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From symmetry

The U.S. and CERN upgrade their relationship

A new agreement paves the way for joint projects between the United States and CERN. Image: Sandbox Studio

Today in a White House ceremony in Washington, D.C., representatives from the U.S. Department of Energy, the U.S. National Science Foundation and the European research center CERN signed a cooperation agreement that lays the groundwork for continued joint research in particle physics and advanced computing both at CERN and in the United States.

The agreement succeeds an existing U.S.-CERN agreement, signed in 1997 and set to expire in 2017, that was the basis for significant U.S. participation in research at the Large Hadron Collider. The new agreement aligns the United States' and CERN's long-term strategies for particle physics and provides for "reciprocity," opening the way for potential CERN participation in U.S.-hosted experiments, including prospective projects focused on neutrinos.

"Today's agreement not only enables U.S. scientists to continue their vital contribution to the important work at CERN, but it also opens the way to CERN's participation in experiments hosted in the United States," says Energy Secretary Ernest Moniz in a press release. "As we've seen, international collaboration between the United States and CERN helps provide a foundation for groundbreaking discoveries that push crucial scientific frontiers and expand our understanding of the universe."

The signing of the new agreement sets the stage for a new level of cooperation. CERN already has established a test facility that is being used to refurbish the 760-ton ICARUS neutrino detector before it is shipped to DOE's Fermi National Accelerator Laboratory for use in a suite of experiments to search for a new type of neutrino. At the same time, more than 1,700 scientists from U.S. institutions are working on the next phase of the LHC experiments.

"I am delighted to sign this agreement," says CERN Director General Rolf Heuer in the press release. "It allows us to look forward to a fruitful long-term collaboration with the United States, in particular in guiding the Large Hadron Collider to its full potential over many years through a series of planned upgrades. This agreement is also historic since it formalizes CERN's participation in U.S.-based programs such as prospective future neutrino facilities for the first time."

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Photos of the Day

Getting ready to bloom

These mayapple flowers will bloom in a couple of weeks. Photo: Patrick Sheahan, AD
You can also find purple trillium in the woods by Wilson Hall. Photo: Patrick Sheahan, AD
In the News

The excitement behind a renewed agreement

From the National Science Foundation Directorate for Mathematical and Physical Sciences, May 7, 2015

One of the great pleasures of leading the Mathematical and Physical Sciences Directorate at NSF is the chance to witness events that influence the course of science for many years. Today at the White House, the United States signed a new agreement with the European Organization for Nuclear Research, better known as CERN. This agreement renews our nation's partnership in one of the world's preeminent research institutions and its centerpiece, the large hadron collider (LHC). Scientists at the LHC first confirmed the Higgs particle's existence, and now they intend to learn about additional exotic particles, dark matter, and other fundamental aspects of our universe.

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Frontier Science Result: CMS

Weak angles

Studying the angles at which muons are emitted during the decay of a Z boson is an important study of particle physics. The precision studies that CMS researchers intend to do over the next few years require this being understood in great detail.

Particle physics research involves many different approaches, whether it is looking for undiscovered particles of proposed theories or searching for something entirely new. It is also about revisiting familiar topics in unfamiliar environs to see if something unexpected presents itself. Just like tugging a loose thread can unravel an entire sweater, digging into an unexplained measurement on a familiar topic has occasionally occasioned a rewrite of the textbooks.

In today's measurement, CMS physicists took a hard look at the Z boson, which is one of the best studied of the subatomic particles. Z bosons decay in many ways, but one of the cleanest and easiest to study is when it decays into two muons, which are heavy cousins of electrons.

You can do an analysis in any reference frame, from one in which the particle is moving to one that is stationary. If you do your analysis properly, you will draw the same conclusions in any frame. So CMS scientists picked the easiest frame, specifically one in which the Z boson was stationary. In such a frame, only a few properties define the particle. The Z boson is electrically neutral and massive. It also decays only via the weak nuclear force. Given the measured mass of the Z boson and decay muons, many of the details of how the muons are emitted are determined completely via energy and momentum conservation. The muons are emitted back to back and with a specific energy.

The one thing that is not predetermined is the angle at which the muon pair is emitted. That angle is related to the spin of the Z boson. The Z boson has spin (which has a complex meaning in the quantum world). Also, the angle is influenced by the nature of the weak force, which prefers certain spins over others.

To simplify the analysis, the experimenters expressed the various possible angular distributions using trigonometric functions. It turns out that you can describe the expected distribution using five functions, and the analysis reduces to five simple numbers that say just how much of each function is needed to describe the data.

The analyzers then determined these five numbers and plotted how they changed as a function of the momentum and angle of the Z boson in the reference frame of the LHC collision. They found minor discrepancies between data and theory and ascribe the difference not to a discovery, but rather to insufficiently precise theoretical calculations. Analyses of this kind are a crucial precursor to doing precision measurements at the LHC, and theoretical physicists are studying this measurement with great interest.

Don Lincoln

These U.S. CMS scientists made important contributions to this analysis.
These U.S. researchers have taken leadership roles in the design, commissioning, operation and upgrades of the CMS forward pixel detector. This detector is a crucial component for nearly every CMS analysis.
In the News

Galactic smash-ups turn on the lights around black holes

From New Scientist, May 5, 2015

Looks like something left the lights on. The supermassive black holes at the cores of some galaxies give off a tremendous amount of light. It comes from superheated discs of gas that slowly spiral into the maws of the black holes, but where all that gas came from has been debated for decades. Now, observations reveal tell-tale signs of debris that suggest ancient galactic crashes flipped the light switch in the brightest of these "active galaxies".

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