In this chapter we examine various aspects of experimentation that directly interacts with the accelerator design. Of particular concern in this area is the background to the physics experiments that are caused by the beams passing through the detector.
The characteristics of background events at JLC will be very different from those at typical colliders, except the SLC. The features of the background strongly depend on numerous operational parameters of the accelerator, such as the beam aspect ratio (typically ), a high beam intensity (particles/bunch) and possible tails in the particle distribution that deviates from a Gaussian distribution. The population of low energy pairs that are created during collisions are directly related to the beam aspect ratio, while the tail is mostly responsible for synchrotron radiation and muon background. The optimization of the machine operational parameters must be considered by taking this ``interaction" between the experimentation and the machine into account. The highest-priority goal here is, of course, to maximize the luminosity while minimizing the background. With such a motivation in mind, the effects of pairs have been estimated by detailed Monte Carlo simulations with the proposed JLC-1 detector, in addition to simulations of masking of synchrotron radiation and the attenuation of the muon flux that are produced by interactions of the beams with upstream collimator materials.
Another important issue is the need for measurements of the distribution of the center-of-mass energy within each beam collision, hereafter called the ``luminosity spectrum.'' At TeV linear colliders, particles in the colliding beams loose a significant amount of energy before ``collisions" take place. This is due to the emission of synchrotron radiation in a strong electromagnetic field produced by the opposite beam, known as the ``beamstrahlung" phenomenon. Therefore, the effective luminosity at is always smaller than the nominal value that does not take beamstrahlung into account. The luminosity spectrum as a function of the center-of-mass energy depends on the magnitude of beamstrahlung. Knowledge on such issues is very important for conducting precision measurements, especially for studies of toponium physics and detailed investigations of SUSY physics, which are research opportunities unique to linear colliders. A method based on the measurement of acollinearity angles in Bhabha scattering events is examined as a possible technique to measure the luminosity spectrum.
Detailed engineering design studies for the interaction region are not ready at this moment, and, thus, they will not be given in this chapter. No consideration of the support system of the final focus quadrupole magnets and the heavy masking system are given. The designs of the extraction beam lines and measurements of electron polarizations are not discussed, either. These issues are left for subsequent design studies in the near future.