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  • richardmitnick 12:30 pm on June 7, 2016 Permalink | Reply
    Tags: , ,   

    From Symmetry: “The neutrino cocktail” 

    Symmetry Mag


    Laura Dattaro

    Neutrino flavours. Kamioka Observatory/ICRR/University of Tokyo

    Neutrinos are a puzzling mixture of three flavors and three masses. Scientists want to measure it down to the last drop.

    For a neutrino, travel is truly life-changing. When one of the tiny particles ends its 500-mile journey from Fermilab’s neutrino source to the NOvA experiment’s detector in Minnesota, it may arrive in an entirely different state than when it started.

    FNAL NOvA experiment
    FNAL NOvA experiment

    The particles, which zip through most matter without any interaction at all, can change from one of the three known neutrino varieties into another, a phenomenon known as oscillation.

    Due to quantum mechanics, a traveling neutrino is actually in several different states at once. This is a result of a property known as mixing, and though it sounds esoteric, it’s necessary for some of the most important reactions in the universe—and studying it may hold the key to one of the biggest puzzles in particle physics.

    Though mixing happens with several types of particles, physicists are focusing on lepton mixing, which occurs in one kind of lepton, the elusive neutrino. There are three known types, or flavors, of neutrinos—electron, muon and tau—and also three mass types, or mass states. But unlike objects in our everyday world, where an apple is always heavier than a grape, neutrino mass states and flavors do not have a one-to-one correspondence.

    “When we say there’s mixing between the masses and the flavors, what we mean is that the electron flavor is not only one mass of neutrino,” says Kevin McFarland, a physics professor at Rochester University and co-spokesperson for the MINERvA neutrino experiment at the Department of Energy’s Fermilab.


    At any given point in time, a neutrino is some fraction of all three different mass states, adding up to 1. There is more overlap between some flavors and some mass states. When neutrinos are in a state of definite mass, scientists say they’re in their mass eigenstates. Physicists use the term mixing angle to describe this overlap. A small mixing angle means there is little overlap, while maximum mixing angle describes a situation where the parameters are as evenly mixed as possible.

    Mixing angles have constant values, and physicists don’t know why those particular values are found in nature.

    “This is given by nature,” says Patrick Huber, a theoretical physicist at Virginia Tech. “We very much would like to understand why these numbers are what they are. There are theories out there to try to explain them, but we really don’t know where this is coming from.”

    In order to find out, physicists need large experiments where they can control the creation of neutrinos and study their interactions in a detector. In 2011, the Daya Bay experiment in China began studying antineutrinos produced from nuclear power plants, which generate tens of megawatts of power in antineutrinos.

    Daya Bay, China
    Daya Bay, China

    That’s an astonishing number; for comparison, beams of neutrinos created at labs are in the kilowatt range. Just a year later, scientists working there nailed down one of the mixing angles, known as theta13 (pronounced theta one three).

    The discovery was a crucial one, confirming that all mixing angles are greater than zero. That property is necessary for physicists to begin using neutrino mixing as a probe for one of the greatest mysteries of the universe: why there is any matter at all.

    According to the Standard Model of cosmology, the Big Bang should have created equal amounts of matter and antimatter. Because the two annihilate each other upon contact, the fact that any matter exists at all shows that the balance somehow tipped in favor of matter. This violates a rule known as charge-parity symmetry, or CP symmetry.

    Standard Model of Cosmology Inflation Lambda Model
    Standard Model of Cosmology Inflation Lambda Model

    One way to study CP violation is to look for instances where a matter particle behaves differently than its antimatter counterpart. Physicists are looking for a specific value in a mixing parameter, known as a complex phase, in neutrino mixing, which would be evidence of CP violation in neutrinos. And the Daya Bay result paved the way.

    “Now we know, OK, we have a nonzero value for all mixing angles,” says Kam Biu-Luk, spokesperson for the Daya Bay collaboration. “As a result, we know we have a chance to design a new experiment to go after CP violation.”

    Information collected from Daya Bay, as well as ongoing neutrino experiments such as NOvA at Fermilab and T2K in Japan, will be used to help untangle the data from the upcoming international Deep Underground Neutrino Experiment (DUNE).

    T2K map


    This will be the largest accelerator-based neutrino experiment yet, sending the particles on an 800-mile odyssey into massive detectors filled with 70,000 total tons of liquid argon. The hope is that the experiment will yield precise data about the complex phase, revealing the mechanism that allowed matter to flourish.

    “Neutrino oscillation is in a sense new physics, but now we’re looking for new physics inside of that,” Huber says. “In a precision experiment like DUNE we’ll have the ability to test for these extra things beyond only oscillations.”

    Neutrinos are not the only particles that exhibit mixing. Building blocks called quarks exhibit the property too.

    Physicists don’t yet know if mixing is an inherent property of all particles. But from what they know so far, it’s clear that mixing is fundamental to powering the universe.

    “Without this mixing, without these reactions, there are all sorts of critical processes in the universe that just wouldn’t happen,” McFarland says. “It seems nature likes to have that happen. And we don’t know why.”

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 8:21 am on June 3, 2016 Permalink | Reply
    Tags: , , , Searching for dark matter using IceCube cascades   

    From IceCube: “Searching for dark matter using IceCube cascades” 

    IceCube South Pole Neutrino Observatory

    02 Jun 2016
    Sílvia Bravo

    IceCube searches for dark matter in the galactic center and halo have shown competitive results with other neutrino telescopes. IceCube has also searched for dark matter annihilations in the Sun that resulted in the world’s best limits for masses of around 100-200 GeV.

    The IceCube Collaboration presents a new search for dark matter annihilation from the galactic center and halo using cascade events, i.e., particle showers created by the interaction of electron and tau neutrinos and Z-boson mediated muon neutrinos. Scientists searched for interactions starting in the DeepCore subarray between May 2011 and May 2012 and found no neutrino excess with respect to the background-only hypothesis, which allowed them to derive upper limits on dark matter candidates with masses between 30 GeV and 10 TeV. These results have been submitted today to the European Physical Journal C.

    Comparison of upper limits on the velocity-averaged WIMP self-annihilation cross section versus WIMP mass. This work (IC86 Halo Casc.) is compared to ANTARES and previous IceCube searches with different detector configurations. Also shown are upper limits from gamma-ray searches from dwarf spheroidal galaxies (dSphs) by FermiLAT, MAGIC and VERITAS, as well as a recent limit from the combination of FermiLAT and MAGIC results. The three shaded areas indicate allowed regions if the electron+positron flux excess seen by FermiLAT, H.E.S.S. and the positron excess seen by PAMELA (3 sigma in dark green, 5 sigma in light green and gray area, respectively) would be interpreted as originating from dark-matter annihilations. The natural scale denotes the minimum value of the velocity-averaged cross section needed for WIMPs to be the solution to the dark matter problem as thermal relics. Image: IceCube Collaborartion.

    There are several theoretical models that predict the effects of the self-annihilation of WIMPs (weakly interacting massive particles), the dark matter candidate type tested in this study, in the Milky Way. A search using all neutrino flavors is more sensitive to models in which WIMPs annihilate preferably to leptons, i.e., creating a flux of electron and tau neutrinos. However, all-flavor searches can also test other WIMPs models.

    IceCube researchers have used one year of data to test a new channel for dark matter searches, which resulted not only in an independent measurement but also improved previous IceCube searches for masses above 200 GeV and previous results from other neutrino telescopes ffor masses below 1 TeV. “This is another example of the rich physics possibilities that the DeepCore extension brought to IceCube,” says Carlos Pérez de los Heros, an IceCube researcher at Uppsala University and a corresponding author of this work.

    The study is based on events that start inside the DeepCore subarray, which are selected by using surrounding IceCube strings as a veto region. This selection eliminates most of the atmospheric muon background. By using cascade-like events, the atmospheric neutrino background—made up of only muon neutrinos, which usually show up as a track—is also greatly reduced.

    IceCube results, like those from other neutrino telescopes, are not yet competitive with atmospheric Cherenkov telescopes and gamma-ray satellites.

    Cherenkov Telescope Array, http://www.isdc.unige.ch/cta/
    Cherenkov Telescope Array, http://www.isdc.unige.ch/cta/

    NASA/Fermi Telescope
    NASA/Fermi Telescope


    However, neutrinos provide an alternative way to search for dark matter that is also much less dependent on the underlying dark matter distribution. Thus, IceCube results are more robust, and they also probe channels, e.g., the direct annihilation to neutrinos, that are not available to gamma-based detectors.

    + Info “All-flavour Search for Neutrinos from Dark Matter Annihilations in the Milky Way with IceCube/DeepCore,” The IceCube Collaboration: M.G.Aartsen et al, Submitted to European Physical Journal C, arxiv.org/abs/1606.00209

    See the full article here .

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    ICECUBE neutrino detector
    IceCube is a particle detector at the South Pole that records the interactions of a nearly massless sub-atomic particle called the neutrino. IceCube searches for neutrinos from the most violent astrophysical sources: events like exploding stars, gamma ray bursts, and cataclysmic phenomena involving black holes and neutron stars. The IceCube telescope is a powerful tool to search for dark matter, and could reveal the new physical processes associated with the enigmatic origin of the highest energy particles in nature. In addition, exploring the background of neutrinos produced in the atmosphere, IceCube studies the neutrinos themselves; their energies far exceed those produced by accelerator beams. IceCube is the world’s largest neutrino detector, encompassing a cubic kilometer of ice.

  • richardmitnick 2:20 pm on May 31, 2016 Permalink | Reply
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    From Yale: “PROSPECT experiment will search for sterile neutrinos, thanks to $3M DOE grant” 

    Yale University bloc

    Yale University

    May 31, 2016

    Jim Shelton

    Refueling of the High Flux Isotope Reactor at Oak Ridge National Laboratory (ORNL). Antineutrinos are emitted from the decays of the fission products. (Image by Genevieve Martin/ORNL)

    Buoyed by a $3 million federal grant, a Yale University-led experiment will explore key questions about the elusive particles called neutrinos — and potentially improve the way we monitor and safeguard nuclear reactors in the process.

    The U.S. Department of Energy grant from the Office of High Energy Physics will be used to build a first-of-its-kind, short-distance detection device for the Precision Oscillation and Spectrum Experiment (PROSPECT), a project involving 68 scientists and engineers from 10 universities and four national laboratories.

    The detection instrument will be constructed at Yale’s newly renovated Wright Laboratory and later be deployed at the High Flux Isotope Reactor at Oak Ridge National Laboratory, in Tennessee. The PROSPECT experiment has been in development for more than three years.

    “It’s an excellent marriage of fundamental science and potential applications,” said Karsten Heeger, a Yale physicist, director of Wright Lab, and principal investigator for PROSPECT. “We want to better understand the emission of neutrinos from a reactor and study the fundamental properties of elementary particles. By going very close to a research reactor — less than 10 meters from the reactor core — PROSPECT will have unparalleled sensitivity to study the energy distribution of neutrinos as they leave the reactor.”

    “PROSPECT represents almost four years of dedicated research and development by our team of national laboratories and universities,” said Nathaniel Bowden, co-spokesperson for PROSPECT and a physicist at Lawrence Livermore National Laboratory. “Drawing on our extensive expertise in neutrino physics, liquid scintillator development, and reactor monitoring applications, PROSPECT has a mature, construction-ready system design that will result in a world-leading measurement.”

    PROSPECT collaborators assemble a prototype scintillation detector. (Image courtesy of PROSPECT collaboration)

    A great deal of scientific research is currently focused on neutrinos, which are subatomic particles that move through the universe with almost no mass and no electrical charge. Incredibly difficult to detect, neutrinos’ properties and behavior may hold answers to fundamental questions about the nature of matter in the universe.

    One such property is oscillation — neutrinos’ ability to change among three known types, or “flavors.” The discovery of this process, in 1998, was recognized with the 2015 Nobel Prize in physics and the 2016 Breakthrough Prize. Part of its significance comes from the glimpse it gives scientists into the possible existence of matter beyond the parameters of the Standard Model of Particle Physics.

    One way scientists are studying neutrino oscillation is by detecting neutrinos created within nuclear reactors, such as the Daya Bay Nuclear Power Plant in China.

    Daya Bay, China
    “Daya Bay, China

    The Daya Bay experiment recently found that fewer antineutrinos were being emitted than physicists had predicted. PROSPECT, by moving closer to a reactor core, will try to find out why.

    “Previous neutrino detectors have gone deep underground, to reduce interference from cosmogenic backgrounds,” said PROSPECT co-spokesperson H. Pieter Mumm, of the National Institute of Standards and Technology. “PROSPECT will, for the first time, make a precision measurement of reactor antineutrinos with a detector operating at the Earth’s surface, something never before accomplished. Such a demonstration could open up new opportunities for neutrino physics and nuclear safeguards.”

    The successful operation of a relatively compact neutrino detector on the surface would demonstrate a way to remotely monitor nuclear reactors via the detected neutrino flux.

    PROSPECT also will search for “sterile” neutrinos. These are hypothesized particles — a fourth type of neutrino — that interact outside of the existing parameters of the Standard Model of Particle Physics. Sterile neutrinos would represent a new form of matter and could explain the observed deficit of reactor neutrinos in Daya Bay and other experiments.

    Heeger noted the experiment’s potential, adding, “PROSPECT addresses one of the outstanding puzzles in the field of neutrino physics and has the potential for a paradigm-changing discovery in particle physics.”

    Additional collaborators on PROSPECT include Brookhaven National Laboratory, Drexel University, Georgia Institute of Technology, Illinois Institute of Technology, Le Moyne College, the University of Tennessee-Knoxville, Temple University, the University of Waterloo, the College of William and Mary, and the University of Wisconsin-Madison.

    The High Flux Isotope Reactor at Oak Ridge National Laboratory is operated with funding from the U.S. Department of Energy’s Office of Science, Office of Basic Energy Sciences.

    For Yale and the Wright Lab, PROSPECT also symbolizes a new focus on designing and building instruments for innovative physics experiments in specialized settings — from inside nuclear reactors to the temperature extremes of the South Pole.

    Yale’s PROSPECT team includes Heeger; research scientists Henry Band, James Nikkel, and Tom Wise; postdoctoral researcher Tom Langford; graduate students Danielle Norcini and Jeremy Gaison; and technical staff members Jeff Ashenfelter and Frank Lopez.

    For more information about PROSPECT, visit its website.

    For more information about Wright Laboratory, visit its website.

    See the full article here .

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    Yale University Campus

    Yale University comprises three major academic components: Yale College (the undergraduate program), the Graduate School of Arts and Sciences, and the professional schools. In addition, Yale encompasses a wide array of centers and programs, libraries, museums, and administrative support offices. Approximately 11,250 students attend Yale.

  • richardmitnick 1:27 pm on May 31, 2016 Permalink | Reply
    Tags: 000 meters below, 1000 metres below, , ,   

    From Symmetry: “1,000 meters below” 

    Symmetry Mag

    Rashmi Shivni

    Meet the world’s deepest underground physics facilities.

    A constant shower of energetic subatomic particles rains down on Earth’s surface. Born from cosmic ray interactions in the upper atmosphere, this invisible drizzle creates noisy background radiation that obscures the signatures of new particles or forces that scientists seek. The solution is to move experiments under the best natural umbrella we have: the Earth’s crust.

    Underground facilities, while difficult to build and access, are ideal hubs for observing rare particle interactions. The rock overhead shields experiments from the pesky particle precipitation, preventing things like muons from interfering. For the last few decades, underground physics facilities have laid claim to some of the world’s largest, most complex detection experiments, contributing to important physics discoveries.

    “In the early 1960s, researchers at the Kolar Gold Fields in India and the East Rand Gold Mine in South Africa realized if they go deep enough underground, it might be possible to clearly detect high-energy particles from atmospheric cosmic ray collisions,” says Henry Sobel, a co-US-spokesperson on the Super-Kamiokande experiment at the Kamioka Observatory. “Both groups reported the first observation of atmospheric neutrinos at various depths underground.”

    Even with entire facilities sitting below the surface, extremely sensitive detectors often require additional shielding against stray particles and the small amount of radiation from the rock and equipment. One example is the Sanford Underground Research Facility’s Large Underground Xenon (LUX) experiment, which seeks dark matter particles called WIMPs, or weakly interacting massive particles.

    “Going underground eliminates most of the radioactivity, but not all of it, so we used a 72,000-gallon water shield to keep neutrons and gamma rays out of the LUX experiment,” says Harry Nelson, a LUX researcher and spokesperson for the upcoming LUX-Zeplin experiment at Sanford Lab.

    Scientists at underground facilities around the world—and their creative colleagues closer to the surface—maintain different experiments working toward a common goal: answering questions about the nature of matter and energy. Learn more about the facilities 1000 meters or more below the surface that are digging deep into the secrets of the universe.

    Kamioka Observatory
    1000 meters below, est. 1983

    Super-Kamiokande Detector
    Super-Kamiokande Detector

    Previously known as the Kamioka Underground Observatory, the facility dwells in the Mozumi Mine in Hida, Gifu Prefecture, Japan. Operational or former mines actually make great homes for underground facilities because it is cost-effective to use existing giant holes inside mountains or the earth rather than dig new ones.

    Kamioka’s original focus was on understanding the stability of matter through a search for the spontaneous decay of protons using an experiment called Kamiokande. Since neutrinos are a major background to the search for proton decay, the study of neutrinos also became a major effort for the observatory.

    Now known as the Kamioka Observatory, the facility detects neutrinos coming from supernovae, the sun, our atmosphere and accelerators. In 2015, Takaaki Kajita was awarded the Nobel Prize in physics for the discovery of atmospheric neutrino oscillation by the Super-Kamiokande experiment. The Nobel Prize is shared with the Sudbury Neutrino Observatory in Canada.

    Stawell Underground Physics Laboratory
    1000 meters below, under construction

    SUPL is under construction at the active Stawell Gold Mine in Victoria, Australia. The facility will work in close collaboration with the Gran Sasso National Laboratory in Italy, which made significant strides in dark matter research through a possible detection of WIMPs. SUPL will see whether the amount of dark matter in certain galaxies changes depending on Earth’s position.

    Because Australia is in the Southern Hemisphere and has opposite seasons to Italy, this seasonal dark matter experiment will also test Italy’s results to learn more about WIMPs and dark matter. There are two proposed dark matter experiments for SUPL: SABRE (Sodium-iodide with Active Background REjection) and DRIFT-CYGNUS (Directional Recoil Identification From Tracks – CosmoloGY with NUclear recoilS).

    Boulby Underground Laboratory

    DRIFT-II under construction at Boulby

    1100 meters below, est. 1998

    Inside the operational Boulby Potash and Salt Mine on the northeast coast of England sits the Boulby Lab. It is a multidisciplinary, deep underground science facility operated by the UK’s Science and Technology Facilities Council. The depth and the support infrastructure make the facility well-suited for traditional low-background underground studies such as dark matter searches and cosmic ray experiments. Scientists also study a wide range of sciences beyond physics, for example geology and geophysics, environmental and climate studies, life in extreme environments on Earth, and the development of rover instrumentation for exploration of life beyond Earth.

    The dark matter search currently underway at Boulby is DRIFT-II – a directional dark matter search detector. The lab previously hosted the ZEPLIN-II and III experiments, predecessors to the upcoming LUX-ZEPLIN experiment at Sanford Lab. Boulby still supports the LZ experiment with ultralow-background material activity measurements, which is important to all sensitive dark matter and rare-event studies.

    India-based Neutrino Observatory

    INO, a collaboration of about 25 national institutes and universities hosted by the Tata Institute of Fundamental Research, will primarily be an underground facility for non-accelerator-based high-energy physics. The observatory will focus its study on atmospheric muon neutrinos using a 50-kiloton iron calorimeter to measure certain characteristics of the elusive particles.

    INO will also expand into a more general science facility and host studies in geological, biological and hydrological research. Construction of the INO underground observatory in Pottipuram, Tamil Nadu, India is awaiting approvals by the state government.

    Gran Sasso National Laboratory
    INFN Gran Sasso ICARUS
    1400 meters below, est. 1987

    The Gran Sasso National Laboratory in Italy is the largest underground laboratory in the world. It is a high-energy physics lab that conducts many long-term neutrino, dark matter and nuclear astrophysical experiments.

    The lab’s OPERA experiment is especially noteworthy for detecting the first tau neutrino candidates that emerged (through oscillation) from a muon neutrino beam sent by CERN in 2010. From 2012 to 2015, the experiment at Gran Sasso subsequently announced the detection of the second, third, fourth and fifth tau neutrinos, confirming their initial result.

    Gran Sasso also collaborates with the Department of Energy’s Fermi National Accelerator Laboratory on a short-distance neutrino program. After it is refurbished at CERN, the ICARUS experiment from Gran Sasso will join two other experiments at Fermilab to search for a fourth proposed kind of neutrino, the sterile neutrino.

    Centre for Underground Physics in Pyhäsalmi
    1440 meters below, est. 1997

    The University of Oulu in Finland operates CUPP in Europe’s deepest metal mine—the Pyhäsalmi Mine. As the mine prepares to close by the end of this decade, the local community established Callio Lab (CLab) to rent out space to science and industrial operators, CUPP being one of them. The main level, at 1420 meters, houses all of the equipment, offices and restaurants. It also houses the world’s deepest sauna.

    The facility’s main experiment is EMMA, the Experiment with MultiMuon Array, in Lab 1 at 75 meters.

    EMMA is used to study cosmic rays and high-energy muons that pass through the Earth to better understand atmospheric and cosmic particle interactions. CUPP also conducts some low-background muon flux measurements and radiocarbon research for future liquid scintillators in Lab 2 at 1430 meters.

    Sanford Underground Research Facility
    SURF logo
    Sanford Underground levels
    Sanford Underground Research Facility
    1480 meters below, est. 2011

    Sanford Lab is the deepest underground physics lab in the United States and sits in the former Homestake Gold Mine in the Black Hills of South Dakota. It was the site of Ray Davis’ solar neutrino experiment, which used dry cleaning fluid to count neutrinos from the sun. The experiment found only one-third of the neutrinos expected, the result known as the solar neutrino problem. In 1998, SNO and Kamioka discovered neutrino oscillations, which proved that neutrinos were changing type as they traveled. Davis won the Nobel Prize in physics in 2002.

    The facility now houses the LUX experiment (looking for dark matter), Majorana Demonstrator (researching the properties of neutrinos), and geological, engineering and biological studies. Sanford Lab will also host the Deep Underground Neutrino Experiment, which will use detectors filled with 70,000 tons of liquid argon to study neutrinos sent from Fermilab, 800 miles away.

    Modane Underground Laboratory
    1700 meters below, est. 1982

    Located in Modane, France, and situated in the middle of the Frejús Road Tunnel, the multidisciplinary lab hosts experiments in particle, nuclear and astroparticle physics, environmental sciences, biology and nano- and microelectronics.

    Headed by the French National Center for Scientific Research and the Genoble-Alpes University, Modane Lab’s main fundamental physics activities include SuperNEMO and EDELWEISS, which study neutrino physics and dark matter detection, respectively.

    The lab also hosts international experiments with the Joint Institute for Nuclear Research in Dubna, Russia, and the Czech Technical University in Prague, Czech Republic.

    Baksan Neutrino Observatory
    1750 meters below, est. 1973

    Hidden beneath the Caucasus Mountains and next to the Baksan River, BNO began working as one of the first underground particle physics observatories in the then Soviet Union. Like other underground facilities, BNO wanted to reduce the amount of background radiation as much as possible. The lab’s location is not only underground but also far from nuclear power plants—another source of background noise for experiments.

    BNO’s current neutrino experiments are the Soviet-American Gallium Experiment (SAGE), the Baksan Underground Scintillation Telescope (BUST) and the upcoming Baksan Experiment on Sterile Transitions (BEST). There is also a new search for hypothesized particles called axions, candidates for dark matter.

    Agua Negra Deep Experiment Site
    1750 meters below, proposed

    Situated in the mountains on the border of Chile and Argentina, ANDES will study neutrinos and dark matter, as well as plate tectonics, biology, nuclear astrophysics and the environment. Along with SUPL, it is one of two proposed deep underground labs in the Southern Hemisphere.

    ANDES is an international laboratory, not just a host for international experiments. It will become home to a large neutrino detector and aims to detect supernovae neutrinos and geoneutrinos, complementing results of the Northern Hemisphere labs and experiments. This location is ideal as the site is far from nuclear facilities and extremely deep in the mountains, both of which help reduce background noise.


    2070 meters below, est. 2009

    SNOLAB is the deepest physics facility in North America and operates in a working nickel mine in Ontario, Canada. The entire 5000m2 facility is a class 2000 cleanroom with fewer than 2000 particles per cubic foot. Everyone who enters the lab must shower on the way in and put on a clean set of special cleanroom clothes.

    SNOLAB conducts highly sensitive experiments for research on dark matter and neutrinos. Among them are DEAP-3600, PICO, HALO, MiniCLEAN and SNO+. Scientists also plan to install the next generation of a cryogenic dark matter search, SuperCDMS, in the lab once testing is complete.

    Late last year, Arthur McDonald was awarded the Nobel Prize in physics for the discovery of neutrino oscillation made in 1998 at the Sudbury Neutrino Observatory, the predecessor of SNOLAB. The Nobel Prize is shared with the Kamioka Observatory in Japan for their Super-K neutrino experiment.

    China Jinping Underground Laboratory
    2400 meters below, est. 2010

    CJPL is the deepest physics facility in the world, tucked inside the Jinping Mountain in the Sichuan province in southwest China. The site is ideal for its low cosmic-ray muon flux, which means the facility has far less noise from background radiation than many other underground facilities. And because the facility is built under a mountain, there is horizontal access (for things like vehicles) rather than vertical access (through a mine shaft).

    Two experiments housed at the facility are trying to directly detect dark matter: the China Dark Matter Experiment (CDEX) and PandaX. CJPL will also observe neutrinos from different sources, such as the sun, Earth, atmosphere, supernova bursts and potentially dark matter annihilations, in hopes of better understanding the elusive particles’ properties. In the coming months, an astronuclear physics study and a one-ton prototype of a neutrino detector will move into CJPL-II.

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 6:54 pm on May 29, 2016 Permalink | Reply
    Tags: "Physics: Invest in neutrino astronomy", , ,   

    From Nature: “Physics: Invest in neutrino astronomy” 

    Nature Mag

    25 May 2016
    Spencer Klein

    Spencer Klein calls for bigger telescope arrays to catch particles from the most energetic places in the Universe.

    An optical sensor begins its 2,500-metre journey down a borehole to become part of the IceCube neutrino detector in Antarctica. Blaine Gudbjartsson, IceCube/NSF, U Wisconsin

    Neutrino astronomy is poised for breakthroughs. Since 2010, the IceCube experiment in Antarctica — 5,160 basketball-sized optical sensors spread through a cubic kilometre of ice — has detected a few score energetic neutrinos from deep space. Although these are exciting finds that raise many questions, this paltry number of extraterrestrial particles is too few to tell their origins or to test fundamental physics. To learn more will require a new generation of neutrino observatories.

    U Wisconsin ICECUBE neutrino detector
    IceCube neutrino detector interior
    “U Wisconsin ICECUBE neutrino detector at the South Pole

    Neutrinos are subatomic particles that interact only weakly, so they can travel far through space and even penetrate Earth. IceCube detects highly energetic neutrinos, with energies above about 100 gigaelectronvolts (1 GeV is 109 electronvolts, roughly the rest mass of a proton). These are produced when cosmic rays — high-energy protons or heavier nuclei from space — interact with matter or light. This might happen either at the sites where the cosmic rays are produced, or later when the rays enter Earth’s atmosphere and collide with gas molecules, releasing a cascade of elementary particles. Neutrinos produced in the atmosphere are hundreds of times more numerous than the astrophysical ones.

    Many physics puzzles stand to be solved by neutrino astronomy1. One is the origin of the ultra-high-energy cosmic rays. In 1962, the Volcano Ranch array in New Mexico detected an enormous shower of particles coming from one cosmic ray smashing into the upper atmosphere with a kinetic energy of above 1011 GeV — equivalent to the energy of a tennis serve packed into a single atomic nucleus.

    Tens more such events have been detected since. But 50 years on, physicists still have no idea how nature accelerates elementary particles to such high energies. The energies far exceed the range of Earth-bound accelerators such as the Large Hadron Collider (LHC) near Geneva, Switzerland; mimicking them would require a ring the size of Earth’s orbit around the Sun.

    There is also much we need to find out about neutrinos themselves — their accurate masses, how they transform from one type (flavour) into another, and whether other predicted forms (such as ‘sterile’ neutrinos) exist. Neutrinos could also help to find dark matter, invisible material that has a part in controlling the motions of stars, gas and galaxies. Decaying or annihilating dark matter could produce energetic neutrinos that would be visible to neutrino telescopes.

    The downside of neutrinos’ weak interactions is that an enormous detector is required to catch enough particles to distinguish the few space-borne ones from the many more originating from Earth’s atmosphere. IceCube is the largest neutrino-detection array in operation but it is too small, and further data collection is probably too slow to yield major breakthroughs in the next decade.

    Bigger neutrino observatories, with volumes that are 10–100 times greater than that of IceCube, are essential to explore the most energetic processes in the Universe. Determining the masses of different types of neutrino and studying how neutrinos interact with matter within Earth could distinguish or rule out some models of extra spatial dimensions and address key concerns for high-energy nuclear physics such as the density of gluons (which mediate forces between quarks) in heavy nuclei.

    Designs for neutrino telescopes are on the drawing board and could be up and running in five to ten years — if the astro-, particle- and nuclear-physics communities can come together and coordinate funding. A complementary set of several neutrino observatories would test physics at energies beyond the LHC’s at a fraction of the cost — tens to hundreds of millions, rather than tens of billions, of dollars.

    More questions than answers

    IceCube, which became fully operational in Antarctica in 2010 (and with which I have been involved since 2004), detects blue light: Cherenkov radiation that is emitted by the charged particles produced when energetic neutrinos interact with atomic nuclei in water or ice. Computers comb through the data to look for interactions — long tracks or radial cascades of particles emanating from a point (see ‘Neutrino observatory‘). IceCube sees more than 50,000 neutrino candidates per year. Fewer than 1% are from space.


    There are several ways to distinguish cosmic from atmospheric neutrinos. The highest-energy events are more likely to be astrophysical. Atmospheric neutrinos are accompanied by particle showers, which can be seen with detectors on the ice surface. Muons, short-lived subatomic particles produced in these showers, are 500,000 times more numerous than neutrinos, and can also penetrate the ice; so signals accompanied by muons travelling downwards from the sky are probably atmospheric in origin. That leaves extremely energetic events with light trails that are travelling upwards (through Earth) or that originate from a point within the array volume as potentially astrophysical in origin.

    Since 2010, IceCube has seen about 60 astrophysical neutrino candidates2, 3. Other experiments are too small to detect any such neutrinos; these include ANTARES, an array of strands of detectors anchored to the floor of the Mediterranean Sea off Marseilles, France, and another similar array in Lake Baikal, Russia. Their detection rate of astrophysical neutrinos is as high as could be expected — if there were more neutrinos, they would drain the cosmic rays of most of their energy4. So finding the astrophysical sources of the neutrinos should be easy. The fact that we have not is a growing puzzle.

    Setup view of Antares neutrino detector.
    28 August 2009
    François Montanet

    So far, neutrinos do not seem to be coming from particular sites on the sky5, although several groups have suggested a weak link to the plane of the Milky Way. And analyses disfavour the many sites once thought likely to have accelerated energetic cosmic rays and neutrinos, including γ-ray bursts (GRBs) and active galactic nuclei (AGNs).

    GRBs are short bursts of powerful γ-rays that are picked up by satellites. They are thought to emanate either from a black hole coalescing with a neutron star or another black hole (producing a rapid burst lasting less than 2 seconds); or from the slower collapse of supermassive stars (bursts lasting seconds or minutes). Particles are accelerated by the implosion or explosion. Of more than 800 GRBs examined by IceCube scientists, none was accompanied by a burst of neutrinos, implying that GRBs can produce at most 1% of the astrophysical neutrinos seen by IceCube6.

    AGNs are galaxies that at their centres have supermassive black holes accreting gas. Particles may be accelerated to relativistic speeds in jets of material that are blasted out from the black hole. But IceCube sees no associations between energetic neutrinos and active galaxies with jets that point towards Earth, suggesting that active galaxies explain at most 30% of the neutrinos7.

    Other unlikely sources include starburst galaxies, which contain dusty regions of intense star formation that are riddled by supernova explosions8; magnetars, which are neutron stars surrounded by strong magnetic fields that expel powerful bursts of neutrinos for a few days (these should have been seen by IceCube); and supernova remnants, whose magnetic fields are too weak to explain the most energetic neutrinos9, even though they are believed to be responsible for most lower-energy (up to about 1016 eV) cosmic rays seen in the Galaxy.

    More exotic possibilities remain untested: as-yet-unseen supermassive dark-matter particles that annihilate and produce energetic neutrinos; or the decay of cosmic ‘strings’, discontinuities in space-time left over from the Big Bang.

    IceCube has also tested alternative physics theories. It has constrained how neutrinos ‘oscillate’ from one flavour to another and set limits on the properties of dark matter and on the constituents of high-energy air showers.

    A string of optical modules of the KM3NeT array. Paolo Piattelli

    Next generation

    There are two ways forward: enlarge the current optical arrays to collect more neutrinos, or find other strategies for isolating the highest energy neutrinos that must be cosmic in origin. These approaches cover different energy ranges and thus complementary physics. Both merit support.

    First, larger optical Cherenkov telescopes could be deployed in ice or a lake, sea or ocean — similar to IceCube or ANTARES but with more efficient optical sensors and cheaper technology.

    Cherenkov Telescope Array
    Cherenkov Telescope Array

    Several groups have developed advanced designs for these concepts but lack funding. The detectors could be constructed and operational by the early 2020s. For IceCube, technical improvements would include more efficient drilling technology and sensors that fit in narrower bore holes, which are cheaper to drill.

    Different sites offer different benefits. Antarctica offers a large expanse of clear, compacted ice and infrastructure. But arrays in the Northern Hemisphere, for example, in the Mediterranean, can more directly observe astrophysical neutrinos from the centre of the Galaxy that have passed through Earth, without having to reject down-going atmospheric neutrinos, as a southern site would have to. The absence of potassium-40 and the lower bioluminescence in fresh water (which contribute to background light and can confuse the reconstruction of particle tracks), and the presence of a frozen surface during the winter, simplifying construction, make Lake Baikal an attractive site.

    The second approach requires catching neutrinos with energies above 108 GeV. Neutrinos this energetic are rare — IceCube has seen none — and an array of at least 100 km3 would be needed to capture enough events. Because optical Cherenkov light travels only tens of metres in ice or water, covering such a volume would require millions of sensors and would be expensive.

    A more practical way is to search for radio emissions from neutrino interactions with the Antarctic ice sheet. When the neutrinos hit an atomic nucleus in the ice, they create a shower of charged particles that give off radio waves in the 50 megahertz to 1 gigahertz frequency range, as well as visible light. Radio waves can propagate for kilometres through ice. So an radio-sensing array over 100 km3 could be more sparsely populated with instruments, with roughly one station per cubic kilometre. The radio pulses from neutrinos with energies above 108 GeV should be strong enough for antennas in the ice to pick up. Two international groups are building prototypes and have sought funding to expand (I am involved with one, ARIANNA).

    Development of hexagonal radio array for the ARIANNA ultra-high-energy neutrino detector. University of California Irvine, Dr. Steven Barwick (Principal Investigator)

    Green light

    With a range of affordable, next-generation designs shovel-ready, decisions about design priorities need to be made and grants deployed. The main obstacles are limited national science budgets and funding-agency silos. Neutrino astronomy falls between the particle-, nuclear- and astrophysics communities, which need to pool resources to realize the promise of these techniques.

    First, one or both of the successors to IceCube and ANTARES should be funded and built. An upgraded IceCube experiment (IceCub-Gen2) and the Cubic Kilometre Neutrino Telescope (KM3NeT), a proposed European project, are both strong candidates (see ‘Next-generation neutrino telescopes’). If necessary, the teams coordinating IceCube, KM3NeT and the Gigaton Volume Detector10, a proposed Russian array, should explore merging these collaborations to focus on a single large detector at the most cost-effective site. Funding should be sought from a wider range of agencies, including those focused on particle and nuclear physics.

    Second, at least one 100-km3 radio-detection array needs to get the go ahead. Because such a project can be done only in Antarctica, the onus is on the US National Science Foundation, which is the largest supporter of Antarctic research and realistically the only group that has adequate logistical resources to pull off such a project. Many non-US groups are interested, and collaborations should be set up and costs shared internationally. Once proven, such an array could be expanded to cover 1,000 km3 by around 2030 to monitor the ultra-high-energy Universe.

    By finding the astrophysical sources of ultra-energetic neutrinos and cosmic rays — or ruling out remaining models — the next generation of neutrino observatories is guaranteed to make discoveries.

    Nature 533, 462–464 (26 May 2016) doi:10.1038/533462a

    Spencer Klein is a senior scientist in the Nuclear Science Division, Lawrence Berkeley National Laboratory, and a research physicist at the University of California, Berkeley, Berkeley, California, USA.

    See the full article here .

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    Nature is a weekly international journal publishing the finest peer-reviewed research in all fields of science and technology on the basis of its originality, importance, interdisciplinary interest, timeliness, accessibility, elegance and surprising conclusions. Nature also provides rapid, authoritative, insightful and arresting news and interpretation of topical and coming trends affecting science, scientists and the wider public.

  • richardmitnick 6:46 am on May 28, 2016 Permalink | Reply
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    From Business Insider via IceCube: “Step inside some of the biggest, coolest experiments in the world” 

    U Wisconsin IceCube South Pole Neutrino Observatory

    Business Insider logo

    May 19, 2016,
    Ali Sundermier

    Scientists call it the “ghost particle.”

    It has almost no mass, travels at essentially the speed of light, and has evaded scientific confirmation for three decades.

    Meet the neutrino, which scientists hope will help them answer dozens of critical questions about the universe, including why it’s full of matter.

    Neutrinos are produced when radioactive elements decay. They gush out of the sun, other stars, and even our own bodies. They also travel through huge amounts of matter without even flinching.

    So how do you study a particle that can pass through a light-year of lead without being stopped? With some really big experiments. Take a look:

    The GERmanium Detector Array (GERDA) looks for neutrinos by monitoring the electrical activity inside pure Germanium crystals isolated deep under a mountain in Italy. The scientists who operate GERDA are hoping to spot a very rare type of radioactive decay.

    When the Big Bang gave birth to our universe 13.7 billion years ago, it should have produced equal amounts of matter and antimatter, scientists say. And when matter and antimatter collide, they destroy each other, leaving behind nothing but energy.

    And yet, here we are.

    If the scientists are able to spot the decay they’re looking for, it could imply that a neutrino can be both a particle and an antiparticle at the same time, which would explain why the universe favored matter and why you’re here today.

    The Canadian Sudbury Neutrino Observatory (SNO) is buried roughly a mile underground. It was originally built in the 1980s but was recently repurposed to form SNO+.

    SNO+ will investigate neutrinos from Earth, the sun, and even supernovae. At its heart is a huge plastic sphere filled with 800 tons of a special fluid called liquid scintillator. The sphere is surrounded by a shell of water and held in place by ropes. It’s monitored by an array of about 10,000 extremely sensitive light detectors called photomultiplier tubes (PMTs).

    When neutrinos interact with other particles in the detector, they produce light in the liquid scintillator, which the PMTs are designed to pick up.

    Thanks to the original SNO detector, scientists now know there at least three different kinds, or “flavors,” of neutrinos, which they change back and forth between as they speed through space.

    IceCube neutrino detector interior
    Meet the largest neutrino detector in the world. IceCube, located at the South Pole, uses 5,160 sensors distributed over a billion tons of ice to spot high-energy neutrinos from extremely violent cosmic sources like exploding stars, black holes, and neutron stars.

    When neutrinos crash into water molecules in the ice, they release high-energy eruptions of subatomic particles that can stretch as far as six city blocks, Symmetry reports. These particles move so quickly that they emit a brief cone of light, called Cherenkov radiation. That’s what IceCube’s detectors pick up.

    The scientists hope to use this information to reconstruct the path of the neutrinos and identify their source.

    Daya Bay is a neutrino experiment that uses three experimental halls buried in the hills of Daya Bay, China. Six cylindrical detectors, each containing 20 tons of liquid scintillator, are clustered in the halls and surrounded by close to 1,000 PMTs. They are submerged in pools of pure water to block out any surrounding radiation.

    A nearby group of six nuclear reactors churns out “millions of quadrillions of harmless electron antineutrinos every second.” This stream of antineutrinos interacts with the liquid scintillator to emit brief flashes of light, which are picked up by the PMTs.

    Daya Bay is built to investigate neutrino oscillations. Just like neutrinos, antineutrinos change between different flavors. Scientists at Daya Bay are trying to figure out how many antineutrinos evade detection at the farthest detector because they’ve changed flavors.

    Super-Kamiokande (Super K) is a neutrino observatory a little over 3,000 feet underground beneath the mountains of western Japan. The massive detector contains 50,000 tons of pure water surrounded by about 11,200 PMTs, which staff must fix by boat.

    Similar to IceCube, Super K detects neutrinos using Cherenkov radiation. And Super K beat SNO to the punch in 1998 by being the first observatory to find strong evidence of neutrinos oscillating between flavors, which also showed that the tiny particles have mass.

    Now, its researchers are shooting an underground, 180-mile-long beam of neutrinos at the detector to further investigate these oscillations. For another upcoming experiment, Deep Underground Neutrino Experiment (DUNE), scientists plan to send a beam of neutrinos roughly five times that distance.
    SEE ALSO: How scientists use a giant telescope in Antarctica to study the strangest particle in the universe
    DON’T MISS: The neutrino: a guide to the invisible particle that has astronomers so excited

    See the full article here .

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    ICECUBE neutrino detector
    IceCube is a particle detector at the South Pole that records the interactions of a nearly massless sub-atomic particle called the neutrino. IceCube searches for neutrinos from the most violent astrophysical sources: events like exploding stars, gamma ray bursts, and cataclysmic phenomena involving black holes and neutron stars. The IceCube telescope is a powerful tool to search for dark matter, and could reveal the new physical processes associated with the enigmatic origin of the highest energy particles in nature. In addition, exploring the background of neutrinos produced in the atmosphere, IceCube studies the neutrinos themselves; their energies far exceed those produced by accelerator beams. IceCube is the world’s largest neutrino detector, encompassing a cubic kilometer of ice.

  • richardmitnick 5:37 pm on May 27, 2016 Permalink | Reply
    Tags: , IC86-2016 physics run, ,   

    From IceCube: “IC86-2016, or a new physics run for IceCube” 

    IceCube South Pole Neutrino Observatory

    27 May 2016
    Sílvia Bravo

    The IceCube Lab at the South Pole collects data from over 5,000 light sensors. Around one terabyte (TB) of data is recorded every day, which is then filtered, cleaned, and sent to the north over satellite. Image: Sven Lidstrom, IceCube/NSF

    “On behalf of the operations group, I’m happy to report that as of run 127950 on 2016-05-20, 20:38:47 UTC, we have started the IC86-2016 physics run.” With these words, every IceCuber learned that we were entering a new year of data for IceCube. The mail was sent by John Kelley, who manages the detector operations in IceCube.

    But what makes a new physics run special when IceCube is already taking data 99% of the time every day of the year? Well, data samples are delivered to IceCube researchers for analysis in one-year blocks. When the IceCube Collaboration searches for cosmic neutrinos or measures neutrino oscillations, it uses at least one year of data. Sure, scientists may sometimes use two or more years of data, too, but they will never use 1.5 years.

    The reason is that updates to the data-taking system as well as detector calibrations are done yearly and need to be taken into account when analyzing the data. “It’s exciting that after more than five years since the completion of IceCube, we’re still expanding the physics reach of the detector by deploying new trigger and filter algorithms,” said Kelley when talking about the start of the IC86-2016 physics run.

    But before detailing the updates, let’s summarize the IC86-2015 physics run in three numbers: 8,810 hours of data, 99.8% detector uptime and 97.9% analysis-ready data, also called clean uptime. Take a look at the numbers of the 2014 run. Since detector performance is so high, continued improvements by the IceCube operations group yield only small changes now. Still, they provided an extra 52 hours of interesting astrophysical data. As you know, very high energy neutrinos are rare—very rare, in fact. So every hour counts!

    So, now let’s talk about the updates implemented for this new physics run. Detectorwise, four new surface detectors, which were deployed during the 2015 polar season, are now fully integrated into the data acquisition system. “These add to the previous IceTop tanks and increase the efficiency to veto atmospheric background events when searching for astrophysically interesting events,” says Matt Kauer, who is the IceCube run coordinator. More surface detectors are planned for deployment in the upcoming seasons.

    The IceCube team at the South Pole deploying the surface scintillation detectors. Image: Delia Tosi, IceCube/NSF

    Also related to the surface component of IceCube, our team in Delaware developed a new IceTop trigger that has now been deployed. It uses the closely-spaced infill tanks at the center of the detector to detect low-energy cosmic ray air showers.

    Other important updates include targeting an improvement for multimessenger searches within the international astrophysics and astronomy community. The quality of the event selection for track-like neutrino events has been enhanced. The very high energy alerts, which use events that start within the detector and throughgoing tracks, are now based on better online reconstructions. IceCube is currently generating about one event alert each month and about four per day at lower energy thresholds.

    More significant changes have been made to the optical and gamma-ray follow-up systems, which analyze neutrinos for clustering in space or time and send alerts to other telescopes in case of an interesting coincidence. These systems had previously run at the South Pole, “but this year, neutrino events are transferred to the northern hemisphere over an Iridium satellite link and are typically available for analysis within 30 seconds after they are recorded,” describes Jim Braun, a software developer in the IceCube detector operations team. Advantages of analyzing these events using systems at UW-Madison include the ability to view sky maps in real-time, easier maintenance of analysis algorithms, and the ability to send alerts to other telescopes in a straightforward manner.

    Still another interesting update is the new monopole filter, designed to search for hypothetical magnetic monopoles with moderate velocities (0.1 to 0.75 times the speed of light) and developed by our team in Wuppertal.

    If the last run provided about 13 very high energy neutrinos detected—we have not yet looked at the data, but by now we know more or less what nature will provide us—, the new efforts to improve IceCube contributions to multimessenger campaigns across experiments will boost their impact. “In order to track down the source of these astrophysical neutrino events, it’s important to get the information from these events in the hands of the scientific community as quickly as possible so they can quickly look for a counterpart signal in their telescopes,” explains Erik Blaufuss, who is the IceCube analysis coordinator.

    See the full article here .

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    ICECUBE neutrino detector
    IceCube is a particle detector at the South Pole that records the interactions of a nearly massless sub-atomic particle called the neutrino. IceCube searches for neutrinos from the most violent astrophysical sources: events like exploding stars, gamma ray bursts, and cataclysmic phenomena involving black holes and neutron stars. The IceCube telescope is a powerful tool to search for dark matter, and could reveal the new physical processes associated with the enigmatic origin of the highest energy particles in nature. In addition, exploring the background of neutrinos produced in the atmosphere, IceCube studies the neutrinos themselves; their energies far exceed those produced by accelerator beams. IceCube is the world’s largest neutrino detector, encompassing a cubic kilometer of ice.

  • richardmitnick 3:38 pm on May 27, 2016 Permalink | Reply
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    From Symmetry: “Low-mass particles that make high-mass stars go boom” 

    Symmetry Mag


    Matthew R. Francis

    Simulations are key to showing how neutrinos help stars go supernova.


    When some stars much more massive than the sun reach the end of their lives, they explode in a supernova, fusing lighter atoms into heavier ones and dispersing the products across space—some of which became part of our bodies. As Joni Mitchell wrote and Crosby Stills Nash & Young famously sang, “We are stardust, we are golden, we are billion-year-old carbon.”

    Illustration by Sandbox Studio, Chicago with Corinne Mucha

    However, knowing this and understanding all the physics involved are two different things. We can’t make a true supernova in the lab or study one up close, even if we wanted to. For that reason, computer simulations are the best tool scientists have. Researchers program equations that govern the behavior of the ingredients inside the core of a star to see how they behave and whether the outcomes reproduce behavior we see in real supernovae. There are many ingredients, which makes the simulations extraordinarily complicated—but one type of particle could ultimately drive supernova explosion: the humble neutrino.

    Neutrinos are well known for being hard to detect because they barely interact with other particles. However, the core of a dying star is a remarkably dense environment, and the nuclear reactions produce vast numbers of neutrinos. Both these things increase the likelihood of neutrinos hitting other particles and transferring energy.

    “We can estimate on a sheet of paper roughly how much energy neutrinos may deliver,” says Hans-Thomas Janka, a supernova researcher at the Max Planck Institute for Astrophysics in Garching, Germany. “The question still remains: Is that compatible with the detailed picture? What we need is to combine all the physics ingredients which play a role in the core of a collapsing star.”

    Things fall apart, the center cannot hold

    Typically, all the nuclear fusion in a star happens in its core: That’s the only place hot and dense enough. In turn, the nuclear fusion supplies enough energy to keep the core from compressing under its own gravity. But when a star heavier than eight times the mass of our sun exhausts its nuclear fuel and fusion halts, the core collapses catastrophically. The result is a core-collapse supernova: a shock wave from the collapse tears the star apart while the core shrinks into a neutron star or black hole. The explosion leads to more nuclear fusion and the spread of nuclei into interstellar space, where it can eventually be used in making new stars and planets. (The other major supernova type involves an exploding white dwarf, the source of many other common atoms.)

    Core-collapse supernovae are rare and extremely violent phenomena, sometimes outshining whole galaxies at their peak. The last relatively close-by supernova appeared in the sky in 1987, in the neighboring galaxy known as the Large Magellanic Cloud. Even if a supernova exploded close enough to observe in detail (while being far enough to be safe), we can’t see deep inside to where the action is.

    However, 24 neutrinos from the 1987 supernova showed up in particle detectors (built for studying proton decay) [I have seen this before, but no one ever says how they know this to be factual]. These neutrinos were likely born in nuclear reactions deep in the exploding star’s interior and confirmed theoretical predictions from the 1960s, when astrophysicists first began to study exploding stars.

    Supernova research really took off in the 1980s with growing computer power and the realization that a full understanding of core collapse would need to incorporate a lot of complicated physics.

    “Core-collapse supernovae involve a huge variety of effects involving all four fundamental forces,” says Joshua Dolence of the US Department of Energy’s Los Alamos National Laboratory. “The predicted outcome of collapse—even the most basic question of ‘Does this star explode?’—can depend on how these effects are incorporated into simulations.”

    In other words, if you don’t do the simulations right, the supernova never happens. While some stars may collapse directly into black holes instead of exploding, astronomers see both supernova explosions and their aftermaths (the most famous example being the Crab Nebula).

    Supernova remnant Crab nebula. NASA/ESA Hubble
    Supernova remnant Crab nebula. NASA/ESA Hubble

    Some simulations don’t ever show a kaboom, which is a problem: The energy released during the burst of neutrinos is enough to stall out the supernova before it explodes.

    If neutrinos cause the problem, they may also solve it. They carry energy away from one part of the dying star, but they may also transfer it to the stalled-out shockwave, breaking the stalemate and making the supernova happen. It’s not the only hypothesis, but currently it’s the best guess astrophysicists have, and most of the large computer simulations seem to support it so far. However, some of the most energetic supernovae—known as hypernovae—don’t seem to abide by the same rules, so it’s possible something other than neutrinos are responsible. What that something else might be is anyone’s guess.

    Explosions in the sky

    Core-collapse supernovae are natural laboratories for extreme physics. They involve particle physics, strong gravity as described by general relativity and nuclear physics, all mixed up with strong magnetic fields. All of those aspects must be implemented in computer code, which necessarily involves tough decisions about what details to include and what to leave out.

    “The major open questions revolve around understanding which physical effects are crucial to a quantitative understanding of supernova explosions,” Dolence says. His own work at Los Alamos involves testing the assumptions going into the various theoretical models for explosions and developing faster code to save on precious computer time. Janka’s work in Europe, by contrast, involves modeling the neutrino behavior as exactly as possible.

    Currently, both detailed and simplified approaches are needed, until researchers know exactly what physical processes are involved deep inside the dying star. Both methods use tens of millions of hours of computer time, distributed across multiple computers working in parallel. Even with certain simplifying assumptions, these simulations are some of the biggest around, meaning they require supercomputers at large research centers: the Leibniz Computing Center in Germany; the Barcelona Supercomputing Center in Spain; Los Alamos, Oak Ridge National Laboratory and Princeton University in the United States, and just a handful of others.

    “We have no proof so far except our calculations that neutrinos are the cause of the explosion,” Janka says. “We need to compare models with [astronomical] observations in the future.”

    The world’s current neutrino experiments are poised to catch neutrinos from the next event and are connected by the Supernova Early Warning System. But in the absence of a nearby supernova, massive supercomputer simulations are all we have. In the meantime, those simulations could still teach us about the extreme physics of dying stars and what role neutrinos play in their deaths.

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 8:23 pm on May 24, 2016 Permalink | Reply
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    From SURF: “DUNE building prototype cryostats” 

    SURF logo
    Sanford Underground levels

    Sanford Underground Research facility

    May 24, 2016
    Connie Walker

    SURF DUNE Cryostats

    In the next frontier of particle physics, scientists with the Long-Baseline Neutrino Facility and associated Deep Underground Neutrino Experiment (LBNF/DUNE) hope to make discoveries about neutrinos that could answer fundamental questions about the origins of the universe, learn more about the properties of neutrinos and do further studies in proton decay. They will do this by sending a beam of neutrinos 800 miles through the Earth from Fermi National Accelerator Lab [FNAL] in Batavia, Ill., to underground detectors at the Sanford Underground Research Facility in Lead, S.D.

    But before they can begin that work, they need to be sure the detectors and cryogenic systems will work the way they need them to. That’s where engineer David Montanari comes in.

    Montanari, the cryogenics infrastructure project manager for the LBNF Far Site Facilities and the U.S. liaison at CERN for LBNF, oversees the design of the cryogenic systems that will cool and
    purify the detectors. It’s a big experiment—DUNE will be 100 times bigger than any liquid-argon particle detectors that have come before—that requires big prototypes.

    FNAL DUNE Argon tank at SURF
    FNAL DUNE Argon tank at SURF


    “Large cryogenis systems are not a mystery. They have been done before and they exist in the industry,” Montanari said. For example, he said, the gas industry uses large tanks to store and cool natural gas and move the liquefied version around the world. “There are large air separation plants where they’ve produced liquid argon and liquid nitrogen—the liquid gases that we use in our
    experiments—and they can make it pure. The point is always that we want to make it super pure; that is what separates us from industry.”

    DUNE scientists chose liquid argon for its ability to detect the different types of neutrinos. To keep it in a liquid state, it must be cooled to minus 300 degrees Fahrenheit (minus 184 degrees Celsius or 88 degrees Kelvin).

    The large DUNE prototypes being designed now are not be the first. Scientists built and tested a small, 35-ton at Fermilab.

    “This proves that that we can make a cryostat and we can put a detector inside and we can achieve the purity we need,” Montanari said. “Now, we want to do it bigger and and make sure the bigger
    one is pure as well.”

    The new prototypes will consist of a dual-phase detector that will contain argon in both its liquid and gaseous forms, and a single-phase detector that will need liquid argon only. Although the cryostats will be identical dimensionwise, they will have independent cryogenic systems designed to accommodate the needs of each.

    “This is important because we want to optimize the design and construction,” Montanari said. “So, by the time we go to LBNF/DUNE, we know how to make it and how to make it faster and better.”

    In a presentation at the recent DUNE Collaboration meeting, co-spokesperson Mark Thomson, professor of physics at the Universityof Cambridge, said the goal is to have the prototypes completed by the fall of 2018. “In comparison,” he said, “the Empire State Building was built in 400 days.”

    It’s an aggressive timeline, but one with a purpose, Montanari said. The prototypes will be built at CERN and the Collaboration plans to use a particle beam producedby a particle accelerator to
    test the prototypes. “The timing is essential because the DUNE collaboration wants to take physics data with the beam as long as there is a beam.”

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    About us.
    The Sanford Underground Research Facility in Lead, South Dakota, advances our understanding of the universe by providing laboratory space deep underground, where sensitive physics experiments can be shielded from cosmic radiation. Researchers at the Sanford Lab explore some of the most challenging questions facing 21st century physics, such as the origin of matter, the nature of dark matter and the properties of neutrinos. The facility also hosts experiments in other disciplines—including geology, biology and engineering.

    The Sanford Lab is located at the former Homestake gold mine, which was a physics landmark long before being converted into a dedicated science facility. Nuclear chemist Ray Davis earned a share of the Nobel Prize for Physics in 2002 for a solar neutrino experiment he installed 4,850 feet underground in the mine.

    Homestake closed in 2003, but the company donated the property to South Dakota in 2006 for use as an underground laboratory. That same year, philanthropist T. Denny Sanford donated $70 million to the project. The South Dakota Legislature also created the South Dakota Science and Technology Authority to operate the lab. The state Legislature has committed more than $40 million in state funds to the project, and South Dakota also obtained a $10 million Community Development Block Grant to help rehabilitate the facility.

    In 2007, after the National Science Foundation named Homestake as the preferred site for a proposed national Deep Underground Science and Engineering Laboratory (DUSEL), the South Dakota Science and Technology Authority (SDSTA) began reopening the former gold mine.

    In December 2010, the National Science Board decided not to fund further design of DUSEL. However, in 2011 the Department of Energy, through the Lawrence Berkeley National Laboratory, agreed to support ongoing science operations at Sanford Lab, while investigating how to use the underground research facility for other longer-term experiments. The SDSTA, which owns Sanford Lab, continues to operate the facility under that agreement with Berkeley Lab.

    The first two major physics experiments at the Sanford Lab are 4,850 feet underground in an area called the Davis Campus, named for the late Ray Davis. The Large Underground Xenon (LUX) experiment is housed in the same cavern excavated for Ray Davis’s experiment in the 1960s.
    LUX/Dark matter experiment at SURFLUX/Dark matter experiment at SURF

    In October 2013, after an initial run of 80 days, LUX was determined to be the most sensitive detector yet to search for dark matter—a mysterious, yet-to-be-detected substance thought to be the most prevalent matter in the universe. The Majorana Demonstrator experiment, also on the 4850 Level, is searching for a rare phenomenon called “neutrinoless double-beta decay” that could reveal whether subatomic particles called neutrinos can be their own antiparticle. Detection of neutrinoless double-beta decay could help determine why matter prevailed over antimatter. The Majorana Demonstrator experiment is adjacent to the original Davis cavern.

    Another major experiment, the Long Baseline Neutrino Experiment (LBNE)—a collaboration with Fermi National Accelerator Laboratory (Fermilab) and Sanford Lab, is in the preliminary design stages. The project got a major boost last year when Congress approved and the president signed an Omnibus Appropriations bill that will fund LBNE operations through FY 2014. Called the “next frontier of particle physics,” LBNE will follow neutrinos as they travel 800 miles through the earth, from FermiLab in Batavia, Ill., to Sanford Lab.

    Fermilab LBNE

  • richardmitnick 6:32 am on May 13, 2016 Permalink | Reply
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    From NASA Fermi: “NASA’s Fermi Telescope Helps Link Cosmic Neutrino to Blazar Blast” 

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    NASA/Fermi Telescope

    April 28, 2016
    By Francis Reddy
    NASA’s Goddard Space Flight Center, Greenbelt, Md.

    Nearly 10 billion years ago, the black hole at the center of a galaxy known as PKS B1424-418 produced a powerful outburst. Light from this blast began arriving at Earth in 2012. Now astronomers using data from NASA’s Fermi Gamma-ray Space Telescope and other space- and ground-based observatories have shown that a record-breaking neutrino seen around the same time likely was born in the same event.

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    NASA Goddard scientist Roopesh Ojha explains how Fermi and TANAMI uncovered the first plausible link between a blazar eruption and a neutrino from deep space. Credits: NASA’s Goddard Space Flight Center

    “Neutrinos are the fastest, lightest, most unsociable and least understood fundamental particles, and we are just now capable of detecting high-energy ones arriving from beyond our galaxy,” said Roopesh Ojha, a Fermi team member at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and a coauthor of the study. “Our work provides the first plausible association between a single extragalactic object and one of these cosmic neutrinos.”

    Although neutrinos far outnumber all the atoms in the universe, they rarely interact with matter, which makes detecting them quite a challenge. But this same property lets neutrinos make a fast exit from places where light cannot easily escape — such as the core of a collapsing star — and zip across the universe almost completely unimpeded. Neutrinos can provide information about processes and environments that simply aren’t available through a study of light alone.

    The IceCube Neutrino Observatory, built into a cubic kilometer of clear glacial ice at the South Pole, detects neutrinos when they interact with atoms in the ice.

    U Wisconsin ICECUBE neutrino detector
    IceCube neutrino detector interior
    U Wisconsin ICECUBE neutrino detector

    This triggers a cascade of fast-moving charged particles that emit a faint glow, called Cerenkov light, as they travel, which is picked up by thousands of optical sensors strung throughout IceCube. Scientists determine the energy of an incoming neutrino by the amount of light its particle cascade emits.

    To date, the IceCube science team has detected about a hundred very high-energy neutrinos and nicknamed some of the most extreme events after characters on the children’s TV series “Sesame Street.” On Dec. 4, 2012, IceCube detected an event known as Big Bird, a neutrino with an energy exceeding 2 quadrillion electron volts (PeV). To put that in perspective, it’s more than a million million times greater than the energy of a dental X-ray packed into a single particle thought to possess less than a millionth the mass of an electron. Big Bird was the highest-energy neutrino ever detected at the time and still ranks second.

    Where did it come from? The best IceCube position only narrowed the source to a patch of the southern sky about 32 degrees across, equivalent to the apparent size of 64 full moons.

    Enter Fermi. Starting in the summer of 2012, the satellite’s Large Area Telescope (LAT) witnessed a dramatic brightening of PKS B1424-418, an active galaxy classified as a gamma-ray blazar.

    NASA/Fermi LAT
    NASA/Fermi LAT

    An active galaxy is an otherwise typical galaxy with a compact and unusually bright core. The excess luminosity of the central region is produced by matter falling toward a supermassive black hole weighing millions of times the mass of our sun. As it approaches the black hole, some of the material becomes channeled into particle jets moving outward in opposite directions at nearly the speed of light. In blazars, one of these jets happens to point almost directly toward Earth.


    Fermi LAT images showing the gamma-ray sky around the blazar PKS B1424-418. Brighter colors indicate greater numbers of gamma rays. The dashed arc marks part of the source region established by IceCube for the Big Bird neutrino (50-percent confidence level). Left: An average of LAT data centered on July 8, 2011, and covering 300 days when the blazar was inactive. Right: An average of 300 active days centered on Feb. 27, 2013, when PKS B1424-418 was the brightest blazar in this part of the sky. Credits: NASA/DOE/LAT Collaboration

    During the year-long outburst, PKS B1424-418 shone between 15 and 30 times brighter in gamma rays than its average before the eruption. The blazar is located within the Big Bird source region, but then so are many other active galaxies detected by Fermi.

    The scientists searching for the neutrino source then turned to data from a long-term observing program named TANAMI. Since 2007, TANAMI has routinely monitored nearly 100 active galaxies in the southern sky, including many flaring sources detected by Fermi. The program includes regular radio observations using the Australian Long Baseline Array (LBA) and associated telescopes in Chile, South Africa, New Zealand and Antarctica. When networked together, they operate as a single radio telescope more than 6,000 miles across and provide a unique high-resolution look into the jets of active galaxies.

    Australian Long Baseline Array
    Australian Long Baseline Array map

    ATNF TANAMI array Australia
    ATNF TANAMI array Australia

    Radio images from the TANAMI project reveal the 2012-2013 eruption of PKS B1424-418 at a wavelength of 8.4 GHz. The core of the blazar’s jet brightened by four times, producing the most dramatic blazar outburst TANAMI has observed to date. Credits: TANAMI

    Three radio observations of PKS B1424-418 between 2011 and 2013 cover the period of the Fermi outburst. They reveal that the core of the galaxy’s jet had brightened by about four times. No other galaxy observed by TANAMI over the life of the program has exhibited such a dramatic change.

    “We combed through the field where Big Bird must have originated looking for astrophysical objects capable of producing high-energy particles and light,” said coauthor Felicia Krauss, a doctoral student at the University of Erlangen-Nuremberg in Germany. “There was a moment of wonder and awe when we realized that the most dramatic outburst we had ever seen in a blazar happened in just the right place at just the right time.”

    In a paper* published Monday, April 18, in Nature Physics, the team suggests the PKS B1424-418 outburst and Big Bird are linked, calculating only a 5-percent probability the two events occurred by chance alone. Using data from Fermi, NASA’s Swift and WISE satellites, the LBA and other facilities, the researchers determined how the energy of the eruption was distributed across the electromagnetic spectrum and showed that it was sufficiently powerful to produce a neutrino at PeV energies.

    NASA/SWIFT Telescope
    NASA/SWIFT Telescope

    NASA/Wise Telescope
    NASA/Wise Telescope

    “Taking into account all of the observations, the blazar seems to have had means, motive and opportunity to fire off the Big Bird neutrino, which makes it our prime suspect,” said lead author Matthias Kadler, a professor of astrophysics at the University of Wuerzburg in Germany.

    Francis Halzen, the principal investigator of IceCube at the University of Wisconsin–Madison, and not involved in this study, thinks the result is an exciting hint of things to come. “IceCube is about to send out real-time alerts when it records a neutrino that can be localized to an area a little more than half a degree across, or slightly larger than the apparent size of a full moon,” he said. “We’re slowly opening a neutrino window onto the cosmos.”

    For more information about NASA’s Fermi, visit:


    *Science paper:
    Coincidence of a high-fluence blazar outburst with a PeV-energy neutrino event

    See the full article here .

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    NASA’s Fermi Gamma-ray Space Telescope is an astrophysics and particle physics partnership, developed in collaboration with the U.S. Department of Energy and with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States.

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