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Posts Tagged ‘detector’

This article appeared in symmetry on April 22, 2015.

The world’s largest liquid-argon neutrino detector will help with the search for sterile neutrinos at Fermilab. Photo: INFN

The world’s largest liquid-argon neutrino detector will help with the search for sterile neutrinos at Fermilab. Photo: INFN

Mysterious particles called neutrinos seem to come in three varieties. However, peculiar findings in experiments over the past two decades make scientists wonder if a fourth is lurking just out of sight.

To help solve this mystery, a group of scientists spearheaded by Nobel laureate Carlo Rubbia plans to bring ICARUS, the world’s largest liquid-argon neutrino detector, across the Atlantic Ocean to the United States. The detector is currently being refurbished at CERN, where it is the first beneficiary of a new test facility for neutrino detectors.

Neutrinos are some of the most abundant and yet also most mysterious particles in the universe. They have tiny masses, but no one is sure why—or where those masses come from. They interact so rarely that they can pass through the entire Earth as if it weren’t there. They oscillate from one type to another, so that even if you start out with one kind of neutrino, it might change to another kind by the time you detect it.

Many theories in particle physics predict the existence of a sterile neutrino, which would behave differently from the three known types of neutrino.

“Finding a fourth type of neutrinos would change the whole picture we’re trying to address with current and future experiments,” says Peter Wilson, a scientist at Fermi National Accelerator Laboratory.

The Program Advisory Committee at Fermilab recently endorsed a plan, managed by Wilson, to place a suite of three detectors in a neutrino beam at the laboratory to study neutrinos—and determine whether sterile neutrinos exist.

Over the last 20 years, experiments have seen clues pointing to the possible existence of sterile neutrinos. Their influence may have caused two different types of unexpected neutrino behavior seen at the Liquid Scintillator Neutrino Detector experiment at Los Alamos National Laboratory in New Mexico and the MiniBooNE experiment at Fermilab.

Both experiments saw indications that a surprisingly large number of neutrinos may be morphing from one kind to another a short distance from a neutrino source. The existence of a fourth type of neutrino could encourage this fast transition.

The new three-detector formation at Fermilab could provide the answer to this mystery.

In the suite of experiments, a 260-ton detector called Short Baseline Neutrino Detector will sit closest to the source of the beam, so close that it will be able to detect the neutrinos before they’ve had a chance to change from one type into another. This will give scientists a baseline to compare with results from the other two detectors. SBND is under construction by a team of scientists and engineers from universities in the United Kingdom, the United States and Switzerland, working with several national laboratories in Europe and the US.

The SBND detector will be filled with liquid argon, which gives off flashes of light when other particles pass through it.

“Liquid argon is an extremely exciting technology to make precision measurements with neutrinos,” says University of Manchester physicist Stefan Soldner-Rembold, who leads the UK project building a large section of the detector. “It’s the technology we’ll be using for the next 20 to 30 years of neutrino research.”

Farther from the beam will be the existing 170-ton MicroBooNE detector, which is complete and will begin operation at Fermilab this year. The MicroBooNE detector was designed to find out whether the excess of particles seen by MiniBooNE was caused by a new type of neutrino or a new type of background. Identifying either would have major implications for future neutrino experiments.

Finally, farthest from the beam would be a liquid-argon detector more than four times the size of MicroBooNE. The 760-ton detector was used in the ICARUS experiment, which studied neutrino oscillations at Gran Sasso Laboratory in Italy using a beam of neutrinos produced at CERN from 2010 to 2014.

Its original beam at CERN is not optimized for the next stage of the sterile neutrino search. “The Fermilab beamline is the only game in town for this type of experiment,” says physicist Steve Brice, deputy head of Fermilab’s Neutrino Division.

And the ICARUS detector “is the best detector in the world to detect this kind of particle,” says Alberto Scaramelli, the former technical director of Gran Sasso National Laboratory. “We should use it.”

Rubbia, who initiated construction of ICARUS and leads the ICARUS collaboration, proposed bringing the detector to Fermilab in August 2013. Since then, the ICARUS, MicroBooNE and SBND groups have banded together to create the current proposal. The updated plan received approval from the Fermilab Program Advisory Committee in February.

“The end product was really great because it went through the full scrutiny of three different collaborations,” says MicroBooNE co-leader Sam Zeller. “The detectors all have complementary strengths.”

In December, scientists shipped the ICARUS detector from the Gran Sasso laboratory to CERN, where it is currently undergoing upgrades. The three-detector short-baseline neutrino program at Fermilab is scheduled to begin operation in 2018.

Kathryn Jepsen

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Sonic Copper Cleaning

Saturday, February 7th, 2015

IMG_7979Today we cleaned parts to go into the detector using a sci-fi piece of machinery called a “sonic bath”.

On CUORE, we’re looking for a faint signal of radioactivity. That means we can’t let anything swamp that signal: we have to clean away the normal low-level of dirt present in the atmosphere and biological systems. Even something as normal as a banana has so much naturally-occurring radiation that the “banana-year” is a (someone irreverent and imprecise) unit of measurement for backgrounds of dark matter experiments.

The parts we’re cleaning will be guide tubes for a calibration system. Through them, we’ll place wires close to the detector, then remove them again when it’s time for the main data taking. The calibration wires have a measured amount of radioactivity, and we use that known signal to calibrate the other signals within CUORE.

We used a sonic bath to clean the parts: they’re in a bag with soap water, inside a larger tub filled with tap water. To agitate everything (like the dasher in a clothes washer) the machine uses sound. It’s a bit like the little machines that some people use to clean their contact lenses, but larger: about the size of a laundry room sink, or a restaurant kitchen sink.

IMG_8002My favorite part of the process was the warning on the side: running with an empty bath could cause burnout of the ultrasonic coupler. “The ultrasonic coupler” sound like something out of science fiction: like a combination of “sonic screwdriver” and “flux capacitor”. But it’s not fiction– this is just what we need to do for our daily work!

The noise it makes sounds a bit like an electric fly zapper: a low level electric buzz and cackle, with a faint hiss hinting that there’s something higher pitched above that. It’s practically impossible to hear the main frequency because it’s pitched so much higher than human hearing: the noise is at 30-40kHz, and a child can usually hear as high as 20kHz. Some of the lower resonances fall into an audible range, which is what makes it sound like there’s more going on than I can hear.

In the smaller machine (about the size of a bathroom sink), the agitation noise was more audible, almost headache-inducing in long doses. Since I just watched the fourth Harry Potter movie, it reminded me of the recorded mermaid message: you can only hear it when you’re underwater. If you’re in air, it sounds like a screech instead of a message. Knowing the line between science fiction and fact, I didn’t actually stick my ear in the water (and we wore earplugs in the lab).

IMG_7992There’s a funny effect with some of the bubbles in the tub. They get caught in vibrational nodes within the water, so even though they’re clearly made of air, they don’t rise to the top. It’s like an atom trap made of lasers holding a single atom in place, except this works at a macroscopic level so it’s more intuitive. Seeing the modes in action is a little reward for having worked through all those Jackson problem sets where we deconvolved arbitrary functions in various ways.

When the parts come out at the end, and after we repeat the process with some citric acid (like what you find in lemon juice) and then rinse everything, the rods are a completely different color. They’ve gone from a dead-leaf brown to a peachy pink, all shiny and bright and hopeful. It’s a clean start for a new detector. We preserved the clean exteriors by sealing them in vacuum bags,  and told the chem lab supervisor we were done for the day.

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The dilution refrigerator is the coldest cooling stage for the CUORE detector. It keeps the crystals cold enough that the heat can be detected from a single radioactive decay. The purpose of CUORE is to study the energy spectrum of these decays, so it’s vital that the surroundings be cold. Here’s how it works.

The CUORE cryostat dilution unit

The CUORE cryostat dilution unit

What CUORE Does

CUORE is looking for a kind of radioactive decay that’s extremely rare if indeed it happens at all. It’s never been observed before. It’s called “neutrinoless double beta decay:” a decay emitting two electrons but no neutrinos. Lots of radioactive elements undergo beta decay and emit electrons. Some emit two at once, in a double interaction. That’s accompanied by two neutrinos. The special case that CUORE investigates is the theoretical possibility that the neutrinos annihilate each other before the interaction is completed, so no neutrinos come out.

This can happen only if neutrinos are their own antiparticles, which is an amazingly interesting possibility. Whether or not neutrinos are their own antiparticles is one of the great open questions in neutrino physics today. In the process of investigating this, we also will learn about absolute neutrino masses, two neutrino double beta decay, and a whole host of experimental techniques.

How Cold Helps

Making the detector profoundly cold makes this search possible. Heat is the main signal, so any extra heat floating around is background noise. But additionally, the signal itself gets stronger at lower temperatures. The heat capacity is a strong function of temperature: the colder you go, the less heat it takes to create a change in temperature. So by making the detector colder, the amount of heat deposited by a single decay creates a larger change in temperature, making it more distinguishable from background noise.

The temperatures we’re considering here are measured in millikelvin. For perspective, let’s look at some other cold things. At the South Pole (where my grad school experiment IceCube is) the outdoor temperature ranges between 0 and -100 Fahrenheit, or 255 to 200 Kelvin (K). Liquid argon boils at 87K. Liquid nitrogen boils off at 77K. The cosmic microwave background is at 2.7K. The temperature we’re hoping to use is 10mK or less, which makes CUORE the coldest cubic meter in the universe. The advancement CUORE represents isn’t simply the temperature but also the volume. It might not be the coldest place in the universe, but it’s the coldest place as big as a cubic meter.

A Mixture of Helium Isotopes

"Phase
There’s a trick we use to cool down our helium so much. Helium comes in two isotopes: 3He and 4He. When they get cold enough, both of them become superfluids, but at different temperatures: 2.2K for 4He and 1mK for 3He. The refrigerator operates between these two, so the 4He is superfluid but the 3He is only a regular liquid. By simple 3He evaporation, we can get it down to about 300mK. The key to our trick is that when you mix the two isotopes together, the mixture can become even colder than either would be individually. It splits into two phases, and by making one phase change into the other, we can pump out more heat.

When you cool a mixture of 3He and 4He to very nearly zero (below 867mK), the mixture separates into two different phases. One phase contains more 3He, so we call it the concentrated phase. The other contains less 3He, so we call it the dilute phase. We have a tube going down into the dilute phase and pumping away 3He, shifting the balance of the concentrations in the two phases. As we pump away 3He from the dilute phase, more 3He changes phase from the concentrated phase to take its place and maintain an equilibrium. As each atom changes phase, it absorbs heat because of the lower enthalpy in the dilute phase. The faster we pump out 3He, and the more 3He changes phase, the more cooling power the system has. The power of the cooling engine in limited by the interface area between the two phases, so large area makes more power.

The process of cooling something by pumping away from the dilute phase shows up in another, more familiar context: it’s the same process as when we cool tea by blowing away the steam. More tea can evaporate, cooling what remains.

Throughout this process, we follow the 3He for “dilute” and “concentrated” naming conventions for a couple of reasons. First, the stuff that’s circulating through the system is nearly all 3He and only a little 4He. The 4He stays in its superfluid state within the mixing chamber while the 3He is pumped through condensing lines. There can be a tiny tiny bit of 4He that creeps along the tubes up the pumps (yes, “creep” is the technical term to use here, literally), where it can evaporate and be pumped along with the 3He, but that’s usually less than 1%. The second reason we follow the 3He is that it’s extremely expensive and rare, but that’s a different topic, and it involves international politics in the nuclear age.

[1] Image from F. Pobell: Matter and Methods at Low Temperature, 2nd ed., Springer-Verlag, New York (1995), via G. Ventura and L. Risegari: The Art of Cryogenics Low-Temperature Experimental Techniques, Elsevier, Oxford (2008).

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How to build your own particle detector

Wednesday, January 21st, 2015

This article ran in symmetry on Jan. 20, 2015

Make a cloud chamber and watch fundamental particles zip through your living room! Image: Sandbox Studio, Chicago

Make a cloud chamber and watch fundamental particles zip through your living room! Image: Sandbox Studio, Chicago

The scale of the detectors at the Large Hadron Collider is almost incomprehensible: They weigh thousands of tons, contain millions of detecting elements and support a research program for an international community of thousands of scientists.

But particle detectors aren’t always so complicated. In fact, some particle detectors are so simple that you can make (and operate) them in your own home.

The Continuously Sensitive Diffusion Cloud Chamber is one such detector. Originally developed at UC Berkeley in 1938, this type of detector uses evaporated alcohol to make a ‘cloud’ that is extremely sensitive to passing particles.

Cosmic rays are particles that are constantly crashing into the Earth from space. When they hit Earth’s atmosphere, they release a shower of less massive particles, many of which invisibly rain down to us.

When a cosmic ray zips through a cloud, it creates ghostly particle tracks that are visible to the naked eye.

Building a cloud chamber is easy and requires only a few simple materials and steps:

Materials:

  • Clear plastic or glass tub (such as a fish tank) with a solid lid (plastic or metal)
  • Felt
  • Isopropyl alcohol (90% or more. You can find this at a pharmacy or special order from a chemical supply company. Wear safety goggles when handling the alcohol.)
  • Dry ice (frozen carbon dioxide. Often used at fish markets and grocery stores to keep products cool. Wear thick gloves when handling the dry ice.)

Steps:

  1. Cut the felt so that it is the size of the bottom of the fish tank. Glue it down inside the tank (on the bottom where the sand and fake treasure chests would normally go).
  2. Once the felt is secured, soak it in the isopropyl alcohol until it is saturated. Drain off any excess alcohol.
  3. Place the lid on top of dry ice so that it lies flat. You might want to have the dry ice in a container or box so that it is more stable.
  4. Flip the tank upside down, so that the felt-covered bottom of the tank is on top, and place the mouth of the tank on top of the lid.
  5. Wait about 10 minutes… then turn off the lights and shine a flashlight into your tank.
Artwork by: Sandbox Studio, Chicago

What is happening inside your cloud chamber?

The alcohol absorbed by the felt is at room temperature and is slowly evaporating into the air. But as the evaporated alcohol sinks toward the dry ice, it cools down and wants to turn back into a liquid.

The air near the bottom of the tank is now supersaturated, which means that it is just below its atmospheric dew point. And just as water molecules cling to blades of grass on cool autumn mornings, the atmospheric alcohol will form cloud-like droplets on anything it can cling to.

Particles, coming through!

When a particle zips through your cloud chamber, it bumps into atmospheric molecules and knocks off some of their electrons, turning the molecules into charged ions. The atmospheric alcohol is attracted to these ions and clings to them, forming tiny droplets.

The resulting tracks left behind look like the contrails of airplane—long spindly lines marking the particle’s path through your cloud chamber.

What you can tell from your tracks?

Many different types of particles might pass through your cloud chamber. It might be hard to see, but you can actually differentiate between the types of particles based on the tracks they leave behind.

Short, fat tracks

Sorry—not a cosmic ray. When you see short, fat tracks, you’re seeing an atmospheric radon atom spitting out an alpha particle (a clump of two protons and two neutrons). Radon is a naturally occurring radioactive element, but it exists in such low concentrations in the air that it is less radioactive than peanut butter. Alpha particles spat out of radon atoms are bulky and low-energy, so they leave short, fat tracks.

Long, straight track

Congratulations! You’ve got muons! Muons are the heavier cousins of the electron and are produced when a cosmic ray bumps into an atmospheric molecule high up in the atmosphere. Because they are so massive, muons bludgeon their way through the air and leave clean, straight tracks.

Zig-zags and curly-cues

If your track looks like the path of a lost tourist in a foreign city, you’re looking at an electron or positron (the electron’s anti-matter twin). Electrons and positrons are created when a cosmic ray crashes into atmospheric molecules. Electrons and positrons are light particles and bounce around when they hit air molecules, leaving zig-zags and curly-cues.

Forked tracks

If your track splits, congratulations! You just saw a particle decay. Many particles are unstable and will decay into more stable particles. If your track suddenly forks, you are seeing physics in action!

 

 

Sarah Charley

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The Ties That Bind

Sunday, January 18th, 2015
Cleaning the ATLAS Experiment

Beneath the ATLAS detector – note the well-placed cable ties. IMAGE: Claudia Marcelloni, ATLAS Experiment © 2014 CERN.

A few weeks ago, I found myself in one of the most beautiful places on earth: wedged between a metallic cable tray and a row of dusty cooling pipes at the bottom of Sector 13 of the ATLAS Detector at CERN. My wrists were scratched from hard plastic cable ties, I had an industrial vacuum strapped to my back, and my only light came from a battery powered LED fastened to the front of my helmet. It was beautiful.

The ATLAS Detector is one of the largest, most complex scientific instruments ever constructed. It is 46 meters long, 26 meters high, and sits 80 metres underground, completely surrounding one of four points on the Large Hadron Collider (LHC), where proton beams are brought together to collide at high energies.  It is designed to capture remnants of the collisions, which appear in the form of particle tracks and energy deposits in its active components. Information from these remnants allows us to reconstruct properties of the collisions and, in doing so, to improve our understanding of the basic building blocks and forces of nature.

On that particular day, a few dozen of my colleagues and I were weaving our way through the detector, removing dirt and stray objects that had accumulated during the previous two years. The LHC had been shut down during that time, in order to upgrade the accelerator and prepare its detectors for proton collisions at higher energy. ATLAS is constructed around a set of very large, powerful magnets, designed to curve charged particles coming from the collisions, allowing us to precisely measure their momenta. Any metallic objects left in the detector risk turning into fast-moving projectiles when the magnets are powered up, so it was important for us to do a good job.

ATLAS Big Wheel

ATLAS is divided into 16 phi sectors with #13 at the bottom. IMAGE: Steven Goldfarb, ATLAS Experiment © 2014 CERN

The significance of the task, however, did not prevent my eyes from taking in the wonder of the beauty around me. ATLAS is shaped somewhat like a large barrel. For reference in construction, software, and physics analysis, we divide the angle around the beam axis, phi, into 16 sectors. Sector 13 is the lucky sector at the very bottom of the detector, which is where I found myself that morning. And I was right at ground zero, directly under the point of collision.

To get to that spot, I had to pass through a myriad of detector hardware, electronics, cables, and cooling pipes. One of the most striking aspects of the scenery is the ironic juxtaposition of construction-grade machinery, including built-in ladders and scaffolding, with delicate, highly sensitive detector components, some of which make positional measurements to micron (thousandth of a millimetre) precision. All of this is held in place by kilometres of cable trays, fixings, and what appear to be millions of plastic (sometimes sharp) cable ties.

Inside the ATLAS Detector

Scaffolding and ladder mounted inside the precision muon spectrometer. IMAGE: Steven Goldfarb, ATLAS Experiment © 2014 CERN.

The real beauty lies not in the parts themselves, but rather in the magnificent stories of international cooperation and collaboration that they tell. The cable tie that scratched my wrist secures a cable that was installed by an Iranian student from a Canadian university. Its purpose is to carry data from electronics designed in Germany, attached to a detector built in the USA and installed by a Russian technician.  On the other end, a Japanese readout system brings the data to a trigger designed in Australia, following the plans of a Moroccan scientist. The filtered data is processed by software written in Sweden following the plans of a French physicist at a Dutch laboratory, and then distributed by grid middleware designed by a Brazilian student at CERN. This allows the data to be analyzed by a Chinese physicist in Argentina working in a group chaired by an Israeli researcher and overseen by a British coordinator.  And what about the cable tie?  No idea, but that doesn’t take away from its beauty.

There are 178 institutions from 38 different countries participating in the ATLAS Experiment, which is only the beginning.  When one considers the international make-up of each of the institutions, it would be safe to claim that well over 100 countries from all corners of the globe are represented in the collaboration.  While this rich diversity is a wonderful story, the real beauty lies in the commonality.

All of the scientists, with their diverse social, cultural and linguistic backgrounds, share a common goal: a commitment to the success of the experiment. The plastic cable tie might scratch, but it is tight and well placed; its cable is held correctly and the data are delivered, as expected. This enormous, complex enterprise works because the researchers who built it are driven by the essential nature of the mission: to improve our understanding of the world we live in. We share a common dedication to the future, we know it depends on research like this, and we are thrilled to be a part of it.

ATLAS Collaboration Members

ATLAS Collaboration members in discussion. What discoveries are in store this year? IMAGE: Claudia Marcelloni, ATLAS Experiment © 2008 CERN.

This spring, the LHC will restart at an energy level higher than any accelerator has ever achieved before. This will allow the researchers from ATLAS, as well as the thousands of other physicists from partner experiments sharing the accelerator, to explore the fundamental components of our universe in more detail than ever before. These scientists share a common dream of discovery that will manifest itself in the excitement of the coming months. Whether or not that discovery comes this year or some time in the future, Sector 13 of the ATLAS detector reflects all the beauty of that dream.

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This article appeared in Fermilab Today on Nov. 26, 2014

The plastic scintillator extrusion line, shown here, produces detector material for export to experiments around the world. Photo: Reidar Hahn

The plastic scintillator extrusion line, shown here, produces detector material for export to experiments around the world. Photo: Reidar Hahn

Small, clear pellets of polystyrene can do a lot. They can help measure cosmic muons at the Pierre Auger Observatory, search for CP violation at KEK in Japan or observe neutrino oscillation at Fermilab. But in order to do any of these they have to go through Lab 5, located in the Fermilab Village, where the Scintillation Detector Development Group, in collaboration with the Northern Illinois Center for Accelerator and Detector Design (NICADD), manufactures the exclusive source of extruded plastic scintillator.

Like vinyl siding on a house, long thin blocks of plastic scintillator cover the surfaces of certain particle detectors. The plastic absorbs energy from collisions and releases it as measurable flashes of light. Fermilab’s Alan Bross and Anna Pla-Dalmau first partnered with local vendors to develop the concept and produce cost-effective scintillator material for the MINOS neutrino oscillation experiment. Later, with NIU’s Gerald Blazey, they built the in-house facility that has now exported high-quality extruded scintillator to experiments worldwide.

“It was clear that extruded scintillator would have a big impact on large neutrino detectors,” Bross said, “but its widespread application was not foreseen.”

Industrially manufactured polystyrene scintillators can be costly — requiring a labor-intensive process of casting purified materials individually in molds that have to be cleaned constantly. Producing the number of pieces needed for large-scale projects such as MINOS through casting would have been prohibitively expensive.

Extrusion, in contrast, presses melted plastic pellets through a die to create a continuous noodle of scintillator (typically about four centimeters wide by two centimeters tall) at a much lower cost. The first step in the production line mixes into the melted plastic two additives that enhance polystyrene’s natural scintillating property. As the material reaches the die, it receives a white, highly reflective coating that holds in scintillation light. Two cold water tanks respectively bathe and shower the scintillator strip before it is cool enough to handle. A puller controls its speed, and a robotic saw finally cuts it to length. The final product contains either a groove or a hole meant for a wavelength-shifting fiber that captures the scintillation light and sends the signal to electronics in the most useful form possible.

Bross had been working on various aspects of the scintillator cost problem since 1989, and he and Pla-Dalmau successfully extruded experiment-quality plastic scintillator with their vendors just in time to make MINOS a reality. In 2003, NICADD purchased and located at Lab 5 many of the machines needed to form an in-house production line.

“The investment made by Blazey and NICADD opened extruded scintillators to numerous experiments,” Pla-Dalmau said. “Without this contribution from NIU, who knows if this equipment would have ever been available to Fermilab and the rest of the physics community?”

Blazey agreed that collaboration was an important part of the plastic scintillator development.

“Together the two institutions had the capacity to build the resources necessary to develop state-of-the-art scintillator detector elements for numerous experiments inside and outside high-energy physics,” Blazey said. “The two institutions remain strong collaborators.”

Between their other responsibilities at Fermilab, the SDD group continues to study ways to make their scintillator more efficient. One task ahead, according to Bross, is to work modern, glass wavelength-shifting fibers into their final product.

“Incorporation of the fibers into the extrusions has always been a tedious part of the process,” he said. “We would like to change that.”

Troy Rummler

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The World’s Largest Detector?

Wednesday, August 13th, 2014

This morning, the @CERN_JOBS twitter feed tells us that the ATLAS experiment is the world’s largest detector:

CERN_JOBS Tweet Largest Detector

Weighing over 7,000 tons, 46 meters long, and 25 meters high, ATLAS is without a doubt the particle detector with the greatest volume ever built at a collider. I should point out, though, that my experiment, the Compact Muon Solenoid, is almost twice as heavy at over 12,000 tons:

CMS

CMS is smaller but heavier — which may be why we call it “compact.” What’s the difference? Well, it’s tough to tell from the pictures, in which CMS is open for tours and ATLAS is under construction, but the big difference is in the muon systems. CMS has short gaps between muon-detecting chambers, while ATLAS has a lot of space in order to allow muons to travel further and get a better measurement. That means that a lot of the volume of ATLAS is actually empty air! ATLAS folks often say that if you could somehow make it watertight, it would float; as a CMS member, I heartily recommend attempting to do this and seeing if it works. ;)

But the truth is that all this cross-LHC rivalry is small potatoes compared to another sort of detector: the ones that search for neutrinos require absolutely enormous volumes of material to get those ghostlike particles to interact even occasionally! For example, here’s IceCube:

"Icecube-architecture-diagram2009" by Nasa-verve - IceCube Science Team - Francis Halzen, Department of Physics, University of Wisconsin. Licensed under Creative Commons Attribution 3.0 via Wikimedia Commons - https://commons.wikimedia.org/wiki/File:Icecube-architecture-diagram2009.PNG#mediaviewer/File:Icecube-architecture-diagram2009.PNG

Most of its detecting volume is actually antarctic ice! Does that count? If it does, there may be a far bigger detector still. To follow that story, check out this 2012 post by Michael Duvernois: The Largest Neutrino Detector.

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A second chance at sight

Monday, February 17th, 2014

This article appeared in symmetry on February 4, 2014.

Silicon microstrip detectors, a staple in particle physics experiments, provide information that may be critical to restoring vision to some who lost it.

Silicon microstrip detectors, a staple in particle physics experiments, provide information that may be critical to restoring vision to some who lost it.

In 1995, physicist Alan Litke co-wrote a particularly prescient article for Scientific American about potential uses for an emerging technology called the silicon microstrip detector. With its unprecedented precision, this technology was already helping scientists search 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 many mysteries of the brain.

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

“The starting point and the motivation was fundamental physics,” says Litke, who splits his time between University of California, Santa Cruz, and CERN. “But once you have 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 diode strips, to detect charged particles. As a particle passes through the silicon, a localized current is generated. This current can be detected on the nearby strips and measured with high spatial resolution and accuracy.

Litke and collaborators with expertise in, and inspiration from, the development of silicon microstrip detectors, fabricated two-dimensional arrays of microscopic electrodes to study the complex circuitry of the retina. In the experiments, a slice of retinal tissue is placed on top of one of the arrays. Then a movie—a variety of visual stimuli including 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 are simultaneously recorded. This electrical activity is what would normally be sent as signals to the brain and translated into visual perceptions.

This process allowed Litke and his collaborators to help decipher the retina’s coded messages to the brain and to create a functional connectivity map of the retina, showing the strengths of connections between the input and output neurons. That in itself was important to neurobiology, but Litke wanted to take this research further, to not just record neural activity but also to stimulate it. Litke and his team designed a system in which they stimulate retinal and brain tissue with precise electrical signals and study the kinds of signals the tissue produces in response.

Such observations have led to an outpouring of new neurobiology and biomedical applications, including studies for the design of a retinal prosthesis, a device that can restore 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 video camera—something similar to Google Glass. A small computer would process the collected images and generate a pattern of electrical signals that would, in turn, stimulate the retina’s output neurons. In this way, the pattern of electrical signals that a naturally functioning eye would create could be replicated. The studies with the stimulation/recording system are being carried out in collaboration with neurobiologist E. J. Chichilnisky (Salk Institute and Stanford University) and physicist Pawel Hottowy (AGH University of Science and Technology, Krakow). The interdisciplinary and international character of the research highlights its origins in high energy physics.

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

“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 of neurobiology. In 2013, President Obama announced the BRAIN—Brain Research through Advancing Innovative Neurotechnologies—Initiative, with the aim of mapping the entire neural circuitry of the human brain. A Nature Methods paper laying out the initiative’s scientific priorities noted that “advances in the last decade have made it possible to measure neural activities in large ensembles of neurons,” citing Litke’s arrays.

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

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Heat: Adventures in the World's Fiery Places (Little Brown, 2013). If you haven't already fallen in love with the groundbreaking science that's taking place at RHIC, this book about all things hot is sure to ignite your passion.

Bill Streever, a biologist and best-selling author of Cold: Adventures in the World’s Frozen Places, has just published his second scientific survey, which takes place at the opposite end of the temperature spectrum. Heat: Adventures in the World’s Fiery Places features flames, firewalking, and notably, a journey into the heart of the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory.

I accompanied Streever for a full-day visit in July 2011 with physicist Barbara Jacak of Stony Brook University, then spokesperson of the PHENIX Collaboration at RHIC. The intrepid reporter (who’d already tagged along with woodland firefighters and walked across newly formed, still-hot volcanic lava—among other adventures described in the book) met with RHIC physicists at STAR and PHENIX, descended into the accelerator tunnel, and toured the refrigeration system that keeps RHIC’s magnets supercold. He also interviewed staff at the RHIC/ATLAS Computing Facility—who face the challenge of dissipating unwanted heat while accumulating and processing reams of RHIC data—as well as theorists and even climate scientists, all in a quest for understanding the ultrawarm.

The result is an enormously engaging, entertaining, and informative portrayal of heat in a wide range of settings, including the 7-trillion-degree “perfect” liquid quark-gluon plasma created at RHIC, and physicists’ pursuit of new knowledge about the fundamental forces and interactions of matter. But Streever’s book does more: It presents the compelling story of creating and measuring the world’s hottest temperature within the broader context of the Lab’s history, including its role as an induction center during both World Wars, and the breadth and depth of our current research—from atoms to energy and climate research, and even the Long Island Solar Farm.

“Brookhaven has become an IQ magnet, where smart people congregate to work on things that excite geniuses,” he writes.

Streever’s own passion for science comes across clearly throughout the book. But being at “the top of the thermometer” (the title of his final chapter, dedicated in part to describing RHIC) has its privileges. RHIC’s innermost beam pipes—at the hearts of its detectors, inside which head-on ion collisions create the highest temperature ever measured in a laboratory—have clearly left an impression:

“… I am forever enthralled by Brookhaven’s pipes. At the top of the thermometer, beyond any temperature that I could possibly imagine, those pipes explore conditions near the beginning of the universe … In my day-to-day life, bundled in a thick coat or standing before my woodstove or moving along a snow-covered trail, I find myself thinking of those pipes. And when I think of them, I remember that at the top of the thermometer lies matter with the audacity to behave as though it were absolutely cold, flowing like a perfect liquid…”

There’s more, a wonderful bit more that conveys the pure essence of science. But I don’t want to spoil it. Please read and share this book. The final word is awe.

The book is available for purchase through major online retailers and in stores.

-Karen McNulty Walsh, BNL Media & Communications Office

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A Change of Pace

Monday, February 4th, 2013

Some physicists and engineers from Purdue and DESY, and me, at the beamline we used to test new pixel designs

Every so often, a physicist needs a vacation from doing data analysis for the Higgs boson search. A working vacation, something that gets you a little closer to the actual detector you work on. So last week, I was at the DESY laboratory in Hamburg, Germany, helping a group of physicists and engineers study possible changes to the design of individual pixels in the CMS Pixel Detector. (I’ve written before about how a pixel detector works.) We were at DESY because they had an electron beam we could use, and we wanted to study how the new designs performed with actual particles passing through them. Of course, the new designs can’t be produced in large scale for a few years — but we do plan to run CMS for many, many years to come, and eventually we will need to upgrade and replace its pixel detector.

What do you actually do at a testbeam? You sit there as close to 24 hours a day as you can — in shifts, of course. You take data. You change which new design is in the beam, or you change the angle, or you change the conditions under which it’s running. Then you take more data. And you repeat for the entire week.

So do any of the new designs work better? We don’t know yet. It’s my job to install the software to analyze the data we took, and to help study the results, and I haven’t finished yet. And yes, even “working on the detector” involves analyzing data — so maybe it wasn’t so much of a vacation after all!

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