Anyons, anyone?

August 31, 2011 | 4:37 pm

All particles in nature fall into one of two classes, bosons or fermions. In nature this dichotomy stands firm. But the mathematics reveals the dividing line to be a gradated space where particles can exist as something in between bosons and fermions, much as any hue of green occupies a place in the yellow-to-blue spectrum.

Anyons in an optical lattice are predicted to exhibit a characteristic signature in their density distribution (rainbow-colored curve). This distribution can be directly measured in experiments, thus providing a striking tool for the unambiguous detection of anyons. The inset is an illustration of conditional hopping of atoms in a lattice. Image: Nature Publishing Group, London

In 1982 physicist Frank Wilczek gave these interstitial particles the name anyon. Anyons have never been created, but a researcher at the Ludwig Maximilian University of Munich believes he can bring them into the observable world.

LMU theorist Tassilo Keilmann has developed an experimental design to bring anyons out of the woodwork with the help of cold atoms and lasers.

“You’re creating artificial particles,” Keilmann said. “In the context of cold atoms, there’s a unique advantage in that you can manipulate the anyons one by one, so you can manipulate everything,” Here, ‘cold’ is on the order of 10^-10 kelvins.

Manipulating particles one by one is almost a requirement if you’re trying to split the difference between bosons and fermions, since what distinguishes one from the other is whether the particles are physically allowed to congregate in the same space.

“As a tool for engineering quantum materials, the ability to see particles is invaluable,” says Jonathan Simon, a postdoctoral associate in Markus Greiner’s group at Harvard University. The group plans to carry out Keilmann’s proposal at the end of the year.

Fermions are particles with half-integer spin (spin ½ or spin 3/2, for example). Two or more identical fermions can’t coexist in the same space. For instance, two electrons with both of their spins pointing up are forbidden from occupying the same energy level around an atomic nucleus.

Identical bosons, on the other hand, are allowed crowd together in the same space. Photons and other particles with integer spin (spin 1, spin 2) are in the boson family.

If bosons are bosons and fermions are fermions and never the twain shall meet, then their identities should be completely independent of any situation you put them in. But a mathematical proof shows that in one- or two-dimensional systems, you can manipulate the situation in a way that pulls bosons into fermion territory.

Keilmann’s experimental design involves an optical lattice – a grid of lasers. Particles are nestled in the spaces between laser boundaries like eggs in an egg crate. Depending on the intensity of the laser light, the particles have an easier or harder time getting in and out, and so may congregate or isolate.

“For a shallow egg carton, the eggs can still roll around even as they bump into each other,” Simon says. “But once you make the egg carton deep enough you end up with one egg per well.”

The idea is to set up the optical egg crate with some prescribed boson arrangement, use a laser to give them some energy, and watch to see which of them hop from their own well to a different well. The energy they’re given isn’t enough to hop over the energy boundary by the laser, which means they’ll have to tunnel through the barrier to get to another site. In quantum mechanical systems, tunneling happens on occasion, and it’s no big deal. But tunneling doesn’t usually depend on what’s on the other side of the barrier.

Once excited by a laser, the boson may hop to an empty well, or it may hop to one that’s already occupied, and will lose some energy as it tunnels. If the theory bears out, the chances of a boson hopping to another site and the amount of energy it has post-hop will depend on the occupancy of that site. That means that you can reasonably predict whether it will congregate or isolate through this conditional hopping.

In an article published in Nature, Keilmann shows that this conditional hopping, as the phenomenon is called, of bosons can be exploited to create anyons.

If bosons show a more fermionic side, isolating itself depending on how its neighbors are arranged, then there’s some play between the behavior of gregarious bosons and hermetic fermions. That play is the realization of anyons, the in-between particles.

The raw material for Keilmann’s experimental design is the boson rubidium 87. Simon’s group starts with a small cloud of these particles, cools them to a few nanokelvin, and lets them settle in the optical lattice. The lattice itself is generated by projecting laser light through a telescope developed by the Harvard group to look at the individual atoms in the lattice. The light that comes through the microscope illuminates the atoms. The lattice pattern is designed according to the needs of the experiment – it can be hexagonal, square, shallow, deep. The lattice traits determine the atoms’ organization inside it.

“They can point up or down and they’re shaking in each well,” Simon says. “We can measure that – their orientation, how much they’re shaking.”

The marriage of Keilmann’s research, supported financially by LMU and Wellness Heaven, with the fine-tuned setup at Harvard may uncover a class of particles that, as it applies to any particle, isn’t really a class at all: any particle is an anyon by virtue of its existence. The name is Wilczek’s little joke.

“Any anyon can be anything between a boson or a fermion,” Keilmann says. “Wilczek is a funny guy.”

Leah Hesla

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Fermilab astrophysicist describes faster way to board airplanes…and proves it

August 30, 2011 | 10:29 am

Almost everyone has been there: you rush to the airport only to stand in line and watch your plane board at what feels like a snail’s pace. Yet few people take the time to come up with a better solution and even fewer see their idea tested.

Fermilab particle astrophysicist Jason Steffen found a method that would allow quicker boarding for airplane passengers.

Frustration and luck helped Fermilab astrophysicist Jason Steffen accomplish both.

In 2008, after a particularly blood-boiling wait in an airport, the frequent flier  decided to put his skills developing algorithms to track potentially habitable planets and dark matter particles to use developing a computer model to virtually load passengers. After testing several loading patterns, Steffen determined that loading in groups spaced two or three rows apart makes the process much more efficient. The improvement in boarding time depends on the size of the airplane. Spacing out passengers was key to allowing simultaneous depositing of luggage in over-head bins.

Although Steffen was sure his formula worked, it was still just theory on paper that needed flesh and bone testing.

Enter This vs. That, a new science program that uses often quirky experiments to test the merits of everyday choices such as what burns hotter in your grill – natural gas or propane. The show is being distributed internationally by MIPCOM and under discussion for Internet release in the United States. Jon Hotchkiss, producer of the program, came across Steffen’s paper on the Internet shortly after his own molasses-like airplane boarding experience, and a new episode was born.

“As much as This vs. That is entertaining, I also wanted there to be a take away,”  Hotchkiss said. “I wanted to provide answers to questions that people have in their daily lives.”

The show flew Steffen to Los Angeles during his vacation earlier this year to test five models of airplane boarding, including Steffen’s preferred method, on a mock 757 airplane in a movie sound stage. Steffen and Hotchkiss measured the plane’s interior to make sure it conformed with the specifications of a real 757. Seventy-two people, and their luggage, were loaded with boarding order and seat number randomized. Steffen was a little taken back at first by the producer’s call but said that, “When someone offers to take you’re theoretical work and test it; you should jump at the chance.”

During the filming, Steffen’s nerves were put to the test by the show’s co-host comedian Marc DeCarlo, who also hosts the Travel Channel’s Taste of America and Windy City LIVE’s  man-about-town segments. Steffen wasn’t allowed to know the time it took for each boarding method until the end of the episode and DeCarlo kept implying that Steffen shouldn’t quit his day job.

“I was watching people load and this one girl was slow,” Steffen said. “I kept thinking, ‘Man this last girl is going to make me look bad. Put the bag in the overhead bin already’. But once the time ‘three minutes’ came out of DeCarlo’s mouth, I knew I had it.” Steffen’s method was nearly twice as fast as the nearest competing method.

You can read about Steffen’s method and the sound-stage test in his white paper posted Sunday on the preprint server arXiv.

The first 7 ½ minutes of the This vs. That episode testing Steffen’s method can be viewed here and a few clips of Steffen’s boarding method.

The program’s Twitter feed will announce the U.S. release date of the full one-hour episode, pending a distribution contract.

Tona Kunz

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LHCb experiment sees Standard Model physics

August 29, 2011 | 11:47 am

Over the weekend, the LHCb experiment at the Large Hadron Collider released new results bolstering the Standard Model of particle physics.

The collaboration announced that their precision measurements disagreed with earlier results from experiments at the Tevatron at Fermilab. This summer, the CDF experiment announced seeing small excesses over the expected amount of decays of mesons composed of bottom and strange quarks into a pair of muons.

The Standard Model predicts that this decay should happen infrequently. It should take more than 350 trillion collisions for scientists to see it. But if physicists observe it more often than that, it can mean that something beyond the Standard Model is affecting the process.

Looking for excesses like this is one way to search for supersymmetry. Not seeing this type of enhancement does not, however, rule out the existence of supersymmetry, said Sheldon Stone, group leader of experimental elementary particle physics at Syracuse University.

“There is still a lot of room for new physics to appear,” he said.

Kathryn Grim

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Beams to order from table-top accelerators

August 26, 2011 | 3:50 pm

Berkeley Lab published the following story on August 22, 2011. For more about table-top accelerators, read Crashing the Size Barrier in symmetry magazine.

A laser pulse through a capillary filled with hydrogen plasma creates a wake that can accelerate an electron beam to a billion electron volts in just 3.3 centimeters. The same LOASIS accelerating structure has been modified to tune stable, high-quality beams from 100 to 400 million electron volts. (Photos by Roy Kaltschmidt, Berkeley Lab Public Affairs)

Laser plasma accelerators offer the potential to create powerful electron beams within a fraction of the space required by conventional accelerators – and at a fraction of the cost. Their promise for the future includes not only compact high-energy colliders for fundamental physics but diminutive sources of intensely bright beams of light, spanning the spectrum from microwaves to gamma rays – a new kind of ultrafast light source for investigating new materials, biological structures, and green chemistry. Compared to today’s giant science facilities, “table-top” laser plasma accelerators may eventually be able to do equally powerful research with minimal environmental impact.

To reach these goals, laser plasma accelerators must be able to produce high-quality, stable electron beams and tune those beams to the users’ needs. The LOASIS program at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) has already demonstrated high-quality beams up to a billion electron volts in a mere 3.3 centimeters; the BELLA project will reach 10 billion electron volts in a single meter.

Now the LOASIS team has demonstrated a simple way to tune highly stable beams through a wide range of energies. They describe their methods in the journalNature Physics.

Surfing the wave

“To describe how a laser plasma accelerator works, I use the analogy of a surfer riding a wave,” says Wim Leemans, who heads the LOASIS program in Berkeley Lab’s Accelerator and Fusion Research Division. “The surfers are the electrons themselves. The waves form when a laser pulse plows through a plasma.”

In a plasma, atomic nuclei (ions) are separated from electrons, and immensely strong electric fields can build up between the oppositely charged particles when they are separated by the waves behind a powerful laser pulse. Some of the electrons in the plasma are swept up by the waves and are quickly accelerated to high energy.

“In this case the wave is a tsunami, and it doesn’t much matter what the surfers do; they’ll be carried along,” Leemans says. “That’s called self-trapping. But there are other ways a surfer can catch a wave. Real surfers can gauge the size and speed of an oncoming wave and start paddling to match its momentum.”

Attempts to create tunable electron beams through momentum-matching have been tried, by injecting electrons into the accelerating field – first giving them a boost using colliding laser pulses to catch the wave, then using a different drive-laser pulse to excite a wave on which those surfing electrons can be accelerated to high energies. It’s an approach that demands sophisticated timing and synchronization, and along with other tuning methods for one-stage accelerators, requires electron injection that’s localized in space and time.

“But there’s a third way of helping a surfer catch a wave,” Leemans says, “and that’s by slowing the wave until even slow surfers can catch it – then increasing the speed of the wave.” In other words, a two-stage process – and this turns out to be the secret to tunable, high-quality electron beams.

For their experiments the Berkeley Lab scientists modified the same 3.3-centimeter LOASIS accelerator and the same 40-trillion-watt peak-power drive laser, dubbed TREX, they used to produce the first billion-electron-volt beam. The accelerator is a block of titanium sapphire with a narrow capillary through it, filled with hydrogen gas that’s ionized to a plasma by a jolt of electricity, just before the drive-laser pulse enters.

“Two-stage” acceleration

Slowing the laser wake and then speeding it up requires controlling the wake’s phase velocity. To modify the LOASIS system for “two-stage,” tunable acceleration, the researchers introduced a supersonic jet of helium gas that passes through the accelerator’s hydrogen-filled capillary at the upstream front end. This sharply increases the density of electrons in the subsequent plasma. The plasma density then falls off rapidly downstream.

A laser plasma accelerator uses a laser pulse (red and blue disks, extreme right) to create a wake through a plasma, creating strong electric fields. Like surfers on a wave, free electrons ride the wake and are accelerated to high energies. Only the electron bunch propelled by the first wave (white glow) is shown in this simulation. (Simulation by Jean-Luc Vay and Cameron Geddes)

“The extra density itself serves as a lens to focus the laser to higher intensity, and the laser is focused right where the extra density is beginning to decrease,” says Leemans. Here at the edge of the “density downramp,” the slower waves trap electrons more readily. “The waves in the wake are falling farther behind the laser pulse as it enters the region of lower density.”

Density control is only one way to control wave velocity, however. Another method is through laser intensity – an unexpected gift from Albert Einstein’s Special Theory of Relativity. Leemans explains, “The particles in the plasma waves have slowed because of the increased density, but they’re still moving relativistically, near the speed of light,”

Carl Schroeder, a theoretician with LOASIS and an author of the Nature Physics paper, says that “as the laser is focused, its intensity increases, driving larger and larger plasma waves.  Larger waves increase the relativistic mass effect. This reduces the frequency of the wave and stretches the wavelength. The peaks of the waves fall even farther behind the laser pulse.”

Says experimenter Tony Gonsalves, first author of the Nature Physics paper, “If we simply end the plasma there, we have a stable low-energy accelerator. But with a second stage we can accelerate the electron beam to much higher energy, and we can tune that energy.”

The same drive-laser pulse whose wake has been slowed by plasma density and laser intensity now powers into the low-density region of the accelerator; the following waves, carrying their extra load of electron “surfers,” rapidly catch up.

“Tuning the energy is possible because by changing the density or location of the higher-density plasma, we can change its focusing power, the intensity of the laser pulse, and how much the pulse spreads out in the following lower-density plasma,” Gonsalves says. “This allows us to tune the acceleration length and the final beam energy. The stability we achieve over our tunable range is quite amazing.”

By tailoring plasma density in the two zones over the length of the accelerator, the LOASIS researchers were able to tune the energy of the electron beams over a range from 100 million electron volts to 400 million electron volts, while maintaining energy stability to within a few percent.

Leemans says, “Tailoring plasma density longitudinally this way is a concept that shows a new path to the level of sophisticated tuning for accelerators and light sources that users of conventional facilities just take for granted. It’s a major step toward perfecting the laser plasma light sources and accelerators of the future.”

- Paul Preuss

Guest author

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Particle accelerators help develop new cancer fighting drug

August 26, 2011 | 1:45 pm

Light sources are the ultimate app for particle physics. Researchers around the world use the powerful X-ray beams that light sources create for materials science, protein structure analysis, historical research, pharmaceutical research and drug development and the list keeps going. Argonne National Laboratory published the following story on August 25, 2011 about contributions that the Advanced Photon Source made to developing a new drug to treat skin cancer. For more examples about the applications of particle physics, visit Accelerators for America’s Future. 

Powerful x-ray technology developed at the U.S. Department of Energy Office of Science’s (DOE-SC’s) national laboratories, including the Advanced Photon Source at Argonne National Laboratory, has enabled the discovery of a groundbreaking new drug treatment for malignant melanoma, the deadliest form of skin cancer. The drug, Zelboraf (vemurafenib), received Food and Drug Administration (FDA) approval on Wednesday, August 17, 2011. In revealing the structures of diseased and disease-causing molecules at their basic level, the DOE-SC’s extremely bright x-ray light sources enable scientists to develop potential new treatments.

The protein crystallographic structure of the new anti-cancer drug, vemurafenib, is the green honeycomb structure at middle left. Four dotted red lines show where it attaches to a target area in the mutated enzyme, disabling it from promoting the growth of tumors. Image courtesy of Plexxikon Inc.

“This technology is a wonderful example of how innovations at our national laboratories lead to discoveries in a wide variety of fields,” said Energy Secretary Steven Chu. “In this case, we are pleased to have been involved in research that has shown great promise in the battle against life-threatening melanoma.”

An increasing number of drug discovery companies and medical researchers are turning to the powerful x-ray facilities at the DOE national laboratories to probe the causes of disease and develop new treatments by revealing new insights into a wide range of diseases. Researchers from Plexxikon Inc., the drug discovery company that developed the melanoma treatment, used x-ray light sources at Argonne and two other DOE national laboratories—SLAC National Accelerator Laboratory and Lawrence Berkeley National Laboratory—to determine the specific, three-dimensional protein structure of a mutated enzyme that tells melanoma cancer cells to multiply uncontrollably. The research at the APS was carried out at the Structural Biology Center Collaborative Access Team x-ray beamline 19-BM.

The researchers used the technique called macromolecular x-ray crystallography to determine the protein structure in order to develop a drug that would prevent the enzyme from multiplying. The newly FDA-approved drug, Zelboraf (vemurafenib), was extremely successful during clinical trials in disrupting the disease and extending the lives of those diagnosed with it.

“Plexxikon’s drug discovery approach is critically dependent on harnessing the power of x-ray crystallography, and the role of DOE facilities in enabling the development of compounds like vemurafenib has been fundamental,” said Gideon Bollag, Senior Vice President for Research at Plexxikon. “With the insight we gain from the three-dimensional structures, we have an atomic road map to rationally optimize our drug candidates.”

In addition to this treatment for melanoma, the x-ray light sources at the DOE-SC labs have revealed new insights into diseases such as Alzheimer’s disease, swine flu, autoimmune disorders, bird flu, hepatitis, and the common cold.

The original DOE press release can be read here.

Guest author

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Being sensitive is a good thing, at least when you’re a particle accelerator

August 25, 2011 | 3:44 pm

Fermilab Today published the following story on August 25, 2011. 

CDF (red) and DZero (yellow) recorded the East Coast earthquake. Image courtesy of Todd Johnson, AD

CDF (red) and DZero (yellow) recorded the Colorado earthquake. Image courtesy of Todd Johnson, AD

On Tuesday, Aug. 23, the Tevatron accelerator knew something none of the people operating it knew. It felt what employees didn’t, and it reported the news faster than the media could upload it to the Internet.

A 5.9-magnitude earthquake had struck the East Coast, and the super-sensitive Tevatron felt it as it happened about 600 miles away. It had also registered a similar quake in Colorado the night before.

The quakes were recorded by sensors on large underground focusing magnets that compress particle beams from the four-mile Tevatron ring into precision collisions at the CDF and DZero detectors. The sensors keep these areas most sensitive to misalignment under constant surveillance. Quakes can jiggle small numbers of particles – less than one percent of the beam – out of alignment and force the shutdown of parts of the three-story detectors to avoid damage. Tevatron operators compare the sensor recordings with updates from the U.S. Geological Survey to rule out natural causes before having to spend time diagnosing machine trouble that caused beam movement.

Typically, two quakes occurring in this short a timeframe would cause headaches for those who run the Tevatron, but fortunately the machine didn’t have beam in the tunnels at the time.

The Tevatron has recorded more than 20 earthquakes from all over the globe, as well as the deadly tsunamis in Sumatra in 2005 and in Japan in March.

Tona Kunz

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Surprise difference in neutrino and antineutrino mass lessening with new measurements from a Fermilab experiment

August 25, 2011 | 10:50 am

Fermilab issued the following press release on August 25, 2011. 

BATAVIA, Illinois — The physics community got a jolt last year when results showed for the first time that neutrinos and their antimatter counterparts, antineutrinos, might be the odd man out in the particle world and have different masses. This idea was something that went against most commonly accepted theories of how the subatomic world works.

This graph demonstrates that the new MINOS antineutrino result (blue) is more precise than last year’s result (red), as reflected by the smaller oval, and the new result is in better agreement with the mass range of the 2010 neutrino result (black), reflected by the overlap of the blue and red ovals.

A result released today (August 25) from the MINOS experiment at the Department of Energy’s Fermi National Accelerator Laboratory appears to quell concerns raised by a MINOS result in June 2010 and brings neutrino and antineutrino masses more closely in sync.

By bringing measurements of neutrinos and antineutrinos closer together, this new MINOS result allows physicists to lessen the potential ramifications of this specific neutrino imbalance. These ramifications include: a new way neutrinos interact with other particles, unseen interactions between neutrinos and matter in the earth and the need to rethink everything known about how the universe works at the tiniest levels.

“This more precise measurement shows us that these particles and their antimatter partners are very likely not as different as indicated earlier. Within our current range of vision it now seems more likely that the universe is behaving the way most people think it does,” said Rob Plunkett, Fermilab scientist and co-spokesman of MINOS. “This new, additional information on antineutrino parameters helps put limits on new physics, which will continue to be searched for by future planned experiments.”

University College London Physics Professor and MINOS co-spokesperson Jenny Thomas presented this new result – the world’s best measurement of muon neutrino and antineutrino mass comparisons — at the International Symposium on Lepton Photon Interactions at High Energies in Mumbai, India.

MINOS nearly doubled its data set since its June 2010 result from 100 antineutrino events to 197 events. While the new results are only about one standard deviation away from the previous results, the combination rules out concerns that the previous results could have been caused by detector or calculation errors. Instead, the combined results point to a statistical fluctuation that has lessened as more data is taken.

Physicists measured the differences between the squared masses between two types of neutrinos and compared them to the squared masses between two types of antineutrinos, a quantity called delta m squared. The 2010 result found, as a whole, that the range of mass difference in the neutrinos was about 40 percent less for antineutrinos, while the new result found a 16 percent difference.

“The previous results left a 2 percent chance that the neutrino and antineutrino masses were the same. This disagrees with what theories of how neutrinos operate predicted,” Thomas said. “So   we have spent almost a year looking for some instrumental effect that could have caused the difference. It is comforting to know that statistics were the culprit.”

Because several neutrino experiments operating and planned across the globe rely on neutrino and antineutrino measurements being the same as part of their calculations, the new MINOS result hopefully removes a potential hurdle for them.

Fermilab’s accelerator complex is capable of producing intense beams of either muon antineutrinos or muon neutrinos to send to the two MINOS detectors, one at Fermilab and one in Minnesota. This capability allows the experimenters to measure the mass difference parameters. The measurement also relies on the unique characteristics of the MINOS far detector, particularly its magnetic field, which allows the detector to separate the positively and negatively charged muons resulting from interactions of antineutrinos and neutrinos, respectively.

The antineutrinos’ extremely rare interactions with matter allow most of them to pass through the Earth unperturbed. A small number, however, interact in the MINOS detector, located 735 km away from Fermilab in Soudan, Minnesota. During their journey, which lasts 2.5 milliseconds, the particles oscillate in a process governed by a difference between their mass states.

Further analysis will be needed by the upcoming Fermilab neutrino experiments NOvA and MINOS+ to close the mass difference even more. Both experiments will use an upgraded accelerator beam generated at Fermilab that will emit more than double the number of neutrinos. This upgraded beam is expected to start operating in 2013.

The MINOS experiment involves more than 140 scientists, engineers, technical specialists and students from 30 institutions, including universities and national laboratories, in five countries: Brazil, Greece, Poland, the United Kingdom and the United States. Funding comes from: the Department of Energy’s Office of Science and the National Science Foundation in the U.S., the Science and Technology Facilities Council in the U.K; the University of Minnesota in the U.S.; the University of Athens in Greece; and Brazil’s Foundation for Research Support of the State of São Paulo (FAPESP) and National Council of Scientific and Technological Development (CNPq).

Fermilab is a national laboratory supported by the Office of Science of the U.S. Department of Energy, operated under contract by Fermi Research Alliance, LLC.

The DOE Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit http://science.energy.gov.

Press Release

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Cloud-formation study at CERN to influence climate models

August 25, 2011 | 7:13 am

CLOUD spokesperson Jasper Kirkby in front of the experiment. Photo credit: CERN

Scientists on an experiment at CERN announced today that there is more to cloud formation than previously thought. Their study, published in the journal Nature, looked at the effects on cloud formation of vapors and cosmic rays in the atmosphere. The results could help improve the accuracy of climate models.

The CLOUD experiment at CERN studied the formation of new aerosol particles, tiny liquid or solid particles suspended in the atmosphere. These particles are thought to be responsible for a large fraction of the seeds that form clouds. Increases in atmospheric aerosol particles cool the climate by brightening clouds and reflecting sunlight away from Earth. The increased amount of aerosol in the atmosphere caused by human activities is thought to have offset a large fraction of the warming caused by greenhouse gases.

Current climate models assume that sulphuric acid and ammonia, the vapors most likely to cluster together and form new particles, cause this particle formation with nothing other than water. But the CLOUD experiment found that these vapors account for only 1/10 to 1/1000 of new aerosol particles that appear in the lower atmosphere.

“It was a big surprise to find that aerosol formation in the lower atmosphere isn’t due to sulphuric acid, water and ammonia alone,” said the experiment’s spokesperson, Jasper Kirkby. “Now it’s vitally important to discover which additional vapors are involved, whether they are largely natural or of human origin, and how they influence clouds. This will be our next job.”

Two groups of Americans participate in the CLOUD experiment: A professor and a student from California Institute of Technology and the company Aerodyne Research Inc. Professor Richard Flagan at Caltech provided the experiment with an instrument he had developed to classify the size of particles down to a single nanometer.

Scientists in the CLOUD collaboration also studied the effect of cosmic rays on aerosol formation. They found atmospheric ionization caused by cosmic rays increased the formation of aerosol particles by up to a factor of 10, particularly in the cool temperatures above the lower atmosphere, where CLOUD has found sulphuric acid and water vapor can form new aerosols without the help of additional vapors.

The result leaves open the possibility that cosmic rays could influence climate. However, scientists will need to determine what other vapors are involved before they can reach any conclusions about their role.

Read the CERN press release on these results.

Kathryn Grim

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Physicist tapes together particle data

August 23, 2011 | 8:00 am

Magnetic tape, the transformative medium that made it possible for 1990s teenagers to commit carefully curated pop songs to cassettes and present them like audio billets-doux to their crushes, has long been superannuated by hard drives. Getting a mix from Pandora just isn’t the same.

Selex on exhibit at the Chicago Art Department. Selex is made from 400 data storage tapes from Fermilab’s charmed baryon experiment Selex. It’s part of the exhibit Tape: A Celebration. Image: Chicago Art Department

The difference in sensibility is just as true for physics experiments.

As homage to tape and physics, MIT postdoctoral associate Teppei Katori, who works at Fermilab, created the art piece Selex. Named for a fixed-target charmed baryon experiment that ran in Fermilab’s Tevatron from 1996-97, Selex is part of the exhibit Tape: A Celebration currently showing at the Chicago Art Department in the city’s Pilsen neighborhood.

“It’s the only digital tape piece in the exhibit,” Katori says, noting that the exhibit’s other dozen or so pieces are related to analog tape. “There are no analog tapes in particle physics. I’m a bit biracial.”

In Selex, Katori’s intent is to capture the sharpness and precision needed in science data, creating clean lines and stark contrast using 400 actual data storage tapes from the Selex experiment.

These black, 8-millimeter digital tape cassettes, affixed at their short sides to a white paper background, spell out the word ‘SELEX’. The background is photocopied pages of the 2005 Physical Review Letters paper on Selex’s most highly cited discovery. Suspended from the ceiling by chains, the piece also comprises more tapes lying flat on the floor beneath it, forming a rectangular carpet of cassettes.

In physics experiments today, data tapes are stored in and accessed at remote computing farms. Out of experimenters’ sight, they are also almost always out of mind. But in the bygone era recalled by Selex, tapes were at scientists’ fingertips. Katori’s piece is a nostalgic recollection of that immediacy.

It’s also a nod to early digitization, Katori says. Because the word SELEX is formed from discrete cassettes rather than, say, a continuous unreeled strip, it calls to mind the formation of lettering such as that from a dot matrix. And because these cassettes are jumbo-sized dots, it also recalls the style of a pastime that has come a long way over the decades:

“It’s like the classic video games where the graphics are made of huge dots, like Super Mario Bros.,” Katori says. “It’s like it’s made from a low number of bits.”

The Selex tapes, though, are anything but low-bit. Each small cassette contains 5 gigabytes of data, not too shabby considering how big your average 5-gig drive would have been in 1997. The Selex experiment required 3,000 of them to store its data.

Selex scientists were on the hunt for charmed baryons, particles made of three quarks and including at least one charm quark.

“These things are hard to make and hard to see – they’re heavier than two-quark mesons and you don’t get as many,” says Fermilab’s Peter Cooper, deputy spokesperson for Selex. With more than 120 scientists from 20 institutions in 10 different countries working on Selex, researchers gathered enough information over the two-year lifetime of Selex to describe the mass, lifetime, decay modes and other basic properties of charmed baryons such as _C and _C.

The cover of Physical Review Letters, volume 89, number 11, featured an event that demonstrated the discovery by Selex scientists of the double-charmed baryon.

“There’s a whole list of physics questions associated with the heavy family of the proton and neutron,” Cooper says. Protons and neutrons, themselves baryons, are available in nature. Other baryons have to be made in the laboratory. The Selex finding that made the cover of Physical Review Letters was the discovery of the double-charmed baryon _cc⁺.

“No one had ever seen it before,” he says.

And without tape, particles wouldn’t be seen at all.

With Selex, Katori celebrates an important experiment in particle physics history and the medium that made it and many other science discoveries possible.

As for any concern for the fate of data now enshrined in Selex, it all lives in a more permanent place. For older physics experiments such as Selex, once the data on outmoded storage materials is transferred to modern hardware, the usual life cycle of these materials concludes either at a recycling plant or in a neglected box. For the lives of Selex tapes, it was the latter. The particular tapes for Katori’s work were those that contained backup data, and were in Cooper’s possession when Katori set out to create Selex. As the tapes were the sole property of Selex, it was decided that they be recycled in an artistic matter rather than undergoing the unseemly and less artistic fate of a shredder.

If you’re in the Chicago area, you can visit the Chicago Art Department to view Katori’s Selex and other tributes to tape. View photos of works in the exhibit.

Leah Hesla

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LHC experiments eliminate more Higgs hiding spots

August 22, 2011 | 9:06 am

Fermi National Accelerator Laboratory and Brookhaven National Laboratory issued the following press release on August 22, 2011.

BATAVIA, IL and UPTON, NY – Two experimental collaborations at the Large Hadron Collider, located at CERN laboratory near Geneva, Switzerland, announced today that they have significantly narrowed the mass region in which the Higgs boson could be hiding.

The ATLAS and CMS experiments excluded with 95 percent certainty the existence of a Higgs over most of the mass region from 145 to 466 GeV. They announced the new results at the biennial Lepton-Photon conference, held this year in Mumbai, India.

“Each time we add new data to our analyses, we close in more on where the Higgs might be hiding,” said Darin Acosta, a University of Florida professor and deputy physics coordinator for the CMS experiment.

More than 1,700 scientists, engineers and graduate students from the United States collaborate on the experiments at the LHC, most of them on the CMS and ATLAS experiments, through funding by the Department of Energy Office of Science and the National Science Foundation. Brookhaven National Laboratory serves as the U.S. base for participation in the ATLAS experiment, and Fermi National Accelerator Laboratory serves as the U.S. base for participation in the CMS experiment.

The Higgs particle is the last not-yet-observed piece of the theoretical framework known as the Standard Model of particles and forces. According to the Standard Model, the Higgs boson explains why some particles have mass and others do not.

“The more data the experiments collect, the more scientists can say with greater statistical certainty,” said Konstantinos Nikolopoulos, a physicist at Brookhaven National Laboratory on the ATLAS experiment. “The LHC has been providing that data at an impressive rate. The machine has been functioning beyond expectations.”

Scientists on ATLAS and CMS both announced seeing small, possible hints of the Higgs boson at the European Physical Society meeting in July. Those hints have become less pronounced as scientists have increased the amount of data in their analysis.

“These are exciting times for particle physics,” said CERN’s research director, Sergio Bertolucci. “Discoveries are almost assured within the next twelve months. If the Higgs exists, the LHC experiments will soon find it. If it does not, its absence will point the way to new physics.”

The experiments are on track to at least double the amount of data they have collected by the end of the year.

Read the CERN press release here.

Press Release

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