Thursday, Aug. 22, 2013

Have a safe day!

Thursday, Aug. 22

2:30 p.m.
Theoretical Physics Seminar - Curia II
Speaker: Roberto Vega-Morales, Northwestern University
Title: Golden Obsessions: Identifying the Higgs Through the Golden Channel

3:30 p.m.

Friday, Aug. 23

3:30 p.m.

4 p.m.
Joint Experimental-Theoretical Physics Seminar - One West
Speaker: Kevin McFarland, Rochester University
Title: New Results from T2K

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Thursday, Aug. 22

- Breakfast: Canadian bacon, egg and cheese Texas toast
- Breakfast: corned-beef hash and eggs
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Chez Leon

Friday, Aug. 23
- Crab cocktail with parmesan chip
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- Berry-filled cinnamon crepes

Wednesday, Aug. 28
- Assorted stuffed summer vegetables
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- Buttered crepes with caramel and pecans

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Tracking particles with LArIAT

Members of the LArIAT team gather for a weekly meeting. The graphic shows tracks from an electron and from a photon seen in the LArTPC detector. Photo: Flavio Cavanna

A neutrino is a tricky thing: It rarely interacts with other particles, and it doesn't leave a track as it enters a detector. But a relatively new technology, called a liquid-argon time projection chamber, is helping scientists to understand them. MicroBooNE, the second phase of the Booster Neutrino Experiment, is one example of a LArTPC, and in order to help it do its job, scientists are first building a test detector called LArIAT—essentially a mini MicroBooNE.

LArIAT—Liquid-Argon TPC In A Test beam—is a small version of MicroBooNE, with a capacity for about three-quarters of a ton of liquid argon instead of MicroBooNE's 170 tons. Its aim is to study particle tracks to better understand how different types of particles—in particular electrons and photons—interact in liquid argon, and how these interactions appear in the collected data.

"Understanding what a proton track looks like in comparison to a pion track or a kaon track is one of the goals of LArIAT," said Jennifer Raaf, a spokesperson for the experiment.

LArIAT consists of a time projection chamber immersed in a cylinder of liquid argon. The TPC, a type of detector, has planes of ultra-sensitive wires that record when ionization electrons in the sea of argon touch them, allowing physicists to reconstruct the path of a particle through the argon.

The detector is bombarded with charged particles, such as pions, protons and electrons, from one of the test beams at the Fermilab Test Beam Facility. Future neutrino experiments such as MicroBooNE and LBNE will receive beams of neutrinos, which don't create any tracks as they enter the detector. Scientists on those experiments will have to look at the output from the collisions in order to deduce which kind of neutrino interacted, like crime scene sleuthing at the subatomic level.

"With a test beam, you can tag what types of particles are going in and then you can characterize how the detector responds to different types of particles," Raaf said. "And that's useful for every future and existing liquid-argon TPC. We're providing a kind of calibration for future experiments."

LArIAT started in earnest in February 2012 with a team of about 10 members. Now the collaboration has swelled to about 50 people, who are currently at work completing the experiment's physical construction. Much of the detector will be made of repurposed pieces from ArgoNeuT, a previous liquid-argon TPC. The team has also received parts from the CDF detector, which is being deconstructed.

The collaboration has placed an emphasis on recruiting younger scientists, said Flavio Cavanna, another LArIAT spokesperson. The liquid-argon TPC is a relatively new technology that is seeing increasing use in the field, he said, and training young scientists in its use now will help in the future.

"We try more than ever to look for groups with young people because we believe that this is an experiment that is a present investment for future experiments," Cavanna said.

The team hopes to begin receiving test beam in October and to start taking data in spring of 2014.

Laura Dattaro

From symmetry

Daya Bay furthers neutrino knowledge

A new Daya Bay result advances our understanding of neutrinos by precisely measuring their oscillation behavior at different energies. Photo: University of California, Lawrence Berkeley National Laboratory

Scientists on an experiment that in 2012 revealed an important aspect of neutrinos announced this week that they had further contributed to our understanding of the puzzling elementary particles.

Neutrinos come in three flavors, and they oscillate, or change from one to another, as they travel—unlike any other fundamental particle we know. On Wednesday members of the Daya Bay experiment announced that they had made the first measurement of how neutrino oscillation varies with neutrino energy at a short distance. The Daya Bay detectors (pictured above) study neutrinos produced by a set of reactors at a nuclear power plant in Southern China near Hong Kong.

Read more

Kathryn Jepsen

From symmetry

Fermi's first five years

In its first five years gazing at the gamma-ray sky, the Fermi Gamma-ray Space telescope provided new insights into cosmic puzzles ranging from dark matter to blazars—and added a few new puzzles to the list. Photo: NASA/Aurore Simonnet, Sonoma State University, Sandbox Studio

On June 11, 2008, what was then the Gamma-ray Large Area Space Telescope rode a Delta II rocket into low-Earth orbit. After two months of tests and checks and calibrations, on August 11, 2008, NASA declared GLAST open for business as astrophysics' premier eye on the gamma-ray sky. Five years, a name change, a near miss with a defunct Soviet spy satellite, and countless surprises later, the spacecraft now known as the Fermi Gamma-ray Space Telescope is still going strong, with another five-year mission stretching ahead of it.

Read more

Lori Ann White

Frontier Science Result: CDF

Which way did it go?

The differential cross section for top-antitop production is measured. The observed forward-backward asymmetry is described by an expansion in Legendre polynomials. The polynomials from a1 to a7 are measured.

For several years, CDF and DZero physicists have been studying a puzzle in the production of top quarks at the Tevatron: The outgoing top quarks prefer to travel in the same direction as the incoming protons (forward) and the top antiquarks prefer to go in the opposite direction (backward). The Standard Model predicts a small amount of such "forward-backward asymmetry," but the observed asymmetry is much larger and raises the question of whether the Standard Model calculation is deficient or something else is going on.

In a new study, instead of just counting tops that go forward and backward, CDF looks in detail at the angle between the top quark and the proton direction. The shape of this angular distribution is a prediction of the Standard Model, and the comparison to the data can potentially illuminate whether the asymmetry is just more of the Standard Model effect or something else.

In order to quantify the shape, CDF breaks it down into a sum of standard shapes called Legendre functions. These functions measure the amount of "wiggle" in a curve: the first function is flat, the second is a line, the third has one oscillation, the next has two oscillations and so forth. The amount of each that goes into a given shape is the Legendre coefficient. CDF finds that the distribution of the top quark angle agrees with the Standard Model prediction except for the coefficient of the first Legendre function, which describes a linear correction to the angular distribution. This one coefficient is responsible for the anomalously asymmetric production of top quarks.

Using the full CDF run II data set, the first coefficient a1 is measured to be 0.40 ± 0.12, while the Standard Model prediction is 0.15 +0.07/-0.03. This sharpens the search for an explanation of the asymmetry. Some nonstandard theories involving a new heavy partner of the gluon (axigluon) would include such a linear term. Alternatively, any missing ingredient in the Standard Model calculations would need to have this form. There is unfortunately too much uncertainty in the Tevatron measurement to point one way or another, but when applied to the much larger top quark samples at the LHC, this powerful new technique can perhaps provide further clues to the mystery of the top quark asymmetry.

Learn more

edited by Andy Beretvas

These CDF physicists contributed to this data analysis. Top row from left: Dan Amidei, Ryan Edgar, Dave Mietlicki and Tom Schwarz, all from the University of Michigan. Bottom row from left: Jon Wilson and Tom Wright, both from the University of Michigan, and Joey Huston from Michigan State University.
Photo of the Day

Softshell on the move

Last week this softshell turtle—roughly 12 inches wide—slowly made its way across Road C to the north side of Bulrush Pond, located northwest of the Industrial Building Complex. It did so with help from Security Lieutenant Donna Iraci and Liliana Rivera, who directed vehicles to go around it as they came down Road C. Photo: Bill Barker, CCD
In the News

Oddball space neutrinos may be spawn of dark matter

From New Scientist, Aug. 15, 2013

The first deep space neutrinos to be detected since the 1980s may be the spawn of mystery dark matter. That would explain puzzling features of these particles—and suggest an unusual identity for dark matter.

Neutrinos, ghostly subatomic particles, are routinely produced by the sun and on Earth, but apart from those seen after a 1987 supernova explosion, none had been detected from beyond the solar system.

Read more


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NALWO Aug. 29

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Scottish country dancing meets Tuesday evenings in Auditorium

International folk dancing in Auditorium for summer

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