box. “It took 10 riggers over an hour of strenuous, delicate work” to put it back, Kierans wrote on her blog.

    Finally, on December 27 the silvery white balloon was filled with helium and cut loose, taking COSI up to the dark space above the Earth’s atmosphere.

    Jubilation at the successful launch did not last long. Just 40 hours later, a leak in the balloon forced the team to bring it back down. “It will be tough to get science data out of that short flight,” Kierans says. “But we will learn a lot. We made the decision to bring it down where we could get everything back and rebuild.”

    COSI was fully recovered by Kierans, who made three trips by twin otter plane to the Polar Plateau just over the Transantarctic Mountains—known as the “great flat white”—to disassemble and load up the instruments.

    Every inch of their flesh was covered to prevent frostbite. “This was not what I signed up for when I started out in physics,” she says. “But don’t get me wrong—I love it!”
    Big sky, big bang

    Last in line was SPIDER, which uses six telescopes designed to create extremely high-fidelity images of the polarization of the sky at certain wavelengths—or “colors”—of light. Scientists will use the images to search for patterns in the cosmic microwave background, the oldest light ever observed. Such patterns could provide evidence for the period of rapid expansion in the early universe known as cosmic inflation.

    Rising 118,000 feet above the Earth, the 6500-pound SPIDER is able to observe over six times more sky than Earth-based CMB experiments like BICEP.

    “Large sky coverage is the best way to be able to say whether or not the signal appears the same no matter where you look,” explains Jones, SPIDER lead.

    With just days remaining in the launch window after the COSI launch, SPIDER took advantage of a good patch of weather on the last possible day—New Year’s Eve in the US.

    5
    SPIDER reflects its first rays of Antarctic sun with its Mylar sun shields after being rolled out of the bay. Photo by: Zigmund Kermish, SPIDER

    The team started out at 4 a.m. with what seemed like perfect weather, but the winds higher up were too fast and the launch was put on hold for about five hours. Eventually the winds died down and SPIDER was back on track to fly.

    “The launch, in particular the final few minutes once the balloon filled and released, represents the culmination of over eight years of work. It is a thrill. At the same time it is truly frightening,” Jones says.

    Princeton University graduate student Anne Gambrel left this note on the experiment’s “SPIDER on the Ice” blog: “Over the next couple of hours, we all huddled around our computers, and as each subsystem came online, working as designed, we all cheered. By 9 p.m., we were at float altitude and nothing had gone seriously wrong. I went home and slept like a rock as others got all of the details sorted and started taking data on the CMB.”

    Around and around she goes

    During the first 24 hours after their launch, the ANITA team constantly observed and tuned the instruments from the base. “There were six of us rotating in and out of the controls, while others were sleeping in cardboard boxes next to commanders,” Schoorlemmer says.

    The balloons are tracked in their circular flight around the continent, watched carefully for the optimal time to call them back to Earth.

    “Once the balloon is launched, you only have historical record to guide your intuition about where it will go,” Jones says. “No one really knows.”

    ANITA was up in the air for 22 days and 9 hours and was able to collect about twice the data of the experiment’s last polar flight.

    The instruments came down near the Australian Antarctic Station on January 9. “The Australians volunteered their services in recovering the instruments. They will go on a vessel up to Hobart and be picked up by the team in spring,” Miki says.

    SPIDER flew for about 17 days, generating approximately 85 GB of data each day, mainly from snapshots taken at about 120 images per second.

    6
    This map shows SPIDER’s flight path and final resting place. Courtesy of: John Ruhl, SPIDER

    “It’s a daunting analysis task,” Jones says. But his team will eventually combine the data to make an image of the southern hemisphere representing about 10 percent of the full sky.

    SPIDER was brought down on January 17, 1500 miles from launch location “before it could go over the water and possibly not come back,” Jones says.

    The SPIDER team received assistance from the British Antarctic Survey in recovering the data. “Our experiment weighed roughly 6200 pounds, and we got back about 180,” Jones says. The rest, including the science cameras and most electronics, will remain on the West Antarctic plateau over the southern hemisphere winter.
    Other discoveries

    Finally arriving in New Zealand post-recovery, a few of the scientists went to the botanical gardens to lie on the grass.

    “To be able to walk barefoot in it!” Miki says. “I remember landing at 6 o’clock in the morning, walking out of the airport and actually smelling plants and the rain.”

    While the landscape, the science, the instruments, engineering and logistics of such balloon experiments are impressive, the Antarctic researchers were just as taken with the stalwart souls that make them happen.

    “The biggest surprise for me was the people,” Kierans says. “The contractors who work at McMurdo devote half the year to be in the harshest of continents, and they are some of the most interesting people I’ve ever met.”

    Miki concurs. “You’d be surprised who you might find working as support staff there. There was a lawyer taking a break from law; PhDs driving dozers. Some are just out of college and others are seasoned Antarctic veterans.”

    The staff is as friendly as they are professional, Miki says. “They’ll invite ‘beakers’ (what they call scientists) to parties, knitting circles, hikes, etc. With a peak population of over 900 people living in close quarters, getting along is essential.”
    Miki also reflected on the strong friendships made: “Maybe it’s the 24 hours of sunlight, living in close proximity, minimal privacy, long work hours, the desolation in which we are all immersed. Maybe it’s just that the ice attracts amazing, brilliant, talented people from around the world.”

    For Jones, the commitment such adventure-ready researchers show to their work goes above and beyond.

    “We were always supportive, always competitive, sometimes strained, sometimes ecstatic,” he says. “It’s an honor to be able to work with such talented people who are selflessly devoted to learning more about how Nature works at a fundamental level.”

    8
    Looking down on McMurdo Station and McMurdo Sound from Observation Hill. Clio Sleator, COSI

    8
    COSI team members Alex Lowell, and Clio Sleator and Christian Miki from ANITA watch the launch of COSI from a distance required by safety regulations. Jeffrey Filippini, SPIDER

    9
    Just minutes after COSI was launched, the instrument is barely visible. The balloon hasn’t yet expanded to its full size, which happens when it reaches lower pressures at float altitudes. The final shape is more like a pumpkin. Jeffrey Filippini, SPIDER

    10
    The SPIDER parachute is prepared for launch. Jeffrey Filippini, SPIDER

    11
    SPIDER team members inspect waveplates that rotate the polarization of the light that enters the telescopes. Anne Gambrel, SPIDER

    12
    SPIDER generated about 85 GB of data each day of its flight. Anne Gambrel, SPIDER

    123
    SPIDER landed right side up and then fell on its back about 1500 miles from where it launched. Sam Burrell, British Antarctic Survey

    14
    ANITA waits on the “dance floor,” where GPS and communication systems are tested. Harm Schoorlemmer, ANITA

    15
    The ANITA team took the appearance of this Emperor penguin on the edge of the launch pad as a “blessing from the Antarctic gods.” Christian Miki, ANITA

    16
    ANITA’s balloon is ready to take the experiment into the big blue during launch. Harm Schoorlemmer, ANITA

    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 1:05 pm on April 30, 2015 Permalink | Reply
    Tags: , , , , Symmetry Magazine   

    From Symmetry: “DECam’s far-out forays” 

    Symmetry

    April 30, 2015
    Liz Kruesi

    1
    Photo by Reidar Hahn, Fermilab

    The Dark Energy Camera does even more than its name would lead you to believe.

    The Dark Energy Survey, which studies the accelerating expansion of our universe, uses one of the most sensitive observing tools that astronomers have: the Dark Energy Camera.

    Built at Fermi National Accelerator Laboratory and situated on the Victor Blanco 4-meter telescope in Chile, the camera spends 30 percent of each year collecting light from clusters of galaxies for DES.

    CTIO Victor M Blanco 4m Telescope
    CTIO Victor M Blanco 4m Telescope interior
    CTIO Victor Blanco 4-meter telescope

    Another chunk of time goes to engineering and upgrades. The remaining one-third is split up among dozens of other observing projects.

    A recent symmetry article looked at some of those projects—the ones that are studying objects within our solar system. In this follow-up, we give a sampling of how DECam has been used to reach even farther into the universe.

    Studying stellar oddballs

    The sun is a “normal” star, humming along, fusing hydrogen to helium in its core. Most of the stars in the universe produce energy this way. But the cosmos contains a whole collection of stranger stellar objects, such as white dwarfs, brown dwarfs and neutron stars. They also include exploding stars called supernovae. Ten projects use the DECam to study these stellar varieties.

    Armin Rest, an astronomer at the Space Telescope Science Institute in Baltimore, Maryland, leads two of those projects. In the past two years, he has spent 28 nights at the Blanco Telescope looking for supernovae.

    In both projects, Rest looks for light released during stellar explosions that has bounced off dust clouds on its way to our night sky. These “light echoes” preserve information about the blasts that caused them—for example, what type of star exploded and how it exploded.

    “It is as if we have a time machine with which we can travel back in time and take a spectrum with modern instrumentation of an event that was seen on Earth hundreds of years ago,” Rest says.

    DECam’s expertise in taking fast pictures of big areas makes this search much more efficient than it would be with other instruments, Rest says.

    Following streams of stars

    Astronomers have found many streams of stars winding tens of degrees across our sky. These streams are the telltale signs of galaxies interacting with one another. The gravity of one galaxy can rip the stars out of another.

    Yale University’s Ana Bonaca is working on a project that uses DECam to map the stars in one such stream. It extends from Palomar 5, a conglomeration of thousands of stars at the outskirts of our galaxy. Palomar 5 is one of the lowest-mass objects being torn apart by the Milky Way, “which means that its streams are very narrow and preserve a better record of past interactions,” Bonaca says.

    2
    Palomar 5

    Scientists are hoping to tease out of these observations information about dark matter, which accounts for some 80 to 90 percent of our galaxy’s mass.

    Scientists expect that in a narrow stellar stream, clumps of dark matter will create density variations. If you can map the density variations in such a stream, you can learn how the dark matter is distributed. This is where DECam’s strength comes in: The sensitive instrument collects light from deep imaging across large fields speckled with long, narrow stellar streams.

    Ten other projects are using the instrument for similar research.

    Bonaca and colleagues expect to publish their findings later this year. “Our preliminary maps of the Palomar 5 stream show tantalizing evidence for density variations along the stream,” she says.

    Digging for galaxies

    Our galaxy is just one of at least 100 billion galaxies in the universe. Those other galaxies are the focus of eight projects using the Dark Energy Camera.

    The DECam Legacy Survey, for one, is currently imaging all of the galaxies in 6700 square degrees of sky. The plan, says David Schlegel of the Lawrence Berkeley National Laboratory, is to combine the information gathered from DECam and two telescopes located at Arizona’s Kitt Peak National Observatory with the images, spectral data and distance measurements collected via the long-running Sloan Digital Sky Survey.

    “The combination of the Legacy Survey imaging plus SDSS spectroscopy will be used for studying the evolution of galaxies, the halo of our Milky Way and other things we’ve likely not thought of yet,” Schlegel says.

    SDSS Telescope
    SDSS Telescope at Apache Moint, NM, USA

    The other goal of the survey is to identify some 30 million targets to study with the Dark Energy Spectroscopic Instrument [DESI}, a recently approved instrument that will be installed on the Mayall 4-meter telescope at Kitt Peak.

    NOAO Mayall 4 m telescope exterior
    NOAO Mayall 4 m telescope interior
    Mayall 4-meter telescope

    Dark Energy Spectroscopic Instrument
    DESI

    Members of the Legacy Survey team have been releasing their observations nearly immediately to other researchers and the public. They have much more observing time ahead of them: In total, the project was awarded 65 nights on the Blanco telescope and DECam. So far they’ve used only 22.

    Weighing the clusters

    Most of the galaxies in our universe are gathered in groups and clusters, drawn together by the gravity of the clumps of dark matter in which they formed. Scientists are using DECam to study how matter (including dark matter) is distributed within clusters holding hundreds to thousands of galaxies.

    When you observe a galaxy cluster, you also collect light from objects that lie behind that cluster. In the same way an old, imperfect window warps the light from a streetlamp, a cluster’s galaxies, gas, and dark matter shear and stretch any background light that passes through. Astronomers analyze this bending of light from background galaxies, an effect called “gravitational lensing,” to map the mass distribution of a galaxy cluster and even measure its total mass.

    Seven projects use the DECam for such studies. Ian Dell’Antonio of Brown University leads one of them. He and colleagues study the 10 largest galaxy clusters that fit within the DECam field of view; all of them are between about 500 million and 1.4 billion light-years from Earth.

    The researchers are about halfway through their dozen observing nights. They have so far differentiated between gravitational lensing by galaxy cluster Abell 3128 and gravitational lensing by another background cluster. They estimate the mass of Abell 3128 is about 1000 trillion times the mass of our sun, and they have identified several clumps of dark matter, Dell’Antonio says.

    The Dark Energy Camera’s large field of view is crucial to this research, but so is the camera’s design, Dell’Antonio says. “DECam was designed to have an unusually uniform focus across the field of view and with special detectors to keep the camera in focus throughout the night. Put all these things together, and you’ve got an excellent camera for gravitational lensing studies.”

    And, it seems, for just about any other type of astronomical imaging scientists can think of.

    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 12:03 pm on April 29, 2015 Permalink | Reply
    Tags: , , , Symmetry Magazine   

    From Symmetry: “Natural SUSY’s last stand” 

    Symmetry

    April 29, 2015
    Mike Ross

    1
    Photo by Claudia Marcelloni De Oliveira, CERN

    Either Supersymmetry will be found in the next years of research at the Large Hadron Collider, or it isn’t exactly what theorists hoped it was.

    One of the big questions scientists are asking with experiments at the Large Hadron Collider is this: Does every fundamental particle we know about have a hidden partner that we have yet to meet?

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

    A popular set of theories predict that they do.

    The first run of the LHC came and went without any of these partner particles turning up. But a recent paper shows that the real test of the theories that predict their existence could happen during the next run, when particles will collide at higher energies than ever before.

    These theoretical partner particles come from the idea of Supersymmetry, or SUSY, a mathematical framework developed over the past 40 years that could answers questions such as: Are all of the forces we know just parts of a single, unified force? How is the Higgs boson so light? What is dark matter? Is the world made up of the tiny, vibrating strings described by string theory?

    A key aspect of SUSY is that each of the dozens of particles in the Standard Model of particle physics must have a partner, called a superparticle or sparticle.

    3
    Standard Model of Particle Physics. The diagram shows the elementary particles of the Standard Model (the Higgs boson, the three generations of quarks and leptons, and the gauge bosons), including their names, masses, spins, charges, chiralities, and interactions with the strong, weak and electromagnetic forces. It also depicts the crucial role of the Higgs boson in electroweak symmetry breaking, and shows how the properties of the various particles differ in the (high-energy) symmetric phase (top) and the (low-energy) broken-symmetry phase (bottom).

    Supersymmetry standard model
    Standard Model of Supersymmetry

    Scientists think all of these sparticles must ultimately decay into a light, stable particle. If they are light enough, supersymmetric particles that interact through the strong force, such as supersymmetric quarks (squarks) or supersymmetric gluons (gluinos), could be produced at large rates at the LHC.

    There are many different manifestations of Supersymmetry, explains theorist JoAnne Hewett of SLAC National Accelerator Laboratory. A subset of them are known as “natural” theories. That is, they could answer many of the questions above. Their lightest sparticle could be the dark matter particle. The math could work out for all of the forces to have come from a single origin. They could help explain the mass of the Higgs boson.

    Data from the LHC’s first run, from 2010 to 2013, snuffed out any hope that the simplest natural version of SUSY exists.

    “But, there are millions of possible models consistent with natural Supersymmetry that have not been explored,” says Hewett’s advisee, Stanford graduate student Matthew Cahill-Rowley.

    According to a paper they worked on together with two other physicists, the second run of the LHC will investigate nearly all of them.

    Supersymmetry is enormously complex. Even its minimal form involves more than 100 independent parameters. To deal with this, theorists have over the years proposed several higher-level conditions that simplify the theory and reduce the number of parameters. These theories can predict ranges of possible masses for sparticles that might turn up at the LHC.

    2
    Courtesy of: JoAnne Hewett, SLAC

    The figure above shows a plot of some 300,000 more complex SUSY models, identified by their squark and gluino masses on the vertical and horizontal axes, respectively. Colors indicate the fraction that have already been excluded by experiments at the LHC. Darker colors indicate a higher fraction excluded. Regions that are black have been totally ruled out.

    Any points lying below and to the left of the dashed white line represent models that, in SUSY’s most simplified version, are excluded by the LHC.

    3
    Courtesy of: JoAnne Hewett, SLAC

    A second image shows which regions can be discovered or ruled out in the second run of the LHC. Almost every natural SUSY theory falls into that category.

    SUSY may be too complicated to ever truly rule out. But if it doesn’t turn up at the LHC in the next run, it’s not quite the SUSY scientists were looking for.

    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 3:10 pm on April 28, 2015 Permalink | Reply
    Tags: , , , Symmetry Magazine   

    From Symmetry: “AMS results create cosmic ray puzzle” 

    Symmetry

    April 15, 2015
    Sarah Charley

    1
    Courtesy of NASA

    New results from the Alpha Magnetic Spectrometer experiment defy our current understanding of cosmic rays.

    New results from the Alpha Magnetic Spectrometer experiment disagree with current models that describe the origin and movement of the high-energy particles called cosmic rays.

    These deviations from the predictions might be caused by dark matter, a form of matter that neither emits nor absorbs light. But, according to Mike Capell, a senior researcher at the Massachusetts Institute of Technology working on the AMS experiment, it’s too soon to tell.

    “It’s a real head scratcher,” Capell says. “We cannot say we are seeing dark matter, but we are seeing results that cannot be explained by the conventional wisdom about where cosmic rays come from and how they get here. All we can say right now is that our results are consistently confusing.”

    The AMS experiment is located on the International Space Station and consists of several layers of sensitive detectors that record the type, energy, momentum and charge of cosmic rays. One of AMS’s scientific goals is to search for signs of dark matter.

    Dark matter is almost completely invisible—except for the gravitational pull it exerts on galaxies scattered throughout the visible universe. Scientists suspect that dark matter is about five times as prevalent as regular matter, but so far have observed it only indirectly.

    If dark matter particles collide with one another, they could produce offspring such as protons, electrons, antiprotons and positrons. These new particles would look and act like the cosmic rays that AMS usually detects, but they would appear at higher energies and with different relative abundances than the standard cosmological models forecast.

    “The conventional models predict that at higher energies, the amount of antimatter cosmic rays will decrease faster than the amount of matter cosmic rays,” Capell says. “But because dark matter is its own antiparticle, when two dark matter particles collide, they are just as likely to produce matter particles as they are to produce antimatter particles, so we would see an excess of antiparticles.”

    This new result compares the ratio of antiprotons to protons across a wide energy range and finds that this proportion does not drop down at higher energies as predicted, but stays almost constant. The scientists also found that the momentum-to-charge ratio for protons and helium nuclei is higher than predicted at greater energies.

    “These new results are very exciting,” says CERN theorist John Ellis. “They’re much more precise than previous data and they are really going to enable us to pin down our models of antiproton and proton production in the cosmos.”

    In 2013 and 2014 AMS found a similar result for the proportion of positrons to electrons—with a steep climb in the relative abundance of positrons at about 8 billion electronvolts followed by the possible start of a slow decline around 275 billion electronvolts. Those results could be explained by pulsars spitting out more positrons than expected or accelerating supernovae remnants, Capell says.

    “But antiprotons are so much heavier than positrons and electrons that they can’t be generated in pulsars,” he says. “Likewise, supernova remnants would not propagate antiprotons in the way we are observing.”

    If this antimatter excess is the result of colliding dark matter particles, physicists should see a definitive bump in the relative abundance of antimatter particles with a particular energy followed by a decline back to the predicted value. Thus far, AMS has not collected enough data to see this full picture.

    “This is an important new piece of the puzzle,” Capell says. “It’s like looking at the world with a really good new microscope—if you take a careful look, you might find all sort of things that you don’t expect.”

    Theorists are now left with the task of developing better models that can explain AMS’s unexpected results. “I think AMS’s data is taking the whole analysis of cosmic rays in this energy range to a whole new level,” Ellis says. “It’s revolutionizing the field.”

    See the full article here.

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    Symmetry is a joint Fermilab/SLAC publication.


     
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