Experimental Approaches at Linear Colliders

Abstract

Precision measurements have played a vital role in our understanding of elementary particle physics. Experiments performed using e{sup +}e{sup -} collisions have contributed an essential part. Recently, the precision measurements at LEP and SLC have probed the standard model at the quantum level and severely constrained the mass of the Higgs boson [1]. Coupled with the limits on the Higgs mass from direct searches [2], this enables the mass to be constrained to be in the range 115-205 GeV. Developments in accelerator R and D have matured to the point where one could contemplate construction of a linear collider with initial energy in the 500 GeV range and a credible upgrade path to {approx} 1 TeV. Now is therefore the correct time to critically evaluate the case for such a facility. The Working Group E3, Experimental Approaches at Linear Colliders, was encouraged to make this evaluation. The group was charged with examining critically the physics case for a Linear Collider (LC) of energy of order 1 TeV as well as the cases for higher energy machines, assessing the performance requirements and exploring the viability of several special options. In addition it was asked to identify the critical areas where Rmore » and D is required (the complete text of the charge can be found in the Appendix). In order to address this, the group was organized into subgroups, each of which was given a specific task. Three main groups were assigned to the TeV-class Machines, Multi-TeV Machines and Detector Issues. The central activity of our working group was the exploration of TeV class machines, since they are being considered as the next major initiative in high energy physics. We have considered the physics potential of these machines, the special options that could be added to the collider after its initial running, and addressed a number of important questions. Several physics scenarios were suggested in order to benchmark the physics reach of the linear collider and persons were appointed to maintain contacts with the relevant activities in the various Physics Working Groups. Special options considered were precision electroweak studies that could be done by running the collider at and near the Z pole (so called Giga Z running); collisions involving {gamma}{gamma}, e{sup -}e{sup -}, or e{gamma} interactions; and positron beam polarization. The following questions were posed in order to focus the discussions: (1) In view of the fact that the luminosity is a function of energy, what are the trade-offs involved in selecting the energy. (2) What is the argument for proceeding with the construction of a Linear collider as soon as possible rather than waiting for data from LHC? (3) In the context of a definite physics scenario, what is a realistic run plan? i.e. How much luminosity at each energy? (4) What should be the initial energy of a linear collider and to what energy should that machine extended?« less