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IceCube Neutrino Observatory constrains the origin of cosmic rays

Thursday, April 19, 2012

 

Although cosmic rays were discovered 100 years ago, their origin remains one of the most enduring mysteries in physics. Now, the IceCube Neutrino Observatory, a massive detector in Antarctica, is honing in on how the highest energy cosmic rays are produced.

Cosmic rays are electrically charged particles, such as protons, that strike Earth from all directions, with energies up to one hundred million times higher than those created in man-made accelerators. The intense conditions needed to generate such energetic particles have focused physicists’ interest on two potential sources: the massive black holes at the centers of active galaxies, and the exploding fireballs observed by astronomers as gamma ray bursts (GRBs).

IceCube is using neutrinos, which are believed to accompany cosmic ray production, to explore these theories. In a paper published in the April 19 issue of the journal Nature, the IceCube collaboration – which includes a Georgia Institute of Technology scientist -- describes a search for neutrinos emitted from 300 gamma ray bursts observed, most recently in coincidence with the SWIFT and Fermi satellites, between May 2008 and April 2010. Surprisingly, they found none - a result that contradicts 15 years of predictions and challenges one of the two leading theories for the origin of the highest energy cosmic rays.

“The result of this neutrino search is significant because for the first time we have an instrument with sufficient sensitivity to open a new window on cosmic ray production and the interior processes of GRBs,” said IceCube spokesperson and University of Maryland physics professor Greg Sullivan. “The unexpected absence of neutrinos from GRBs has forced a re-evaluation of the theory for production of cosmic rays and neutrinos in a GRB fireball and possibly the theory that high energy cosmic rays are generated in fireballs.”

IceCube is a high energy neutrino telescope at the geographical South Pole in Antarctica, operated by a collaboration of 250 physicists and engineers from the United States, Germany, Sweden, Belgium, Switzerland, Japan, Canada, New Zealand, Australia and Barbados. The IceCube Neutrino Observatory was built under a National Science Foundation (NSF) Major Research Equipment and Facilities Construction grant, with assistance from partner funding agencies around the world. The NSF Office of Polar Programs continues to support the project with a maintenance and operations grant. Construction was finished in December 2010.

“One of the main objectives of IceCube is to search for the sources of the highest energy cosmic rays,” explained Ignacio Taboada, an assistant professor in the Georgia Tech School of Physics who has been involved in IceCube since its planning stages. “Gamma ray bursts have always been high on the list of potential sources for cosmic rays. Though not completely ruled out, the mechanisms by which GRBs could produce these cosmic rays are now significantly constrained by these results. We will keep looking for the sources, and our chances of finding them will increase as we accumulate more data to improve our sensitivity.”

IceCube observes neutrinos by detecting the faint blue light produced in neutrino interactions in ice. Neutrinos are of a ghostly nature; they can easily travel through people, walls, or the planet Earth. To compensate for the antisocial nature of neutrinos and detect their rare interactions, IceCube is built on an enormous scale. One cubic kilometer of glacial ice, enough to fit the great pyramid of Giza 400 times, is instrumented with 5,160 optical sensors embedded up to 2.5 kilometers deep in the ice.

GRBs, the universe’s most powerful explosions, are usually first observed by satellites using X-rays and/or gamma rays. GRBs are seen about once per day, and are so bright that they can be seen from half way across the visible universe. The explosions usually last only a few seconds, and during this brief time they can outshine everything else in the universe.

“Although we have not discovered where cosmic rays come from, we have taken a major step towards ruling out one of the leading predictions,” said IceCube principal investigator and University of Wisconsin - Madison physics professor Francis Halzen.

Improved theoretical understanding and more data from the compete IceCube detector will help scientists better understand the mystery of cosmic ray production. IceCube is currently collecting more data with the finalized, better calibrated, and better understood detector.

For more information about IceCube, visit www.icecube.wisc.edu.

Summary: 

Georgia Tech physicist contributes to study of gamma ray bursts

Intro: 

Georgia Tech physicist contributes to study of gamma ray bursts

Alumni: 

IceCube Neutrino Observatory Explores Origin of Cosmic Rays

Wednesday, April 18, 2012

Although cosmic rays were discovered 100 years ago, their origin remains one of the most enduring mysteries in physics. Now, the IceCube Neutrino Observatory, a massive detector in Antarctica, is honing in on how the highest energy cosmic rays are produced.

Cosmic rays are electrically charged particles, such as protons, that strike Earth from all directions, with energies up to one hundred million times higher than those created in man-made accelerators. The intense conditions needed to generate such energetic particles have focused physicists’ interest on two potential sources: the massive black holes at the centers of active galaxies, and the exploding fireballs observed by astronomers as gamma ray bursts (GRBs).

IceCube is using neutrinos, which are believed to accompany cosmic ray production, to explore these theories. In a paper published in the April 19 issue of the journal Nature, the IceCube collaboration – which includes a Georgia Institute of Technology scientist -- describes a search for neutrinos emitted from 300 gamma ray bursts observed, most recently in coincidence with the SWIFT and Fermi satellites, between May 2008 and April 2010. Surprisingly, they found none - a result that contradicts 15 years of predictions and challenges one of the two leading theories for the origin of the highest energy cosmic rays.

“The result of this neutrino search is significant because for the first time we have an instrument with sufficient sensitivity to open a new window on cosmic ray production and the interior processes of GRBs,” said IceCube spokesperson and University of Maryland physics professor Greg Sullivan. “The unexpected absence of neutrinos from GRBs has forced a re-evaluation of the theory for production of cosmic rays and neutrinos in a GRB fireball and possibly the theory that high energy cosmic rays are generated in fireballs.”

IceCube is a high energy neutrino telescope at the geographical South Pole in Antarctica, operated by a collaboration of 250 physicists and engineers from the United States, Germany, Sweden, Belgium, Switzerland, Japan, Canada, New Zealand, Australia and Barbados. The IceCube Neutrino Observatory was built under a National Science Foundation (NSF) Major Research Equipment and Facilities Construction grant, with assistance from partner funding agencies around the world. The NSF Office of Polar Programs continues to support the project with a maintenance and operations grant. Construction was finished in December 2010.

“One of the main objectives of IceCube is to search for the sources of the highest energy cosmic rays,” explained Ignacio Taboada, an assistant professor in the Georgia Tech School of Physics who has been involved in IceCube since its planning stages. “Gamma ray bursts have always been high on the list of potential sources for cosmic rays. Though not completely ruled out, the mechanisms by which GRBs could produce these cosmic rays are now significantly constrained by these results. We will keep looking for the sources, and our chances of finding them will increase as we accumulate more data to improve our sensitivity.”

IceCube observes neutrinos by detecting the faint blue light produced in neutrino interactions in ice. Neutrinos are of a ghostly nature; they can easily travel through people, walls, or the planet Earth. To compensate for the antisocial nature of neutrinos and detect their rare interactions, IceCube is built on an enormous scale. One cubic kilometer of glacial ice, enough to fit the great pyramid of Giza 400 times, is instrumented with 5,160 optical sensors embedded up to 2.5 kilometers deep in the ice.

GRBs, the universe’s most powerful explosions, are usually first observed by satellites using X-rays and/or gamma rays. GRBs are seen about once per day, and are so bright that they can be seen from half way across the visible universe. The explosions usually last only a few seconds, and during this brief time they can outshine everything else in the universe.

“Although we have not discovered where cosmic rays come from, we have taken a major step towards ruling out one of the leading predictions,” said IceCube principal investigator and University of Wisconsin - Madison physics professor Francis Halzen.

Improved theoretical understanding and more data from the compete IceCube detector will help scientists better understand the mystery of cosmic ray production. IceCube is currently collecting more data with the finalized, better calibrated, and better understood detector.

For more information about IceCube, visit www.icecube.wisc.edu.

 

Media Contact: 

John Toon

Research News & Publications Office

jtoon@gatech.edu

(404) 894-6986

Summary: 

In a paper published in the journal Nature, scientists using data from the IceCube Neutrino Observatory describe a search for neutrinos emitted from 300 gamma ray bursts. The study's findings contradict 15 years of predictions and challenge one of the leading theories for the origin of the highest energy cosmic rays.

Intro: 

In a paper published in the journal Nature, scientists using data from the IceCube Neutrino Observatory describe a search for neutrinos emitted from 300 gamma ray bursts. The study's findings contradict 15 years of predictions and challenge one of the leading theories for the origin of the highest energy cosmic rays.

Alumni: 

Gravish awarded 2012 IMPACT Award

Monday, April 9, 2012

Nick Gravish has been awarded a 2012 Auxiliary Services IMPACT Scholarship Award.

This $4000 scholarship award is an acknowledgment of the superior IMPACT Nick has made at Georgia Tech and his outstanding efforts to impact our community.  Each year Auxiliary Services awards IMPACT Scholarships to men and women who can demonstrate that they have made positive impacts on the Georgia Tech community.

Gravish is a fourth year physics graduate student in the Professor Dan Goldman's Complex Rheology and Biomechanics lab in the School of Physics.
 

Summary: 

Nick Gravish has been awarded a 2012 Auxiliary Services IMPACT Scholarship Award.

Intro: 

Nick Gravish has been awarded a 2012 Auxiliary Services IMPACT Scholarship Award.

Alumni: 

Researchers Develop Blueprint for Nuclear Clock Accurate Over Billions of Years

Wednesday, March 21, 2012

A clock accurate to within a tenth of a second over 14 billion years -- the age of the universe -- is the goal of research being reported this week by scientists from three different institutions. To be published in the journal Physical Review Letters, the research provides the blueprint for a nuclear clock that would get its extreme accuracy from the nucleus of a single thorium ion.

Such a clock could be useful for certain forms of secure communication -- and perhaps of greater interest -- for studying the fundamental theories of physics. A nuclear clock could be as much as one hundred times more accurate than current atomic clocks, which now serve as the basis for the global positioning system (GPS) and a broad range of important measurements.

"If you give people a better clock, they will use it," said Alex Kuzmich, a professor in the School of Physics at the Georgia Institute of Technology and one of the paper's co-authors. "For most applications, the atomic clocks we have are precise enough. But there are other applications where having a better clock would provide a real advantage."

For the full article, please go to this link.

Summary: 

Precision of Nuclear Clock Depends on Single Atom of Thorium

Intro: 

Precision of Nuclear Clock Depends on Single Atom of Thorium

Alumni: 

Researchers Develop Blueprint for Nuclear Clock Accurate Over Billions of Years

Monday, March 19, 2012

A clock accurate to within a tenth of a second over 14 billion years -- the age of the universe -- is the goal of research being reported this week by scientists from three different institutions. To be published in the journal Physical Review Letters, the research provides the blueprint for a nuclear clock that would get its extreme accuracy from the nucleus of a single thorium ion.

Such a clock could be useful for certain forms of secure communication -- and perhaps of greater interest -- for studying the fundamental theories of physics. A nuclear clock could be as much as one hundred times more accurate than current atomic clocks, which now serve as the basis for the global positioning system (GPS) and a broad range of important measurements.

"If you give people a better clock, they will use it," said Alex Kuzmich, a professor in the School of Physics at the Georgia Institute of Technology and one of the paper's co-authors. "For most applications, the atomic clocks we have are precise enough. But there are other applications where having a better clock would provide a real advantage."

In addition to the Georgia Tech physicists, researchers in the School of Physics at the University of New South Wales in Australia and at the Department of Physics at the University of Nevada also contributed to the study. The research has been supported by the Office of Naval Research, the National Science Foundation and the Gordon Godfrey fellowship.

Early clocks used a swinging pendulum to provide the oscillations needed to track time. In modern clocks, quartz crystals provide high-frequency oscillations that act like a tuning fork, replacing the old-fashioned pendulum. Atomic clocks derive their accuracy from laser-induced oscillations of electrons in atoms. However, these electrons can be affected by magnetic and electrical fields, allowing atomic clocks to drift ever so slightly -- about four seconds in the lifetime of the universe.

Because neutrons are much heavier than electrons and densely packed into the atomic nucleus, they are less susceptible to these perturbations than the electrons. A nuclear clock should therefore be less affected by environmental factors than its atomic cousin.

"In our paper, we show that by using lasers to orient the electrons in a very specific way, we can use the neutron of an atomic nucleus as the clock pendulum," said Corey Campbell, a research scientist in the Kuzmich laboratory and the paper's first author. "Because the neutron is held so tightly to the nucleus, its oscillation rate is almost completely unaffected by any external perturbations."

To create the oscillations, the researchers plan to use a laser operating at petahertz frequencies -- 10 (15) oscillations per second -- to boost the nucleus of a thorium 229 ion into a higher energy state. Tuning a laser to create these higher energy states would allow scientists to set its frequency very precisely, and that frequency would be used to keep time instead of the tick of a clock or the swing of a pendulum.

The nuclear clock ion will need to be maintained at a very low temperature -- tens of microkelvins -- to keep it still. To produce and maintain such temperatures, physicists normally use laser cooling. But for this system, that would pose a problem because laser light is also used to create the timekeeping oscillations.

To solve that problem, the researchers include a single thorium 232 ion with the thorium 229 ion that will be used for timekeeping. The heavier ion is affected by a different wavelength than the thorium 229. The researchers can then cool the heavier ion, which lowers the temperature of the clock ion without affecting the oscillations.

"The cooling ion acts as a refrigerator, keeping the clock ion very still," said Alexander Radnaev, a graduate research assistant in the Kuzmich lab. "This is necessary to interrogate the clock ion for very long and to make a very accurate clock that will provide the next level of performance."

Calculations suggest that a nuclear clock could be accurate to 10 (-19), compared to 10 (-17) for the best atomic clock.

Because they operate in slightly different ways, atomic clocks and nuclear clocks could one day be used together to examine differences in physical constants. "Some laws of physics may not be constant in time," Kuzmich said. "Developing better clocks is a good way to study this."

Though the research team believes it has now demonstrated the potential to make a nuclear clock -- which was first proposed in 2003 -- it will still be a while before they can produce a working one.

The major challenge ahead is that the exact frequency of laser emissions needed to excite the thorium nucleus hasn't yet been determined, despite the efforts of many different research groups.

"People have been looking for this for 30 years," Campbell said. "It's worse than looking for a needle in a haystack. It's more like looking for a needle in a million haystacks."

But Kuzmich believes that problem will be solved, allowing physicists to move to the next generation of phenomenally accurate timekeepers.

"Our research shows that building a nuclear clock in this way is both worthwhile and feasible," he said. "We now have the tools and plans needed to move forward in realizing this system."

 

Research News & Publications Office

Georgia Institute of Technology

75 Fifth Street, N.W., Suite 314

Atlanta, Georgia  30308  USA

 

Media Relations Contacts: John Toon (404-894-6986)(jtoon@gatech.edu) or Abby Robinson (404-385-3364)(abby@innovate.gatech.edu).

Writer: John Toon

 

 

 

 

 

 

Media Contact: 

John Toon

Research News & Publications Office

404-894-6986

jtoon@gatech.edu

Summary: 

A clock accurate to within a tenth of a second over 14 billion years – the age of the universe – is the goal of research being reported this week in the journal Physical Review Letters. The research provides the blueprint for a nuclear clock based on a single thorium ion.

Intro: 

A clock accurate to within a tenth of a second over 14 billion years – the age of the universe – is the goal of research being reported this week in the journal Physical Review Letters. The research provides the blueprint for a nuclear clock based on a single thorium ion.

Alumni: 

Physicists receive GT Fire Awards

Monday, March 19, 2012

Two School of Physics faculty have recently received funding from the Georgia Tech Fund for Innovation in Research and Education (GT FIRE). The GT FIRE program was created in order to inspire innovation in research and education at Georgia Tech. “The program is off to a great start,” said Rafael L. Bras, provost and executive vice president for academic affairs. “The submitted proposals mesh well with our strategic plan, and that was our hope.” “Innovation in research is critical for us to lead and set the science, technology and policy agenda for the United States and the world,” said Steve Cross, executive vice president for research. “I am happy to support GT FIRE in stimulating faculty thinking and creativity.”

Dr. Harold Kim received an award for "A single-cell study to investigate the functional impact of chromosomal landscape."  By correlating expression noise of identical genes placed at different locations on the genome, Kim will create a construction of the segregation map of genes inside the nucleus of a cell.  The funds will be used for a pilot study aimed to construct the segregation map of genes inside the nucleus of a cell. Prof. Kim will correlate expression noise of two identical genes placed at various locations on the yeast genome and investigate whether this correlation can be used to infer physical distance inside the nucleus.

Dr. Daniel Goldman received an award for "Micro-Labs: A hands-on course in experiment, theory and computation in Nonlinear Science/Complex Systems."  Using GT FIRE funds, Prof. Goldman will develop a course in Nonlinear Science/Complex Systems which will emphasize and demonstrate the creativity and critical thinking skills involved in scientific inquiry through participation in hands-on “micro-labs.” These will be short and intense laboratory experiences in which creative problem solving and hypothesis generation will be utilized to design and build an experiment, collect and analyze data, and compare data to a model, all in a single week while working in a laboratory with Prof. Goldman and a graduate student TA. The course will show students that original, cutting-edge science is accessible to them now, with skills and tools they already have or, with guidance, can readily develop.

Summary: 

Two School of Physics faculty have recently received funding from the Georgia Tech Fund for Innovation in Research and Education (GT FIRE). The GT FIRE program was created in order to inspire innovation in research and education at Georgia Tech.

Intro: 

Two School of Physics faculty have recently received funding from the Georgia Tech Fund for Innovation in Research and Education (GT FIRE). The GT FIRE program was created in order to inspire innovation in research and education at Georgia Tech.

Alumni: 

Physics Faculty Awarded Promotion and Tenure

Thursday, March 15, 2012

Congratulations to Physics faculty Mike Schatz, Markus Kindermann and Joshua Weitz, who have been granted promotions at Georgia Tech.  Dr. Schatz was promoted to the rank of professor, and Dr. Kindermann and Dr. Weitz to the rank of associate professor with tenure.

Summary: 

Physics Faculty Awarded Promotion and Tenure

Intro: 

Physics Faculty Awarded Promotion and Tenure

Alumni: 

Physics Alumnus Wins 2012 Sigma Xi Best Thesis Award

Wednesday, March 14, 2012

School of Physics PhD alumnus and current postdoc Chen Li is a recipient of the 2012 Sigma-Xi Best PhD thesis Award.

Li defended his thesis, "Biological, Robotic, and Physics Studies to Discover Principles of Legged Locomotion on Granular Media", in November and graduated in December (advisor: Daniel Goldman). In July, he will join Prof. Robert Full's Poly-PEDAL Lab at UC Berkeley as a Miller Fellow.

Congratulations!

Summary: 

School of Physics PhD alumnus and current postdoc Chen Li is a recipient of the 2012 Sigma-Xi Best PhD thesis Award

Intro: 

School of Physics PhD alumnus and current postdoc Chen Li is a recipient of the 2012 Sigma-Xi Best PhD thesis Award

Alumni: 

Scientists Score Another Victory Over Uncertainty in Quantum Physics Measurements

Sunday, February 26, 2012

Most people attempt to reduce the little uncertainties of life by carrying umbrellas on cloudy days, purchasing automobile insurance or hiring inspectors to evaluate homes they might consider purchasing. For scientists, reducing uncertainty is a no less important goal, though in the weird realm of quantum physics, the term has a more specific meaning.

For scientists working in quantum physics, the Heisenberg Uncertainty Principle says that measurements of properties such as the momentum of an object and its exact position cannot be simultaneously specified with arbitrary accuracy. As a result, there must be some uncertainty in either the exact position of the object, or its exact momentum. The amount of uncertainty can be determined, and is often represented graphically by a circle showing the area within which the measurement actually lies.

Over the past few decades, scientists have learned to cheat a bit on the Uncertainty Principle through a process called “squeezing,” which has the effect of changing how the uncertainty is shown graphically. Changing the circle to an ellipse and ultimately to almost a line allows one component of the complementary measurements – the momentum or the position, in the case of an object – to be specified more precisely than would otherwise be possible. The actual area of uncertainty remains unchanged, but is represented by a different shape that serves to improve accuracy in measuring one property.

This squeezing has been done in measuring properties of photons and atoms, and can be important to certain high-precision measurements needed by atomic clocks and the magnetometers used to create magnetic resonance imaging views of structures deep inside the body. For the military, squeezing more accuracy could improve the detection of enemy submarines attempting to hide underwater or improve the accuracy of atom-based inertial guidance instruments.

Now physicists at the Georgia Institute of Technology have added another measurement to the list of those that can be squeezed. In a paper appearing online February 26 in the journal Nature Physics, they report squeezing a property called the nematic tensor, which is used to describe the rubidium atoms in Bose-Einstein Condensates, a unique form of matter in which all atoms have the same quantum state. The research was sponsored by the National Science Foundation (NSF).

“What is new about our work is that we have probably achieved the highest level of atom squeezing reported so far, and the more squeezing you get, the better,” said Michael Chapman, a professor in Georgia Tech’s School of Physics. “We are also squeezing something other than what people have squeezed before.”

Scientists have been squeezing the spin states of atoms for 15 years, but only for atoms that have just two relevant quantum states – known as spin ½ systems. In collections of those atoms, the spin states of the individual atoms can be added together to get a collective angular momentum that describes the entire system of atoms.

In the Bose-Einstein condensate atoms being studied by Chapman’s group, the atoms have three quantum states, and their collective spin totals zero – not very helpful for describing systems. So Chapman and graduate students Chris Hamley, Corey Gerving, Thai Hoang and Eva Bookjans learned to squeeze a more complex measure that describes their system of spin 1 atoms: nematic tensor, also known as quadrupole.

Nematicity is a measure of alignment that is important in describing liquid crystals, exotic magnetic materials and some high temperature superconductors.

“We don’t have a spin vector pointing in a particular direction, but there is still some residual information in where this collection of atoms is pointing,” Chapman explained. “That next higher-order description is the quadrupole, or nematic tensor. Squeezing this actually works quite well, and we get a large degree of improvement, so we think it is relatively promising.”

Experimentally, the squeezing is created by entangling some of the atoms, which takes away their independence. Chapman’s group accomplishes this by colliding atoms in their ensemble of some 40,000 rubidium atoms.

“After they collide, the state of one atom is connected to that of the other atom, so they have been entangled in that way,” he said. “This entanglement creates the squeezing.”

Reducing uncertainty in measuring atoms could have important implications for precise magnetic measurements. The next step will be to determine experimentally if the technique can improve the measurement of magnetic field, which could have important applications.

“In principle, this should be a straightforward experiment, but it turns out that the biggest challenge is that magnetic fields in the laboratory fluctuate due to environmental factors such as the effects of devices such as computer monitors,” Chapman said. “If we had a noiseless laboratory, we could measure the magnetic field both with and without squeezed states to demonstrate the enhanced precision. But in our current lab environment, our measurements would be affected by outside noise, not the limitations of the atomic sensors we are using.”

The new squeezed property could also have application to quantum information systems, which can store information in the spin of atoms and their nematic tensor.

“There are a lot of things you can do with quantum entanglement, and improving the accuracy of measurements is one of them,” Chapman added. “We still have to obey Heisenberg’s Uncertainty Principle, but we do have the ability to manipulate it.”

Research News & Publications Office
Georgia Institute of Technology
75 Fifth Street, N.W., Suite 314
Atlanta, Georgia  30308  USA

Media Relations Contacts: John Toon (404-894-6986)(jtoon@gatech.edu) or Abby Robinson (404-385-3364)(abby@innovate.gatech.edu)

Writer: John Toon

Media Contact: 

John Toon

Research News & Publications Office

404-894-6986

jtoon@gatech.edu

Summary: 

Uncertainty affects the accuracy with which measurements can be made in quantum physics. To reduce this uncertainty, physicists have learned to "squeeze" certain measurements. Researchers are now reporting a new type of measurement that can be squeezed to improve precision.

Intro: 

Uncertainty affects the accuracy with which measurements can be made in quantum physics. To reduce this uncertainty, physicists have learned to "squeeze" certain measurements. Researchers are now reporting a new type of measurement that can be squeezed to improve precision.

Alumni: 

Dr. Constantine Yannouleas awarded as 2012 APS Outstanding Referee

Thursday, February 16, 2012

Congratulations to Senior Research Scientist Dr. Constantine Yannouleas, who has been awarded as a 2012 APS Outstanding Referee. 

A research scientist with the School of Physics and the Center for Computational Materials Science at Georgia Tech since 1992, he will be attending the  recognition ceremony at the 2012 APS March meeting in Boston, MA.

Summary: 

Dr. Constantine Yannouleas awarded as 2012 APS Outstanding Referee

Intro: 

Dr. Constantine Yannouleas awarded as 2012 APS Outstanding Referee

Alumni: 

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