The ttbar Threshold and Machine Parameters at the NLC

Abstract

One of the problems in the design of a high energy e+e- linear collider is the distribution of the luminosity as a function of real collision energy, dL/dE, due to initial state radiation, beamstrahlung, and the energy spread of the collider. These effects smear a sharp feature in the cross section of e+e- -> hadrons such as the ttbar threshold into a flatter structure. This study reviews the impact on dL/dE of these effects as a function of machine parameters, explores some methods of measuring dL/dE with Bhabha scattering, how the dL/dE flattens the ttbar cross section near threshold, and the effect the dL/dE measurement has on extracting parameters of the top quark, such as the mass and width, in a 2.5/fb scan of the ttbar threshold.