Friday, April 12, 2013

Have a safe day!

Friday, April 12

3:30 p.m.

4 p.m.
Joint Experimental-Theoretical Physics Seminar - One West
Speaker: Mark Mattson, Wayne State University
Title: D0-D0: Mixing with the Full CDF Data Set

8 p.m.
Fermilab Lecture Series - Auditorium
Speaker: Chris Quigg
Title: The World According to Higgs
Tickets: $7

Monday, April 15


3:30 p.m.


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Wilson Hall Cafe

Friday, April 12

- Breakfast: blueberry-stuffed French toast
- New England clam chowder
- Cajun turkey burger
- Enchilada-style beef-and-bean or bean-only burrito
- Smart cuisine: Greek fish florentine
- Baked ham and Swiss ciabatta
- Assorted pizza
- Shrimp and crab scampi

Wilson Hall Cafe menu
Chez Leon

Friday, April 12

Wednesday, April 17
- Assortment of quiches
- Marinated cucumber salad
- Mixed-berry sorbet with cookies

Chez Leon menu
Call x3524 to make your reservation.


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Physics in a Nutshell

The gluon and the strong nuclear force

The strong nuclear force holds together the protons and neutrons in the nucleus of an atom. This is actually a side effect of its function binding quarks together to make the protons and neutrons themselves. The particle of the strong force is called the gluon because of the strong force's glue-like properties.

The strongest of the subatomic forces is the aptly named strong nuclear force. In the realm in which it operates, it is about 100 times stronger than the next-strongest force (electromagnetism). But it isn't just its strength that distinguishes it from the other forces. It has other properties that differ from, for instance, the features of a magnet. The force between two magnets extends over a long distance and becomes stronger as the magnets are brought closer to one another. In contrast, the strong nuclear force is a lot more like glue. If you have two marbles made sticky by some kind of adhesive, they will cling together when they are made to touch each other. However, once the two marbles are separated by even a very small distance, they no longer feel any attractive force at all.

In homage to the force's commonalities with how glue behaves, the force-carrying particle for the strong force is called the gluon. Gluons are responsible for binding protons and neutrons together inside the nucleus of an atom. This is crucial for building atoms, but this nuclear binding is actually a side effect of what the gluon really does—hold together the quarks that make up protons and neutrons. In high-energy physics experiments, it is the quark-quark binding that is of the greatest interest.

The distance over which the nuclear force is active is about 1 femtometer (10-15 or one quadrillionth of a meter). To give an idea of just how mind-bogglingly small that is, if a proton were as thick as a sheet of paper, by comparison you'd be so big that, if you stood on the Earth, your head would touch the Sun.

In the last Nutshell, we were introduced to the photon, the quantum of the electromagnetic force. Because the photon is electrically neutral—that is, it has no electric charge—photons don't interact with each other. In contrast, every gluon has a strong nuclear charge. Thus gluons interact not only with quarks, but also with other gluons. This gluon self-interaction property is one of the reasons that the strong force acts like glue instead of magnets.

The charge of the nuclear strong force is known as color. In a subatomic context, three colors—red, blue and green—are carried by the three quarks in a proton, resulting in a simple color scheme. In contrast, the force-carrying gluons have a rather complex color palette, one with a mix of both color (the charge carried by quarks) and anticolor (the charge carried by antiquarks). In total, there are eight different color combinations that gluons can carry. (If you're wondering why three colors and three anticolors combine to make eight gluons and not nine, the answer can be found here.)

Gluons were discovered at the German laboratory DESY in the late 1970s. They play a key role in many of the studies performed at the Tevatron and the LHC.

Don Lincoln

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Photo of the Day

Plain expanse

Clouds above Feldott farm barn begin to clear after Monday morning's rain. The barn is located next to the bison pasture on the Fermilab site. Photo: David Butler, PPD
In Brief

IPPOG meeting at Fermilab

Twenty-two scientists and educators met at Fermilab last week for the first meeting of the International Particle Physics Outreach Group held in the United States. Photo: Reidar Hahn

The International Particle Physics Outreach Group (IPPOG) held its first meeting in the United States at Fermilab from April 4 to 6. The network of scientists, informal science educators and communication specialists working across the globe sponsors masterclasses and hosts a resources database. The membership currently includes representatives from member states of CERN as well as Ireland, Romania and the United States, five major experiments at CERN's Large Hadron Collider, and prominent laboratories and institutions in Europe.

Each year physicists invite about 10,000 high-school students in 37 countries to come to one of about 160 universities or research centers to be physicists for a day in a masterclass institute. In this International Masterclasses series, active scientists give insight into topics and methods of basic research, enabling students to analyze ALICE, ATLAS and CMS data. Like an international research collaboration, participants from several institutes join a videoconference with scientists at CERN or Fermilab for discussion and combination of their results. This year there were 190 institutes and 49 videoconferences—37 at CERN and 12 at Fermilab.

The online IPPOG resources database contains tools and resources to bring the excitement of particle physics to students and the public. Categories include activities, programs and events, media, professional development and coaching, and exhibits.

Marge Bardeen

Frontier Science Result: MINOS

Exceeding the speed limit? Measuring neutrinos to the nanosecond

This graph shows the "bunch" formed from all neutrino events recorded at the MINOS far detector over the two-month run period. The blue distribution shows neutrinos that have traveled the 735 kilometers from Fermilab to Soudan and interacted in the middle of the MINOS detector. The open red distribution shows neutrinos that have interacted in the rock surrounding the detector and produced a muon, which has been detected in MINOS, arriving on average a nanosecond later as expected.

The fastest man on the planet is Jamaican sprinter Usain Bolt. To measure his speed, he races on an accurately measured track, with the starting pistol and photo-finish system synchronized to an accurate clock. In order to determine whether neutrinos are the fastest particles on the planet (and in response to the OPERA experiment's subsequently corrected September 2011 measurement of the neutrino velocity at 0.002 percent faster than light), MINOS must accurately measure both the 735-kilometer distance between its two detectors, at Fermilab and in Soudan, Minnesota, and the time it takes for a neutrino to travel between them.

Measuring this time to an accuracy of a billionth of a second requires scrupulous care and attention to detail. Optic fibers change length with changing temperature, and thresholds in electronics drift over time and in response to environmental conditions. All delays must be measured redundantly, and preferably in situ, to eliminate the possibility of human or instrumental error. Atomic clocks by each detector serve as a time reference but are not accurate enough by themselves. The offset and drift between clocks at the two sites is measured with redundant GPS receivers—more sophisticated than those in cellphones, but operating on the same principles. Each of the 32 GPS satellites contains atomic clocks that are regularly synchronized with each other and with the master clock on the ground. By comparing the time signal received from at least four satellites, a GPS receiver can determine its position and time.

For neutrinos, there is an extra complication. We observe Usain Bolt by recording the light reflected from his body, which does not materially affect his progress. For neutrinos, however, the act of observation is also an act of destruction: Once it has interacted in the detector, the neutrino no longer exists. The neutrinos observed in the two MINOS detectors are not the same particles.

To determine the speed of the neutrino, we exploit the fact that the accelerator clusters protons together in short "bunches" in order to accelerate them. The neutrino beam inherits the timing distribution of the parent protons. We can't tell whether an individual neutrino came from the beginning or the end of a bunch, but with enough neutrinos we can build up a picture of the shape of the bunch and determine its average timing.

The result? Neutrinos travel at the speed of light, to an accuracy of one part in a million. The speed of light remains the unchallenged world champion.

MINOS is grateful to the many people throughout Fermilab who helped us design and install a new timing system on very short notice in order to make this measurement. This measurement was made in collaboration with precise time experts from the United States Naval Observatory and the National Institute for Standards and Technology, to whom we are indebted for sharing their timing expertise with us.

—Phil Adamson

The particles represented here in red (associated with the red curve in the above graph) are expected to travel on average a foot farther than those represented in blue (represented in the blue curve above) since there's a change of direction at the interaction in the rock. The red particles are seen to arrive a nanosecond later, as expected.
In the News

Peaceful matter-antimatter pairing looks more real

From New Scientist, April 6, 2013

Matter and antimatter have been caught coexisting—again. A second attempt to detect long-sought Majorana fermions, particles that can act as their own antiparticle, has come up positive, suggesting the strange particles are real.

Read more


Today's New Announcements

Barn dance - April 14

The World According to Higgs - Chris Quigg - today

Wonders of Science - April 14

Fermilab Heartland Blood Drive - April 15-16

Fermilab Arts Series: Barynya: Music & Dance of Russia - April 20

UChicago: Willy Wonka - movie and science demos - April 21

Engineering Group to hold seminars at Fermilab - April 26

Snowmass Young survey

Fermilab-CERN Hadron Collider Physics Summer School open for applications

Web queries security changes

Reminder - FSA debit card PIN required

International folk dancing meets Thursday evenings in Kuhn Barn

Indoor soccer

Fermilab Golf League

Indian Creek Riding Club

Chicago Fire discount tickets

Find new classified ads on Fermilab Today.