Friday, June 27, 2014

Have a safe day!

Friday, June 27

3:30 p.m.

4 p.m.
Joint Experimental-Theoretical Physics Seminar - One West
Speaker: Jahred Adelman, Yale University
Title: Searches for New Physics at ATLAS Using Pair Production of Higgs Bosons

Monday, June 30


3:30 p.m.

4 p.m.
All Experimenters' Meeting - Curia II

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Wilson Hall Cafe

Friday, June 27

- Breakfast: French bistro breakfast
- Breakfast: chorizo and egg burrito
- Smoky Mountain chicken breast sandwich
- Smart cuisine: chicken vincenza with pasta
- Vegetarian eggplant lasagna
- Cuban panino
- Breakfast-for-lunch omelet bar
- New England clam chowder
- Texas-style chili
- Assorted pizza by the slice

Wilson Hall Cafe menu
Chez Leon

Friday, June 27

Wednesday, July 2
- Ham and gruyere crepes
- Mixed greens with herb vinaigrette
- Lemon blueberry poundcake

Chez Leon menu
Call x3524 to make your reservation.


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Physics in a Nutshell

Subatomic traction

The trajectories of protons in the LHC are controlled by magnetic fields. An upward-pointing magnetic field (B) applies a force (F) to the right on protons flowing through the beam pipe (into the plane of the picture), and this steers them around the (imperceptible) curve of the ring. Image courtesy of Jim Pivarski

Manipulating small objects, such as the cogs of an old-fashioned watch, is difficult with bulky fingers, so special tools are needed to fit them together into a working system. The emerging field of nanotechnology is concerned with manipulating objects the size of atoms and making molecular machines. Protons, electrons and other subatomic particles are hundreds of thousands of times smaller than an atom, so even the techniques of nanotechnology cannot help. How do you grab and move a proton?

Perhaps surprisingly, all you need are simple electric and magnetic fields, such as what might be covered in a first-year physics class. There are two basic interactions: Electric fields accelerate positively charged particles in the direction that the electric field points, and magnetic fields accelerate them at right angles to the magnetic field and the particle's original direction of motion.

The latter case is illustrated in the photo of an LHC section above. Positively charged protons travel through the beam pipe, and magnets around the beam produce an upward-pointing magnetic field. The direction that is perpendicular to both the protons' trajectories and the upward-pointing field is to the right. By always turning the protons toward the center of the ring, they stay within the beam pipe as it curves around its 17-mile circumference.

The trick is building a strong enough magnet to keep 7-TeV protons within the ring — the LHC magnets need to produce 8.3 teslas of field strength, which is 130,000 times stronger than the Earth's field. This is accomplished by making the coils of wire in the electromagnet out of superconducting wire. The bulk of an LHC magnet is for cryogenics to keep the wires at a low enough temperature to superconduct (hold a current with zero resistance).

Although a magnetic field can bend the path of a stream of protons, it cannot increase their speeds. This is because the magnetic force is always perpendicular to the direction of the protons' motions. To accelerate protons up to 7 TeV, one needs a force pointing in the direction of their motion, which can only be accomplished by an electric field.

Strong, steady electric fields are hard to build, since they tend to discharge by emitting an electric spark. Strong oscillating fields — also known as radio waves — are easier, since they switch directions before a spark has a chance to develop. Unfortunately for an accelerator, this means that the electric field is pointing in the wrong direction half of the time. The solution is to replace a continuous beam with a staccato beam of short pulses known as bunches, and coordinate the bunches to enter the electric field only at those moments when it is pointing in the right direction. Needless to say, the timing is tricky.

The basic physics of a proton accelerator is straightforward enough to be within reach of a first-year physics student, but building an accelerator for energy or intensity frontier physics pushes the limits of modern technology. A minute to learn, a lifetime to master.

Jim Pivarski

Want a phrase defined? Have a question? Email

One proton beam at the LHC is propelled forward by electric fields and inward by magnetic fields, thus traveling in a clockwise direction. A second proton beam is similarly steered by electric and magnetic fields in the opposite direction, guided to collide with the first.
Video of the Day

MicroBooNE detector move

On Monday the MicroBooNE detector — a 30-ton vessel that will be used to study ghostly particles called neutrinos — was transported three miles across the Fermilab site and gently lowered into the laboratory's Liquid-Argon Test Facility. This three-and-a-half-minute video and shows the process of getting the MicroBooNE detector to its new home. View the video. Video: Fermilab
In the News

All the sky — all the time: UK astronomers debate involvement in the Large Synoptic Survey Telescope (LSST)

From the Royal Astronomical Society, June 21, 2014

Astronomers will discuss the case for UK involvement in the Large Synoptic Survey Telescope project (LSST) on Monday 23 June at the National Astronomy Meeting in Portsmouth.

The LSST will be sited at Cerro Pachón in the Chilean Andes and will have a primary mirror 8.4 metres in diameter, making it one of the largest single telescopes in the world, as well as the world's largest digital camera, comprising 3.2 billion pixels. It will achieve first light in 2020 and its main sky survey will begin in 2022.

Uniquely, the LSST will be able to see a large patch of sky, 50 times the area of the full Moon, in each snapshot. It will also move quickly, taking more than 800 images each night and photographing the entire southern sky twice each week.

A powerful data system will compare new images with previous ones to detect changes in brightness and position of all the objects detected. As just one example, this could be used to detect and track potentially hazardous asteroids that might impact the Earth and cause significant damage.

Read more

Frontier Science Result: DES

Dark Energy Survey discovers exotic type of supernova

The Milky Way rises over the Cerro Tololo Inter-American Observatory in northern Chile. The Dark Energy Survey operates from the largest telescope at the observatory, the 4-meter Victor M. Blanco Telescope (left). Photo courtesy of Andreas Papadopoulos

The first images taken by the Dark Energy Survey after it began in August 2013 have revealed a rare, "superluminous" supernova (SLSN) that erupted in a galaxy 7.8 billion light-years away. The stellar explosion, called DES13S2cmm, easily outshines most galaxies in the universe and could still be seen in the data six months later, at the end of the first of what will be five years of observing by DES.

Supernovae are very bright, shining anywhere from 100 million to a few billion times brighter than the sun for weeks on end. Thousands of these brilliant stellar deaths have been discovered over the last two decades, and the word "supernova" itself was coined 80 years ago. Type Ia supernovae, the most well-known class of supernovae, are used by cosmologists to measure the expansion rate of the universe.

But SLSNe are a recent discovery, recognized as a distinct class of objects only in the past five years. Although they are 10 to 50 times brighter at their peak than type Ia supernovae, fewer than 50 have ever been found. Their rareness means each new discovery brings the potential for greater understanding — or more surprises.

It turns out that even within this select group of SLSNe, DES13S2cmm is unusual. The rate at which it is fading away over time is much slower than for most other SLSNe that have been observed to date. This change in brightness over time, or light curve, gives information on the mechanisms that caused the explosion and the composition of the material ejected. DES can constrain the potential energy source for DES13S2cmm thanks to the exceptional photometric data quality available. Only about 10 SLSNe are known that have been similarly well-studied.

Although they are believed to come from the death of massive stars, the explosive origin of SLSNe remains a mystery. The DES team tried to explain the luminosity of DES13S2cmm as a result of the decay of the radioactive isotope nickel-56, known to power normal supernovae. They found that, to match the peak brightness, the explosion would need to produce more than three times the mass of our sun of the element. However, the model is then unable to reproduce the rate at which DES13S2cmm brightened and faded.

A model that is more highly favored in the literature for SLSNe involves a magnetar: a neutron star that rotates once every millisecond and generates extreme magnetic fields. Produced as the remnant of a massive supernova, the magnetar begins to "spin down" and inject energy into the supernova, making the supernova exceptionally bright. This model is better able to produce the behavior of DES13S2cmm, although neither scenario could be called a good fit to the data.

DES13S2cmm was the only confirmed SLSN from the first season of DES, but several other promising candidates were found that could not be confirmed at the time. More are expected in the coming seasons. The goal is to discover and monitor enough of these rare objects to enable them to be understood as a population.

Although designed for studying the evolution of the universe, DES will be a powerful probe for understanding superluminous supernovae.

Chris D'Andrea and Andreas Papadopoulos, Institute of Cosmology and Gravitation, University of Portsmouth

Before (left) and after (center) images of the region where DES13S2cmm was discovered. On the right is a subtraction of these two images, showing a bright new object at the center — a supernova. Image: Dark Energy Survey
The DES13S2cmm superluminous supernova was discovered by Andreas Papadopoulos (right), a graduate student at the University of Portsmouth and lead author on a forthcoming paper about the supernova. Chris D'Andrea (left) is a postdoctoral researcher at Portsmouth and leads the DES supernova spectroscopic follow-up program. Photo courtesy of Andreas Papadopoulos
Photo of the Day

View from the desk of an intern

It's windows as far as the lens can see at the desk of Mehreen Sultana. Photo: Mehreen Sultana, WDRS

Today's New Announcements

Reception for COO Vicky White - June 30

Sitewide domestic hydrant flushing - June 28-29

Swim lessons session 2 deadline - June 30

Artist reception - July 2

Lecture - Technology for Advanced Neural Prostheses - July 11

Register for the C++ Fermilab software school - Aug. 4-8

New updates available for Mac computers

FermiWorks training for managers with direct reports

Construction work at Main Ring Road and AZero

Outdoor soccer

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