The 19th-century German statesman Otto von Bismarck said that laws are like sausages – it’s better not to see them being made. The US budget, when it finally appears, eventually becomes law. With the GDE mandate and the associated R&D programme for the ILC coming to an end with the final handover of the Technical Design Report (TDR) in summer 2013, this year’s budget process was awaited with a more than normal degree of trepidation by those of us strongly influenced by the end product. This unease proved justified, for when the presidential budget was released in February 2012, it dramatically reduced the ILC funding for FY13. Commentary on this move was provided at the subsequent High Energy Physics Advisory Panel (HEPAP) meeting when Jim Siegrist, Head of the DOE Office of High Physics, reported that the five-year GDE R&D plan was successfully completed but that they could see no project on the near horizon. He also pledged that the US would continue to be involved in the international planning at a low level.
So what does this mean in a practical sense? Well, to first order, I suspect it means what it says: further significant US investment in the ILC R&D programme will require (among other things) serious movement towards a construction project by the global community. Implicit in the statement, however, is the recognition that the maturity of the technical developments under the GDE programme are good enough to support such a project proposal by the high-energy physics community. Thus in one move the ball has been squarely hit back on our side of the court – where is the project?
There are several elements needed to achieve approval of a project of this size and complexity: science, a design, a host and willing participants. The science case must be compelling. In this regard the recent announcement of the Higgs-like particle at the LHC is a major boost. The nominal 500-GeV centre-of-mass energy on which the TDR design is based could be higher than necessary if a Higgs-factory approach is favoured. Physics beyond the Standard Model represents a known unknown, to quote a recent US cabinet secretary. Physics beyond the Standard Model could also affect the desired energy of a future collider. The flexibility of the linear collider approach is a great virtue in this regard as a phased approach to the ultimate machine energy is feasible. These issues are under active consideration in the various regional strategy analyses, which will report within the next year (the EU strategy, the Asian roadmap, and the US Snowmass conference on the Mississippi). Ultimately I believe an ICFA endorsement of whatever emerges will be necessary to proceed.
Besides a solid science case, we need a reliable accelerator design and cost estimate. In this regard the GDE programme has been pivotal, and with the impending release of the TDR, a great deal of uncertainty has been removed. As mentioned earlier, the US funding reduction can be viewed as a sign that we are ready to go (among other interpretations!).
The linear collider must be sited somewhere and this step requires a host. Of necessity the host entity assumes the major project responsibility, both technical and financial. The as yet site-unspecific TDR will need to become a site-specific engineering design, much of which can only be done by the host. In addition to the linear collider itself, some form of central laboratory complex will be necessary, adding to the host investment. High-energy physics is a fascinating and compelling endeavour, but it does not come cheap. Encouragingly, these issues are starting to be considered in Japan as part of the siting studies currently in progress.
The final requirement is the establishment of a global collaboration to execute the project. The GDE has provided a strong technical collaboration, but the resources for a major construction project will need several countries to show a significant political willingness to participate. The political climate for international science is worthy of a column in itself. Suffice to say that this will be a major challenge over the next few years.
So where does this leave the US programme? Two-thirds of the US effort during the GDE era was related to superconducting radiofrequency technology development. We are fortunate that there are several other projects under consideration in the US that are also interested in 1.3-GHz ILC-like components, and the generic General Accelerator Development programme will continue to offer support in this area. Fermilab will continue to fabricate and test cryomodules in the NML facility, albeit at lower priority than before. The ultimate goal of a three-cryomodule string test with beam is in doubt, though.
The US’s Thomas Jefferson National Accelerator Facility will also continue to work on higher gradients, though again with reduced priority. R&D in other systems areas, principally aimed at hardware development, will wind down over the next several months in a coherent way. Collaboration within the various technical working groups will continue with reduced resources allocated to these efforts. Although the details of this evolution of the US programme are still being worked out, with the baseline design work and the R&D goals of the GDE largely completed, a reduced US effort will hopefully be sufficient to carry the project forward for the foreseeable future while bigger issues are decided.
Besides pondering the mysteries of sausages, Otto von Bismarck was responsible for the unification of modern Germany. High-energy physics needs to follow his lead in pursuit of the next major facility. Progress in science is inexorable but a united approach generally helps. The new, broader, linear collider collaboration under Lyn Evans, the director for the new linear collider organisation, is an important step in this direction.