A joint Fermilab/SLAC publication

march 2015dimensionsofparticlephysicssymmetry

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Table of contents

Breaking: LHC restart back on track

Breaking: The dawn of DUNE

Breaking: Better cosmic candles to illuminate dark energy

Contest: Physics Madness: The Fundamental Four

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breakingMarch 31, 2015

LHC restart back on trackThe Large Hadron Collider has overcome a technical hurdle andcould restart as early as next week.By Kathryn Jepsen

On Monday, teams working on the Large Hadron Collider resolved a problem that hadbeen delaying the restart of the accelerator, according to a statement from CERN.

On March 24, the European physics laboratory announced that a short circuit toground had occured in one of the connections with an LHC magnet. LHC magnets aresuperconducting, which means that they can maintain a high electrical current with zeroelectrical resistance. To be superconducting, the LHC magnets must be chilled to almostminus 460 degrees Fahrenheit.

The short circuit ocurred between a superconducting magnet and its diode. Diodeshelp protect the LHC's magnets by diverting electrical current into a parallel circuit if themagnets lose their superconductivity.

When teams discovered the problem, all eight sections of the LHC were alreadycooled to operating temperature. To fix the problem, they knew that they might have to gothrough a weeks-long process of carefully rewarming and then recooling one section.

The short circuit was caused by a fragment of metal caught between the magnet andthe diode. After locating the fragment and examining it via X-ray, engineers andtechnicians decided to try to melt it. They could do this in a way similar to blowing a fuse.Importantly, the technique would not require them to warm up the magnets.

They injected almost 400 amps of current into the diode circuit for a few milliseconds.Measurements made today showed the short circuit had disappeared.

Now the teams must conduct further tweaks and tests and restart the finalcommissioning of the accelerator. The LHC could see beams as early as next week.

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Photo by: Maximilien Brice, CERNLike what you see? Sign up for a free subscriptionto symmetry!

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breakingMarch 25, 2015

The dawn of DUNEA powerful planned neutrino experiment gains new members, newleaders and a new name.By Jennifer Huber and Kathryn Jepsen

The neutrino experiment formerly known as LBNE has transformed. Since January, itscollaboration has gained about 50 new member institutions, elected two newspokespersons and chosen a new name: Deep Underground Neutrino Experiment, orDUNE.

The proposed experiment will be the most powerful tool in the world for studying hard-to-catch particles called neutrinos. It will span 800 miles. It will start with a near detectorand an intense beam of neutrinos produced at Fermi National Accelerator Laboratory inIllinois. It will end with a 10-kiloton far detector located underground in a laboratory at theSanford Underground Research Facility in South Dakota. The distance between the twodetectors will allow scientists to study how neutrinos change as they zip at close to thespeed of light straight through the Earth.

This will be the flagship experiment for particle physics hosted in the US, says JimSiegrist, associate director of high-energy physics for the US Department of EnergysOffice of Science. Its an exciting time for neutrino science and particle physicsgenerally.

In 2014, the Particle Physics Project Prioritization Panel identified the experiment as atop priority for US particle physics. At the same time, it recommended the collaborationtake a few steps back and invite more international participation in the planning process.

Physicist Sergio Bertolucci, director of research and scientific computing at CERN,took the helm of an executive board put together to expand the collaboration andorganize the election of new spokespersons.

DUNE now includes scientists from 148 institutions in 23 countries. It will be the firstlarge international project hosted by the US to be jointly overseen by outside agencies.

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This month, the collaboration elected two new spokespersons: Andr Rubbia, aprofessor of physics at ETH Zurich, and Mark Thomson, a professor of physics at theUniversity of Cambridge. One will serve as spokesperson for two years and the other forthree to provide continuity in leadership.

Rubbia got started with neutrino research as a member of the NOMAD experiment atCERN in the 90s. More recently he was a part of LAGUNA-LBNO, a collaboration thatwas working toward a long-baseline experiment in Europe. Thomson has a long-terminvolvement in US-based underground and neutrino physics. He is the DUNE principleinvestigator for the UK.

Scientists are coming together to study neutrinos, rarely interacting particles thatconstantly stream through the Earth but are not well understood. They come in threetypes and oscillate, or change from type to type, as they travel long distances. They havetiny, unexplained masses. Neutrinos could hold clues about how the universe began andwhy matter greatly outnumbers antimatter, allowing us to exist.

The science is what drives us, Rubbia says. Were at the point where the nextgeneration of experiments is going to address the mystery of neutrino oscillations. Its aunique moment.

Scientists hope to begin installation of the DUNE far detector by 2021. Everybodyinvolved is pushing hard to see this project happen as soon as possible, Thomson says.

Courtesy of: FermilabLike what you see? Sign up for a free subscription to symmetry!

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breakingMarch 26, 2015

Better cosmic candles toilluminate dark energyUsing a newly identified set of supernovae, researchers have founda way to measure distances in space twice as precisely as before.By Manuel Gnida

Researchers have more than doubled the precision of a method they use to measurelong distances in spacethe same one that led to the discovery of dark energy.

In a paper published in Science, researchers from the University of California,Berkeley, SLAC National Accelerator Laboratory, the Harvard-Smithsonian Center forAstrophysics and Lawrence Berkeley National Laboratory explain that the improvementallows them to measure astronomical distances with an uncertainty of less than 4percent.

The key is a special type of Type Ia supernovae.

Type Ia supernovae are thermonuclear explosions of white dwarfsthe very denseremnants of stars that have burned all of their hydrogen fuel. A Type Ia supernova isbelieved to be triggered by the merger or interaction of the white dwarf with an orbitingcompanion star.

For a couple of weeks, a Type Ia supernova becomes increasingly bright before itbegins to fade, says Patrick Kelly, the new studys lead author from the University ofCalifornia, Berkeley. It turns out that the rate at which it fades tells us about the absolutebrightness of the explosion.

If the absolute brightness of a light source is known, its observed brightness can beused to calculate its distance from the observer. This is similar to a candle, whose lightappears fainter the farther away it is. Thats why Type Ia supernovae are also referred toas astronomical standard candles.

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The 2011 Nobel Prize in Physics went to a trio of scientists who used these standardcandles to determine that our universe is expanding at an accelerating rate. Scientiststhink this is likely caused by an unknown form of energy they call dark energy.

Measurements using these cosmic candles are far from perfect, though. For reasonsthat are not yet understood, the distances inferred from supernova explosions seem to besystematically linked to the environments the supernovae are located in. For instance, themass of the host galaxy appears to have an effect of 5 percent.

In the new study, Kelly and his colleagues describe a set of Type Ia supernovae thatallow distance measurements that are much less dependent on such factors. Using datafrom NASAs GALEX satellite, the Sloan Digital Sky Survey and the Kitt Peak NationalObservatory, they determined that supernovae located in host galaxies that are rich inyoung stars yield much more precise distances.

The scientists also have a likely explanation for the extraordinary precision. Itappears that the corresponding white dwarfs were fairly young when they exploded,Kelly says. This relatively small spread in age may cause this particular set of Type Iasupernovae to be more uniform.

For their study, the scientists analyzed almost 80 supernovae that, on average, were400 million light years away. On an astronomical scale, this is a relatively short distance,and light emitted by these sources stems from rather recent cosmic times.

An exciting prospect for our analysis is that it can be easily applied to Type Iasupernovae in larger distancesan approach that will let us analyze distances moreaccurately as we go further back in time, Kelly says.

This knowledge, in turn, may help researchers draw a more precise picture of theexpansion history of the universe and could provide crucial clues about the physicsbehind the ever increasing speed at which the cosmos expands.

The intense ultraviolet emission from stars within a circle surrounding thesesupernovae (shown in white) reveals the presence of hot, massive stars and suggeststhat the supernovae result from the disruption of comparatively young white dwarf stars.

Courtesy of: Patrick Kelly/University of California, BerkeleyLike what you see? Sign up fora free subscription to symmetry!

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contestMarch 31, 2015

Physics Madness: TheFundamental FourWhich physics machine has the power to go all the way?By Lauren Biron

The competition is fierce, and only four fantastic pieces of physics equipment emergedfrom the fray. Below are your Fundamental Four match-ups, so get voting to make sureyour favorite makes it to the Grand Unified Championship.

You have until midnight PDT on Thursday, April 2, to vote in this round. Come backon April 3 to see if your pick advanced and vote in the final round.

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The Fundamental FourMatch 1

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Large Hadron ColliderThe LHC is the most powerful particle accelerator in the world. The machine

accelerates protons and other ions close to the speed of light and guides them around a17-mile tunnel using magnets that generate fields 100,000 times as strong as theEarths. Scientists smash particles together to recreate in miniature the conditions afterthe big bang. Experiments at the LHC discovered the Higgs boson in 2012. When itrestarts this year, the LHC will search for things like supersymmetry, dark matter andextra dimensions.

More info

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Fermi TelescopeThe Fermi Space Telescope peers into the gamma ray universe, gathering

information about objects emitting high-energy light to answer questions about blackholes, pulsars, dark matter, quantum gravity and cosmic rays. The telescope, which orbitsthe Earth every 95 minutes, has already recorded the highest-energy gamma ray burstand solar flare ever observed by scientists. It also discovered and studied more than 150gamma-ray pulsars, several dozen of which are seen to pulse only in gamma rays.

More info

Match 2

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Hubble Space TelescopeSince it was launched into space in 1990, Hubble has taken stunning images of

galaxies and nebulae in ultraviolet, visible and near-infrared wavelengths. It helpednarrow down the Hubble constant, the rate at which the universe is expanding, whichhelps drive our understanding of dark energy. Scientists used Hubble to discover Plutosfifth moon, find evidence of proto-planetary disks, and identify black holes at the center ofgalaxies.

More info

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Dark Energy CameraBoasting a staggering 570 megapixels, DECam is the most powerful digital camera in

the world. It hunts dark energy, the mysterious force pushing the universe apart, as a partof the Dark Energy Survey. But thats not all it does. While surveying the skies, it alsocomes across goodies such as asteroids, supernovae and trans-Neptunian objects. Froma mountaintop in Chile, DECam can see light from up to 8 billion light-years away andcapture more than 100,000 galaxies in each snapshot.

More info

Out in Round 2

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Planck

This space telescope, run by the European Space Agency with significantparticipation from NASA, gave us the worlds most precise map of the universe in themoments after the big bang. Through Planck, scientists have refined the standard modelof cosmology and homed in on the properties of neutrinos.

More info

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Holometer

Using a laser and mirrors, the Holometer is probing the smallest scale of spacethePlanck scale, 10 trillion trillion times smaller than an atomto determine if the universe islike a hologram. Scientists are checking to see if the information of our universe could becoded in tiny packets in two dimensions, creating a pixelated universe that just appearssmooth and three-dimensional from our everyday perspective.

More info

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Super KSuper-Kamiokande is a massive neutrino experiment containing 50,000 tons of

ultrapure water, housed 1000 meters below a mountain in Japan. Super K helpsresearchers study whether protons decay and is one of the heavy hitters of neutrinoresearch. It collected the largest sample of solar neutrinos in real time and was the firstexperiment to detect oscillations of atmospheric neutrinos. Its observations implied thatthe ghostly particleswhich were predicted to be masslesshave a mass after all, amystery that has yet to be explained.

More info

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IceCubeMade of a cubic kilometer of Antarctic ice, IceCube is the worlds largest neutrino

detector. In 2013, some of the 5,000+ sensors strung down 86 holes drilled into the icepicked up signals from the highest-energy neutrinos ever found, nicknamed Bert, Ernieand Big Bird. IceCube scientists aim to discover the cosmic sources that produce thesehigh-speed intergalactic visitors. The site is also an enormous muon detector that seesmore than 100 billion muons every year.

More info

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Out in Round 1

LUX

The Large Underground Xenon dark-matter detector is the current record-holder formost sensitive experiment searching for the most popular type of dark matter particle. Itssix-foot titanium tank holds liquid xenon at minus 150 degrees Fahrenheit a mile belowground in a former gold mine. LUX made news in 2013 when it released the worlds moststringent constraints on dark-matter particles and shot down potential hints of dark matterreported by other groups.

More info

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Borexino

This massive solar neutrino detector, located in a cavern in the Gran Sassomountains in Italy, contains 300 tonnes of active liquid scintillator within an 11-metersphere surrounded by 2000 photomultiplier tubes. Solar neutrinos interact with thescintillator, letting scientists measure the rate of nuclear reactions powering the sun. In2014, scientists used it to discover that the sun releases as much energy today as it did100,000 years ago. Borexino also found evidence of geoneutrinos, particles created byradioactive decay within the Earth.

More info

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CEBAFThe Continuous Electron Beam Accelerator Facility at Jefferson Lab was the worlds

first large-scale application of superconducting radio-frequency (SRF) technology. Theaccelerator, which has been upgraded and is now running at almost three times itsoriginal design energy, is a powerful tool to investigate the structure of an atoms nucleusdown to the level of quarks and the glue that holds them together.

More info

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Daya BayThe Daya Bay Reactor Neutrino Experiment, based in China, uses 110-ton

antineutrino detectors to track the ghostly particles produced at nearby nuclear powerplants. The experiment is known for discovering a hard-to-measure property of neutrinooscillations, a key piece of the neutrino puzzle scientists had been trying to solve for adecade. While gathering information on how neutrinos morph from one type to another,Daya Bay detectors amassed the most data on antineutrinos from a group of nuclearreactors to date.

More info

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DEAP

The DEAP-3600 detector at Canadas SNOLAB is scheduled to begin taking datalater this spring. Located 2km below ground in Vale Creighton Mine, it will be the mostsensitive particle detector to search for the most sought-after type of dark matter, theWIMP. Its massive sphere, which will contain 565 imperial gallons of liquid argon, will be20 times more sensitive to finding these types of particles than the current best.

More info

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Fermilab Neutrino Beam

When youre trying to study particles as hard to detect as neutrinos, it helps to makeyour own and start with a whole bunch of them. Fermilabs particle accelerators makethe most powerful beam of high-energy neutrinos in the world. Two focusing horns tunethe energy and shape of the beam and then send the neutrinos straight through the earthto detectors 450 and 500 miles away. Upgrades to the accelerator complex will increasethe beams intensity even further.

More info

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RHICBrookhaven Labs Relativistic Heavy Ion Collider was the first machine to create

quark-gluon plasma, a state of matter that existed a fraction of a second after the bigbang. At the time, it was the hottest matter ever produced in a laboratory. RHIC is theonly machine in the world able to collide beams of polarized protons and was the first thatcould collide ions as heavy as gold.

More info

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LIGOThe Laser Interferometer Gravitational-Wave Observatory will use the worlds largest

precision optical instruments to test Einsteins prediction that massive objects moving inspace send out ripples in spacetime. LIGO seeks to measure these ripples as theydisturb beams of light traveling through its 4-kilometer tunnels and to use them to furtherinvestigate the nature of gravity and the cosmos. Its instruments are so sensitive, theycan see a change on the scale of a thousandth the size of a proton.

More info

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