What can be expected from accelerator-based facilities, the center of the traditional high-energy physics effort? The search for the Higgs boson and for supersymmetric partners of the known particles is a primary focus of the programs at the highest-energy accelerators, such as at the Tevatron at Fermilab and the Large Hadron Collider (LHC) at CERN and even at the next large accelerator to be built after the LHC, which will be designed to perform incisive studies of these particles’ properties.

Accelerator experiments permit irreplaceable measurements for exploring the Standard Model and beyond, including studies of neutrino masses and the violation charge-parity (CP) symmetry (see Chapter 5, section “Dark Energy”), as well as the creation of an exotic form of matter known as the quark-gluon plasma to mimic an important phase in the early universe. Accelerators are also capable of seeing manifestations of extra dimensions that are macroscopic. This possibility, a recent speculation from string theory, has profound implications for understanding the physics of the very early universe. Experimental signatures include the apparent loss of energy in particle interactions, which, in fact, has gone off into the additional dimensions. Experiments at the Tevatron and the LHC should have significant sensitivity to this exciting possibility.

Rather than address ongoing and proposed accelerator programs that are reviewed elsewhere by other responsible scientific groups (laboratory program committees, the NRC, and the DOE/NSF High Energy Physics Advisory Panel and the Nuclear Science Advisory Committee), this committee focuses on identifying additional and complementary opportunities for the use of new techniques and technologies to probe the most fundamental questions at the interface between particle physics and astronomy and astrophysics. This chapter discusses, in turn, experiments seeking signatures of unification, identifying the dark matter, and probing the very foundations of our science.

LOOKING FOR SIGNATURES OF UNIFICATION

The hypothesis that a single unified theory can account for the three separate forces of the Standard Model is attractive in many ways. Such a theory would organize the quarks and leptons into a simple, beautiful structure and would explain the patterns of charges, which otherwise seem quite arbitrary. And most impressively, by including low-energy supersymmetry, it would account quantitatively for the relative values of the different observed coupling strengths.



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