Director's Corner

24 August 2006

Barry Barish

Revisiting the ILC Parameters

An innocent looking little document entitled "Parameters for the Linear Collider" dated 30 September 2003 has to a large extent determined the present baseline design of the ILC. We have used this document as if it were "a requirements document," and the baseline design has flowed down from those requirements. Of course, that document was never intended to play such a critical role, and now that we are entering a period in which we want to optimise cost to performance, we must both understand how the parameters effect cost and how they affect performance (or science potential). For this reason, the International Linear Collider Steering Committee (ILCSC) has recently taken the step to reactivate its parameter group, which will provide us the necessary partner in doing this optimisation, first for the ILC reference design and later for our engineering design.

Rolf-Dieter Heuer, chair of the ILCSC Linear Collider Parameters Subcommittee

The ILCSC has written a draft mandate given below for this new study that is already being discussed with the GDE and the detector communities.

The ILCSC sub-group on parameters is asked to

  • Revisit the Baseline Machine performance and Energy Upgrade parameters it had established two years ago, taking into account possible new insights and developments
  • Discuss, together with the GDE and WWS, all areas of the RDR design optimisation affecting the performance parameters
  • Revisit the Options Beyond the Baseline Machine it had established two years ago, and provide clear cost versus performance guidance as its effects the initial machine configuration
  • Extend the performance parameters also to the main detector components, such as tracking and calorimetry, in order to provide guidance for the selection of optimal and possibly complementary detector configurations
  • Make a report (and interim report if necessary) well in phase of the development of the RDR

Some of the items in this mandate, especially the next to last one involving the detector components, go beyond the original charge of this committee and may be modified before the charge is finalised.

In principle, for the accelerator reference design, we would like to do a parametric analysis of cost to performance (science potential) for the key parameters used for the design (energy, luminosity, etc), and analyses of the importance and trade-offs for the discrete parameters (like the number of interaction regions, positron polarisation, etc). Another dimension to this analysis is whether some capabilities can be included as options for upgrades, rather than in the design of the initial machine?

It should be evident that doing a first-rate job of this analysis of cost to performance for the key parameters will be crucial both to our ability to come forward with a well considered machine design and for defending and making the case for the ILC design and cost we propose. We plan to work closely with the reconstituted parameter group, who will give us a strong partner in doing this analysis. In fact, Rolf Heuer participated in our GDE Executive Committee meeting last week. We had initial discussions as to how to accomplish these goals, as well as to alert Rolf to the areas in which early feedback can be most helpful for our RDR preparations.

I would like to emphasise that we have already taken steps and will continue to directly involve the detector community, through the World Wide Study (WWS), in evaluating the scientific impact of whatever design changes are proposed to our baseline.

-- Barry Barish