The International Linear Collider and other proposed high energy e+ e- machines aim to measure with unprecedented precision Standard Model quantities and new, not yet discovered phenomena. One of the main requirements for achieving this goal is a mea
surement of the incident beam energy with an uncertainty close to 1e-4. This article presents the analysis of data from a prototype energy spectrometer commissioned in 2006--2007 in SLACs End Station A beamline. The prototype was a 4-magnet chicane equipped with beam position monitors measuring small changes of the beam orbit through the chicane at different beam energies. A single bunch energy resolution close to 5e-4 was measured, which is satisfactory for most scenarios. We also report on the operational experience with the chicane-based spectrometer and suggest ways of improving its performance.
Prospects to search for a new massless neutral gauge boson, the paraphoton, in e+ e- collisions at center-of-mass energies of 0.5 and 1 TeV are studied. The paraphoton naturally appears in models with abelian kinetic mixing. A possible realistic mode
l independent lowest order effective Lagrangian contains magnetic interactions of the paraphoton with the Standard Model fermion fields. These interactions are proportional to the fermion mass and grow with energy, with however very weak paraphoton couplings to ordinary matter. At the ILC, a potentially interesting process to search for the paraphoton is its radiation off top quarks, so that the event topology to be searched for is a pair of acoplanar top quark jets with missing energy. By combining many discriminating features of signal and background events efficient paraphoton event selection was achieved allowing to set limits for the top-paraphoton coupling. Arguments in favor of the missing energy as the paraphoton with spin 1 are discussed.
