A joint Fermilab/SLAC publication

february 2014dimensionsofparticlephysicssymmetry

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Table of contents

Gallery: Imagine the beam

Signal to background: DECam pinpoints asteroid

Breaking: Scientists complete the top quark puzzle

Breaking: ‘Black widow’ pulsars consume their mates

Breaking: Cosmic rays on demand

Day in the life: Statistically significant

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gallery

February 25, 2014

Imagine the beamA former physicist uses accelerator data to create artisticvisualizations.By Andres Wanner, Emily Carr University of Art and Design and Simon FraserUniversity

Sixteen years after graduating as a nuclear physicist, following a long period of workingas a digital designer and educator, Andres Wanner again immersed himself in a physicsenvironment at TRIUMF, Canada’s national laboratory for particle and nuclear physics.Midway through a second Masters degree in Visual Arts, he was curious to revisit hisscientific past from a different, artistic perspective.

With the support of his supervisor, Ingrid Koenig, an artist who often engages inconversation with scientists, Wanner had the opportunity to spend 12 weeks as a residentartist exploring the “heart” of TRIUMF: the world’s largest cyclotron, a giant machineaccelerating a beam of protons used for experiments and medical treatments. He decideduse available data to create a visual representation of the cyclotron's particle beam, andwrote about his process for symmetry.

My art deals with technological precision, uncertainties and errors—areas all relevant toTRIUMF’s cyclotron. Once again stationed at the laboratory, excited about the prospectof working with such a big machine, I began a digital data visualization project aimed attranslating the particle beam’s properties—with a focus on its inaccuracies andfluctuations—into aesthetic imagery.

I was given a desk in the theory students’ workroom, as well as access to both theelectronic data that describes the particle beam and, most importantly, the TRIUMFoperators who are responsible for maintaining the beam and keeping it on track withmicrometer precision. I was given free access to the tremendous amount of datagenerated to this end: position, width, height and shape profiles of the particle beam atdifferent points along its course, recorded in 5 minute intervals and ranging back severalyears.

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Using visualization software called Processing, I started producing speculativepictures based on this data: What kind of traces would the beam leave, if it were used asa recording tool or if its motions were traced on a photosensitive plate? Of course, thatwas a hypothetical question, as the beam is invisible, enclosed within vacuum tubes intowhich no human gaze can enter. Yet it’s a natural question to ask.

In hallway conversations, I asked how people imagined the beam—scientists,operators, communication professionals, students and visitors—everyone had mentalimages, sometimes based on science, in other cases alluding to science-fiction images oflaser beams or starship fuses. I learned that the beams’ focus alternates betweenhorizontal and vertical, resulting in a spiral ribbon shape. If the beam were immersed inair, it would indeed glow like a Star-Trek laser beam. Informed speculations about itscolor ranged from white—a mix of all color wavelengths—to red—the scientific conventionfor representing the positively charged proton.

Expanding on these informal conversations, I conducted an anonymous survey onhow the TRIUMF community imagined the beam. The survey revealed more imaginativemental images varying between blue, violet, beige, golden or “colorless” beams, whilemost agreed that they envision a bright “intense glow.” People described the shape andtexture of the beam as a “very thin, very straight, bright thread,” “rigid wire,” “series ofcollimated red dots,” or compared it to “bunches of protons making racecar sounds” or“flying smarties.”

I also sourced images from pop-culture, observing that beams are often representedas glowing in intense saturated colors. They are usually depicted with sharp, definededges, sometimes surrounded by a glowing halo. Typically straight, thin and focused, butoccasionally in zigzag or other shapes, they can be slightly transparent and sometimespossess an inner texture or structure.

Inspired and informed by all these sources, I developed the series “HypotheticalBeam,” which represents the irregular shape of the beam, amplified but based on actualdata. It implements the characteristic glow prevalent in my research outcomes, whileactual beam data was used as a base for developing these new and surprising shapes.

The picture “Sketchbook of the Beam” is reminiscent of a drawing on paper; Iwondered what a pencil would draw, if attached to the beam. In this work, I related erratic

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beam movements with the casual, colloquial language operators used to describe theoperation of the beam in an electronic logbook. They reported “down time,” a drivegetting “stuck,” and many “trips”—jargon describing different malfunctions. In contrast,they used terms like a “smooth shift” or a “fairly happy” radio frequency, a machine“performing stably,” or “no other interesting events.” Anecdotal information alsoillustrated the routine of workdays spent monitoring technical devices: “Chased a mouseout of the control room” or “A Silent Night—Merry Christmas.”

The residency at TRIUMF allowed me to revisit my past as a nuclear scientist. Manythings reminded me of my experience 16 years ago: seemingly disorganized cables in thelaboratories, the rubbery smell of science equipment, even the informal but concentratedatmosphere in the theory students’ office. I found the environment more welcoming thanexpected. Scientists were open-minded towards my investigations, I could feel a sense ofcomplicity and common ground when we talked: Like a research scientist, I was driven bya vision, a quest for something meaningful.

Overall, this project links the daily routine of operating a machine with thesuperhuman ambition of exploring the universe. The visualizations amplify the surprisingfluctuations and oscillations of the beam, freely exploring data to create inspired formsthat need not faithfully represent scientific meaning. With these images, I seek a way oftalking about science—not in an educational manner, but by creating an empathicconnection to the personal experience of being engaged in the scientific adventure.

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Sketch Beam Traces

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Courtesy of: Andres Wanner

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signal to background

February 25, 2014

DECam pinpoints asteroidWhen weather prevented other telescopes from tracking a potentiallyhazardous asteroid, the Dark Energy Camera stepped in.By Leah Hesla

For seven minutes earlier this month, two Fermilab physicists moonlighted asastronomers who, like the Men in Black, were positioned to protect the Earth from thescum of the universe.

On February 3, Alex Drlica-Wagner and Steve Kent were in Chile taking data for theDark Energy Survey when they received an email stating that a satellite telescope hadpicked up signs of a potentially hazardous asteroid, one whose orbit might soon meetwith Earth’s.

The message had come from a scientist at NASA's Jet Propulsion Laboratory. Badweather in the northern hemisphere had foiled attempts by JPL’s two go-to cameras tophotograph the asteroid, hindering the lab’s ability to predict its orbit. Could the DarkEnergy Camera take a bit of time off from its usual task of imaging distant galaxies totake pictures of this near-Earth object?

“We know about thousands of these asteroids,” Kent says. “Of course, one we didn’tknow about hit Russia last year, so there’s a lot of interest.”

Since the asteroid was new on the orbital block, astronomers had only a rough idea ofwhere it was headed. They did know it would soon pass in line with the sun and thus bedifficult to spot in photographs.

“If we didn’t follow up on it within two days, they weren’t going to be able to follow itup anytime soon,” Drlica-Wagner says. “Because of the weather and the uncertainty ofthe predictions, DECam was the only thing that could pull it off.”

Given Chile’s clear skies and DECam’s large field of view, Drlica-Wagner and Kentwere fairly confident they could catch the asteroid on camera in five takes, even if its

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predicted location was only an estimate. They punched in the coordinates JPL gave themand took their shots. Seven minutes later, they had photos.

The asteroid turned up in all five, though it wasn’t immediately apparent. The imageshad to be processed by the National Optical Astronomy Observatory in Tucson, Ariz., andcoordinates submitted to the Minor Planet Center in Cambridge, Mass., to figure out theorbit. The results were then sent to JPL.

The asteroid looked just like the faint stars that it shared the photos with, except forone characteristic—it appeared in different positions in the five images, just the way acartoon dot would move in a flipbook.

Apollo-class asteroid 2014 BE63 looks like a faint star in the images taken by the DarkEnergy Camera in Chile. Click here to see the asteroid in motion.

Courtesy of: Steve Kent, Fermilab

After combining the pictures with the satellite data, the asteroid-tracking crew broughtgood news.

At its closest approach to Earth on March 1, newly discovered Apollo-class asteroid2014 BE63 will be 18 million miles away.

The Dark Energy Camera scientists were glad to come to the aid of fellowastronomers.

“In astronomy there are always things that are time-critical in nature. People will say,‘You’re at the telescope. Can you do something for me?’” Kent says. “It’s a bit of atradition to help when you can.”

He added jokingly, “In this case, saving the Earth was an extra factor, so we thought itwas generous.”

A version of this article originally appeared inFermilab Today.

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breaking

February 24, 2014

Scientists complete the top quarkpuzzleFermilab's CDF and DZero experiments have discovered the lastpredicted way to produce the top quark, the heaviest elementaryparticle.

Scientists on the CDF and DZero experiments at Fermi National Accelerator Laboratoryhave found the final predicted way of creating a top quark, completing a picture of thisparticle nearly 20 years in the making.

The two collaborations jointly announced on February 21 that they had observed oneof the rarest methods of producing the elementary particle—creating a single top quarkthrough the weak nuclear force, in what is called the “s-channel.” For this analysis,scientists from the CDF and DZero collaborations sifted through data from more than 500trillion proton-antiproton collisions produced by the Tevatron particle accelerator (picturedabove) from 2001 to 2011. They identified about 40 particle collisions in which the weaknuclear force produced single top quarks in conjunction with single bottom quarks.

Top quarks are the heaviest and among the most puzzling elementary particles. Theyweigh even more than the Higgs boson—as much as an atom of gold—and only twomachines have ever produced them: Fermilab’s Tevatron and the Large Hadron Colliderat CERN. There are several ways to produce them, as predicted by the theoreticalframework known as the Standard Model, and the most common one was the first onediscovered: a collision in which the strong nuclear force creates a pair consisting of a topquark and its antimatter cousin, the anti-top quark.

Collisions that produce a single top quark through the weak nuclear force are rarer,and the process scientists on the Tevatron experiments have just announced is the mostchallenging of these to detect. This method of producing single top quarks is among therarest interactions allowed by the laws of physics. The detection of this process was oneof the ultimate goals of the Tevatron, which for 25 years was the most powerful particle

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collider in the world.

This diagram shows a single top quark being created through the weak force. A quark interacts with an antiquark, forming a W boson, a particle that mediates theweak force. The W boson then decays into a top quark and an antibottom quark, which can be seen in the CDF and DZero detectors.

Illustration by: Fermilab

“This is an important discovery that provides a valuable addition to the picture of theStandard Model universe,” says James Siegrist, US Department of Energy AssociateDirector of Science for High Energy Physics. “It completes a portrait of one of thefundamental particles of our universe, by showing us one of the rarest ways to createthem.”

Searching for single top quarks is like looking for a needle in billions of haystacks.Only one in every 50 billion Tevatron collisions produced a single s-channel top quark,and the CDF and DZero collaborations only selected a small fraction of those to separatethem from background, which is why the number of observed occurrences of thisparticular channel is so small. However, the statistical significance of the CDF and DZerodata exceeds that required to claim a discovery.

“Kudos to the CDF and DZero collaborations for their work in discovering thisprocess,” says Saul Gonzalez, program director for the National Science Foundation.“Researchers from around the world, including dozens of universities in the UnitedStates, contributed to this important find.”

The CDF and DZero experiments first observed particle collisions that created singletop quarks through a different process of the weak nuclear force in 2009. Thisobservation was later confirmed by scientists using the Large Hadron Collider.

Scientists from 27 countries collaborated on the Tevatron CDF and DZeroexperiments and continue to study the reams of data produced during the collider’s run,using ever more sophisticated techniques and computing methods.

“I’m pleased that the CDF and DZero collaborations have brought their study of thetop quark full circle,” says Fermilab Director Nigel Lockyer. “The legacy of the Tevatronis indelible, and this discovery only makes the breadth of that research even moreremarkable.”

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Fermilab published a version of this article as a press release.

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breaking

February 21, 2014

‘Black widow’ pulsars consumetheir matesWith a deadly embrace, 'spidery' pulsars devour their partners. Onesuch pulsar is the first rapidly spinning black widow to be discoveredusing only gamma rays.

Black widow spiders and their Australian cousins, known as redbacks, are notorious forkilling and devouring their partners. Astronomers have noted similar behavior among tworare breeds of binary system that contain rapidly spinning neutron stars, also known aspulsars, and have named them accordingly.

“The essential features of black widow and redback binaries are that they place anormal but very low-mass star in close proximity to a [rapidly spinning] pulsar, which hasdisastrous consequences for the star,” says Roger Romani, a member of the KavliInstitute for Particle Astrophysics and Cosmology, an institute run jointly by Stanford andSLAC National Accelerator Laboratory.

So far, astronomers have found at least 18 black widows and nine redbacks within theMilky Way, and additional members of each class have been discovered within the denseglobular star clusters that orbit our galaxy. The main difference between the two is thatblack widow systems contain stars that are both physically smaller and of much lowermass than those found in redbacks.

‘Spider’ pulsars

When a massive star explodes as a supernova, the crushed core it leaves behind—aneutron star—squeezes more mass than the sun into a ball no larger than Washington,DC.

Young, an isolated neutron stars rotate a few thousand times per minute and emitbeams of radio, visible light, X-rays and gamma rays. They also generate powerful

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outflows, or “winds,” of high-energy particles. The power for all this derives from theneutron star’s rapidly spinning magnetic field. Over time, as solitary pulsars wind down,their emissions fade.

Thirty-two years ago, astronomers discovered a new, much faster class of pulsars. These neutron stars spin at astonishing speeds, up to 43,000 revolutions per minute.Today, more than 300 of these so-called millisecond pulsars have been cataloged.

While young pulsars usually appear in isolation, more than half of millisecond pulsarshave a stellar partner, suggesting that interactions with a normal star can make neutronstars spin faster. But how did isolated millisecond pulsars get their kick?

Enter black widows and their kin.

“The high-energy emission and wind from the pulsar basically heats and blows off thenormal star’s material and, over millions to billions of years, can eat away the entirestar,” says Alice Harding, an astrophysicist at NASA’s Goddard Space Flight Center inGreenbelt, Maryland. “These systems can completely consume their companion stars,and that’s how we think solitary millisecond pulsars form.”

For astronomers, an exciting aspect of the black widow and redback systems is theopportunity to observe how the stellar companion intercepts energy from the pulsar. Ineffect, the star serves as a vanity mirror, showing the pulsar’s emissions in tremendousdetail.

J1311

The Fermi Gamma-ray Space Telescope, which orbits the Earth, excels at locatingmillisecond pulsars, with more than four dozen found to date. Pulsars stand out to Fermias prominent gamma-ray sources, but searching for their pulsations in Fermi data isextraordinarily difficult without knowing more about the system. Follow-up surveys withradio telescopes are usually the first to pick up actual pulses, providing confirmation thatthe object is indeed a pulsar. By narrowing down the timing and other parameters, radiostudies also enable Fermi scientists to also tease out the gamma-ray pulses from Fermidata.

When Romani began investigating a source of pulses found by Fermi now known asPSR J1311-3430 (J1311, for short), he imaged the system in visible light. This revealed afaint star that changed color from an intense blue to a dull red—hot and cold, forstars—every hour and a half. Romani conjectured that the star was orbiting and beingdramatically heated by a compact object, most likely a pulsar, and suggested that thesystem was a new black widow.

His measurements indicate that the side of the star facing the pulsar is heated to morethan 21,000 degrees Fahrenheit, more than twice as hot as the sun’s surface. The coolred side reveals the true color of the pipsqueak star, glowing at a temperature of 5000Fahrenheit or lower. From these temperatures, the scientists estimate that the companionis between 12 and 17 times the mass of Jupiter.

Holger Pletsch at the Albert Einstein Institute in Hannover, Germany, led aninternational team on an effort to comb through four years of Fermi LAT data in a searchfor gamma-ray pulses from J1311. The orbital information established by Romani’s worksignificantly narrowed the search, but the unknown pulsar parameters still left 100 millionbillion combinations to explore. Nevertheless, armed with a new, more efficient method,they detected a millisecond pulsar that rotates 390 times a second—more than 23,000rpm.

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J1311 is the first millisecond pulsar ever detected using only gamma rays.

J1311 and other black widow and redback binaries offer unique natural laboratoriesfor studying pulsars up close through the disastrous effects on their partners, which aredistorted by the neutron star’s tidal pull, inflamed by its gamma rays, pummeled withparticles accelerated to near the speed of light, and ultimately evaporated in a breakup ofcosmic proportions.

A version of this article was originally published by NASA.

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breaking

February 19, 2014

Cosmic rays on demandAt SLAC National Accelerator Laboratory, researchers are using aparticle accelerator to help them search for the source of ultra-high-energy cosmic rays.By Lori Ann White

In a test facility at SLAC National Accelerator Laboratory, scientists have set the stage foran experiment that mimics what happens when incredibly energetic particles hit ouratmosphere. The experiment should help them learn to use a new method of detectingthese particles—with radio waves.

The undertaking requires the lab’s historic linear accelerator, 3000 pounds of whiteplastic blocks, giant radio antennas and a set of powerful magnetic coils.

The experiment is part of ANITA, the Antarctic Impulse Transient Antenna project,which has been sending balloon-borne instruments into the upper atmosphere since2006. But the results could benefit a broad range of other experiments.

“We’re looking for the cosmic particle accelerators responsible for the most energeticparticles ever detected,” says Konstantin Belov, a research physicist from the Universityof California, Los Angeles, and principal investigator of the experiment at SLAC.

Ultra-high-energy cosmic rays originate far beyond the borders of our galaxy, butcan—and have—hit Earth’s atmosphere with as much energy as a baseball traveling at 60mph.

“These particles are far more powerful than anything created in an accelerator built byhumans,” Belov says. “And since they’re too powerful to be deflected by the magneticfields of any galaxies or even galaxy clusters they pass, they should point directly back totheir origin.”

That could be a giant black hole at the heart of a primordial galaxy or an even moreexotic phenomenon such as a magnetic monopole or cosmic string, he says. Using radio

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waves to detect the cosmic rays could help solve this mystery.

Researchers Konstantin Belov (left) and Keith Bechtol look over the magnetic coilsthat will impersonate the Earth's magnetic field.

Courtesy of: Brian Rauch

Cast and crew

To help them with their search for the origin of ultra-high-energy cosmic rays, theresearchers are simulating what happens when such a particle slams into the upperatmosphere, collides with a random air molecule and produces an “air shower”—acascade of secondary particles and different types of radiation that shower down towardthe ground. They want to check their theoretical models of how this happens.

That’s where the magnets, plastic blocks, radio antennas and accelerated electronsin SLAC’s End Station Test Beam Facility come in. The researchers are using them tocreate artificial air showers that can be compared to computer simulations built frommodels.

Electrons accelerated to high speeds in the linac play the role of secondary particlesin an air shower. The plastic blocks are stand-ins for the Earth’s atmosphere, and aseries of magnetic coils simulates the Earth’s magnetic field. As the electrons hit theplastic in this magnetic field, they give off radio waves, which are measured by antennaslocated several feet away on the far wall.

Belov says that results look good so far, with the radio waves they’re detectingfollowing theoretical models.

“When we turned on the magnets we saw a beautiful signal in perfect agreement withwhat we predicted,” he says.

Stellar performance

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Belov cautions that there’s still some work to do before researchers will be able to useradio waves to completely map air showers, but they’ve made a very good start, and hehopes the ANITA flight scheduled for the next Antarctic summer can take advantage ofthe method.

In fact, he says, the team at SLAC has yet to hit the most difficult part of theirexperiment.

“We’ll need to find enough people to take it all apart,” he says. Belov knows aperformance isn’t really over until you strike the stage.

A version of this article was originally published by SLAC.

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day in the life

February 20, 2014

Statistically significantMichelangelo D’Agostino taps his physics ingenuity daily as a datascientist.By Heather Rock Woods

Michelangelo D’Agostino took a few forays into the world outside particle physics beforeconfidently switching to a career in data science, where he exercises his physics musclesto generate results in politics, business and societal issues like energy and health.

“I love being able to use my statistical and programming skills in an environmentwhere you can quickly see the impact that you're having on the world,” D’Agostino says.

Opting for data science—a mix of computer programming, database work, statisticalanalysis and machine learning—wasn’t a forgone conclusion. After college, D’Agostinotaught high school physics for a year and entered graduate school at the University ofCalifornia, Berkeley, expecting he’d eventually become a professor and teach.

At UC Berkeley, his work focused on the IceCube Neutrino Observatory at the SouthPole, where thousands of sensors under the ice detect nearly massless but extremelyenergetic neutrinos from exploding stars and other cataclysmic events. D’Agostino ransimulations to help distinguish whether particles hitting the sensors were of interest ornot. On the side, he wrote about science for The Berkeley Science Review and evenspent a summer as a writing intern for The Economist.

After earning his PhD, he secured a postdoctoral research position at ArgonneNational Laboratory, just outside his Chicago hometown. He spent two years calibratinginstruments for a neutrino experiment in France, working with people from all over theworld and playing with the data to help find a parameter that helps explain neutrinooscillations.

Still adventurous, D’Agostino decided to test his physics-learned skills in the widerworld when he came across a job ad for data specialists for the 2012 Obama campaignat Chicago headquarters.

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D’Agostino says that when he approached a mentor, Argonne High Energy PhysicsDirector Harry Weerts, about leaving particle physics for a year, he received unreservedlysupportive advice.

“He told me that every time he wanted to do something that people told him he wascrazy to do, it was the best decision,” D’Agostino says.

So D’Agostino took the leap and joined the campaign—and discovered that the workwas surprisingly similar to what he had been doing in particle physics.

“In particle physics, we build statistical models to tell us the probability of an event inthe detector being signal or background. On the campaign, we built models that would tellus how likely someone was to support Obama, donate money or volunteer,” he says. Allthat without having to scrub toilets as he had at the South Pole (see his account of thelatter experience in The Economist).

Happy with the research-like challenges to solve in data science, D’Agostino soughtto stay in his new field. When the campaign ended, he signed up with Chicago startupBraintree, which aids online businesses in securely processing credit card payments.

Last summer, D’Agostino also mentored graduate and undergraduate fellows in theData Science for Social Good program at the University of Chicago. Projects includedimproving metro bus service, encouraging youth to attend college, and predicting energysavings possible in different building types (in partnership with Lawrence BerkeleyNational Laboratory).

“Michelangelo is not only smart, but also very quick at picking up a lot of newinformation, making himself invaluable and critical in a campaign full of data nerds, andan impressive mentor as well,” says Rayid Ghani, chief scientist for the Obamacampaign, director of the Social Good summer program, and research director of theComputation Institute, a joint initiative between the University of Chicago and Argonne.

In January, D’Agostino moved to Civis Analytics, a relatively new consulting companyfounded by former Obama campaign data specialists. There, he helps nonprofits,governments and companies learn from their troves of data to meet their goals andchallenges.

His ability to glean results from big datasets came from physics, of course. Physicsalso schooled him in teaching himself what he needed to know to take on tough newproblems in a constantly changing world.

“I think there’s something about particle physics that trains you especially well,” heconcludes. “I would not have traded in my experience in particle physics for anything.”

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