The Sciences

Discovering the Quantum Universe

Cosmic VarianceBy JoAnne HewettMay 23, 2006 10:07 PM


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It's out! This long awaited report has made its debut! 16 of us spent a large fraction of last summer writing a snazzy report that explains the excitement of 21st-century particle physics to audiences who are not science experts - at the request of folks at DOE and NSF. A somewhat technical version was submitted to the EPP2010 panel, and a less technical version has just been publicly launched at a Congressional R&D caucus amidst great fanfare. Brian Greene of Elegant Universe fame gave the presentation and brought along his buddy, Alan Alda, to smooze with members of Congress. Who said particle physics doesn't have star power?!

The full title of the report is Discovering the Quantum Universe: the Role of Particle Accelerators. It lays out a realm of possible discoveries that are waiting for us at the higher energies that will be probed at the Large Hadron Collider (LHC), and their relationship to discovery opportunities at the proposed International Linear Collider (ILC). The basic premise is that Particles Tell Stories, i.e., there are two steps in the path to learning how the quantum universe works:

1. Discovery of a new particle 2. Discovery of the theory behind the new particle

Discovery of a new particle, exciting as that would be, is just the opening chapter of a story. The new particles are messengers, and their properties reveal the full story about the nature of matter, energy, space, and time.

The LHC has a broad energy reach and large event rate and will be an excellent tool to sweep out the next energy scale and discover particles. The ILC is a flexible precision machine which can be tuned to isolate the new particles and discover their properties. These properties then reveal the underlying theory which gave rise to the particles. In physicist's language, combined measurements at the ILC and LHC would allow us to construct the fundamental Lagrangian of the new theory. Only then will we understand how the universe works at the next level. The report centers on three main themes:

1. Solving the Mysteries of the Terascale: The LHC should discover the Higgs and other new particles. Experiments at the ILC would then zoom in on these phenomena to discover their secrets. Properties of the Higgs may signal extra dimensions of space or explain the dominance of matter over antimatter. Particle interactions could unveil a universe shaped by supersymmetry. 2. Light on Dark Matter: Most theories of Terascale physics contain new massive particles with the right properties to contribute to dark matter. Such particles would first be produced at the LHC. Experiments at the ILC, in conjunction with dedicated dark matter searches, would then discover whether they actually are dark matter. 3. Connecting the Laws of the Large to the Laws of the Small (Einstein's Telescope): From a vantage point at the Terascale, the ILC could function as a telescope to probe far higher energies. This capability offers the potential for discoveries beyond the direct reach of any accelerator that could be built. In this way, the ILC could bring into focus Einstein's vision of an ultimate unified theory.

Nine discovery scenarios for the LHC and ILC, following the above themes, are then discussed in more detail. We've given them cute names: the Higgs is different, a shortage of antimatter, mapping the dark universe, exploring extra dimensions, dark matter in the laboratory, supersymmetry, matter unification, unknown forces, and a concerto for strings. For each scenario, the report maps out what will be learned from both the LHC and ILC which illustrates the bigger picture of how experiments at the next generation of particle accelerators will address the fundamental questions of the quantum universe.

One of the most challenging aspects of writing the report (at least for me) was to omit the technical jargon in our explanations. Us physicists have a hard time not tossing in words that are unfamiliar to everybody else. For example, we needed to dream up a new name for the energies that will(would) be probed at the LHC(ILC). We call it the TeV scale, scientifically named for the actual energy of 1,000,000,000,000 electron volts. It couldn't be a more dull or meaningless name to a normal person. After immense brainstorming, we decided on the name the Terascale. It still has scientific meaning, the public is more used to it thanks to terascale computing, and it's somewhat catchy â€" we hope. We'll see if it catches on! Some of the panel members also got to experience a photoshoot - as shown here - with pretty good results I'd say.

It's good to see the final report released, and now we will see if it does a good job in describing the excitement of particle accelerator science to a more general audience.

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