Thursday, Aug. 6, 2015
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Muscle Toning registration due Aug. 11

Women's Initiative: "Guiltless: Work/Life Balance" - Aug. 13

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Python Programming Basics is scheduled for Oct. 14-16

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Fermi Singers invite all visiting students and staff

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Scottish country dancing meets Tuesday evenings in Ramsey Auditorium

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In Brief

NOvA presents first physics results today at 2 p.m. in Ramsey Auditorium

The first physics results from Fermilab's biggest experiment are in. Caltech scientist Ryan Patterson of the NOvA experiment will give a Joint Experimental-Theoretical Physics Seminar on its first neutrino oscillation results.

This wine and cheese seminar takes place at an unusual time and location, today at 2 p.m. in Ramsey Auditorium.

From symmetry

The mystery of particle generations

Why are there three almost identical copies of each particle of matter? Image: Sandbox Studio

The Standard Model of particles and interactions is remarkably successful for a theory everyone knows is missing big pieces. It accounts for the everyday stuff we know like protons, neutrons, electrons and photons, and even exotic stuff like Higgs bosons and top quarks. But it isn't complete; it doesn't explain phenomena such as dark matter and dark energy.

The Standard Model is successful because it is a useful guide to the particles of matter we see. One convenient pattern that has proven valuable is generations. Each particle of matter seems to come in three different versions, differentiated only by mass.

Scientists wonder whether that pattern has a deeper explanation or if it's just convenient for now, to be superseded by a deeper truth.

Read more

Matthew R. Francis


Meenakshi Narain reappointed co-coordinator of LPC

Meenakshi Narain

Professor Meenakshi Narain of Brown University has been appointed a second two-year term as LHC Physics Center co-coordinator.

As co-coordinator, Narain has been instrumental in elevating the status of the Fermilab-based LHC Physics Center, or LPC, in the eyes of collaborations around the world, says her fellow co-coordinator Boaz Klima. By fostering a culture of close collaboration and more in-person engagement, she ensured that those who contributed got as good as they gave, Klima said.

Narain helped initiating active discussion groups at the LPC, made the CMS data analysis school ready for Run 2 analysis, and encouraged greater and more meaningful interactions between LPC members, among other contributions.

"She cares about the place, the people, the experiment," Klima said. "She wants it to succeed. Many members of the LPC are very productive members of the collaboration thanks to Meenakshi, and they're just as vital to CMS as those in Geneva. LPC is now a well-respected institution both within and outside CMS."

Narain looks forward to continuing to strengthen the LPC.

"The LPC makes it possible for many of our CMS colleagues to maximize their contributions to the experiment," she said. "I am looking forward to facilitating these contributions for another two years, including hopefully some discoveries during Run 2."

Photos of the Day

Small, white, clean, bright

Foxglove beardtongue (top) and daisy fleabane look happy to meet me. Photo: Leticia Shaddix, PPD
In the News

This LEGO Large Hadron Collider needs to become real

From Popular Mechanics, Aug. 4, 2015

The world's most powerful particle accelerator could become a nifty little LEGO toy. The Large Hadron Collider set, currently up on LEGO Ideas, recreates the inner workings of the giant collider. It includes each component of the 17 mile track where the Higgs boson was discovered, and where the CERN team is actively working to unlock the mechanisms of the universe.

Read more

Physics in a Nutshell

Phase stability

These plots help us visualize electric field versus time in an RF cavity and show positions of early (E), on time (S) and late (L) particles in a beam bunch before and after transition.

We skipped ahead in my last column to discuss accelerator tunes without finishing the subject of acceleration. In an earlier column I attempted to make a convincing argument that the best way to accelerate particles to high energies is to bend them in a circle and pass them through an electric field many times. A practical field for this purpose is one that oscillates sinusoidally at radio frequencies (RF) in a resonant cavity (see above figure). (Multiple cavities are strung together, forming the particle beam's accelerating path.) Today I will discuss beam stability during acceleration in such a field while introducing the problem of transition.

In order for charged particles to be accelerated in an oscillating field, they must be present in the RF cavity during the part of the cycle when the field is oriented to provide an acceleration. Typically bunches are formed in the beam by either knocking out particles that are out of time with upstream devices or letting nature take its course to lose them. This leaves only particles that are in time with the accelerating field. Even so, the nature of the sine wave is such that particles arriving at slightly different times receive slightly different accelerations due to the varying voltage. We can be clever by phasing the RF field so that the faster particles receive a smaller acceleration and the slower particles come later when the field is nearer the peak value (see figure). This results in stable oscillations of the individual particles from the slow part of the bunch to the fast part and back again many times during acceleration. An ideal particle right in the center of the bunch does not oscillate at all. The rest of the particles in the bunch oscillate around the ideal particle. Such oscillations are called synchrotron oscillations.

As usual the real picture is more complicated, and much of the complication is due to Albert Einstein. The theory of special relativity imposes a speed limit c, the speed of light, on the accelerating particles. (Accelerator scientists were not given a vote on this.) As the beam particles approach c during acceleration, the increase in velocity slows, even though the energy continues to rise, due to increasing mass and momentum. Further increases in energy do not change the velocity of the particles. However, the higher-energy particles bend less in the accelerator magnets, causing them to follow a slightly longer path around the accelerator than the lower-energy particles. The result is that the particles with higher energy arrive in the RF cavities late instead of early. The point where orbit times become longer for the higher-energy particles is called transition. To maintain stable beam beyond transition, we must shift the phase of the RF curve so that the beam bunches fall on the right of the RF peak (see figure). This way, the higher-energy particles arrive late to get a smaller acceleration and vice versa with the low-energy particles.

One might ask why the beam is not centered right at the top of the RF wave. This solution is always unstable for the beam, since both early and late particles get smaller accelerations, causing the beam to spread out and be lost. Furthermore, shifting the RF phase to move the beam from one side of the curve to the other at transition cannot be accomplished without incurring some beam loss. All sorts of pulsed magnets, baling wire and chewing gum solutions have been devised to facilitate moving the beam through transition. None of them work perfectly.

Nevertheless, accelerator scientists enjoy problems like this because it gives them an opportunity to be clever, and if they succeed in minimizing the losses, they can pretend they are beating Einstein at his own game. Einstein wouldn't care. He was more interested in trains, twins, clocks and measuring rods.

Roger Dixon

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In memoriam: H.A. Kippenhan Jr.

Former Fermilab employee H.A. Kippenhan Jr., known as Kipp, passed away on Monday, Aug. 3, in Wheaton. He worked in the Computing Division from 1990-2008. Kippenhan will be cremated and buried in a family plot in Wisconsin. There will be no memorial service.

In the News

Only left-handed particles decay

From Nature, Aug. 5, 2015

Only subatomic particles with a left-handed spin decay as a result of one of the fundamental forces, confirming that the Universe has a left-hand bias.

Read more