Friday, March 21, 2014

Have a safe day!

Friday, March 21

3:30 p.m.

4 p.m.
Joint Experimental-Theoretical Physics Seminar - One West
Speaker: Felix Sefkow, DESY
Title: Imaging Calorimeters: The New Look of Hadrons

Monday, March 24

9 a.m.-5:40 p.m.
Joint DES-LSST Workshop - One West
Register in person
Registration fee: $42


3:30 p.m.

4 p.m.
All Experimenters' Meeting - Curia II
Special Topic: XOC Plans

Click here for NALCAL,
a weekly calendar with links to additional information.

Ongoing and upcoming conferences at Fermilab


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Wilson Hall Cafe

Friday, March 21

- Breakfast: potato pancakes
- Breakfast: chorizo and egg burrito
- Baja fish tacos
- Smart cuisine: chana masala
- Tuna noodle casserole
- Honey mustard ham and Swiss panino
- Blackened chicken alfredo
- Tomato basil bisque
- Texas-style chili
- Assorted pizza by the slice

Wilson Hall Cafe menu
Chez Leon

Friday, March 21
- Mixed greens with herb vinaigrette
- Fig and chili-glazed pork tenderloin
- Potato cakes
- Sauteed green beans
- Pecan rum cake

Wednesday, March 26
- Chipotle-honey-glazed salmon
- Green rice
- Sugar snap peas
- Cold lemon souffle

Chez Leon menu
Call x3524 to make your reservation.


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Physics in a Nutshell

Proving special relativity: episode 1

More than 100 years after Einstein penned his theory of special relativity, the Internet is full of people who question his ideas. Yet particle accelerators such as Fermilab's Tevatron and CERN's Large Hadron Collider simply wouldn't work the way they do if Einstein was wrong.

In 1905, Albert Einstein wrote four seminal papers. The most famous was his theory of special relativity, which describes how an object behaves as its speed increases. It predicts the most mind-bending things: Time slows down as speed goes up. Increasing speed also causes the length of an object to shrink. And, according to some science popularizations, an object's mass increases as its velocity approaches the speed of light. (This statement is both kinda-sorta right and terribly wrong — we'll get to that in a future column.) Perhaps its best-known prediction is that no object with mass can go faster than light. This last statement is especially disappointing, as it puts the kibosh on mankind's dreams of zipping around the galaxy and exploring nearby stars.

These predictions are all counterintuitive; we never see these behaviors in our everyday lives. If you're in a high-speed jet fighter, the length of objects doesn't shrink, objects themselves don't get heavier, and time seems to march along at its familiar pace.

The fact that Einstein's predictions and common sense disagree prompts a subset of science enthusiasts to react against the theory of relativity. Science bulletin boards are full of relativity deniers, some holding firmly to the ideas of the 1800s and others espousing ideas that are alternatives to special relativity.

Part of the gap between ordinary experience and Einstein's predictions originates in the velocities involved. Until you get to really fast speeds, special relativity is numerically indistinguishable from the classical physics you learn in a high school or freshman college class. In fact, the difference in physics between the two approaches is less than one percent until you get to a speed of 18,600 miles per second. That's about fast enough to get from Chicago to Honolulu in a second, and not even going the short way — that's going via London. Given that an M-16 rifle bullet barrels through the air at about half a mile per second and that the fastest projectile ever fired moves at about 10 miles per second, it is not surprising that our intuition doesn't accurately predict the behavior of matter under these super-high speeds.

Over the next three columns, we'll talk about relativity with an emphasis on how particle and accelerator physics demonstrates without any doubt that Einstein's ideas are correct. While you'll have to wait for subsequent columns to learn about some detailed evidence, I can tease you with a compelling demonstration of why scientists don't use classical physics when they design accelerators.

Let us use the venerable Fermilab Tevatron as our example. This accelerator was a ring 3.9 miles in circumference. According to relativity, the protons in the accelerator moved at 99.99995 percent the speed of light, or 186,000 miles per second.

Given these figures, relativity predicts that the protons will circle the ring about 48,000 times a second. In contrast, classical physics predicts that the velocity of protons in the Tevatron is about 46 times faster than light and therefore that a proton will orbit the ring about 2,220,000 times a second. Fermilab accelerator scientists observed the expected 48,000 times a second. Score one for relativity.

In the next column, we'll look at the energies and velocities in the various accelerators in the Fermilab complex and explore the idea of relativistic mass. Given the ability of scientists at accelerator laboratories to accelerate particles to high velocity, we are able to confront both classical and relativistic physics with real data. The message from the data is clear: Our universe obeys the laws of relativity.

Don Lincoln

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In Brief

Nominations sought for Employee Advisory Group

If you have insights or suggestions that could help improve Fermilab policies and programs, the Employee Advisory Group needs you.

Nominations are now being accepted for new members to serve on the EAG, which provides Fermilab's senior management with recommendations from an employee perspective. The committee meets once per month and is regularly joined by several members of the senior management team. Fermilab benefits from the EAG's formal recommendations, which come after the EAG studies a topic, as well as the extensive discussions of complex issues.

Nominations are encouraged from all job categories, divisions, sections and centers, and from new and long-time employees. Members serve up to three-year terms, attend monthly meetings and are expected to communicate with their fellow employees about issues under consideration. EAG members spend approximately three to five hours per month (including monthly meetings) on committee-related work.

Nominations are due by April 18. Employees are welcome to nominate their colleagues or to self-nominate.

The EAG steering committee will present an information session on Tuesday, April 8, from noon to 12:30 p.m. in One West. All employees are invited to attend to learn more about the committee and its work. Current EAG members will be available to answer questions.

Nomination forms are available online or in the Office of Communication on the atrium level of Wilson Hall. More information about the EAG is available on the EAG website.

Frontier Science Result:
Theoretical Astrophysics

If it looks like dark matter and acts like dark matter …

An intensity map of the (1- to 3-GeV) gamma-ray excess seen in the direction around the Galactic Center. The spectrum, spatial distribution and brightness of this signal agree well with that expected from annihilating dark matter particles.

Are we seeing dark matter in the gamma-ray sky? It sure looks that way.

Since early in the mission of the Fermi Gamma-ray Space Telescope, a number of scientists have noticed an interesting and fairly bright signal coming from the direction of the Galactic Center. Lisa Goodenough, then of New York University, and I wrote the first couple of papers on this observation in 2009 and 2010. What especially captured our attention was that the spectrum and spatial shape of this signal seemed to match what had been predicted to come from annihilating dark matter particles — an intriguing hint indeed.

The motivation for using gamma-ray telescopes to look for dark matter is simple. In many (if not most) theories of dark matter, when pairs of dark matter particles interact, they can annihilate each other, producing other kinds of energetic particles in their place. Given the large densities of dark matter that are present around the Galactic Center, dark matter particles are expected to annihilate there at a high rate, producing large fluxes of energetic gamma rays.

In our new analysis, we reduced background contamination by making use of only the best-reconstructed events. We also performed a large number of tests and cross checks, many of which had not been carried out before. We examined multiple variations in our background model and looked for anything that might masquerade as a signal. What we found was remarkable: The signal from the Galactic Center was not only robust and statistically significant, but in every respect we could measure, it looked like annihilating dark matter.

The resemblance was astonishing. First, the shape of the observed gamma ray spectrum is in excellent agreement with what we would expect from dark matter particles with a mass of about 35 GeV. Second, the spatial distribution of the photons looks very much like what we calculate based on numerical simulations, approximately spherically symmetric and falling off rapidly with distance from the Galactic Center. And third, the overall brightness of the gamma-ray signal implies a dark matter annihilation cross section (times relative velocity) of about 2x10-26 cm3/s, which is almost exactly the value predicted for a generic dark matter species that was produced in the big bang.

Although one can never be completely certain in science, and future observations and analysis related to this signal will be very important, this gamma-ray signal does look remarkably like annihilating dark matter. If so, it would represent the first detection of dark matter particles. It is an exciting time to be hunting for dark matter.

Learn more about the finding in our new paper, which describes in more detail our updated analysis of the Fermi telescope's gamma-ray data.

Dan Hooper

Photo of the Day

Inklings of spring

The creek off Pine Street near Wilson Hall flows during the thaw that followed last week's snowstorm. Photo: Ruben Carcagno, TD
In the News

CUWiP connects women for success

From APS News, March 2014

Undergraduate women studying physics have gained tremendous opportunities for networking and support over the last few years through the annual Conferences for Undergraduate Women in Physics (CUWiP). Since the first CUWiP in 2006, the number of students has exploded from 29 to over a thousand attending this year's conferences.

Read more


Today's New Announcements

School's Day Out - March 30-April 4

Supervisors needed for SIST interns

Photography contest deadline - today

Two yoga classes offered - register by March 24

Weight Management registration deadline - March 27

2014 FRA Scholarship applications due April 1

LabVIEW seminars scheduled on April 10

MySQL relational database management course - April 22-23

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