Friday, Jan. 3, 2014

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Friday, Jan. 3



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Friday, Jan. 3

- Breakfast: regular breakfast menu
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Chez Leon

Friday, Jan. 3

Wednesday, Jan. 8
- Carrot parsnip soup
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Lucky 13: 1013 protons transferred between Recycler and Main Injector

This plot shows the beam intensities for about a dozen beam cycles in the Recycler (green) and Main Injector (red) on Dec. 19. Each step in the green represents the injection of one full batch of beam from the Booster into the Recycler. Image courtesy of Marty Murphy, AD

Beam intensity in the Recycler and Main Injector recently reached a new high. On Dec. 19, the Accelerator Division successfully transferred just over 1.0 x 1013 protons between the Recycler and Main Injector. Achieving this intensity is a significant milestone and a major step in the process of delivering higher beam power to the NuMI target for NOvA operation.

Photo of the Day

Band of light

The sun sets over the darkening lab grounds. Photo: Allen Rusy, TD
From symmetry

Exhibit brings the LHC to London

Visitors to London's Science Museum can now take a simulated tour of CERN and the Large Hadron Collider. Photo: Noemi Caraban Gonzalez, CERN

The largest scientific experiment ever constructed has claimed some new territory — about 8,600 square feet in South Kensington, London.

The Large Hadron Collider, housed at CERN laboratory on the border of France and Switzerland, is the focus of a new exhibit called Collider in London's Science Museum. Visitors, each armed with an all-access pass, are swept into a multimedia exploration of the 60-year-old laboratory, complete with full-size reconstructions of sights below and above ground.

"Our goal from the outset was to give visitors a genuine appreciation for what the LHC is, the people who work on it and why it matters," says Science Museum Fellow Harry Cliff, a Collider curator and also a University of Cambridge physicist on the LHCb experiment.

Down a flight of stairs from the ground floor of the museum, the scene is set with a room covered in wallpaper made to look like chalkboards, covered in the scrawls of scientists working through complicated equations. Artifacts from the annals of particle physics are on display — including a magnet from Fermi National Accelerator Laboratory's Tevatron, the previous holder of the record for world's biggest accelerator, and an accelerating cavity from the Large Electron Positron collider, the previous occupant of the LHC's 17-mile tunnel.

Visitors are invited to step into the "world's greatest experiment" in timed groups. The first stop is a recreation of CERN's main auditorium, where the leaders of two LHC experiments, ATLAS and CMS, announced the discovery of the Higgs boson on July 4, 2012.

Life-size projections of various physicists appear on the wall; they welcome the group to a moment prior to that date, an exclusive meeting in which the members of the CMS collaboration first saw the plots depicting the Higgs boson. The anxiety and excitement build, with each physicist taking a turn to explain their work leading to that moment — the personal triumphs and the collective effort — until a scientist breathes with relief, "We have it."

Read more

Ashley WennersHerron

In the News

Synopsis: Lumpy universe called into question

From Physics, Dec. 19, 2013

The universe seems to be expanding at an accelerating pace, but perhaps that's only from our perspective. If the Universe is very lumpy and we just happen to live in a relatively empty part, then the imbalance in gravitational forces could mimic a universal acceleration. However, a new analysis in Physical Review Letters shows that an inhomogeneous Universe cannot explain galaxy cluster observations.

Read more

Frontier Science Result: CMS

Spinning tops and spinning top quarks

Spinless particles (such as Higgs bosons) decay in any direction with equal probability, but particles with spin (such as top quarks) prefer to decay along their axis of spin.

When I was asked to write an article on the CMS experiment's measurement of the spin of the top quark, a metaphor immediately suggested itself: spinning tops. However, the more I thought of it, the more I realized how complex the relationship is between a toy top that you can spin with your fingers and a top quark, spinning on its own according to the rules of quantum mechanics.

A toy top is made of trillions of trillions of atoms, so its rotation is easy to define. It is rotating when the lattice of atoms orbit a central axis. If its surface were perfectly smooth and it were not made of granular pieces like atoms, then it would be harder to say that it is or is not rotating around its axis of symmetry — it would look exactly the same at all times. This is a problem when describing the rotation of black holes: All one can see is a knot of pure space-time, no surface wrinkles revolving like a carousel.

Angular momentum is a more fundamental concept than rotation, one that applies equally well to featureless objects like black holes. For an object with a well-defined rotation, angular momentum is proportional to the rate of rotation, but it is also proportional to the mass and diameter squared of the object in a way that depends on shape. If we shrink a top while maintaining its angular momentum, the rotation rate must increase, as it does when a spinning figure skater contracts his or her arms. If we shrink a toy top to an infinitesimal point, like a fundamental particle, the rotation rate would become infinite.

A top quark "spins" in the sense that it has angular momentum and it can transfer that angular momentum to other objects. If quarks are the indivisible, fundamental particles that they appear to be, then they have no parts to turn or rotate in the conventional sense.

Top quarks are too short-lived for their spins to be measured using macroscopic devices, but the spin's influence can be seen in the quark's pattern of decays. Imagine an exploding toy top: More pieces would fly out perpendicular to its axis of rotation than along it. If you only saw the trajectories of the debris, you could infer how much angular momentum the toy had before it exploded. Unfortunately for my metaphor, the top quark prefers to decay along its spin axis, rather than against it, because the mechanism has nothing to do with centrifugal forces.

With a huge sample of top quark decays observed by CMS, physicists selected the 9,000 cleanest events and successfully measured spin-related asymmetries in their decays. These measurements are sensitive to the details of the process that produces top quarks, which aligns the top spins before they decay. Ironically, the top quark's short lifespan is essential for this inference — all other types of quarks lose the spin correlations that they were born with because they interact with each other before decaying.

Jim Pivarski

The physicists pictured above measured correlations in top quark spins using a new technique for this process: They unfolded uncertainties in the observed data, rather than mixing them into the theory prediction.
Professor Joe Incandela of the University of California, Santa Barbara, recently stepped down after two years heading the CMS experiment. During his tenure, CMS had tremendous success, most notably in the discovery of the Higgs boson.

Today's New Announcements

Kyuki-Do begins Monday, Jan. 6

Free weekly Tai Chi Easy, Integral Tai Chi/Qigong classes

Users' center closed today

Butts & Guts - register by today

English country dancing at Kuhn Barn - Sunday, Jan. 5

Wilson Street entrance closed for construction

Float holiday - 2014

Dreamweaver class offered in February

2014 BCBS PPO & PPO Premium plan ID cards

ASM handbooks are online sitewide

Wanted: Are you an AJAS fellow?

Scottish country dancing meets Tuesday evenings in Kuhn Barn

International folk dancing meets Thursday evenings in Kuhn Barn

Indoor soccer

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