A joint Fermilab/SLAC publication

june 2015dimensionsofparticlephysicssymmetry

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Table of contents

Signal to background: Bringing neutrino research back to India

Signal to background: Mathematician to know: Emmy Noether

Application: Making the portable gamma camera

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signal to background

June 23, 2015

Bringing neutrino research backto IndiaThe India-based Neutrino Observatory will provide a home base forIndian particle physicists.By Troy Rummler

Pottipuram, a village in southern India, is mostly known for its farming. Goats graze onthe mountains and fields yield modest harvests of millets and pulses.

Earlier this year, Pottipuram became known for something else: The governmentannounced that, nearby, scientists will construct a new research facility that will advanceparticle physics in India.

A legacy of discovery

From 1951 to 1992, Indian scientists studied neutrinos and muons in a facility locateddeep within what was then one of the largest active gold mines in the world, the KolarGold Fields.

The lab hosted international collaborations, including one that discovered atmosphericneutrinos—elusive particles that shoot out of collisions between cosmic rays and ouratmosphere. The underground facility also served as a training ground for young andaspiring particle physicists.

But when the gold reserves dwindled, the mining operations pulled out. And the lab,unable to maintain a vast network of tunnels on its own, shut down, too. Indian particlephysicists who wanted to do science in their country had to switch to a related field, suchas nuclear physics or materials science.

Almost immediately after the closure of the Kolar lab, plans began to take shape tobuild a new place to study fundamental particles and forces. Physicist Naba Mondal ofthe Tata Institute of Fundamental Research in Mumbai, who had researched at Kolar,

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worked with other scientists to build a collaboration—informally at first, and then officially in2002. They now count as partners scientists from 21 universities and research institutionsacross India.

The facility they plan to build is called the India-based Neutrino Observatory.

Mondal, who leads the INO collaboration, has high hopes the facility will give Indianparticle physics students the chance to do first-class research at home.

“They can't all go to CERN or Fermilab,” he says. “If we want to attract them toscience, we have to have experimental facilities right here in the country.”

INO collaboration meeting 2014, at Iichep Madurai.

Courtesy of: India-based Neutrino Observatory

Finding a place

INO will house large detectors that will catch particles called neutrinos.

Neutrinos are produced by a variety of processes in nature and hardly ever interactwith other matter; they are constantly streaming through us. But they’re not the onlyparticles raining down on us from space. There are also protons and atomic nucleicoming from cosmic rays.

To study neutrinos, scientists need a way to pick them out from the crowd. INOscientists want to do this by building their detectors inside a mountain, shielded by layersof rock that can stop cosmic ray particles but not the slippery neutrinos.

Rock is especially dense in the remote, monolithic hills near Pottipuram. So, thescientists set about asking the village for their blessing to build there.

This posed a challenge to Mondal. India is a large country with 22 officially sanctionedlanguages. Mondal grew up in West Bengal, near Kolkata, more than 1200 miles awayfrom Pottipuram and speaks Bengali, Hindi and English. The residents of Pottipuramspeak Tamil.

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Luckily, some of Mondal’s colleagues speak Tamil, too.

One such colleague is D. Indumathi of the Institute of Mathematical Sciences inChennai. Indumathi spent more than 5 years coordinating a physics subgroup working ondesigning INO’s proposed main detector, a 50,000-ton, magnetized stack of iron platesand scintillator. But her abilities and interests extend beyond the pure physics of theproject.

“I like talking about science to people,” she says. “I get very involved, and I am verypassionate about it. So in that sense [outreach] was also a role that I could naturally takeup.”

She spent about one year talking with residents of Pottipuram, fielding questionsabout whether the experiment would produce a radiation hazard (it won’t) and whetherthe goats would continue to have access to the mountain (they will). In the end, thevillage consented to the construction.

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Courtesy of: India-based Neutrino Observatory

Neutrino physics for a new generation

Young people have shown the most interest in INO, Indumathi says. Students in bothcollege and high school are tantalized by these particles that might throw light on yetunanswered questions about the evolution of the universe. They enjoy discussingresearch ideas that haven’t even found their way into their textbooks.

“[There] is a tremendous feeling of wanting to participate—to be a part of this lab thatis going to come up in their midst,” Indumathi says.

Student S. Pethuraj, from another village in Tamil Nadu, first heard about INO whenhe attended a series of lectures by Mondal and other scientists in his second year of whatwas supposed to be a terminal master’s degree at Madurai Kamaraj University.

Pethuraj connected with the professors and arranged to take a winter course fromthem on particle physics.

“After their lectures my mind was fully trapped in particle physics,” he says.

Pethuraj applied and was accepted to a PhD program expressly designed aspreparation for INO studies at the Tata Institute for Fundamental Research. He is nowcompleting coursework.

“INO is giving me cutting-edge research experience in experimental physics andinstrumentation,” he says. “This experience creates in me a lot of confidence in handlingand understanding the experiments.”

Other young people are getting involved with engineering at INO. The collaborationhas already hired recent graduates to help design the many intricate detector systemsinvolved in such a massive undertaking.

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The impact of the INO will only increase after its construction, especially for those whowill have the lab in their backyard, Mondal says.

“The students from the area—they will visit and talk to the scientists there and get anidea about how science is being done,” he says. “That will change even the culture ofdoing science.”

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signal to background

June 18, 2015

Mathematician to know: EmmyNoetherNoether's theorem is a thread woven into the fabric of the science.By Matthew R. Francis

We are able to understand the world because it is predictable. If we drop a rubber ball, itfalls down rather than flying up. But more specifically: if we drop the same ball from thesame height over and over again, we know it will hit the ground with the same speedevery time (within vagaries of air currents). That repeatability is a huge part of whatmakes physics effective.

The repeatability of the ball experiment is an example of what physicists call “the lawof conservation of energy.” An equivalent way to put it is to say the force of gravitydoesn’t change in strength from moment to moment.

The connection between those ways of thinking is a simple example of a deepprinciple called Noether’s theorem: Wherever a symmetry of nature exists, there is aconservation law attached to it, and vice versa. The theorem is named for arguably thegreatest 20th century mathematician: Emmy Noether.

“Noether's theorem to me is as important a theorem in our understanding of the worldas the Pythagorean theorem,” says Fermilab physicist Christopher Hill, who wrote a bookon the topic with Nobel laureate Leon Lederman.

So who was the mathematician behind Noether’s theorem?

The life of Noether

Amalie Emmy Noether was born in Bavaria (now part of Germany) in 1882. She earnedher doctorate in mathematics in 1907 from the University of Erlangen, which was asocially progressive institution for its day. She stayed at Erlangen to teach for several

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years, though without pay, as women were not technically allowed to teach at universitiesin Germany at the time.

One of the leading mathematicians of the age, David Hilbert, invited her to join him atthe University of Göttingen, where she remained from 1916 until 1933. Liberalized laws inGermany following World War I allowed Noether to be granted a teaching position, butshe was still paid only a small amount for her teaching work.

In 1933, the Nazi regime fired all Jewish professors and followed the next year byfiring all female professors. A Jewish woman, Noether left Germany for the United States.She worked as a visiting professor at Bryn Mawr College, but her time in America wasshort. She died in 1935 at age 53, from complications following surgery.

Many of the leading male mathematicians and physicists of the day eulogized her,including Albert Einstein, who wrote in the New York Times, “However inconspicuouslythe life of these individuals runs its course, none the less the fruits of their endeavors arethe most valuable contributions which one generation can make to its successors.”

Physicists tend to know her work primarily through her 1918 theorem. Butmathematicians are familiar with a variety of Noether theorems, Noetherian rings,Noether groups, Noether equations, Noether modules and many more.

Over the course of her career, Noether developed much of modern abstract algebra:the grammar and the syntax of math, letting us say what we need to in math and science.She also contributed to the theory of groups, which is another way to treat symmetries;this work has influenced mathematical side of quantum mechanics and superstringtheory.

Noether and particle physics

Because their work relies on symmetry and conservation laws, nearly every modernphysicist uses Noether’s theorem. It’s a thread woven into the fabric of the science, partof the whole cloth. Every time scientists use a symmetry or a conservation law, from thequantum physics of atoms to the flow of matter on the scale of the cosmos, Noether’stheorem is present. Noetherian symmetries answer questions like these: If you performan experiment at different times or in different places, what changes and what stays thesame? Can you rotate your experimental setup? Which properties of particles canchange, and which are inviolable?

Conservation of energy comes from time-shift symmetry: You can repeat anexperiment at different times, and the result is the same. Conservation of momentumcomes from space-shift symmetry: You can perform the same experiment in differentplaces, and it comes out with the same results. Conservation of angular momentum,which when combined with the conservation of energy under the force of gravity explainsthe Earth’s motion around the sun, comes from symmetry under rotations. And the listgoes on.

The greatest success of Noether’s theorem came with quantum physics, andespecially the particle physics revolution that rose after Noether’s death. Manyphysicists, inspired by Noether’s theorem and the success of Einstein’s general theoryof relativity, looked at geometrical descriptions and mathematical symmetries to describethe new types of particles they were discovering.

“It's definitely true that Noether's theorem is part of the foundation on which modernphysics is built,” says physicist Natalia Toro of the Perimeter Institute and the Universityof Waterloo. “We apply it every day to deep and well-tested principles like conservationof energy and momentum.”

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According to the law of conservation of electric charge, the total amount of electriccharge going into an experiment must be the same as what comes out, even if particletypes change or if matter hits antimatter and is annihilated. That law has the samesymmetry that a circle has. A perfect circle can be rotated around its center by any angleand it looks the same; the same math describes the quantum mechanical property of anelectron. If the amount of that rotation can change from place to place, the symmetry of acircle yields the entire theory of electromagnetism, which governs everything from thegeneration of electricity to the structure of atoms to matter on cosmic scales. In that way,Noether takes us from a simple symmetry to the world we know.

“Noether's theorem has even greater power than that,” Toro says, “in helping us toorganize our thinking when exploring aspects of the universe where we don't yet knowthe basic laws. That's a tall order, and as we seek experimental answers to thesequestions, symmetries and conservation laws—tightly linked by Noether's theorem—areone of the few theoretical tools that we have to guide us.”

Live from the Perimeter Institute, starting at 5 p.m. PDT / 8 p.m. EDT:Mathematician Peter Olver explores Noether’s life and career, and delves into thecurious history of her famous theorems. Physicist Ruth Gregory looks at thelasting impact of Noether’s theorem, and how it connects with the Standard Modeland Einstein’s general relativity.

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application

June 17, 2015

Making the portable gammacameraThe end of the Cold War and the cancellation of theSuperconducting Super Collider led to the creation of a life-savingmedical device.By Mike Ross

Each year, more than 5 million Americans take a nuclear heart stress test, which imagesblood flow in the heart before and after a brisk walk on a treadmill. The test allowsdoctors to visualize a lack of blood flow that may result from blocked or narrowedcoronary arteries, which are linked to heart disease, the leading cause of death in theUnited States.

The test is conducted with a device called a gamma camera, which also helpsdiagnose dozens of other conditions, from arthritis to renal failure. Invented in the 1950s,gamma cameras used two 500-pound detectors the size of truck tires and cost hundredsof thousands of dollars. As a result, they were usually located only in regional medicalcenters.

But new options are available, thanks to a small company, a national laboratory and,in part, the rise and fall of both the Cold War and the Superconducting Super Collider.

A Cold War camera

The small company is Digirad, which a materials scientist started in 1985 as San DiegoSemiconductors to create and develop applications for complex crystalline materials. Itsname changed to Aurora Technologies in 1991 and to Digirad in 1994.

Sustained by a variety of government R&D contracts, the company’s most successfulearly product was a gamma-ray detector. In 1991, the Defense Advanced Research

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Projects Agency (DARPA) gave the company a contract to do more. The agency askedfor a prototype portable gamma camera—a detector array with readout and displaysystems that could remotely determine the number of nuclear warheads contained withinthe nosecone of a missile. At the camera’s heart were cadmium zinc telluride crystals,which converted gamma rays into electrical signals.

Digirad’s portable gamma camera was to have been a key tool for verifying nuclearweapons reductions. But after the end of the Cold War, the government lost interest.DARPA halted its funding to Digirad in 1993. To survive, the company needed todiversify.

A University of California, San Diego physician who had seen a news story aboutDigirad suggested that the company repurpose the prototype into a revolutionary medicalimaging device. That’s what Digirad set out to create.

Heart-saving gamma rays

To use a gamma camera, physicians first inject into the bloodstream a small amount of ashort-lived radioactive isotope, which sends out gamma rays as it decays. The patientmust then lay very still inside a hospital’s tunnel-like gamma camera for five to 30minutes as its detectors record the isotope’s emissions and create images that showdoctors where the patient’s blood is flowing or blocked.

With the help of a cooperative research agreement with SLAC National AcceleratorLaboratory in 1994 and 1995, Digirad modified its warhead-detecting camera into a muchsmaller, lightweight version of the medical gamma camera. It unveiled its new product in1997.

The camera worked, but its price was higher than hospitals could afford.

“Unfortunately, cadmium zinc telluride was just too expensive to use in a commercialproduct,” says Richard Conwell, then Digirad’s vice president for research anddevelopment.

Unbeknownst to Digirad, the solution to this problem had just been created atLawrence Berkeley National Laboratory.

A Super Collider’s sensor

In the early 1990s, Berkeley Lab electrical engineer Steve Holland was working on silicondetector technology for use in the Superconducting Super Collider, a particle colliderslated to be built in central Texas that would have been twice as large and powerful astoday’s Large Hadron Collider.

Holland’s challenge was to develop a mass-producible low-noise diode componentfor the SSC's many charged-particle detectors that would sense matter streaming fromthe high-energy collisions inside the collider. He did it by creating a diode with a micron-thick electrical-contact layer on the back that could trap noise-creating impuritiesintroduced during fabrication.

In 1993, Congress canceled funding for the Superconducting Super Collider. Thesilicon detector effort seemed doomed to fade into obscurity.

But fellow Berkeley Lab researcher Carolyn Rossington told physicist William Moses,a member of Berkeley Lab’s Life Sciences Division, about Holland’s diode.

Moses was interested in making a compact gamma camera for diagnosing breast

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cancer. It turned out that Holland’s diode was just the thing needed to complete thedesign. The Berkeley Lab team, which included Moses, Rossington and Nadine Wang,described their device at a nuclear medicine and imaging conference in Albuquerque,New Mexico, in November 1997. Digirad scientist Bo Pi was in the audience.

Digirad negotiated with Berkeley Lab for an exclusive license to use Holland’sinnovation in nuclear medicine. After developing new methods to manufacture the diodein commercial quantities, Digirad produced its first portable gamma cameras in 2000. Itsbusiness rejuvenated, Digirad went public in 2004.

Today, Digirad provides onsite gamma imaging services in remote locations andproduces two additional compact gamma cameras that have two or three of the thin,lightweight and adjustable detectors to produce clearer heart images in doctors’ officesor clinics.

Digirad’s portable camera is even valuable to hospitals that already have a largeconventional gamma camera.

“I can roll it into any room in my hospital,” says Dr. Janusz Kikut, Associate Professorand Nuclear Medicine Division Chief at the Vermont Medical Center. “In many urgent orunstable cases, it is faster, safer and less expensive to use this portable camera insteadof transporting the critically ill patients down to the nuclear medicine department.”

“Holland’s diode has been huge for us,” says Virgil Lott, Digirad’s head of diagnosticimaging. “It has enabled us to take faster, higher-quality gamma imaging much closer tomillions of patients.”

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Portable gamma camera from Digirad

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

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