NEUTRINOS FASTER THAN LIGHT. The OPERA presentation.

Below is the video of the OPERA public seminar which covers the set up and surprising results of their experiments.

New test for elusive fundamental particle - anyon - proposed

In quantum physics there are two classes of fundamental particles. Photons, the quanta of light, are bosons, while the protons and neutrons that make up atomic nuclei belong to the fermions. Bosons and fermions differ in their behavior at a very basic level. This difference is expressed in their quantum statistics. In the 1980s a third species of fundamental particle was postulated, which was dubbed the anyon. In their quantum statistics, anyons interpolate between bosons and fermions.

"They would be a kind of missing link between the two known sorts of fundamental particles," says LMU physicist Dr. Tassilo Keilmann. "According to the laws of quantum physics, anyons must exist – but so far it hasn't been possible to detect them experimentally."

An international team of theorists under Keilmann's leadership has now taken an in-depth look at the question of whether it is possible to create anyons in the context of a realistic experiment. Happily for experimentalists, the answer is yes. The theoreticians have come up with an experimental design in which conventional atoms are trapped in a so-called optical lattice. Based on their calculations, it ought to be possible to manipulate the interactions between atoms in the lattice in such a way as to create and detect anyons. In contrast to the behavior of bosons and fermions, the exotic statistics of anyons should be continuously variable between the endpoints defined by the other two particle types.

"These novel quantum particles should be able to hop between sites in the optical lattice," says Keilmann. "More importantly, they and their quantum statistics should be continuously adjustable during the experiment." In that case, it might even be feasible to transmute bosons into anyons and then to turn these into fermions. Such a transition would be equivalent to a novel "statistically induced quantum phase transition", and would allow the anyons to be used for the construction of quantum computers that would be far more efficient than conventional electronic processors. "We have pointed to the first practical route to the detection of anyons," says Keilmann. "Experimentalists should be able to implement the set-up in the course of experiments that are already underway."

Source  EurekaAlert!

LSU researchers see an indication of a new type of neutrino oscillation at the T2K experiment

T2K experiment has first results

BATON ROUGE – LSU Department of Physics Professors Thomas Kutter and Martin Tzanov, and Professor Emeritus William Metcalf, along with graduate and undergraduate students, have been working for several years on an experiment in Japan called T2K, or Tokai to Kamioka Long Baseline Neutrino Oscillation Experiment, which studies the most elusive of fundamental subatomic particles – the neutrino. The team announced they have an indication of a new type of neutrino transformation or oscillation from a muon neutrino to an electron neutrino.

In the T2K experiment in Japan, a beam of muon neutrinos – one of the three types of neutrinos, which also include the electron and tau – was produced in the Japan Proton
Accelerator Research Complex, or J-PARC, located in Tokai village, Ibaraki prefecture, on the east coast of Japan. The beam was aimed at the gigantic Super-Kamiokande underground detector in Kamioka, near the west coast of Japan, 295 km, or 185 miles away from Tokai. An analysis of the detected neutrino-induced events in the Super-Kamiokande detector indicated that a small number of muon neutrinos traveling from Tokai to Kamioka transformed themselves into electron neutrinos.

As part of the experiment, high energy protons were directed onto a carbon target, where their collisions produced charged particles called pions, which travelled through a helium-filled volume where they decayed to produce a beam of the elusive neutrinos. These neutrinos then flew about 200 meters through the earth to a sophisticated detector system capable of making detailed measurements of their energy, direction and type.
"It took the international collaboration about ten years to realize the project and bring it from first idea to first results," said Kutter, leader of the T2K project at LSU. "The entire LSU team is honored to be part of the collaboration and proud to contribute to the experiment. We expect many more results in the near future and look forward to the new research opportunities which are likely to arise from the tantalizing indication of this new neutrino oscillation."

LSU physicists have been part of a number of measurements over the last decade, which include Super Kamiokande, SNO, KamLAND that have shown that neutrinos possess the strange property of neutrino oscillations – one flavor of neutrino can transform into another as it travels through space. This is significant because neutrinos were first predicted theoretically in 1930, first actually detected in 1956 and for 50 years were assumed to have zero mass. But neutrino oscillations require mass.
With mysterious linkage between the three types, neutrinos challenge the understanding of the fundamental forces and basic constituents of matter. They may be related to the mystery of why there is more matter than anti-matter in the universe, and are the focus of intense study worldwide.

Precision measurements of neutrino oscillations can be made using artificial neutrino beams. This was pioneered in Japan by the K2K neutrino experiment in which neutrinos were produced at the KEK accelerator laboratory near Tokyo and were detected using the Super-Kamiokande neutrino detector, a 50,000 ton tank of ultra-pure water located more than half a mile underground in a laboratory 183 miles away near Toyama.
T2K is a more powerful and sophisticated version of the K2K experiment, with a more intense neutrino beam derived from the newly-built main ring synchrotron at the J-PARC accelerator laboratory. The beam was built by physicists from KEK in cooperation with other Japanese institutions and with assistance from American, Canadian, UK and French T2K institutes. The beam is aimed once again at Super-Kamiokande, which has been upgraded for this experiment with new electronics and software.

Before the neutrinos leave the J-PARC facility, their properties are determined by a sophisticated "near" detector, partly based on a huge magnet donated from the CERN accelerator laboratory in Geneva. The CERN magnet was earlier used for the UA1 experiment, which won the Nobel Prize for the discovery of the W and Z bosons which are the basis of neutrino interactions. The LSU team was responsible for building major components of the "near" detector, which provided an important ingredient to the oscillation analysis.
During the next several years, the search will be improved, with the hope that the three-mode oscillation will allow a comparison of the oscillations of neutrinos and anti-neutrinos, probing the asymmetry between matter and anti-matter in the universe.

Source  EurekaAlert!

Neutrinos caught 'shape shifting' in new way

Neutrinos have been caught spontaneously flip-flopping from one type to another in a way never previously seen. Further observations of this behaviour may shed light on how matter came to dominate over antimatter in the universe.

Neutrinos are among the most slippery particles known to physics. They rarely interact with ordinary matter, but massive experiments have been set up to detect the flashes of light produced when they do.

There are three known types, or flavours, of neutrino: electron, muon, and tau. Several experiments have found evidence that some flavours can spontaneously change into others, a phenomenon called neutrino oscillations. For example muon neutrinos can change into tau neutrinos.

 The first T2K neutrino event seen in the Super-Kamiokande in 2010. Each dot is a photomultiplier tube that has detected light (Image: T2K experiment)

Now, results from a Japanese experiment called T2K have tentatively added a new kind of transformation to the list of allowed types – the metamorphosis of muon neutrinos into electron neutrinos.

T2K generates muon neutrinos at the J-PARC accelerator in Tokai, Japan, and sends them in a beam towards the Super-Kamiokande neutrino detector in Kamioka, 295 kilometres away. It began operating in February 2010 and stopped gathering data in March, when Japan was rocked by the magnitude-9 megaquake.

Still tentative

On Wednesday, the team announced that six of the muon neutrinos that started off at J-PARC appear to have transformed into electron neutrinos before reaching Super-Kamiokande, where they were detected. This is the first time anyone has seen electron neutrinos show up in a beam of particles that started off as muon neutrinos.

"It shows the power of our experimental design that with only 2 per cent of our design data we are already the most sensitive experiment in the world for looking for this new type of oscillation," says T2K spokesperson Takashi Kobayashi of Japan's KEK particle physics laboratory.

However, the result is still tentative because of the small number of events seen and because of the possibility – considered rare – that muon neutrinos could be misidentified as electron neutrinos. Still, the researchers say experimental errors should give only 1.5 false events in the amount of data they analysed. There is only a 0.7 per cent chance of producing six false events.

Antimatter counterparts

The transformations appear to be happening relatively frequently. That means researchers will be able to quickly accumulate more events – once the experiment begins running again. The earthquake threw the accelerator used to make the neutrinos out of alignment. After adjustments are made, researchers hope to restart the experiment by year's end.

The researchers may eventually rerun the experiment with a beam of muon antineutrinos to see if their behaviour differs from their normal-matter counterparts.

If differences are found, it could help explain why there is a preponderance of matter in the universe. Standard theories say that matter and antimatter were created in equal amounts in the universe's first instants, but for unknown reasons, matter prevailed.

Skew the balance

Reactions involving neutrinos and antineutrinos in the early universe could have skewed the ratio of matter and antimatter production, leading to our matter-dominated universe. "You need some new laws of physics that aren't the same for matter and antimatter, and neutrino physics is one place you could put such laws," says David Wark of Imperial College London, who is a member of the T2K collaboration.

The US-based MiniBoone experiment recently found hints of an antimatter version of the oscillation seen by T2K. MiniBoone found signs that muon antineutrinos sometimes change into electron antineutrinos.

But physicists are still puzzling over the MiniBoone results. Based on the experiment's design, it should not have seen oscillations unless there are one or more extra types of neutrino that are sterile, meaning they are even more averse to interacting with matter than regular neutrinos.

By contrast, the T2K result can be accommodated without invoking sterile neutrinos.

Source New Scientist

Second team does not see Tevatron's mystery signal

Is particle physics, like beauty, in the eye of the beholder? You would be forgiven for thinking that now that two teams have analysed data from Fermilab's Tevatron collider and come to the exact opposite conclusion about whether that data hints at a new particle.

A task force is being formed to figure out the discrepancy, but the final arbiter may be the Large Hadron Collider in Switzerland, which will ultimately collect more data than the Tevatron.

In April, members of the Tevatron's CDF experiment reported finding a curious signal in the debris from eight years' worth of collisions between protons and antiprotons. The signal hinted at the existence of a particle that was not predicted by the standard model, the leading theory of particle physics. Theorists scrambled to come up with possible explanations, writing dozens of papers on the topic in the following weeks.

Last week, evidence for the signal, or "bump" in the data, seemed to get even stronger. The CDF team reported that it had analysed twice as much data as in April and had still found the bump.

But now, a rival team performing an independent analysis of Tevatron data has turned up no sign of the bump. It is using the same amount of data as CDF reported in April, but this data was collected at a different detector at the collider called DZero.

"Nope, nothing here – sorry," says Dmitri Denisov, a spokesman for DZero.

Different detectors

When the CDF collaboration came out with its result in April, DZero researchers spent a couple of days doing a quick check of their data and saw no bump. But to make sure they were comparing like with like, they spent the next two months painstakingly checking that their analysis resembled that of CDF's as closely as possible.

Today, they are reporting that their analysis shows no bump. "We're basically excluding a signal at well over the 95 per cent confidence level," Denisov told New Scientist. The result shows "good agreement with the standard model".

"Now of course the most interesting question is where are these differences coming from?" he says.

The fact that the detector is different should not come into play, he argues. "It would be really puzzling if it's a physical process that's supposed to exist in nature, and one experiment sees it and another doesn't," he says. "Protons and antiprotons don't know what detector they're colliding in."

Modelling issue?

He does not know what is causing the discrepancy but suspects it may be due to differences in the models that each team uses to describe the data. The studies look at how often collisions between protons and antiprotons produce a W boson, which transmits the weak nuclear force, and a pair of jets of subatomic particles called quarks.

The CDF team found an unexpected abundance of these events – a W boson and a pair of jets – where the mass of the jet pair was about 145 gigaelectronvolts, suggesting that a new particle of that same mass was created (see graph). But other events involving different combinations of particles can mimic the signal of a W boson and a pair of jets. If the CDF team incorrectly modelled the number of those "background" signals, it might make it look as if there were a bump in the data, says Denisov.

Rob Roser, a CDF spokesman, acknowledges that "it could be a modelling issue", but says it is too soon to discount CDF's result. "It's disappointing that the peak didn't just jump out at them too," he told New Scientist. "But just because it didn't doesn't mean there's not something there."

Task force

Roser has not yet had time to look carefully at DZero's paper (pdf), which has been submitted to Physical Review Letters. But he says a cursory look suggests that the discrepancies between the two results may not be as large as it seems. The CDF team estimated that the potential new particle is produced at a certain rate in proton-antiproton collisions, but there is some uncertainty in that rate. If the real rate is at the lower end of CDF's range of possibilities, for example, the discrepancy between the two teams' results is smaller.

"I think we have more work ahead of us before we understand what is going on," says Roser.

A task force, made up of members of both experiments, along with Fermilab theorists Estia Eichten and Keith Ellis, will now try to get to the bottom of the discrepancy, a process that could take months, Roser says.

Roser says the CDF team has only analysed 70 per cent of the data it expects to collect by September and will continue crunching the numbers to see if the bump appears in the full data set. But Denisov says DZero is satisfied with the analysis it has already done. "We do not plan to continue the analysis with the same rigour as we did over the last two months," he says. "We are concentrating on many other things."

Even if the task force's investigation proves inconclusive, both Denisov and Roser say the Large Hadron Collider at CERN will eventually collect enough data to settle the question of whether there is a bump at 145 GeV.

They disagree over when this will happen, though. The LHC collides particles together at higher energies than the Tevatron, which produces more debris in which a new particle could be lurking. This leads Denisov to estimate that the LHC will collect enough data to look for the first evidence of the bump in the next few months.

Roser points out that the LHC collides protons together rather than protons and antiprotons, as happens at the Tevatron. That means that even though it produces some collisions between quarks and antiquarks – which could be important in reproducing the bump – it generates them in smaller numbers than the Tevatron. So Roser estimates it could take the LHC more than a year to make its ruling.

So are the two teams going to be arguing bitterly until then? "It's been a little bit tense over the last few days," laughs Denisov. "But I think it's friendly. I would say it's like two sports teams competing."

"I think it's going to be fun," says Roser. "This is science in progress."

Source New Scientist

Ultracold neutrons for science: UCNs will help to solve mysteries of astrophysics

Mainz has the most powerful source of ultracold neutrons, opening up the possibility of conducting a key experiment to determine the life time of the neutron

Scientists at Johannes Gutenberg University Mainz (JGU) have built what is currently the strongest source of ultracold neutrons. Ultracold neutrons (UCNs) were first generated here five years ago. They are much slower than thermal neutrons and are characterized by the fact that they can be stored in special containers. This property makes them important tools for experiments to investigate why matter dominates over antimatter in our universe and how the lightest elements were created directly after the Big Bang.

"We have commissioned a new UCN source and improved the overall procedure so that we can now generate and store considerably more ultracold neutrons than before and more than anybody else," says Professor Werner Heil of the Institute of Physics at Mainz University. Having so far managed to achieve a density of ten UCN per cubic centimeter, the Mainz research team of chemists and physicists has become one of the global leaders in this research field.

In 2006, the Mainz team, working in cooperation with the Technical University of Munich, produced for the first time ultracold neutrons using the pulsed Mainz TRIGA reactor. Neutrons are created by means of nuclear fission in the TRIGA research reactor in Mainz. These fission neutrons reach speeds up to 30,000 kilometers per second – a tenth of the speed of light. Interaction with light atomic nuclei in the reactor slows them down to a 'thermal' speed of approximately 2,200 meters per second. The apparatus developed by the researchers from Mainz University is then employed: a three meter long tube is inserted in the beam tube of the reactor at the point where there is the highest flux of thermal neutrons. The thermal neutrons undergo extreme velocity deceleration in this tube.

This new source of UCNs in beam tube D of the Mainz TRIGA reactor has just successfully completed its first stress test. In the UCN apparatus the thermal neutrons  are slowed down in two in two steps: first with hydrogen and thereafter with an ice block made of deuterium at minus 270 degrees Celsius. "The neutrons are now so slow that we could run after them," says Professor Werner Heil. The UCNs move to the experimental site at the other end of the tube at a speed of only 5 meters per second. The stainless steel tube is coated inside with nickel to ensure that no neutrons are lost on the way.

The key parameter for the scientists is the UCN density that can be achieved at the site of the experiment – a prerequisite to perform high-precision experiments. "In our first trial, we achieved ten UCN per cubic centimeter in a typical storage volume of ten liters. When we use hydrogen as a pre-moderator and make a few minor changes, we expect fifty UCN per cubic centimeter," explain Dr Thorsten Lauer and Dr Yuri Sobolev, who supervise the system. This is more than sufficient to perform experiments such as measurements to determine the life time of the neutron. With this UCN density, the Mainz research team is now the front-runner in the race to achieve the highest storage density, in which facilities in Los Alamos, Grenoble, Munich and the Swiss city of Villigen are competing.

The life time of a neutron – according to current scientific findings – is approximately 885 seconds, but this number is dominated by systematic errors. The method employed is known as "counting the survivors": the number of neutrons left after a certain decay time is correlated with the known initial number in the sample. Till now, for more precise life time measurements not enough ultracold neutrons were available.

UCN research at Johannes Gutenberg University Mainz is part of the "Precision Physics, Fundamental Interactions and Structure of Matter" (PRISMA) Cluster of Excellence, which is currently applying for additional funding in Germany’s Federal Excellence Initiative. The new UCN source was constructed directly on the university campus by the workshops of the Institutes of Physics and Nuclear Chemistry. Over the last three years, seventeen undergraduates, two doctoral candidates and two post-doctoral students have worked on the UCN project – a field that will provide a great deal of scientific insight in the future.

Source Johannes Gutenberg University

Researchers discover superatoms with magnetic shells

RICHMOND, Va. (June 8, 2011) – A team of Virginia Commonwealth University scientists has discovered a new class of 'superatoms' – a stable cluster of atoms that can mimic different elements of the periodic table – with unusual magnetic characteristics.
The superatom contains magnetized magnesium atoms, an element traditionally considered as non-magnetic. The metallic character of magnesium along with infused magnetism may one day be used to create molecular electronic devices for the next generation of faster processors, larger memory storage and quantum computers.

In a study published online in the Early Edition of the Proceedings of the National Academy of Sciences, the team reports that the newly discovered cluster consisting of one iron and eight magnesium atoms acts like a tiny magnet that derives its magnetic strength from the iron and magnesium atoms. The combined unit matches the magnetic strength of a single iron atom while preferentially allowing electrons of specific spin orientation to be distributed throughout the cluster.

Through an elaborate series of theoretical studies, Shiv N. Khanna, Ph.D., a Commonwealth professor in the VCU Department of Physics, and his team examined the electronic and magnetic properties of clusters having one iron atom surrounded by multiple magnesium atoms. The team included instructor J. Ulises Reveles and Victor M. Medel, a post-doctoral associate, both from VCU; A. W. Castleman Jr., Ph.D., the Evan Pugh Professor of Chemistry and Physics, and Eberly Distinguished chair in Science in the Department of Chemistry at Penn State University; and Prasenjit Sen and Vikas Chauhan from the Harish-Chandra Research Institute in Allahabad, India.

"Our research opens a new way of infusing magnetic character in otherwise non-magnetic elements through controlled association with a single magnetic atom. An important objective was to discover what combination of atoms would lead to a species that is stable as we put multiple units together," said Khanna.
"The combination of magnetic and conducting attributes was also desirable. Magnesium is a good conductor of electricity and, hence, the superatom combines the benefit of magnetic character along with ease of conduction through its outer skin," he said.

The team found that when the cluster had eight magnesium atoms it acquired extra stability due to filled electronic shells that were far separated from the unfilled shells. An atom is in a stable configuration when its outermost shell is full and far separated from unfilled shells, as found in inert gas atoms. Khanna said that such phenomena commonly occur with paired electrons which are non-magnetic, but in this study the magnetic electronic shell showed stability.

According to Khanna, the new cluster had a magnetic moment of four Bohr magnetons, which is almost twice that of an iron atom in solid iron magnets. A magnetic moment is a measure of the magnetic strength of the cluster. Although the periodic table has more than one hundred elements, there are only nine elements that exhibit magnetic character in solid form.
"A combination such as the one we have created here can lead to significant developments in the area of "molecular electronics" where such devices allow the flow of electrons with particular spin orientation desired for applications such as quantum computers. These molecular devices are also expected to help make denser integrated devices, higher data processing, and other benefits," said Reveles.

Khanna and his team are conducting preliminary studies on the assemblies of the new superatoms and have made some promising observations that may have applications in spintronics. Spintronics is a process using electron spin to synthesize new devices for memory and data processing.

Source EurekaAlert!

Stick Up: Antimatter Atoms Trapped for More Than 15 Minutes

CERN physicists have forced flighty atoms of antihydrogen to stick around, potentially affording a better look at how antimatter behaves.

This artist's conception depicts the confined path of an antimatter atom inside the ALPHA trap in light blue. The white tracks depict outflying particles that originate from a matter-antimatter annihilation when the antiatom is released from its trap.

Maybe antimatter is finally ready for its close-up. A team of physicists has succeeded in producing rudimentary atoms of antimatter and holding on to them for several minutes, an advance that holds hope for detailed comparisons of how ordinary atoms of matter compare with their exotic antimatter counterparts.

The researchers, from the ALPHA antimatter experiment at CERN, the European laboratory for particle physics, reported last year the first trapping of antihydrogen, the simplest antimatter atom. But the antihydrogen had at that time been confined for less than two tenths of a second. That interval has now been extended by a factor of more than 5,000. In a study published online June 5 in Nature Physics, the ALPHA group reports having confined antihydrogen for 16 minutes and 40 seconds. The more relevant number for physicists, who often deal in powers of 10, is 1,000 seconds. (Scientific American is part of Nature Publishing Group.)

The subatomic particles of everyday matter—protons, neutrons and electrons—have antimatter cousins; when matter meets antimatter the two annihilate in a burst of energy. And just as the neutral hydrogen atom is made of a single proton bound to an electron, an atom of antihydrogen comprises an antiproton and a positron, the antimatter counterparts, respectively.

But the mutual annihilation between those particles and their ubiquitous matter counterparts makes it challenging to hang on to antimatter for very long, and even more challenging to produce and confine bound atomic arrangements of multiple antiparticles. Neutral anti-atoms such as antihydrogen are especially tricky to confine because they are impervious to electric fields, which can be used to steer charged antiparticles such as antiprotons. Experiments such as ALPHA instead use superconducting magnets to trap their quarry.

Cagey as anti-atoms are, physicists would like to pin them down and compare the properties of antihydrogen with hydrogen, the most abundant element in the universe. Those comparisons might involve laser spectroscopy of the anti-atoms or physical tests of how antihydrogen "feels" the influence of gravity. Any discrepancies between hydrogen and antihydrogen might help explain why matter won out over antimatter in our observable universe. "If one could do that, that would be a huge advance in terms of understanding why we live in a world of matter," says Clifford Surko, a physicist at the University of California, San Diego, who wrote a commentary for Nature Physics accompanying the new study. "There's got to be an asymmetry somewhere, so that's a long-term goal."

The lifetime of antihydrogen in the ALPHA trap is probably sufficient to begin those studies. "We think we're in a position to start measuring something," says ALPHA spokesperson Jeffrey Hangst of Aarhus University in Denmark. Initial studies will involve irradiating the anti-atoms with microwaves to try to engage them in a resonant interaction, flipping their spin like a compass needle swinging from north to south.

Critically, the confinement times achieved by ALPHA imply that the antihydrogen atoms have had time to decay into their lowest-energy, or ground, state. "This method of antihydrogen formation creates them in highly excited states," Surko says. "They're fragile, and for really high-precision measurements of antihydrogen you need them in the ground state."

Hangst says that the jump from trapping times measured in milliseconds to those measured in hundreds of seconds did not stem from any one major advance. But getting antihydrogen atoms to stick in the trap much more often was a big help in improving on last year's confinement experiment. It now takes fewer experimental runs to demonstrate that an antihydrogen atom has been trapped. "What was tricky here was not keeping them but trapping enough of them to do the experiment," he says. "The big technological step here is we're much better now at trapping them at all."

Still the efficiency of trapping is somewhat low—for each antiatom confined by the trap, thousands more from the same batch escape. And in 16 trapping experiments of 1,000 seconds each, only seven antihydrogen atoms were detected in total. (The researchers demonstrate the confinement of antihydrogen by quickly shutting down the superconducting magnets, turning the anti-atoms loose, and watching for matter–antimatter annihilations on the walls of the trap.)

A competing antimatter experiment at CERN, known as ATRAP, has been working toward producing larger numbers of antihydrogen atoms with lower kinetic energies, which would facilitate their trapping. But so far that effort has yet to bear fruit. "We think that it would be good to have more atoms than [the ALPHA rate of] fewer than one atom per trial," says Harvard University physicist Gerald Gabrielse, spokesperson for the ATRAP collaboration. "We would hope not to be publishing a paper that says we see 0.6 atom per trial, but 100 atoms per trial."

The ATRAP group, Gabrielse says, made the choice to increase the number of atoms in the trap rather than increasing the sensitivity of the instruments to detect small numbers of anti-atoms, as ALPHA has done. "Maybe we made the wrong one," he says of that decision. "Certainly we made the one that got less publicity." Nevertheless, Gabrielse says he is encouraged by his competitors' success. "I'm glad that they have demonstrated that you can trap antihydrogen atoms," he says. "I think it shows that if we have more atoms, we'll have time to do some things with them."

Source Scientific American

Lawmakers tour MIT’s Plasma Science and Fusion Center

MIT’s Plasma Science and Fusion Center (PSFC) hosted two senators earlier this week, both of whose independent visits were directed at learning more about fusion as a source of clean energy.

Senior Research Scientist Martin Greenwald (right) discusses the importance of fusion research with Florida Sen. Bill Nelson in front of a port in the Alcator C-Mod tokamak. Photo: Paul Rivenberg

U.S. Sen. Bill Nelson (D-Fla.) toured the PSFC on Monday, May 16. Led by PSFC Senior Research Scientist Martin Greenwald, Nelson viewed the Alcator C-Mod tokamak — a device that uses a magnetic field to confine plasma into a determined shape, allowing for the production of controlled fusion power. A member of the Senate Committee on Commerce, Science, and Transportation, Nelson was familiar with the basics of plasma research and open to learning about fusion's potential as a future source of clean energy.

Then, Tuesday, the PSFC welcomed Sen. Benjamin Downing of the Massachusetts Senate, who also visited Alcator C-Mod. As chair of the Joint Committee on Telecommunications, Utilities and Energy, Downing was interested in learning about the steps necessary to progress toward the goal of fusion-powered energy. The tour, led by Greenwald and Alcator Project Head Earl Marmar, allowed a close-up look at the tokamak, which is currently undergoing maintenance.

Both senators were accompanied by members of their staff and MIT alumnus Reinier Beeuwkes ’67, who facilitated the tours.

Source MIT News

Nuclear Magnetic Resonance With No Magnets

Berkeley Lab nuclear physicists and materials scientists contribute to a remarkable advance in NMR.

Nuclear magnetic resonance (NMR), a scientific technique associated with outsized, very low-temperature, superconducting magnets, is one of the principal tools in the chemist’s arsenal, used to study everything from alcohols to proteins to such frontiers as quantum computing. In hospitals the machinery of NMR’s cousin, magnetic resonance imaging (MRI), is as loud as it is big, but nevertheless a mainstay of diagnosis for a wide range of medical conditions.

Spectroscopy with conventional nuclear magnetic resonance (NMR) requires large, expensive, superconducting magnets cooled by liquid helium, like the one in the background. The Pines and Budker groups have demonstrated NMR spectroscopy with a device only a few centimeters high, using no magnets at all (foreground). A chemical sample in the test tube (green) is polarized by introducing hydrogen gas in the parahydrogen form. The sample’s NMR is measured with an optical-atomic magnetometer, at center; laser beams crossing at right angles pump and probe the atoms in the microfabricated vapor cell. (Click on image for best resolution.) 

It sounds like magic, but now two groups of scientists at Berkeley Lab and UC Berkeley, one expert in chemistry and the other in atomic physics, long working together as a multidisciplinary team, have shown that chemical analysis with NMR is practical without using any magnets at all.

Dmitry Budker of Berkeley Lab’s Nuclear Science Division, a professor of physics at UC Berkeley, is a protean experimenter who leads a group with interests ranging as far afield as tests of the fundamental theorems of quantum mechanics, biomagnetism in plants, and violations of basic symmetry relations in atomic nuclei. Alex Pines, of the Lab’s Materials Sciences Division and UCB’s Department of Chemistry, is a modern master of NMR and MRI. He guides the work of a talented, ever-changing cadre of postdocs and grad students known as the “Pinenuts” – not only in doing basic research in NMR but in increasing its practical applications. Together the groups have extended the reach of NMR by eliminating the use of magnetic fields at different stages of NMR measurements, and have finally done away with external magnetic fields entirely.

Spinning the information
NMR and MRI depend on the fact that many atomic nuclei possess spin (not classical rotation but a quantum number) and – like miniature planet Earths with north and south magnetic poles – have their own dipolar magnetic fields. In conventional NMR these nuclei are lined up by a strong external magnetic field, then knocked off axis by a burst of radio waves. The rate at which each kind of nucleus then “wobbles” (precesses) is unique and identifies the element; for example a hydrogen-1 nucleus, a lone proton, precesses four times faster than a carbon-13 nucleus having six protons and seven neutrons.

Being able to detect these signals depends first of all on being able to detect net spin; if the sample were to have as many spin-up nuclei as spin-down nuclei it would have zero polarization, and signals would cancel. But since the spin-up orientation requires slightly less energy, a population of atomic nuclei usually has a slight excess of spin ups, if only by a few score in a million.
“Conventional wisdom holds that trying to do NMR in weak or zero magnetic fields is a bad idea,” says Budker, “because the polarization is tiny, and the ability to detect signals is proportional to the strength of the applied field.”

The lines in a typical NMR spectrum reveal more than just different elements. Electrons near precessing nuclei alter their precession frequencies and cause a “chemical shift” — moving the signal or splitting it into separate lines in the NMR spectrum. This is the principal goal of conventional NMR, because chemical shifts point to particular chemical species; for example, even when two hydrocarbons contain the same number of hydrogen, carbon, or other atoms, their signatures differ markedly according to how the atoms are arranged. But without a strong magnetic field, chemical shifts are insignificant.

“Low- or zero-field NMR starts with three strikes against it: small polarization, low detection efficiency, and no chemical-shift signature,” Budker says.
“So why do it?” asks Micah Ledbetter of Budker’s group. It’s a rhetorical question. “The main thing is getting rid of the big, expensive magnets needed for conventional NMR. If you can do that, you can make NMR portable and reduce the costs, including the operating costs. The hope is to be able to do chemical analyses in the field – underwater, down drill holes, up in balloons – and maybe even medical diagnoses, far from well-equipped medical centers.”

Hydrogen molecules consist of two hydrogen atoms that share their electrons in a covalent bond. In an orthohydrogen molecule, both nuclei are spin up. In parahydrogen, one is spin up and the other spin down. The orthohydrogen molecule as a whole has spin one, but the parahydrogen molecule has spin zero. 

“As it happens,” Budker says, “there are already methods for overcoming small polarization and low detection efficiency, the first two objections to low- or zero-field NMR. By bringing these separate methods together, we can tackle the third objection – no chemical shift – as well. Zero-field NMR may not be such a bad idea after all.”

Net spin orientation can be increased in various ways, collectively known as hyperpolarization. One way to hyperpolarize a sample of hydrogen gas is to change the proportions of parahydrogen and orthohydrogen in it. Like most gases, at normal temperature and pressure each hydrogen molecule consists of two atoms bound together. If the spins of the proton nuclei point in the same direction, it’s orthohydrogen. If the spins point in opposite directions, it’s parahydrogen.

By the mathematics of quantum mechanics, adding up the spin states of the two protons and two electrons in a hydrogen molecule equals three ways for orthohydrogen to reach spin one; parahydrogen can only be spin zero, however. Thus orthohydrogen molecules normally account for three-quarters of hydrogen gas and parahydrogen only one-quarter.

Parahydrogen can be enhanced to 50 percent or even 100 percent using very low temperatures, although the right catalyst must be added or the conversion could take days if not weeks. Then, by chemically reacting spin-zero parahydrogen molecules with an initial chemical, net polarization of the product of the hydrogenation may end up highly polarized. This hyperpolarization can be extended not only to the parts of the molecule directly reacting with the hydrogen, but even to the far corners of large molecules. The Pinenuts, who devised many of the techniques, are masters of parahydrogen production and its hyperpolarization chemistry.
“With a high proportion of parahydrogen you get a terrific degree of polarization,” says Ledbetter. “The catch is, it’s spin zero. It doesn’t have a magnetic moment, so it doesn’t give you a signal! But all is not lost….”

And now for the magic
In low magnetic fields, increasing detection efficiency  requires a very different approach, using detectors called magnetometers. In early low-field experiments, magnetometers called SQUID were used (superconducting quantum interference devices). Although exquisitely sensitive, SQUID, like the big magnets used in high-field NMR, must be cryogenically cooled to low temperatures.

Optical-atomic magnetometers are based on a different principle – one that, curiously, is something like NMR in reverse, except that optical-atomic magnetometers measure whole atoms, not just nuclei. Here, an external magnetic field is measured by measuring the spin of the atoms inside the magnetometer’s own vapor cell, typically a thin gas of an alkali metal such as potassium or rubidium. Their spin is influenced by polarizing the atoms with laser light; if there’s even a weak external field, they begin to precess. A second laser beam probes how much they’re precessing and thus just how strong the external field is.

Budker’s group has brought optical-atomic magnetometry to a high pitch by such techniques as extending the “relaxation time,” the time before the polarized vapor loses its polarization. In previous collaborations, the Pines and Budker groups have used magnetometers with NMR and MRI to image the flow of water using only the Earth’s magnetic field or no field at all, to detect hyperpolarized xenon gas (but without analyzing chemical states), and in other applications. The next frontier is chemical analysis.
“No matter how sensitive your detector or how polarized your samples, you can’t detect chemical shifts in a zero field,” Budker says. “But there has always been another signal in NMR that can be used for chemical analysis – it’s just that it is usually so weak compared to chemical shifts, it has been the poor relative in the NMR family. It’s called J-coupling.”

Discovered in 1950 by the NMR pioneer Erwin Hahn and his graduate student, Donald Maxwell, J-coupling provides an interaction pathway between two protons (or other nuclei with spin), which is mediated by their associated electrons. The signature frequencies of these interactions, appearing in the NMR spectrum, can be used to determine the angle between chemical bonds and distances between the nuclei.
“You can even tell how many bonds separate the two spins,” Ledbetter says. “J-coupling reveals all that information.”

The resulting signals are highly specific and indicate just what chemical species is being observed. Moreover, as Hahn saw right away, while the signal can be modified by external magnetic fields, it does not vanish in their absence.

A molecule of parahydrogen hydrogenates a styrene molecule to form ethylbenzene. J-coupling reveals the position and orientation of the hydrogen atoms and the carbon-13 atoms to which they bond. The upper panel shows a simulated spectrum, in blue, of coupling between a hydrogen and a carbon in the methyl position. The actual experimental data are in white. The lower panel shows simulation of coupling in the methylene position, in green, with actual data in white. Simulation and experiment are in close agreement, indicating the promise of the zero-field technique for chemical fingerprinting. (Click on image for best resolution.) 

With Ledbetter in the lead, the Budker/Pines collaboration built a magnetometer specifically designed to detect J-coupling at zero magnetic field. Thomas Theis, a graduate student in the Pines group, supplied the parahydrogen and the chemical expertise to take advantage of parahydrogen-induced polarization. Beginning with styrene, a simple hydrocarbon, they measured J-coupling on a series of hydrocarbon derivatives including hexane and hexene, phenylpropene, and dimethyl maleate, important constituents of plastics, petroleum products, even perfumes.

“The first step is to introduce the parahydrogen,” Budker says. “The top of the set-up is a test tube containing the sample solution, with a tube down to the bottom through which the parahydrogen is bubbled.” In the case of styrene, the parahydrogen was taken up to produce ethylbenzene, a specific arrangement of eight carbon atoms and 10 hydrogen atoms.
 
Immediately below the test tube sits the magnetometer’s alkali vapor cell, a device smaller than a fingernail, microfabricated by Svenja Knappe and John Kitching of the National Institute of Standards and Technology. The vapor cell, which sits on top of a heater, contains rubidium and nitrogen gas through which pump and probe laser beams cross at right angles. The mechanism is surrounded by cylinders of “mu metal,” a nickel-iron alloy that acts as a shield against external magnetic fields, including Earth’s.

Ledbetter’s measurements produced signatures in the spectra which unmistakably identified chemical species and exactly where the polarized protons had been taken up. When styrene was hydrogenated to form ethylbenzene, for example, two atoms from a parahydrogen molecule bound to different atoms of carbon-13 (a scarce but naturally occurring isotope whose nucleus has spin, unlike more abundant carbon-12).
J-coupling signatures are completely different for otherwise identical molecules in which carbon-13 atoms reside in different locations. All of this is seen directly in the results. Says Budker, “When Micah goes into the laboratory, J-coupling is king.”

Of the present football-sized magnetometer and its lasers, Ledbetter says, “We’re already working on a much smaller version of the magnetometer that will be easy to carry into the field.”
Although experiments to date have been performed on molecules that are easily hydrogenated, hyperpolarization with parahydrogen can also be extended to other kinds of molecules. Budker says, “We’re just beginning to develop zero-field NMR, and it’s still too early to say how well we’re going to be able to compete with high-field NMR. But we’ve already shown that we can get clear, highly specific spectra, with a device that has ready potential for doing low-cost, portable chemical analysis.”

More information 
“Parahydrogen-enhanced zero-field nuclear magnetic resonance,” by Thomas Theis, Paul Ganssle, Gwendal Kervern, Svenja Knappe, John Kitching, Micah Ledbetter, Dmitry Budker, and Alexander Pines, appears in Nature Physics and is available online at http://www.nature.com/nphys/journal/vaop/ncurrent/abs/nphys1986.html. Theis, Ganssle, and Pines are with Berkeley Lab’s Materials Sciences Division and the UC Berkeley Department of Chemistry, as was Kervern, now at the University of Lyon. Knappe and Kitching are with the National Institute of Standards and Technology. Ledbetter is with UC Berkeley’s Department of Physics, as is Budker, who is also a member of Berkeley Lab’s Nuclear Science Division. This work was supported by the National Science Foundation and DOE’s Office of Science.
More about Alex Pines, the “Pinenuts,” and parahydrogen is at http://newscenter.lbl.gov/feature-stories/2007/08/06/pines-talking/.
More about the work of Dmitry Budker and his group on optical-atomic magnetometers is at http://newscenter.lbl.gov/feature-stories/2010/09/14/putting-a-spin-on-light-and-atoms/.

Source Berkeley Lab

Doppler effect found even at molecular level – 169 years after its discovery

CORVALLIS, Ore. – Whether they know it or not, anyone who's ever gotten a speeding ticket after zooming by a radar gun has experienced the Doppler effect – a measurable shift in the frequency of radiation based on the motion of an object, which in this case is your car doing 45 miles an hour in a 30-mph zone.
But for the first time, scientists have experimentally shown a different version of the Doppler effect at a much, much smaller level – the rotation of an individual molecule. Prior to this such an effect had been theorized, but it took a complex experiment with a synchrotron to prove it's for real.

"Some of us thought of this some time ago, but it's very difficult to show experimentally," said T. Darrah Thomas, a professor emeritus of chemistry at Oregon State University and part of an international research team that today announced its findings in Physical Review Letters, a professional journal.
Most illustrations of the Doppler effect are called "translational," meaning the change in frequency of light or sound when one object moves away from the other in a straight line, like a car passing a radar gun. The basic concept has been understood since an Austrian physicist named Christian Doppler first proposed it in 1842.
But a similar effect can be observed when something rotates as well, scientists say.
"There is plenty of evidence of the rotational Doppler effect in large bodies, such as a spinning planet or galaxy," Thomas said. "When a planet rotates, the light coming from it shifts to higher frequency on the side spinning toward you and a lower frequency on the side spinning away from you. But this same basic force is at work even on the molecular level."

In astrophysics, this rotational Doppler effect has been used to determine the rotational velocity of things such as planets. But in the new study, scientists from Japan, Sweden, France and the United States provided the first experimental proof that the same thing happens even with molecules.
At this tiny level, they found, the rotational Doppler effect can be even more important than the linear motion of the molecules, the study showed.

The findings are expected to have application in a better understanding of molecular spectroscopy, in which the radiation emitted from molecules is used to study their makeup and chemical properties. It is also relevant to the study of high energy electrons, Thomas said.
"There are some studies where a better understanding of this rotational Doppler effect will be important," Thomas said. "Mostly it's just interesting. We've known about the Doppler effect for a very long time but until now have never been able to see the rotational Doppler effect in molecules."

Source  EurekaAlert!

Proton dripping tests a fundamental force in nature

Like gravity, the strong interaction is a fundamental force of nature. It is the essential "glue" that holds atomic nuclei—composed of protons and neutrons— together to form atoms, the building blocks of nearly all the visible matter in the universe. Despite its prevalence in nature, researchers are still searching for the precise laws that govern the strong force. However, the recent discovery of an extremely exotic, short-lived nucleus called fluorine-14 in laboratory experiments may indicate that scientists are gaining a better grasp of these rules.

Fluorine-14 comprises nine protons and five neutrons. It exists for a tiny fraction of a second before a proton "drips" off, leaving an oxygen-13 nucleus behind. A team of researchers led by James Vary, a professor of physics at Iowa State University, first predicted the properties of fluorine-14 with the help of scientists in Lawrence Berkeley National Laboratory's (Berkeley Lab's) Computational Research Division, as well as supercomputers at the National Energy Research Scientific Computing Center (NERSC) and the Oak Ridge Leadership Computing Facility. These fundamental predictions served as motivations for experiments conducted by Vladilen Goldberg's team at Texas A&M's Cyclotron Institute, which achieved the first sightings of fluorine-14.

"This is a true testament to the predictive power of the underlying theory," says Vary. "When we published our theory a year ago, fluorine-14 had never been observed experimentally. In fact, our theory helped the team secure time on their newly commissioned cyclotron to conduct their experiment. Once their work was done, they saw virtually perfect agreement with our theory."

 
This graph shows the flourine-14 supercomputer predictions (far-left) and experimental results (center). The striking similarities between these graphs indicate that researchers are gaining a better understanding of the precise laws that govern the strong force.

He notes that the ability to reliably predict the properties of exotic nuclei with supercomputers helps pave the way for researchers to cost-effectively improve designs of nuclear reactors, to predict results from next generation accelerator experiments that will produce rare and exotic isotopes, as well as to better understand phenomena such as supernovae and neutron stars.
"We will never be able to travel to a neutron star and study it up close, so the only way to gain insights into its behavior is to understand how exotic nuclei like fluorine-14 behave and scale up," says Vary.

Developing a Computer Code to Simulate the Strong Force Including fluorine-14, researchers have so far discovered about 3,000 nuclei in laboratory experiments and suspect that 6,000 more could still be created and studied. Understanding the properties of these nuclei will give researchers insights into the strong force, which could in turn be applied to develop and improve future energy sources.
With these goals in mind, the Department of Energy's Scientific Discovery through Advanced Computing (SciDAC) program brought together teams of theoretical physicists, applied mathematicians, computer scientists and students from universities and national laboratories to create a computational project called the Universal Nuclear Energy Density Functional (UNEDF), which uses supercomputers to predict and understand behavior of a wide range of nuclei, including their reactions, and to quantify uncertainties. In fact, fluorine-14 was simulated with a code called Many Fermion Dynamics–nuclear (MFDn) that is part of the UNEDF project.

According to Vary, much of this code was developed on NERSC systems over the past two decades. "We started by calculating how two or three neutrons and protons interact, then built up our interactions from there to predict the properties of exotic nuclei like fluorine-14 with nine protons and five neutrons," says Vary. "We actually had these capabilities for some time, but were waiting for computing power to catch up. It wasn't until the past three or four years that computing power became available to make the runs."
Through the SciDAC program, Vary's team partnered with Ng and other scientists in Berkeley Lab's CRD who brought discrete and numerical mathematics expertise to improve a number of aspects in the code. "The prediction of fluorine-14 would not have been possible without SciDAC. Before our collaboration, the code had some bottlenecks, so performance was an issue," says Esmond Ng, who heads Berkeley Lab's Scientific Computing Group. Vary and Ng lead teams that are part of the UNEDF collaboration.

"We would not have been able to solve this problem without help from Esmond and the Berkeley Lab collaborators, or the initial investment from NERSC, which gave us the computational resources to develop and improve our code," says Vary. "It just would have taken too long. These contributions improved performance by a factor of three and helped us get more precise numbers."
He notes that a single simulation of fluorine-14 would have taken 18 hours on 30,000 processor cores, without the improvements implemented with the Berkeley Lab team's help. However, thanks to the SciDAC collaboration, each final run required only 6 hours on 30,000 processors. The final runs were performed on the Jaguar system at the Oak Ridge Leadership Computing Facility with an Innovative and Novel Computational Impact on Theory and Experiment (INCITE) allocation from the Department of Energy's Office of Advanced Scientific Computing Research (ASCR).

Source EurekaAlery!

Fundamental question on how life started solved

German and US researchers calculate a carbon nucleus of crucial importance

The researchers published their results in the coming issue of the scientific journal Physical Review Letters.

"Attempts to calculate the Hoyle state have been unsuccessful since 1954," said Professor Dr. Ulf-G. Meißner (Helmholtz-Institut für Strahlen- und Kernphysik der Universität Bonn). "But now, we have done it!" The Hoyle state is an energy-rich form of the carbon nucleus. It is the mountain pass over which all roads from one valley to the next lead: From the three nuclei of helium gas to the much larger carbon nucleus. This fusion reaction takes place in the hot interior of heavy stars. If the Hoyle state did not exist, only very little carbon or other higher elements such as oxygen, nitrogen and iron could have formed. Without this type of carbon nucleus, life probably also would not have been possible.

The search for the "slave transmitter"

The Hoyle state had been verified by experiments as early as 1954, but calculating it always failed. For this form of carbon consists of only three, very loosely linked helium nuclei - more of a cloudy diffuse carbon nucleus. And it does not occur individually, only together with other forms of carbon. "This is as if you wanted to analyze a radio signal whose main transmitter and several slave transmitters are interfering with each other," explained Prof. Dr. Evgeny Epelbaum (Institute of Theoretical Physics II at Ruhr-Universität Bochum). The main transmitter is the stable carbon nucleus from which humans - among others - are made. "But we are interested in one of the unstable, energy-rich carbon nuclei; so we have to separate the weaker radio transmitter somehow from the dominant signal by means of a noise filter."

What made this possible was a new, improved calculating approach the researchers used that allowed calculating the forces between several nuclear particles more precisely than ever. And in JUGENE, the supercomputer at Forschungszentrum Jülich, a suitable tool was found. It took JUGENE almost a week of calculating. The results matched the experimental data so well that the researchers can be certain that they have indeed calculated the Hoyle state.

More about how the Universe came into existence

"Now we can analyze this exciting and essential form of the carbon nucleus in every detail," explained Prof. Meißner. "We will determine how big it is, and what its structure is. And it also means that we can now take a very close look at the entire chain of how elements are formed."

In future, this may even allow answering philosophical questions using science. For decades, the Hoyle state was a prime example for the theory that natural constants must have precisely their experimentally determined values, and not any different ones, since otherwise we would not be here to observe the Universe (the anthropic principle). "For the Hoyle state this means that it must have exactly the amount of energy it has, or else, we would not exist," said Prof. Meißner. "Now we can calculate whether - in a changed world with other parameters - the Hoyle state would indeed have a different energy when comparing the mass of three helium nuclei." If this is so, this would confirm the anthropic principle.

###

The study was jointly conducted by the University of Bonn, Ruhr-Universität Bochum, North Carolina State University, and Forschungszentrum Jülich.

Source EurekaAlert!

Elusive Higgs slips from sight again

Now you see it, now you don't. Rather like a conjurer's white rabbit, the elusive Higgs boson may have slipped from sight again.

A recent report hinted at a glimpse of the long-sought particle at a major detector at the Large Hadron Collider (LHC) at CERN near Geneva, Switzerland. But a second detector has now checked its own data and found no corroborating sign of the particle.

The Higgs boson is thought to endow other particles with mass, but has yet to be observed. Four physicists associated with the LHC's ATLAS detector claimed to have found an anomalous "bump" in its data, possibly due to Higgs particles decaying into pairs of photons. An abstract of their study was leaked online in April.

Bump, what bump? 

Now physicists working on the LHC's other main detector, CMS, have come up empty in an initial search for a similar bump in their data, according to a document shown to New Scientist. So ATLAS's bump may not be due to Higgs particles, after all, but instead down to something mundane, such as an error in the analysis.

The internal CMS document has not been released to the public, so the result is still preliminary, as was the news of the original ATLAS bump, for that matter, which was leaked before it was reviewed or endorsed by the ATLAS collaboration.

Both leaks are a testament to the excitement surrounding the Higgs. With a result this hot on the horizon, expect more fits and starts in the months to come.

Source New Scientist

World's smallest atomic clock on sale

Sandia researchers develop tiny laser that reduced power consumption 1,000-fold

ALBUQUERQUE, N.M. — A matchbook-sized atomic clock 100 times smaller than its commercial predecessors has been created by a team of researchers at Symmetricom Inc. Draper Laboratory and Sandia National Laboratories. The portable Chip Scale Atomic Clock (CSAC) — only about 1.5 inches on a side and less than a half-inch in depth — also requires 100 times less power than its predecessors. Instead of 10 watts, it uses only 100 milliwatts. "It's the difference between lugging around a device powered by a car battery and one powered by two AA batteries," said Sandia lead investigator Darwin Serkland.
Despite common implications of the word "atomic," the clock does not use radioactivity as an energy source. Instead, where an old-fashioned alarm clock uses a spring-powered series of gears to tick off seconds, a CSAC counts the frequency of electromagnetic waves emitted by cesium atoms struck by a tiny laser beam to determine the passage of time. (There's a fuller, more interesting description of this process below.)
Still, given that the CSAC does not actually display the time of day — measured in millionths of a second, its passage would defy the ability of human eyes to read it — why would anyone want it?
The clock's uses are, indeed, specialized. Miners far underground or divers engaged in deep-sea explorations, blocked by natural barriers from GPS signals, could plan precise operations with remote colleagues who also had atomic clocks, because their timing would deviate from each other by less than one millionth of a second in a day.
A CSAC timekeeper would be invaluable to experts using electromagnetic interference to prevent telephone signals from detonating improvised explosive devices, or IEDs. Though GPS signals also would be blocked, a CSAC timekeeper would still function.
On a nationwide scale, relay stations for cross-country phone and data lines, which routinely break up messages into packets of information and send them by a variety of routes before reconstituting them correctly at the end of their voyages, would continue functioning during GPS outages.
The clock's many uses, both military and commercial, are why the Defense Advanced Research Projects Agency (DARPA) funded the work from 2001 until the CSA Clock hit the commercial market in January.
"Because few DARPA technologies make it to full industrial commercialization for dual-use applications, this is a very big deal," said Gil Herrera, director of Sandia's Microsystems and Engineering Sciences Application (MESA) center. "CSAC now is a product with a data sheet and a price."
Cesium atoms are housed in a container the size of a grain of rice developed by Cambridge, Mass.-based Draper Lab. The cesium atoms are interrogated by a light beam from a vertical-cavity surface-emitting laser, or VCSEL, contributed by Sandia. Symmetricom, a leading atomic clock manufacturer, designed the electronic circuits and assembled the components into a complete functioning clock at its Beverly, Mass., location.
"The work between the three organizations was never 'thrown over the wall,'" said Sandia manager Charles Sullivan, using an expression that has come to mean complete separation of effort. "There was tight integration from beginning to end of the project."
Nevertheless, the reduced power consumption that was key to creating the smaller unit required, in addition to a completely new architecture, a VCSEL rather than the previous tool of choice, a rubidium-based atomic vapor lamp.
"It took a few watts to excite the rubidium lamp into a plasmalike state," Serkland said. "Use of the VCSEL reduced that power consumption by more than a thousand times to just two milliwatts." (Serkland's success in attaining this huge power reduction caused some in the clock business to refer to him as "the VCSEL wizard.")
The way the clock keeps time may best be imagined by considering two tuning forks. If the forks vary only slightly in size, a series of regular beats are produced when both forks vibrate. The same principle works in the new clock.
The VCSEL — in addition to being efficient, inexpensive, stable and low-power — is able to produce a very fine, single-frequency beam. The laser frequency, at 335 terahertz (894.6 nanometers), is midway between two hyperfine emission levels of the cesium atom, separated in terms of energy like the two differently sized tuning forks. One level is 4.6 gigahertz above and the other 4.6 gigahertz below the laser frequency. (Hyperfine lines are the energy signatures of atoms.) A tiny microwave generator sends an oscillating frequency that alternates adding and subtracting energy from the incoming laser carrier frequency. Thus, the laser's single beam produces two waves at both hyperfine emission energies. When they interact, the emitted waves produce (like two tuning forks of different sizes) a series of 'beats' through a process known as interference.
A photodiode monitors the slight increase in light transmission through the cesium vapor cell when the microwave oscillator is tuned to resonance. According to the international definition of the second (since 1967) the clock indicates that one second has elapsed after counting exactly 4,596,315,885 cycles (nearly 4.6 gigacycles) of the microwave oscillator signal.
Because magnetism has an influence on cesium atoms, they are shielded from Earth's magnetic field by two layers of steel sheathing.
While this sounds cumbersome, atomic clocks are simpler to maintain than timepieces of a century ago, when a pendulum clock in Paris was the source of the world's exact time. Kept in a room that was temperature- and humidity-controlled, not only would a change of one degree affect the pendulum's swing, but the difficulty of bringing accurate time to the U.S. was extreme: one synchronized a portable clock in Paris and then had to transport it across the ocean by ship, during which time the mechanical clock would inevitably drift from the time of the Paris clock.
A description of the technical details of the clock, available for approximately $1,500, can be found at Symmetricom's website.
Sandia is developing a follow-on technology for DARPA: a trapped-ion-based clock. It will improve timing accuracy at similar size, weight and power to the CSAC. Researches are working on the first compact prototype.

###

Sandia National Laboratories is a multiprogram laboratory operated and managed by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration. With main facilities in Albuquerque, N.M., and Livermore, Calif., Sandia has major R&D responsibilities in national security, energy and environmental technologies, and economic competitiveness.

Source EurekaAlert!

U.S. Collider Offers Physicists a Glimpse of a Possible New Particle

The soon-to-be-retired Tevatron collider has uncovered an unexplained signal that could be a previously unknown particle

Physicists sifting through data generated by the Tevatron particle collider in Illinois have uncovered a signal that neither they nor the long-standing Standard Model of particle physics can explain.

The international team of researchers work with data from CDF, one of the two Tevatron detectors where protons and their antimatter counterparts collide at nearly light speed. The wreckage of those high-energy collisions produces a variety of short-lived particles, which allows physicists a fleeting glimpse into the inner workings of the physical world. The Tevatron, at Fermi National Accelerator Laboratory, is the second-most powerful particle collider in the world after the Large Hadron Collider outside Geneva, Switzerland.

Examining a very specific kind of outcome when protons and antiprotons collide inside the CDF detector, the researchers noticed an unexplained blip in their signal that could be explained by a previously undiscovered elementary particle—but not the Higgs boson, the hotly pursued particle that is theorized to imbue other particles with mass.

The researchers reported their perplexing but unconfirmed new finding in a study posted online April 4 at the physics preprint Web site arXiv.org The researchers have also submitted their results for publication in Physical Review Letters.

The CDF team found that the Tevatron was a bit more prolific than it should be in terms of collisions that yield a heavy elementary particle known as the W boson plus a pair of particulate jets. "What we see is that there a region between 120 and 160 GeV (giga-electron volts) where there is an excess," CDF physicist Viviana Cavaliere of the University of Illinois at Urbana–Champaign explained to a packed Fermilab auditorium April 6. (A giga-, or a billion, electron volts is a unit of particle mass or energy.)

The result is compatible, Cavaliere said, with the collisions producing a W boson plus a hitherto unknown—and even heavier—particle with a mass of about 150 GeV. But that particle appears not to be the Higgs boson, which would be expected to emerge from the collisions alongside a W boson with far less frequency. If CDF has uncovered a new elementary particle, it would be the first such discovery since the tau neutrino was observed at Fermilab in 2000. But in the case of the tau physicists had predicted the particle's existence and had gone out looking for it.

As theorists scramble to figure out just what CDF has found, experimentalists will be working to verify that the detector has found anything at all. The new analysis claims that the data disagree with existing theory to better than three standard deviations, or 3 sigma. Assuming the analysis is correct, that means that there is just a fraction of a 1 percent chance that the effect is a mere statistical glitch. But extraordinary claims demand stronger proof.

"Five sigma is our gold standard," says Brookhaven National Laboratory physicist Sally Dawson, adding that the physics community has seen 3-sigma effects come and go. "If it's true, and if it holds up, it is of course very exciting, because it's completely unexpected," Dawson says. "If it persists, it's very hard to explain theoretically."


"We will learn pretty soon whether it's true or not," says Fermilab theorist Bogdan Dobrescu, who did not contribute to the new study. "This is pretty credible at this stage." If the results hold up, theorists will need to figure out what kind of new particle could fit the bill. "It would be a major breakthrough, especially because this is a particle that no one really predicted to the best of my knowledge," Dobrescu says. "We can try to invent some new particles and see if they have the appropriate properties that we see, but none of the answers are very expected."

The Tevatron, which is slated to shut down for good in the fall, is still collecting data that could strengthen the case for a new particle—or sink it. Cavaliere said that the new analysis began more than a year ago and does not include the latest data from CDF. The team already has already logged a good deal more collisions that await analysis, but Cavaliere cautioned that the expanded data set would not be enough to vault the discovery into the 5-sigma range.

But the physics community will not have to wait long before the new particle gets a reality check. Physicists working with the other detector at the Tevatron, known as DZero, are now replicating the CDF analysis with their own voluminous data set, says Fermilab physicist and DZero co-spokesperson Dmitri Denisov. "We expect we will be able to clarify this topic on a timescale of a few weeks," he says.

Courtesy of Scientific American