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From symmetry

Shrinking the accelerator

Scientists plan to use a newly awarded grant to develop a shoebox-sized particle accelerator in five years. Photo: SLAC National Accelerator Laboratory

The Gordon and Betty Moore Foundation has awarded $13.5 million to Stanford University for an international effort, including key contributions from the Department of Energy's SLAC National Accelerator Laboratory, to build a working particle accelerator the size of a shoebox. It's based on an innovative technology known as "accelerator on a chip."

This novel technique, which uses laser light to propel electrons through a series of artfully crafted glass chips, has the potential to revolutionize science, medicine and other fields by dramatically shrinking the size and cost of particle accelerators.

"Can we do for particle accelerators what the microchip industry did for computers?" says SLAC physicist Joel England, an investigator with the 5-year project. "Making them much smaller and cheaper would democratize accelerators, potentially making them available to millions of people. We can't even imagine the creative applications they would find for this technology."

Robert L. Byer, a Stanford professor of applied physics and co-principal investigator for the project who has been working on the idea for 40 years, says, "Based on our proposed revolutionary design, this prototype could set the stage for a new generation of 'tabletop' accelerators, with unanticipated discoveries in biology and materials science and potential applications in security scanning, medical therapy and X-ray imaging."

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Photo of the Day

The greater geese

nature, wildlife, animal, bird, goose
Two greater white-fronted geese prepare to land in the bison pasture. Photo: Gordon Garcia
In the News

Mysterious glow at Milky Way's center could be dark matter or hidden pulsars

From Scientific American, Nov. 18, 2015

The heart of our galaxy is oddly bright. Since 2009 astronomers have suggested that too much gamma-ray light is shining from the Milky Way's core — more than all the known sources of light can account for. From the beginning scientists have suspected that they were seeing the long-sought signal of dark matter, the invisible form of mass thought to pervade the universe. But two recent studies offer more support for an alternate explanation: The gamma rays come from a group of spinning stars called pulsars that are just slightly too dim to see with current telescopes.

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In the News

Astronomers indirectly spot neutrinos released just 1 second after the birth of the universe

From Scientific American, Nov. 17, 2015

The universe's oldest light hasn't made a pit stop for 13.82 billion years—beginning its journey just 380,000 years after the big bang. That light, the so-called cosmic microwave background (CMB), serves as a familiar hunting ground for astronomers who seek to understand the universe in its infancy. Unfortunately, it also obscures what lies beyond it: the first hundreds of thousands of years of the universe. Now astronomers think they have peeked beyond even the CMB by capturing evidence of neutrinos traveling since the cosmos was just a second old.

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Frontier Science Result: CMS

Lead bottom

Today's article describes what happens when you collide individual protons into lead nuclei. This result helps understand an exciting new state of matter called a quark gluon plasma. Image: CERN

The nice thing about the LHC research program is that it allows scientists to investigate many phenomena. All are exotic, with some pushing the very frontier of knowledge, while some investigate complex phenomena as a means to understand even more complex phenomena.

When two heavy atomic nuclei are slammed together at very high energy, a peculiar thing occurs. The temperatures in these collisions are so high that the protons and neutrons in the nuclei literally melt, and the quarks and gluons that are normally inside the protons and neutrons can move around freely. We call this state of matter a quark-gluon plasma.

In addition, the high collision energy can convert into matter-antimatter pairs, as suggested by Einstein's equation E=mc2. If you want to study what occurs in the collision, you look for types of matter that don't exist as ordinary matter. One example of this more exotic type of matter is bottom quarks. Since they don't generally exist inside the nuclei of atoms, if you see bottom quarks, you know that they were made from the energy of the collision.

Scientists have lots of experience making bottom quarks by colliding two protons together. This is the way we run the LHC for most of the time, and we have made (although not recorded) many billions of bottom quarks. The process is pretty well-understood.

We also can make bottom quarks by colliding two lead nuclei together. We do this at the LHC about one month per year. In these collisions, a total of 416 protons and neutrons are smashed together. Naively, you'd expect that all the protons and neutrons can participate in the collision and that the number of bottom quarks that are made can be easily calculated from the well-understood proton-proton scattering process.

However, we see fewer bottom quarks than we'd expect from lead-lead collisions. The usual explanation is that these bottom quarks have to push their way through the hot quark-gluon plasma. They become tired and slow down, so they don't escape the collision.

But there might be other explanations. Maybe the fact that the colliding protons and neutrons are bound in nuclei (rather that floating freely) influences how their component quarks and gluons are distributed inside them.

To work out this ambiguity, CMS scientists decided to smash together a beam of protons into a beam of lead nuclei. If the lower-than-expected number of bottom quarks in lead-lead collisions was due to the way bottom quarks plow through quark-gluon plasma you'd expect to see no reduction in the production of bottom quarks from these lead-proton collisions, since the quark-gluon plasma is not made in these kinds of collisions. If the effect was due to the moving around of energy inside nuclei, you'd expect to see behavior midway between the proton-proton and lead-lead scattering.

As it happens, scientists observed no reduction in the production of bottom quarks. This strongly suggests that the reduction seen in collisions between two lead nuclei originates in the bottom quarks trying to punch through the quark gluon plasma. Thus this measurement validates our understanding of the behavior of matter hot enough to melt protons and neutrons.

Don Lincoln

These U.S. CMS scientists made important contributions to this analysis.