Thursday, April 9, 2015
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International folk dancing Thursday evenings at Kuhn Barn

English country dancing - April 12

Budker Seminar - April 13

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MS Excel 2013: Introduction offered two half days - April 28 and 30

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MS Word 2013: Introduction offered two half days - May 5 and 7

Interpersonal Communication Skills course - May 20

Managing Conflict (a.m. only) on June 10

Performance review training for managers and supervisors - Aug. 4, 5 and 6

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Absence of gravitational-wave signal extends limit on knowable universe

The Holometer is sensitive to high-frequency gravitational waves, allowing it to look for events such as cosmic strings. Photo: Reidar Hahn

Imagine an instrument that can measure motions a billion times smaller than an atom that last a millionth of a second. Fermilab's Holometer is currently the only machine with the ability to take these very precise measurements of space and time, and recently collected data has improved the limits on theories about exotic objects from the early universe.

Our universe is as mysterious as it is vast. According to Albert Einstein's theory of general relativity, anything that accelerates creates gravitational waves, which are disturbances in the fabric of space and time that travel at the speed of light and continue infinitely into space. Scientists are trying to measure these possible sources all the way to the beginning of the universe.

The Holometer experiment, based at the Department of Energy's Fermilab, is sensitive to gravitational waves at frequencies in the range of a million cycles per second. Thus it addresses a spectrum not covered by experiments such as the Laser Interferometer Gravitational-Wave Observatory, which searches for lower-frequency waves to detect massive cosmic events such as colliding black holes and merging neutron stars.

"It's a huge advance in sensitivity compared to what anyone had done before," said Craig Hogan, director of the Center for Particle Astrophysics at Fermilab.

This unique sensitivity allows the Holometer to look for exotic sources that could not otherwise be found. These include tiny black holes and cosmic strings, both possible phenomena from the early universe that scientists expect to produce high-frequency gravitational waves. Tiny black holes could be less than a meter across and orbit each other a million times per second; cosmic strings are loops in space-time that vibrate at the speed of light.

The Holometer is composed of two Michelson interferometers that each split a laser beam down two 40-meter arms. The beams reflect off the mirrors at the ends of the arms and travel back to reunite. Passing gravitational waves alter the lengths of the beams' paths, causing fluctuations in the laser light's brightness, which physicists can detect.

The Holometer team spent five years building the apparatus and minimizing noise sources to prepare for experimentation. Now the Holometer is taking data continuously, and with an hour's worth of data, physicists were able to confirm that there are no high-frequency gravitational waves at the magnitude where they were searching.

The absence of a signal provides valuable information about our universe. Although this result does not prove whether the exotic objects exist, it has eliminated the region of the universe where they could be present.

"It means that if there are primordial cosmic string loops or tiny black hole binaries, they have to be far away," Hogan said. "It puts a limit on how much of that stuff can be out there."

Detecting these high-frequency gravitational waves is a secondary goal of the Holometer. Its main purpose is to determine whether our universe acts like a 2-D hologram, where information is coded into two-dimensional bits at the Planck scale, a length around ten trillion trillion times smaller than an atom. That investigation is still in progress.

"For me, it's gratifying to be able to contribute something new to science," said researcher Bobby Lanza, who recently earned his Ph.D. conducting research on the Holometer. He is the lead author on an upcoming paper about the result. "It's part of chipping away at the whole picture of the universe."

Diana Kwon

In the News

Watch cosmic rays live and play 'I Spy' for neutrinos

From Physics Central's Buzz Blog, April 7, 2015

A recently completed neutrino detector called NOvA has an online webcam where you can watch cosmic rays collisions in near real-time. Since most of us aren't lucky enough to have a cosmic ray detector at home, this webcam is a nice reminder of just how ubiquitous these energetic particles from the cosmos really are.

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Frontier Science Result: CDF

Happy hunting grounds

This artistic view of a Feynman diagram shows the process of proton colliding with an antiproton, producing a W', which then decays into a top quark and an antibottom quark.

We understand nature in terms of elementary particles interacting through a set of well-known forces, which are mediated by other particles. These are the graviton (mediator of gravity), the photon (mediator of electromagnetism), the gluon (mediator of the strong force), the W and Z bosons (mediators of the weak force) and the Higgs boson. We produce and detect these particles (except the graviton) in large numbers at colliders around the world.

But is that all the universe is made of — a handful of different types of particles? We have good reasons to believe that this is not the case. New forces can exist, and the corresponding mediating particles could be seen at colliders. However, such particles have been hunted extensively at the Large Hadron Collider without success so far. If new forces are hiding so well from physicists' determination to discover them, either they would have to be mediated by very massive bosons or these bosons would have to interact very weakly with ordinary stuff.

The W and Z boson serve as a good model for this kind of exotic stuff: In fact they are both very heavy compared to their peers and interact weakly with ordinary matter. They live very shortly before decaying into more "mundane" particles, most of the time quarks. If new forces were to exist with such properties, then the LHC would not be the best hunting ground because of its enormous production rate of quarks from ordinary forces.

A new analysis of Tevatron data performed by the CDF collaboration searches for the existence of new electrically charged, massive particles (a W' boson) decaying into a top and a bottom quark. Top and bottom quarks leave striking signatures in the detector; W' events would resemble ordinary production of such quarks if not for the extra energy provided by the decay of the parent particle.

The search for a W' with data from the CDF experiment turns out to be the most sensitive for such a heavy particle with mass below 650 GeV (approximately 700 times the proton mass). Unfortunately, no surprise turned out from CDF data. The ball is now again in the hands of the LHC experiments!

Fabrizio Margaroli and Andy Beretvas

Learn more

These scientists are the primary analysts for this result. Top row, from left: Fabio Anza (Oxford University), Giorgio Bellettini (University of Pisa, INFN), Ludovico Bianchi (Forschungszentrum Jülich, Germany), Daniela Bortoletto (Oxford University). Second row, from left: Matteo Cremonesi (Fermilab), Tom Junk (Fermilab), Young-Kee Kim (University of Chicago), Qiuguang Liu (Los Alamos). Third row, from left: Fabrizio Margaroli (Spenzia University of Rome, INFN) and Karolos Potamianos (Berkeley Lab).
Photo of the Day

Wilderness by Wilson

Delicate Queen Anne's lace grows by the Main Ring cooling pond near AZero. Photo: Elliott McCrory, AD
In the News

Years after shutting down, U.S. atom smasher reveals properties of 'God particle'

From Science, April 7, 2015

In a scientific ghost story, a U.S. atom smasher has made an important scientific contribution 3.5 years after it shut down. Scientists are reporting that the Tevatron collider in Batavia, Illinois, has provided new details about the nature of the famed Higgs boson — the particle that's key to physicists' explanation of how other fundamental particles get their mass and the piece in a theory called the standard model. The new result bolsters the case that the Higgs, which was discovered at a different atom smasher, exactly fits the standard model predictions.

"This is a very interesting and important paper, because it's a different mechanism" for probing the Higgs's properties, says John Ellis, a theorist at King's College London and CERN who was not involved in the work. "This is the swan song" for the Tevatron, he says.

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