A joint Fermilab/SLAC publication

february 2014dimensionsofparticlephysicssymmetry

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Table of contents

Application: A second chance at sight

Breaking: A new dark-energy detector on the horizon

Signal to background: Watch the next big neutrino experiment come together

Signal to background: #FollowFriday III: Physicists to follow on Twitter

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application

February 04, 2014

A second chance at sightSilicon microstrip detectors, a staple in particle physics experiments,provide information that may be critical to restoring vision to somewho lost it.By Laura Dattaro

In 1995, physicist Alan Litke co-wrote a particularly prescient article for ScientificAmerican about potential uses for an emerging technology called the silicon microstripdetector. With its unprecedented precision, this technology was already helping scientistssearch for the top quark and, Litke wrote, it could help discover the elusive Higgs boson.He further speculated that it could perhaps also begin to uncover some of the manymysteries of the brain.

As the article went to press, physicists at Fermilab announced the discovery of the topquark, using those very same silicon detectors. In 2012, the world celebrated thediscovery of the Higgs boson, aided by silicon microstrip detectors at CERN. Now Litke’sthird premonition is also coming true: His work with silicon microstrip detectors and slicesof retinal tissue is leading to developments in neurobiology that are starting to helppeople with certain kinds of damage to their vision to see.

“The starting point and the motivation was fundamental physics,” says Litke, whosplits his time between University of California, Santa Cruz, and CERN. “But once youhave this wonderful technology, you can think about applying it to many other fields.”

Silicon microstrip detectors use a thin slab of silicon, implanted with an array of diodestrips, to detect charged particles. As a particle passes through the silicon, a localizedcurrent is generated. This current can be detected on the nearby strips and measuredwith high spatial resolution and accuracy.

Litke and collaborators with expertise in, and inspiration from, the development ofsilicon microstrip detectors, fabricated two-dimensional arrays of microscopic electrodesto study the complex circuitry of the retina. In the experiments, a slice of retinal tissue isplaced on top of one of the arrays. Then a movie—a variety of visual stimuli including

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flashing checkerboards and moving bars—is focused on the input neurons of the retina,and the electrical signals generated by hundreds of the retina’s output neurons aresimultaneously recorded. This electrical activity is what would normally be sent as signalsto the brain and translated into visual perceptions.

Illustration by: Sandbox Studio, Chicago

This process allowed Litke and his collaborators to help decipher the retina’s codedmessages to the brain and to create a functional connectivity map of the retina, showingthe strengths of connections between the input and output neurons. That in itself wasimportant to neurobiology, but Litke wanted to take this research further, to not just recordneural activity but also to stimulate it. Litke and his team designed a system in which theystimulate retinal and brain tissue with precise electrical signals and study the kinds of

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signals the tissue produces in response.

Such observations have led to an outpouring of new neurobiology and biomedicalapplications, including studies for the design of a retinal prosthesis, a device that canrestore sight. In a disease like retinitis pigmentosa or age-related macular degeneration,the eye’s output system to the brain is fine, but the input system has degraded.

In one version of a retinal prosthesis, a patient could wear a small videocamera—something similar to Google Glass. A small computer would process thecollected images and generate a pattern of electrical signals that would, in turn, stimulatethe retina’s output neurons. In this way, the pattern of electrical signals that a naturallyfunctioning eye would create could be replicated. The studies with thestimulation/recording system are being carried out in collaboration with neurobiologist E.J. Chichilnisky (Salk Institute and Stanford University) and physicist Pawel Hottowy (AGHUniversity of Science and Technology, Krakow). The interdisciplinary and internationalcharacter of the research highlights its origins in high energy physics.

In another approach, the degraded input neurons—the neurons that convert light intoelectrical signals—are functionally replaced by a two-dimensional array of siliconphotodiodes. Daniel Palanker, an associate professor at Stanford University, has beenusing Litke’s arrays, in collaboration with Alexander Sher, an assistant professor atUCSC, who completed his postdoctoral work with Litke, to study how a prosthesis of thistype would interact with a retina. Palanker and Sher are also researching retinal plasticityand have discovered that, in patients whose eyes have been treated with lasers, whichcan cause scar tissue, healthy cells sometimes migrate into an area where cells havedied.

“I’m not sure we would be able to get this kind of information without these arrays,”Palanker says. “We use them all the time. It’s absolutely brilliant technology.”

Litke’s physics-inspired technology is continuing to play a role in the development ofneurobiology. In 2013, President Obama announced the BRAIN—Brain Research throughAdvancing Innovative Neurotechnologies—Initiative, with the aim of mapping the entireneural circuitry of the human brain. A Nature Methods paper laying out the initiative’sscientific priorities noted that “advances in the last decade have made it possible tomeasure neural activities in large ensembles of neurons,” citing Litke’s arrays.

“The technology has enabled initial studies that now have contributed to this BRAINInitiative,” Litke says. “That comes from the Higgs boson. That’s an amazing chain.”

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Illustration by: Sandbox Studio, Chicago

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breaking

January 28, 2014

A new dark-energy detector on thehorizonA dark-energy detector under development at Fermilab uses adifferent technique to generate full-color images of astronomicalobjects.By Leah Hesla

The power of the 570-megapixel Dark Energy Camera, which is mapping the southernsky in unprecedented detail, lies in its ability to capture celestial objects millions of light-years away. Scientists are now working toward developing an instrument forcharacterizing these stars and galaxies in even greater detail.

Scientist Juan Estrada is currently leading a Fermilab team to develop a largeinstrument using detectors called MKIDs, short for microwave kinetic inductancedetectors. In the coming years, they’ll use it to obtain more information about theastronomical objects already detected by the Dark Energy Camera, pointing it into thenight sky to capture more information about those objects’ light.

The team builds on the work of a University of California, Santa Barbara, group led byBen Mazin, which developed MKIDs for the visible and infrared spectrum.

“These are small detectors,” Estrada says. “We’d like to convert this technology intosomething for a large instrument for cosmology.”

The Dark Energy Camera is outfitted with 74 charge-coupled devices, better known asCCDs, and its optical filters divide the light from far-off galaxies or stars into one of fivespectral ranges. When a CCD gets a hit from one of the photons from the split-off light, itsends a small signal saying that the light in that filter’s range of wavelengths has comethrough. The data from the five filters are then reassembled into a color picture of thegalaxy or star, much the way a computer monitor layers red, green and blue pixels togenerate full-color images.

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Thus DECam’s filter-and-CCD system gives scientists the rough spectral make-up ofan astronomical object.

An MKID, however, would enhance that five-color rendering many times over. Whenstruck by a visible photon, it produces a flood of so-called quasiparticles, allowing thewavelength for every single photon hitting the MKID to be precisely measured. That, inturn, leads to color images of astronomical objects without the use of optical filters. Thehigher the photon’s energy—or the more towards the violet end of the spectrum it is—themore particles it produces.

MKIDs, which use superconducting material, must be very cold to be able to detectphotons. In testing the current MKID-based prototype instrument, Estrada’s teamrecently brought it to a temperature of 33 millikelvin—the lowest temperature everachieved on site at Fermilab.

Over the next several years, the team hopes to create an MKID prototype instrumentthat can be installed in a telescope on a mountaintop next to DECam for testing. Thismeans assembling it with a compatible mechanical design and high-bandwidth digitalprocessing system.

If all goes well, the team can then look realistically to constructing instrumentsinstalled with MKIDs and, conceivably, with 100,000 light channels. That’s 20 times morechannels than the currently planned next-generation technology.

“We are still some distance away from having a full-on instrument,” Estrada says.“But we are taking the initial steps that would put us closer to this very ambitious goal.”

A version of this article was originally published in Fermilab Today.

Above image: Kevin Kuk and Donna Kubik check the temperature on a cryostat thatcontains the prototype MKID.

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signal to background

January 30, 2014

Watch the next big neutrinoexperiment come togetherA video from Fermilab highlights some of the many steps needed tobuild the largest neutrino experiment in the United States.By Kathryn Jepsen

Coordinating the construction of an international particle physics experiment is never aneasy task.

This is indeed the case for NOvA, a US-based physics experiment that studies abeam of hard-to-catch particles sent an unprecedented 500 miles through the Earthtoward a 14,000-ton particle detector. Building the experiment has required harmonizingthe efforts of several dozen laboratories, universities and companies from the UnitedStates, Brazil, the Czech Republic, Greece, India, Japan, Russia and the UnitedKingdom.

“It sinks in,” says John Perko, a construction technician at the NOvA facility in AshRiver, Minnesota, in a new video about the process of building the NOvA detector. “Itmakes you feel that the whole world’s watching.”

The scientists on the NOvA collaboration have come together to study neutrinos,particles that are abundant in nature but that physicists still don’t quite understand. Theyare mysteriously lightweight, leading physicists to wonder if something other than theHiggs boson gives them their masses. Neutrinos come in three types, and they morphfrom one to another. Scientists think they might hold clues to what caused the imbalancebetween matter and antimatter in our universe.

To study these elusive particles, scientists on the NOvA collaboration designed a setof two detectors—a 300-ton one located near the source of the neutrino beam and a14,000-ton one located in Ash River, Minnesota.

Fermilab recently posted a video highlighting some of the many steps required to build

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these detectors, from extruding 50-foot-long plastic tubes at a company in Manitowoc,Wisconsin, to assembling them into modules at a facility staffed by students at theUniversity of Minnesota, to putting together the world’s largest free-standing plasticstructure.

“I’m familiar with all the neutrino projects that are going on, and getting to actually bea part of one of those projects is pretty exciting,” University of Minnesota physics studentNicole Olsen says in the video.

Workers are scheduled to finish building the detectors this spring, and they plan tofinish outfitting them with electronics in the summer. They have already begun to takedata with portions of the experiment, and their capabilities will only improve as they getcloser to completing construction.

Watch the video above or on Fermilab's YouTube channel.

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signal to background

January 31, 2014

#FollowFriday III: Physicists tofollow on TwitterMeet four more physicists who talk about their work on Twitter in symmetry’s third installment of #FollowFriday.By Sarah Charley

Pop culture can sometimes perpetuate the notion that scientists hide away in ivory towersdoing work unintelligible to the public at large.

But science doesn’t have to be inaccessible or incomprehensible. In this thirdinstallment of the #FollowFriday series, symmetry introduces four more particle physicistswho make the effort to explain what they do—and what they care about—on Twitter.

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Hakeem M. Oluseyi

@HakeemOluseyi

Assistant Professor, Dept. of Physics & Space Sciences,Florida Institute of Technology

Tell us about yourself in 140 characters or less.

I’m an explorer, science mercenary, educator and science communicator.

What areas of physics most interest you?

I’m very interested in research that speaks to the fundamentals of existence. What is itthat we know that ain’t so? What does it mean to be in space? What is space? What istime? How did the universe originate? Consequently, I love cosmology and subatomicphysics. At the same time, I love to invent and innovate. So, I pay attention totechnologies from hardware to software to algorithms to just new ways of thinking.

Why do you use Twitter?

I started using Twitter because, frankly, I was told that I should by lots of people. I like thepublic feel of it versus the personal feel of email for communicating directly with people. Ialso like the ability to see what others are saying and thinking in real time.

What do you usually tweet about?

I usually tweet about my daily activities in science, education, outreach or media… or, Ipass on interesting articles that I find in the tweet-sphere.

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Seth Zenz

@sethzenz

Dicke Fellow,Princeton University Physics Department

Tell us about yourself in 140 characters or less.

I work for Princeton on the CMS experiment at the CERN Large Hadron Collider: Higgssearches, upgrade studies and the pixel detector.

What areas of physics most interest you?

Thinking about what to look for in the next 10 or 20 years of LHC running, how to solvethe technical problems while looking for it… and then what to do after that!

Why do you use Twitter?

I started out on Twitter as an outgrowth of my outreach work on the USLHC/QuantumDiaries blogs. I wanted a place to put ideas that were too short for a post, or which I didn'thave time to post about. Over time I have branched out and now follow quite a range ofscientists and explore broader areas of discussion.

What do you usually tweet about?

My primary focus is to write about particle physics and the lives of particle physicists. Iretweet interesting papers, argue about the implications of the latest Higgs search results,and for a while I was doing a daily #ParticleOfTheDay. But then I also comment on themenu at CERN’s Restaurant 1 or banter with my wife's public Twitter persona as amuseum curator.

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Lisa Randall

@lirarandall

Frank J Baird Professor of Science,Harvard University

Tell us about yourself in 140 characters or less.

I'm a physicist and the author of Warped Passages, Knocking on Heaven's Door and Higgs Discovery.

What areas of physics most interest you?

Particle physics and cosmology.

Why do you use Twitter?

Although I confess I initially signed on to Twitter to learn how to use it to promote Knocking on Heaven's Door, I was quickly converted. I use Twitter to learn about newsevents, new experimental results and sometimes just what friends are up to.

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Sometimes I encounter an interesting new idea or person. And I let people knowabout talks or things I'm writing. I should also mention that Twitter is a very effective wayto procrastinate.

What do you usually tweet about?

I've been told you want to present a somewhat consistent personality on Twitter tomaximize impact—for example, the go-to person for physics results. But I'm not thatperson.

I'll tweet or retweet results I find interesting, but I use Twitter more generally as a wayto comment on what I observe, find interesting or find frustrating. I try to have fun with it.

Jon Butterworth

@jonmbutterworth

Head of Physics & Astronomy,University College London

Tell us about yourself in 140 characters or less.

UCL physics prof. working on ATLAS at the LHC—mainly jets, subjets, Higgs and similar. Guardian science blogger and writing a book.

What areas of physics most interest you?

Collider physics and the Standard Model, because it works so well and I have no ideawhy.

Why do you use Twitter?

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I use it to get information, share information and chat. I like the way it makes differentprofessions and subcultures permeable to each other. I gave a 10-minute talk on exactlythis at UCL, if you're interested.

What do you usually tweet about?

According to a word-chart Twitter UK made for me, about 40 percent particle physics, 20percent education, 20 percent other science and technology, 20 percent food & drink.

I would say about half physics, half random.

Do you have suggestions for our next #FollowFriday? Follow us on Twitter @symmetrymag, and let us know which physicists you recommend.

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