Thursday, April 2, 2015
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Today's New Announcements

B Road closure - today

GCC power outages April 7 and 8

Wilson Hall southwest stair work: temporary access restriction through April 4

Two-step and Waltz workshops at Kuhn Barn - April 5

Networking DNS software upgrade - April 7

Fermilab Village Easter Egg Hunt April 8

Nominations for Employee Advisory Group due April 17

2014 FSA deadline is April 30

Interpersonal Communication Skills course - May 20

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

Mac OS X security patches

Fermilab Board Game Guild

Players needed for 2015 Fermilab co-ed softball league

Pilates registration

Indoor soccer

Changarro restaurant offers Fermilab employee discount


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From symmetry

LHC restart back on track

The Large Hadron Collider has overcome a technical hurdle and could restart as early as next week. Photo: Maximilien Brice, CERN

On Monday, teams working on the Large Hadron Collider resolved a problem that had been delaying the restart of the accelerator, according to a statement from CERN.

On March 24, the European physics laboratory announced that a short circuit to ground had occurred in one of the connections with an LHC magnet. LHC magnets are superconducting, which means that they can maintain a high electrical current with zero electrical resistance. To be superconducting, the LHC magnets must be chilled to almost minus 460 degrees Fahrenheit.

The short circuit occurred between a superconducting magnet and its diode. Diodes help protect the LHC's magnets by diverting electrical current into a parallel circuit if the magnets lose their superconductivity.

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Kathryn Jepsen

In Brief

Fermilab, CERN leadership meet with Congressman Randy Hultgren

From left: Fermilab Director Nigel Lockyer, CERN Director General Rolf Heuer, incoming CERN Director Fabiola Gianotti, Congressman Randy Hultgren.

Last week in Washington, D.C., Fermilab Director Nigel Lockyer joined CERN's current Director General Rolf Heuer and incoming Director General Fabiola Gianotti in discussing the future of particle physics with Congressman Randy Hultgren.

In Brief

Atrium restroom remodeling begins today

Construction on the Wilson Hall atrium-level restrooms is scheduled to begin today, April 2. The work is anticipated to last for four months, with completion anticipated in early August.

Activities involving excessive noise will be scheduled for after 4 p.m. However, much of the work will take place during normal working hours, and some noise will occur then also.

The restrooms will be closed for the duration of the work. Restrooms will be available on the Wilson Hall ground floor and second floor during the renovation.

Photos of the Day

Traveling in herds

Deer gather in the dog training area on Fermilab grounds ... Photo: Bridget Scerini, TD
... and then quickly bound away. Bridget Scerini, TD
This one was spotted by the Pine Street entrance. Photo: Bridget Scerini, TD
Physics in a Nutshell

Observe neutral particles with this one weird trick

A shower produces dozens of particles that could be observed individually (inset figure) or collectively in a calorimeter (bottom).

The previous Physics in a Nutshell introduced tracking, a technique that allows physicists to see the trajectories of individual particles. The biggest limitation of tracking is that only charged particles ionize the medium that forms clouds, bubbles, discharges or digital signals. Neutral particles are invisible to any form of tracking.

Calorimetry, which now complements tracking in most particle physics experiments, takes advantage of a curious effect that was first observed in cloud chambers in the 1930s. Occasionally, a single high-energy particle seemed to split into dozens of low-energy particles. These inexplicable events were called "bursts," "explosions" or "die Stöße." Physicists initially thought they could only be explained by a radical revision of the prevailing quantum theory.

As it turns out, these events are due to two well-understood processes, iterated ad nauseam. Electrons and positrons recoil from atoms of matter to produce photons, and photons in matter split to form electron-positron pairs. Each of these steps doubles the total number of particles, turning a single high-energy particle into many low-energy particles.

This cascading process is now known as a shower. The cycle of charged particles creating neutral particles and neutral particles creating charged particles can be started by either type, making it sensitive to any particle that interacts with matter, including neutral ones. Although the shower process is messy, the final particle energies should add up to the original particle's energy, providing a way to measure the energy of the initial particle — by destroying it.

Modern calorimeters initiate the shower using a heavy material and then measure the energy using ordinary light sensors. To accurately measure the energy of the final photons, this heavy material should also be transparent. Crystals are a common choice, as are lead-infused glass, liquid argon and liquid xenon.

Not all calorimeters are man-made. Neutrinos produce electrons in water or ice, which cascade into showers of electrons, positrons and photons. The IceCube experiment uses a cubic kilometer of Antarctic ice to observe PeV neutrinos — a hundred times more energetic than the LHC's beams. Cosmic rays form showers in the Earth's atmosphere, producing about 4 watts of ultraviolet light and billions of particles. The Pierre Auger Observatory uses sky-facing cameras and 3,000 square kilometers of ground-based detectors to capture both and has measured particles that are a million times more energetic than the LHC's beams.

Jim Pivarski

In the News

Theory of the strong interaction verified

From, March 26, 2015

The fact that the neutron is slightly more massive than the proton is the reason why atomic nuclei have exactly those properties that make our world and ultimately our existence possible. Eighty years after the discovery of the neutron, a team of physicists from France, Germany, and Hungary headed by Zoltán Fodor, a researcher from Wuppertal, has finally calculated the tiny neutron-proton mass difference. The findings, which have been published in the current edition of Science, are considered a milestone by many physicists and confirm the theory of the strong interaction. As one of the most powerful computers in the world, JUQUEEN at Forschungszentrum Jülich was decisive for the simulation.

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In the News

Synopsis: Baryon's innards have molecular structure

From Physics, April 1, 2015

Graduates of Particle Physics 101 know that baryons are made of three quarks. An excited state of the Lambda baryon, Λ(1405), might, however, defy this simple description: the particle behaves like a "molecule" made of a quark pair and a quark triplet. This picture, which can't be explained by the standard quark model, has been debated for almost fifty years. Now it's gaining new support from calculations by theorists at the University of Adelaide, Australia.

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