Calculating the Universe

February 1, 2012 | 9:42 am

This story appeared today in isgtw.

This image shows over a million luminous galaxies at redshifts indicating times when the universe was between seven and eleven billion years old, from which the sample in the current studies was selected. Image by David Kirkby of the University of California at Irvine and the SDSS collaboration.

Since 2000, the three Sloan Digital Sky Surveys (SDSS I, II, and III) have surveyed well over a quarter of the night sky, producing the biggest 3-D color map of the Universe ever made. Now, scientists have used this visual information for the most accurate computation yet of how matter clumped together – from a time when the universe was only half its present age until now.

“The way galaxies cluster together over vast expanses of the sky tells us how both ordinary visible matter and underlying invisible dark matter are distributed, across space and back in time,” said Shirley Ho, an astrophysicist at Lawrence Berkeley National Laboratory and Carnegie Mellon University who led the work. “The distribution gives us cosmic rulers to measure how the universe has expanded, and a basis for calculating what’s in it: how much dark matter, how much dark energy, even the mass of the hard-to-see neutrinos it contains. What’s left over is the ordinary matter and energy we’re familiar with.”

For the present study, Ho and her colleagues first selected 900,000 luminous galaxies from among over 1.5 million such galaxies gathered by the Baryon Oscillation Spectrographic Survey, or BOSS, the largest component of the still-ongoing SDSS III. Most of these are ancient red galaxies, which contain only red stars because all their faster-burning stars are long gone, and which are exceptionally bright and visible at great distances. The galaxies chosen for this study populate the largest volume of space ever used for galaxy clustering measurements. Their brightness was measured in five different colors, allowing the redshift of each to be estimated.

“By covering such a large area of sky and working at such large distances, these measurements are able to probe the clustering of galaxies on incredibly vast scales, giving us unprecedented constraints on the expansion history, contents, and evolution of the universe,” said Berkeley Lab’s Martin White, chair of the BOSS science survey teams. “The clustering we’re now measuring on the largest scales also contains vital information about the origin of the structure we see in our maps, all the way back to the epoch of inflation, and it helps us to constrain – or rule out – models of the very early universe.”

After augmenting their study with information from other data sets, the team derived a number of such cosmological constraints (measurements of the universe’s contents based on different cosmological models). Among the results: in the most widely accepted model, the researchers found – to less than two percent uncertainty – that dark energy accounts for 73 % of the density of the universe.

The team’s results are presented 11 January at the annual meeting of the American Astronomical Society in Austin, Texas, and have been submitted to the Astrophysical Journal. They are currently available online at http://arxiv.org/abs/1201.2137.

Read on at isgtw.org.

- Paul Preuss

Guest author

No Comments »

Clearest picture yet of dark matter points the way to better understanding of dark energy

January 10, 2012 | 1:38 pm

Teams from Fermilab and Berkeley Lab used galaxies from wide-ranging SDSS Stripe 82, a tiny detail of which is shown here, to plot new maps of dark matter based on the largest direct measurements of cosmic shear to date. Image credit: SDSS

Two teams of physicists at the U.S. Department of Energy’s Fermilab and Lawrence Berkeley National Laboratory have independently made the largest direct measurements of the invisible scaffolding of the universe, building maps of dark matter using new methods that, in turn, will remove key hurdles for understanding dark energy with ground-based telescopes.

The teams’ measurements look for tiny distortions in the images of distant galaxies, called “cosmic shear,” caused by the gravitational influence of massive, invisible dark matter structures in the foreground. Accurately mapping out these dark-matter structures and their evolution over time is likely to be the most sensitive of the few tools available to physicists in their ongoing effort to understand the mysterious space-stretching effects of dark energy.

Both teams depended upon extensive databases of cosmic images collected by the Sloan Digital Sky Survey, which were compiled in large part with the help of Berkeley Lab and Fermilab.

“These results are very encouraging for future large sky surveys. The images produced lead to a picture of the galaxies in the universe that is about six times fainter, or further back in time, than is available from single images,” says Huan Lin, a Fermilab physicist and member of the SDSS and the Dark Energy Survey.

Read the rest of the press release issued jointly by Fermi National Accelerator Laboratory and Lawrence Berkeley Lab.

Read more from Fermilab at Quantum Diaries.

Read more from Berkeley Lab below.

Read the rest of this entry »

Guest author

1 Comment »

Gamma-ray telescope designer awarded 2012 Panofsky Prize

October 13, 2011 | 10:46 am

SLAC Today first published this article on October 12, 2011. SLAC managed the development of the Large Area Telescope, the main instrument on the Fermi Gamma-ray Space Telescope. Fermilab also made contributions.

Long-time SLAC physicist William Atwood has been honored with the 2012 Panofsky Prize for his work on the Large Area Telescope, the main instrument on the Fermi Gamma-ray Space Telescope. (Photo courtesy UCSC)

William Atwood, a leading member of the Fermi Gamma-ray Space Telescope collaboration, will receive the 2012 W. K. H. Panofsky Prize in Experimental Particle Physics from the American Physical Society for his work as co-designer of the Large Area Telescope, the main instrument on Fermi, and for using the LAT to investigate the universe in gamma rays.

“Nobody was more surprised than myself” upon learning of the award, Atwood said. Now with the Santa Cruz Institute for Particle Physics, Atwood was a long-time SLAC National Accelerator Laboratory particle physicist who maintains his lab ties through the Fermi collaboration. “I’d just finished my SLAC cyber-security refresher course when I got this email,” he continued. “I thought, ‘Oh, jeez, this is just spam.’” But once Atwood confirmed the email’s contents, he said, he was “blown away.”

In 1970, as a graduate student from Caltech, Atwood joined the team at SLAC that scattered high-energy electrons off protons and neutrons and discovered they were made of something even smaller – quarks. SLAC physicist Richard Taylor, principal investigator, was awarded the 1990 Nobel Prize in Physics for this work. It was obvious in 1970 that Atwood “had tremendous potential,” Taylor said, adding that he “was a remarkable physicist, even then.”

Stanford physicist Peter Michelson, Atwood’s partner in developing the LAT, was not surprised at Atwood’s win. “To capture his contributions in a single quote … I’m struggling,” Michelson said. “Bill’s deep understanding of particle physics led to the original design of the LAT, and what’s flying is essentially that design, which he came up with literally overnight.”

Atwood also adapted the design for use in space and has done substantial scientific work with the LAT, such as contributing “a very efficient algorithm for blind searches for gamma-ray pulsars,” Michelson added.

SLAC managed the development of the LAT, assembled it from parts made at laboratories around the world, and now runs a center that processes LAT data and makes it available to researchers.

Astrophysics and particle physics may seem strange bedfellows, but Atwood has no trouble explaining  how a telescope designer could win an award named after the founding director of a linear accelerator, or how a particle physicist could be enticed to work on a satellite.

“Almost all light comes from something hot,” he said. In astronomical observing terms, visible light comes from the nuclear fires of the stars. Infrared light comes from hot dust and gas. But gamma rays are an exception to this rule. “Stuff can’t get hot enough” to produce photons of light in the gamma-ray range, with energies measured in the millions and billions of electron volts, Atwood said. What that means is that gamma rays show us the “non-thermal universe” – in other words, the part of the sky that heat cannot reveal.

Only extreme conditions can generate gamma rays, Atwood said – “black holes and neutron stars, pulsars. The gamma-ray sky is full of these exotic objects.” And these exotic objects provide the extreme conditions necessary to accelerate particles to high energy.

At first, Atwood said, both the particle physics and the astrophysics communities were skeptical that this telescope was the proper instrument to conduct particle physics research or gamma ray astronomy.

“In the end, a good idea is a good idea and people came around,” he said. In fact, “this instrument would not have been possible without the active participation of both communities.”

Related Link

• Physicist Bill Atwood awarded Panofsky Prize in Experimental Particle Physics

Lori Ann White

No Comments »

Mission control CERN: Inside the AMS-02 command center

October 7, 2011 | 1:58 pm

Inside the AMS control center. Image: CERN

Physicist Mike Capell pointed to a display screen showing images of a semi-cylindrical detector. Every few seconds one or two straight lines appeared, seeming to slice the detector lengthwise.

“That’s particles going through right now,” he said.

The event display, located in the control room for the Alpha Magnetic Spectrometer, or AMS-02, shows cosmic rays passing through the experiment’s particle detector as they fly through space. At the control center, located at CERN’s site in Prevessin, France, Capell is in charge of operations for a team of scientists who rotate in eight-hour shifts, 24 hours a day. They plan to do this for 20 years.

Right now, though, they’ve only just begun. The center opened in June. It still smells like fresh paint.

For most people, CERN probably brings to mind the 27 kilometers of tunnels and magnets that make up the Large Hadron Collider. However, not all the detectors at the European center lie underground. AMS-02, by far the largest fundamental particle physics experiment in space, orbits the Earth as an appendage of the International Space Station. There it detects charged cosmic rays, searching for antimatter and hoping to measure the mass of dark matter in a way impossible to do from beneath our planet’s 60 miles of particle-scattering atmosphere. AMS-01, the experiment’s precursor, flew for 10 days in 1998 on the shuttle Discovery.

The control center at CERN is serene and hushed. Most of the eight people working wear headsets connecting them to Marshall Space Flight Center. If they aren’t directly speaking with the Marshall crew, they are listening in on a constant chatter including communications with the ISS astronauts. “That means we don’t like a lot of ruckus,” Capell said.

The workroom is spacious with a two-story ceiling and tall windows on the sides. Large framed photos of AMS-02 construction and shots of the launch and shuttle make up the decor. At the far end, a live feed from NASA dominates the wall, showing the current position of the ISS over a day/night map of the world. This indicates when the station will lose radio contact with researchers on the ground, which happens periodically due to both its relative location to communication satellites and its position in Earth’s nonuniform magnetic field, a potential signal-jam.

Losing radio contact is not the only complication of running the AMS-02 experiment. The detector includes modifications that keep the experiment running through radiation and extreme temperature fluctuations in space. Dealing with the latter condition is so important to the mission that one person working in the control room is dedicated full-time to monitoring and adjusting the detector’s thermal equipment.

The scientists on shift work at computer stations arranged in a U shape around the room. They are physicists, grad students and postdocs. Most come from LHC experiments, and those who do not are likely to join such experiments, should they leave AMS-02 in the future.

Thirteen people were simultaneously on duty at the control center when post-launch operations first moved from Johnson Space Center to the new site at CERN. Soon Capell realized this was unnecessary. “Everything’s been going just like a clock,” he said. He cut the shifts to five people, with one person often monitoring multiple sub-detectors alone. “It’s not as frantic as I expected it to be.”

One operator in the control center watched a feed from a webcam on the ISS in the corner of her busy computer screen. In the hours when the astronauts sleep, the webcam points Earthward, away from the dreamers. The view of oceans rolling slowly past made for a small window of Zen among a chaotic collection of code.

The AMS-02 team uses these hours to download data in order to avoid excess competition for bandwidth with the other experiments on board the ISS. Keeping up with the data flow is one of the critical functions of the control center, said AMS-02 project manager Trent Martin from his NASA office in Houston. “At times we take as much as one third the bandwidth coming down from the space station.”

Since AMS-02 docked with ISS in May, it has been collecting data on billions of events. “This is laughable by LHC standards,” Capell said, “but in terms of cosmic rays, this is absolutely groundbreaking.” The experiment is the biggest and will be the longest running of its kind, observing particles at the highest energies and masses in history as they naturally occur.

The U.S. Department of Energy provides most of the U.S. scientific funding for AMS-02, covering about 5 percent of the experiment’s costs. Universities and institutes in 16 different countries provide the rest of the funding, as well as more than 600 physicists and engineers led by Nobel Laureate Professor Sam Ting of the Massachusetts Institute of Technology. CERN built the control center as part of its contribution to the experiment. NASA provided shuttle transport and continues to provide technical and safety support for the mission.

“This is by far the largest [collaboration] we’ve worked on at NASA,” Martin said. So many people were involved with AMS-02, he said, that, through rough times over the 17 years of preparation for launch, the project never collapsed. “They still believed in the science.”

Amy Dusto

1 Comment »

EXO releases first results

September 9, 2011 | 10:54 am

SLAC published this article on Sept. 8, 2011.

Cooks think of watched pots. Handymen grumble about drying paint. Kids dread the endless night before Christmas morning.

SLAC engineer Knut Skarpaas with half of the EXO 200 detector.

Turns out physicists have their own expression to convey the concept of “slow,” and now, thanks to the Enriched Xenon Observatory (EXO), they know how slow “slow” really is: The flurry of activity during the 13.75 billion years from the Big Bang to us was positively hasty in comparison.

The expression is “2nubb” and it stands for “two-neutrino double-beta decay”, a rare type of particle decay undergone by certain forms of radioactive elements. In this type of decay, two neutrons, the neutral subatomic particles in the nucleus of an atom, spontaneously decay into two protons, two electrons, and two antineutrinos, which are the antimatter twins of the tiny, nearly massless mystery particles called neutrinos. The EXO team announced yesterday at a conference in Munich that, according to their measurements of two-neutrino double-beta decay in Xe-136, an isotope of xenon, the half-life of the process clocks in at 2.11 x 10²¹ years. In other words, it would take 100 billion times longer than the universe has even existed for half of a sample of this radioactive isotope to decay via the 2nubb decay pathway.

“This represents the slowest Standard Model process ever measured,” said Giorgio Gratta, Stanford University physicist and member of the joint SLAC-Stanford Kavli Institute for Particle Astrophysics and Cosmology, who leads the team. The Standard Model is the best description scientists have for the way all the building blocks of matter, like the aforementioned neutrons, protons and electrons, fit together, and why two-neutrino double-beta decay happens in the first place.

Two-neutrino double-beta decay fits neatly within the Standard Model, “so in this sense the observation was not unexpected,” Gratta said. In fact, this form of decay has been seen before in other elements. “In that sense, it is not even new.”

Even so, the team’s results mean much more than a shot at the Guinness Book of World Records.

The EXO 200 detector is the first to capture the 2nubb decay process in Xe-136, for example, and the measurement is based on little more than a month of data – “remarkably clean” data, with very little interference from background noise, Gratta explained. This solid signal has provided valuable data to theorists, enabling them to resolve puzzling discrepancies between their calculations and the results of previous experiments.

But the experiment is far from over, and the speed and clarity of these early results bode well for the team as they go after their real quarry.

What the EXO 200 team wants to find is another decay process – one that is not only even more fantastically rare than 2nubb, but that no one is certain even exists. It’s called zero-neutrino double-beta decay, or 0nubb, and it is decidedly not a Standard Model process.

In 0nubb, two neutrons once again decay into two protons and two electrons, but the antineutrinos are nowhere to be found. They must have been there; the IRS has nothing on Nature for keeping the books balanced. The two antineutrinos must have annihilated each other, like positrons and electrons can annihilate each other, or protons and anti-protons, or any particle and its antiparticle.

This means in order for 0nubb decay to happen, neutrinos must be their own antiparticles.

Odd as this sounds, the possibility of a particle that could be both itself and its anti-self was hypothesized by an Italian theoretical particle physicist named Ettore Majorana in 1937. Such particles are called Majorana particles, and if they exist physicists would need to get busy revising the Standard Model.

“This is a decay that people have been trying to find for a long time,” Gratta said.

“Zero-neutrino double-beta decay would be a big deal,” agreed Marty Breidenbach, SLAC physicist and EXO team member. He explained how the EXO 200 experiment intends to pursue such a prize. It all comes down to distinguishing between something that’s nearly impossible to see because of its rarity and something that’s clearly impossible to see because it may not even exist.

The team’s chief strategy is to give the 0nubb decays as many opportunities to happen and as few places to hide as possible. A detector chamber filled with 200 kilograms of liquid xenon takes care of the first strategic objective – the xenon has been enriched until it’s 80 percent Xe-136, the double-beta decaying isotope – but the second one is a bit tougher.

In order to make sure they’ll recognize 0nubb – or even 2nubb – decays, the team has had to cut out every other source of radioactivity they could. The equipment, made of ultrapure, ultraclean, non-radioactive materials, was constructed at Stanford University and trucked, not flown – flying would expose it to more cosmic rays – to the Chihuahuan Desert near Carlsbad, New Mexico, where it was installed about a half-mile underground in the salt bed used by the Waste Isolation Pilot Plant, the Department of Energy’s repository for nuclear waste. The choice seems odd, but the reasoning was sound. The same salt that keeps radioactivity from nuclear waste trapped in the repository keeps radioactivity from cosmic rays and decaying rocks out of the EXO 200 detector.

As the low background readings in their initial results show, the EXO 200 strategy seems to be working. According to Breidenbach, the experiment will continue to take data for several years, possibly as many as five, depending on progress with what’s called “full EXO,” an experiment using several tons of Xe-136 that’s currently in development.

“EXO 200 was always intended as a pilot project,” Breidenbach said. “We’re actively doing R&D for full EXO.”

In the meantime, there’s no moss gathering on the EXO collaboration. EXO 200 has already made its mark.

- Lori Ann White

The EXO collaboration comprises researchers from the following institutions: Department of Physics and Astronomy, University of Alabama, Tuscaloosa AL, USA; LHEP, Albert Einstein Center, University of Bern, Bern, Switzerland; Kellogg Lab, Caltech, Pasadena CA, USA; Physics Department, Carleton University, Ottawa ON, Canada; Physics Department, Colorado State University, Fort Collins CO, USA; Physics Department and CEEM, Indiana University, Bloomington IN, USA; Institute for Theoretical and Experimental Physics, Moscow, Russia; Physics Department, Laurentian University, Sudbury ON, Canada; Physics Department, University of Maryland, College Park MD, USA; Physics Department, University of Massachusetts, Amherst MA, USA; Department of Physics, University of Seoul, Seoul, Korea; SLAC National Accelerator Laboratory, Stanford CA, USA; Physics Department, Stanford University, Stanford CA, USA; Technical University Munich, Munich, Germany; Waste Isolation Pilot Plant, Carlsbad NM, USA.

Guest author

No Comments »

Turning data into wild rides through dark domes

July 7, 2011 | 2:57 pm

Ralf Kaehler, right, and Ji-hoon Kim of KIPAC stand before a snapshot of a large-scale reionization simulation. The blue regions indicate hot, ionized hydrogen gas. (Photo by Brad Plummer.)

From their seats in the Morrison Planetarium at the California Academy of Sciences in San Francisco, visitors swoop through a redwood forest, into a single redwood leaf and finally into an individual cell to watch photosynthesis take place. Then they travel back billions of years to watch the first stars wink on, heat up and explode, scattering into space many of life’s essential chemical elements.

The point of the show, “Life: A Cosmic Story,” narrated by Jodie Foster, is that the connections between living things go all the way back to the distribution of dark matter in the early universe;  its gravitational influence allowed the formation of galaxies, stars and  planets.  Unlike shows of a decade ago, all the animations of things we can’t see are based on real scientific data – including visualizations made by researchers at KIPAC, the Kavli Institute for Particle Astrophysics and Cosmology, at SLAC National Accelerator Laboratory and Stanford University.

“Rather than relying purely on artistry and artwork to communicate the science, it’s going to the scientists and using the same data they’re using to create visuals,” said Ryan Wyatt, who directs Morrison Planetarium and the science visualization staff at the California Academy of Sciences. “To my mind that’s incredibly valuable. It’s authentic. It allows people to experience the science in a way they probably can’t do elsewhere.”

This is the third planetarium show that KIPAC scientists Ralf Kaehler and Tom Abel have collaborated on, and the fifth for Abel. “Life” at the Morrison features their animation of the birth and death of the earliest stars, an area in which Abel is a world expert.  A similar visualization appears in “Journey to the Stars,” narrated by Whoopi Goldberg, now playing at New York City’s Hayden Planetarium.  The team also contributed to a show narrated by Liam Neeson that welcomes visitors to the Hayden. For that, they put together a sequence that shows massive galaxies in the early universe colliding, merging and spinning away from each other.

Often created from simulations that scientists have run as part of their research, these visualizations are “kind of a byproduct of this work,” Kaehler says. “And it’s a great way of doing public outreach.” The pair’s work has appeared in books, newspapers, TV shows, exhibits and magazines–including, in February 2003, the first computer-generated image on the cover of National Geographic. 

Science-based planetarium shows are the latest advance in a tradition that dates back centuries. The first attempts were hollow globes, big enough to let a few people inside, pricked with holes to let “starlight” in.  About 85 years ago, the first modern planetarium opened in Munich; a light projector made by the Carl Zeiss Co. splashed starlight onto the dark, concave surface of the dome. Soon planetariums were springing up by the hundreds – from small ones used for teaching to large domes that seated hundreds of people. For many visitors, the technology provided their first glimpse of a truly dark sky, undimmed by city lights. 

In 2000, the opening of the new Hayden Planetarium at the American Museum of Natural History showcased a major leap in technology: The first show based on visualizations of real scientific data. Observations of the locations and brightness of more than 100,000 stars came from the European Space Agency’s Hipparcos satellite. Data on 45,000 galaxies came from an astronomer at the University of Hawaii. And data collected over the years on the Orion Nebula, a giant gas cloud studded with newborn stars, allowed visitors to fly through a stunning 3-D version of the nebula as if on magic carpets.
 

A visualization of a massive star in the early universe. The highly-energetic ultraviolet emissions from the star ionize the gaseous material in its neighborhood. (Visualization: Ralf Kaehler (KIPAC/SLAC) and Tom Abel (KIPAC/Stanford))

Presenting that show required a Silicon Graphics Onyx2 supercomputer, said Wyatt, who worked at the Hayden before joining the Morrison Planetarium. With the huge increases in computing power over the past decade, it can now be done with seven desktop computers.

Planning and developing a planetarium show can take anywhere from 16 months to two years.  For Abel and Kaehler, the process may start six months before the show is slated to go public, with a request for a visualization that will tell a story spanning billions of years in the space of a minute or two.

Abel, an associate professor of physics at SLAC and Stanford, leads KIPAC’s Computational Physics Department and specializes in creating numerical simulations – computer models based on scientific data and complex equations that describe the laws of physics.  Simulations have become a valuable tool – a sort of third arm of science, alongside theory and experiment – for understanding how nature works, allowing researchers to grasp patterns that are otherwise hidden inside reams of data.

A simulation of how the first stars formed might start with a map of the cosmic microwave background radiation, which has been measured in great detail by spacecraft. Scientists think these tiny variations in the energy left over from the big bang provided the gravitational seeds around which stars and galaxies formed.

The simulation software, which usually runs on large computer clusters, divides an enormous region of space, up to hundreds of thousands of light years across, into cubes. Within each of those cubes the software calculates physical quantities, such as the density, temperature, and velocity of hydrogen gas, Kaehler said. Then it divides those cubes into even smaller ones, identifies the regions where stars are most likely to form, and does another round of calculations. This is repeated until the simulation has zoomed in close enough to the star-forming regions to capture all the relevant physics with sufficient accuracy.

A test-rendering of galaxies merging for a show at the Big Bang Theatre in the Hayden Planetarium. Visualization: Ralf Kaehler (KIPAC/SLAC) and Tom Abel (KIPAC/Stanford). Simulation: Ji-hoon Kim (KIPAC).

But that still doesn’t give researchers a picture – just millions and billions of computer-generated numbers.  It’s the job of Kaehler, a research software developer at KIPAC, to turn those numbers into visualizations – both stills and animations – that allow the viewer to grasp what’s happening in a clear and intuitive way.

This involves a lot of software engineering, he said.  “Since we’re building all our 3-D visualization software from scratch, we can tailor everything just the way we need it.  Writing the code is a lot of work, but it also gives us a lot of freedom.”  Among other things, the visualization has to take into account what path the camera will take through the 3-D world the scientists have created, and what colors that world is painted in.

For “Life: A Cosmic Story,” the scientists worked closely with the Academy’s production staff, whose members   could claim a combined total of 120 years of visualization experience, Wyatt said. Kaehler and Abel, he said, “bring their technical savvy and scientific background, and work with our visual sensibilities.”

The Morrison Planetarium draws about 750,000 visitors per year, Wyatt said, and he is working to make “Life” available to the estimated 700 to 800 other planetarium domes that are capable of playing it.  As the show makes it way out into the expanding universe of planetarium fans, it may turn out that Abel and Kaehler’s outreach efforts have a very long reach indeed.

Glennda Chui

No Comments »

TAUWER aims for cosmic heights

June 16, 2011 | 2:25 pm

The origin of ultra-high-energy cosmic rays is a question that makes it onto many top-unsolved-problems-in-physics lists.

The TAUWER experiment looks at particle showers that originate from tau neutrinos that take short paths through the earth (inset). An ideal site to observe these events is a mountain bowl. Image courtesy of Maurizio Iori.

The math says that these particles, which carry in excess of 10¹⁹ electron volts, or eV,  from somewhere in outer space, are far too energetic not to have interacted themselves out of existence before reaching the earth. And yet every year scientists see evidence in the earth’s atmosphere of a handful of these particles, which have several million times the energy of the protons being collided at the Large Hadron Collider.

Scientists are proposing a new experiment, called TAUWER, that would look to tau neutrinos to remove some of the mystery from these strange, over-stimulated cosmic rays.

“The question is, how do they get this energy?” says James Russ, TAUWER collaborator and professor of physics at Carnegie Mellon University. “We don’t know what the mechanism is.”

One idea for the mechanism is a rapid rebounding between plasma shock waves. In places such as those near black holes, where charged matter builds to extreme densities, protons may be ricocheting back and forth between shock wave fronts, accelerating and gathering energy over billions of years. Then one day the proton may escape and come to earth in the form of an ultra-high-energy cosmic ray or UHECR.

If these UHECRs are indeed protons escaped from star systems, they’ll reveal their existence, through a series of interactions, by producing ultra-high-energy neutrinos, neutrinos with energies greater than 10¹⁶ eV—over a billion times more energetic than those produced by supernovas.

TAUWER detectors would examine the particle showers brought on by these neutrinos’ interaction with the earth. The resulting energy measurements of the tau neutrinos could give scientists information about their conjectured parents, the UHECR protons.

“The neutrinos’ energy spectrum tells you about the nature of the protons’ acceleration,” Russ said. “That’s why it’s an interesting measurement to make.”

Collaborators are interested in particular in tau neutrinos – one of three known types – because of the high chance they’ll end up propagating particle showers that their detectors can see.

Rough layout scheme of TAUWER detectors on a mountainside. The straight blue line represents a tau lepton emerging from the earth. The white lines represent shower tracks from the tau lepton decay. Image courtesy of Maurizio Iori.

TAUWER isn’t the only program that’s using neutrinos to get to cosmic rays. The IceCube experiment at the South Pole looks for lower-energy neutrinos as they barrel through the length of the earth’s diameter with energies of up to 10¹⁶ eV. IceCube experimenters are currently busy with creative new schemes to extend their energy reach.

TAUWER picks up where the present IceCube design leaves off. Neutrinos with higher energies may not be able to make it from one end of the planet to the other since they’ll very likely be derailed by the rock in the earth. But if the trip through the earth is short enough, they can still make their way out.

TAUWER detectors would turn their attention particles that fly through short slices of the planet, about 1/13 the diameter of the earth. The neutrinos could, for example, enter San Francisco Bay and, a thousand kilometers later, exit Salt Lake. During these split-second trips through the earth, the ultra-high-energy neutrinos’ interaction with the rock would be close enough to the earth’s surface that its offspring, a tau lepton (a heavy cousin of the electron) could still push its way from beneath the ground into the air. TAUWER detectors, pointed at some angle toward the earth, will see the 1-kilometer-radius particle shower that springs from the tau lepton’s connection with the atmosphere.

The detectors, which have a very high pointing accuracy, can then pick out the direction of the UHECR that started it all. And with enough tau neutrino data, the UHECR phenomenon could very well lose its place on the top-unsolved-problems list – a good thing.

The Pierre Auger experiment in Argentina has also been on a quest to catch glimpses of UHECRs by way of tau neutrinos, but using very different methods. Auger detectors look for UHECRs that come uninterrupted from the sky. TAUWER detectors, on the other hand, would watch the ground to find tau neutrinos that come from below. Russ imagines TAUWER detectors searching for neutrino events from the height of a mountainside. The collaboration is scouting mountain bowls, sites where mountain ridges surround level stretches of land, in Europe, Mexico, and the US.

“A mountain bowl has the lovely feature that it screens horizontal cosmic rays, which are one background source,” Russ said. “You’re sitting on a mountain range that’s looking down on a nice flat space for neutrinos to come up through.”

The collaboration is currently testing a handful of detectors. Once the experiment is running full speed ahead, they’ll run 2,500 small detectors, each about as tall and wide as a CD case. Grouped in fours and spaced about 70 meters apart, the detectors will help map the energy spectrum of tau neutrinos that plow through the earth.

TAUWER collaborators are currently based at Carnegie Mellon University, Sapienza University of Rome and two Turkish institutions in the Bolu and Kars provinces. The TAUWER name is a nod both to the tau neutrino and to the aluminum frames – towers – that support the experiment’s instruments.

“By next summer, we should be ready to find more interested people who want to take on the ice and snow of a mountain environment to help make things work,” Russ said.

Leah Hesla

No Comments »

Bob’s most excellent particle detector adventure

June 13, 2011 | 12:02 pm

One month ago, Fermilab’s Bob Peterson embarked on a month-long journey in the Atlantic Ocean with two cosmic ray muon detectors, collecting data for science and education programs. This offers a chance to study how cosmic ray recordings differ on land and sea and at different latitudes. The data will be accessible to high school students and teachers in several countries who use similar detectors to learn about particle physics. Bob recorded the entire adventure, which concluded last week, in Quantum Diaries. He posted the following entry on May 12, just as his ship was about to pass the equator.

Enduring a branding for QuarkNet science education

Bob Peterson holds part of the electronics for the cosmic ray muon detector. Credit: Tona Kunz

4 May 2011
R/V Polarstern
Latitude: 9-47.1 N
Longitude: 19-46.2 W
off the coast of Guinea
Ship course 320 ° T
Ship velocity 10.1 knots

4 May 2011:
Two days ago, the R/V Polarstern stopped mid-ocean at latitude: 00-00.053S, longitude: 11-39.259W.

By my reckoning, that’s 318 feet south of that east-west line “painted” in the water. Guilty parties were forced into very little rubber rafts and pointed in obscure directions and told to “cross the line”. Only one actually knew which way to go. After circular paddling, which amounted to three times the distance required to cross the line, those guilty of being equator-crossing newbies were initiated as shellbacks .

And what an initiation it was.

Neptune, lord of the sea, and his court rose up out of the Atlantic for the ritual baptism of those who had violated his domain. A trial was held and renaming of the pollywogs was required. Much fun and antics was had by the entire crew as they put on a real show of cruel and dastardly deeds. I could almost hear them cackling like the pirates of days past: “Arrrghhh! Avast ye maties!”

Bathing in stinky slop ensued, ceremonial memorizing of creeds was demanded and kissing of the feet of Neptune’s wives was enjoyed. Men in drag wearing clown shoes slathered in mustard and horseradish sauce stood in for Neptune’s wives. Lovely. I was also assisted by large, burly men with tattoos into a baptismal font made from a large fish basket. Four times I went in it; I must have been extra sinful. Each dunking got nastier as more people were “baptized”.

Finally they branded our stomachs with Neptune’s trident. This was a bit scary because they covered our faces with hoods execution-style and we could hear the metal trident heating in a charcoal grill and sizzling as it pressed onto flesh. Thankfully, when it came to my turn I found out the sizzle was the trident branding a raw piece of meat that then got slapped onto my stomach.  The crew got a great laugh out of our initiation.

We earned certificates for our ceremonial passage and a feast at sunset. Neptune felt the ceremony was befitting and left without taking the ship with him. So I am now the shellback known as Cosmic-Ray Rider, and I have pictures and a certificate to prove it.

Those will have to do because I skipped one of the most permanent parts of the ceremony. While I appreciate all the suggestions of earring types from friends and family, I decided to forego that little ritual. It’s the burly men that punch the hole, and they’re none too delicate.

So, the cosmic ray muon detector gave me my shellback name, but it’s also been my source of grief. Sometimes delicate instruments refuse to cooperate. For me, the trouble has been channel four and a scintillator counter that drops off line. Of course, it’s the one on the bottom of the stack, and it chooses to act up in the middle of the night. Several times in the morning I find it asleep, and that no data was taken during the night. Suspecting a light leak, I rewrapped it twice. Nope; that’s not it. Then I discover a flakey wire into the photo multiplier tube. There must be a short inside that photo multiplier tube. To compensate, I have lowered the coincidence to 3-fold from four so that a particle signal recorded in the three working sections of the detector will count as cosmic ray remnant event. Now, I will at least get some data. A replacement wire is some 8,000 miles away at Fermilab and the parts you can find along our route are pretty wet wheeling, as they say.

After many days in the southeast trade winds, we pushed through the doldrums, an area of still air near the equator that seems to rise rather than blow, and into the northeast trade winds. Other than the stop for the equator crossing, our course and speed have been relentless: 320 ° T, 11 knots; however, the following winds and swell have now turned on the nose and have become quite lumpy. Max, the weather guesser, promises it will get worse. In several days we make a turn to the north and a planned stop at the Canary Islands to pick more scientists.

Glossary:
*Pollywog: Some no good, inexperienced mariner who has never crossed the equator.

*Shellback: The opposite of a pollywog.

*Coincidences: The cosmic ray muon detector looks for what we call coincidences, two signals, one from each photo multiplier tubes, received within a short time. These are reported to the computer; all other signals are vetoed as likely background noise from the photo multiplier tubes.

– Bob Peterson

Guest author

No Comments »

AMS-02 antimatter detector lifting off in 3, 2…

April 29, 2011 | 11:00 am

AMS-02 detector Image courtesy of CERN.

Edit: The shuttle launch has been postponed until May 16 due to heater issues. For the latest news follow @AMS_02.

In about four hours, the Endeavour space shuttle is scheduled to launch from the Kennedy Space Center on its final mission, carrying with it what will be the largest physics experiment to blast into space.

Watch the event live via a CERN webcast or follow the detector on Twitter.

The Endeavour will deliver to the International Space Station the Alpha Magnetic Spectrometer experiment. AMS-02 will bring scientists a new understanding of the makeup of the universe by collecting information from subatomic particles accelerated to energies far beyond those attainable by a man-made particle accelerator.

Astrophysicists postulate that the explosions of stars and other dramatic events in space release high-energy cosmic rays, which can travel for hundreds of millions of light years before reaching Earth. Once the rays collide with Earth’s atmosphere, they can be absorbed or break into showers of particles. Physicists are sending AMS-02 into space in order to catch cosmic rays before that happens.

AMS-02 will search for the unexpected, but scientists have a few items on their wish-lists for the detector, including primordial antimatter and dark matter particles.

Primordial antimatter is antimatter created during the big bang. Scientists think the big bang should have created equal amounts of matter and antimatter. When matter and antimatter meet, they annihilate into particles of light. But the universe as we know it is made almost entirely of matter. If AMS-02 detected antimatter particles in cosmic rays, it could mean that primordial antimatter still exists in abundance; we just haven’t found it yet.

Dark matter is matter that exerts a gravitational pull but does not absorb or emit light. The behavior of galaxies and the way we see them lead scientists to believe that almost a quarter of the universe is made up of dark matter. However, they have yet to detect dark matter particles. Some theories state that dark matter could be made up of particles called neutralinos. If these particles exist, they could collide with one another and produce excesses of charged or neutral particles the AMS-02 could detect.

AMS-02 will collect between 2,000 and 2,500 events per second and is scheduled to remain in orbit at the space station for at least a decade.

Artist's impression of AMS-02 on the International Space Station Image courtesy of CERN.

About three and a half days after today’s lift-off, the shuttle will reach the same orbital configuration as the International Space Station about 200 miles above the Earth. Once it has docked there, astronauts will remove the detector from the shuttle cargo area and attach it to the space station in an extraterrestrial hand-off using two giant robotic arms – one attached to the Endeavour and the other attached to the ISS. Less than an hour after they secure AMS and hook it up to the space station’s electrical supply, the detector will be able to start sending data back to Earth.

For more information about following the launch, see the press release. For more photos and videos, see the AMS-02 website.

Kathryn Grim

1 Comment »

The AMS detector heads for the International Space Station

April 27, 2011 | 11:50 am

The following press release was issued today by CERN.

The AMS particle detector on the space Shuttle Endeavour. Credit: Michele Famigliett

Geneva 27 April 2011. The AMS particle detector will take off on 29 April 2011 at 21.47 CEST onboard the very last mission of the space Shuttle Endeavour. AMS, the Alpha Magnetic Spectrometer, will then be installed on the International Space Station from where it will explore the Universe for a period of over 10 years. AMS will address some of the most exciting mysteries of modern physics, looking for antimatter and dark matter in space, phenomena that have remained elusive up to now.

In laboratories like CERN, physicists observe matter and antimatter behaving in an almost identical way. Each matter particle has an equivalent antiparticle, very similar but with opposite charge. When particles of matter and antimatter meet, they annihilate. Matter and antimatter would have been created in equal amounts at the Big Bang, yet today we live in a Universe apparently made entirely of matter. Does nature have a preference for matter over antimatter? One of the main challenges of AMS will be to address this question by searching for single nuclei of antimatter that would signal the existence of large amounts of antimatter elsewhere in the Universe. To achieve this, AMS will track cosmic rays from outer space with unprecedented sensitivity.

“The cosmos is the ultimate laboratory,” said Nobel laureate and AMS Spokesperson Samuel Ting. “From its vantage point in space, AMS will explore such issues as Antimatter, Dark Matter and the origin of Cosmic Rays. However, its most exciting objective is to probe the unknown because whenever new levels of sensitivities are reached in exploring an unchartered realm, exciting and unimagined discoveries may be expected.”

In the same way that telescopes catch the light from the stars to better understand the Universe, AMS is a particle detector that will track incoming charged particles such as protons, electrons and atomic nuclei that constantly bombard our planet. By studying the flux of these cosmic rays with very high precision, AMS will have the sensitivity to identify a single antinucleus among a billion other particles.

“This is a very exciting moment for basic science,” said CERN Director General Rolf Heuer. “We expect interesting complementarities between AMS and the LHC. They look at similar questions from different angles, giving us parallel ways of addressing some of the Universe’s mysteries.”

AMS may also bring an important contribution to the search for the mysterious dark matter that would account for about 25% of the total mass-energy balance of the Universe. In particular, if dark matter is composed of supersymmetric particles, AMS could detect it indirectly by recording an anomaly in the flux of cosmic rays.

“Never in the history of science have we been so aware of our ignorance,” said AMS Deputy Spokesperson Roberto Battiston. “Today we know that we do not know anything about what makes up 95% of our Universe.”

AMS is a CERN recognized experiment and as such has benefited from CERN’s expertise in integrating large projects, from CERN’s vacuum and magnet groups and from test beam facilities for calibrating the detectors. In addition, the Payload Operation Centre (POC) of AMS will open in June 2011 at CERN, very near to the place where the AMS detector was assembled in clean room facilities. From the POC, physicists will be able to run the AMS detector as well as receive and analyse data arriving from the International Space Station.

AMS is the result of a large international collaboration with a major European participation. It is led by Nobel laureate Samuel Ting and involves about 600 researchers from CERN Member States (Denmark, Finland, France, Germany, Italy, the Netherlands, Portugal, Spain, Switzerland) as well as from China, Korea, Mexico, Taiwan, and the United-States.

Follow the launch of AMS live:

The launch of AMS can be followed live via webcast at: http://webcast.cern.ch
Questions can be asked during the webcast by sending them to @cern on twitter

The live will also be broadcasted through EBU Eurovision services.
A VNR preview will be broadcasted on 28 April 2011, 10:00 – 10:15 GMT.
More information on http://www.eurovision.net/

Videos are available at: http://bit.ly/cernamsfootage
Videos are subject to the CDS conditions of use: http://bit.ly/CDSconditionsofuse

For updates about of AMS, follow @astroparticle and @ams_02

Information about AMS can be found at www.ams02.org

Elizabeth Clements

No Comments »