One of the most evident aspects of the recent LCWS11 meeting in Granada, Spain, was the fact that the linear collider community has developed a meaningful collective consciousness over the past several years as closer integration has taken hold. Granada was the second major joint workshop between the CLIC and ILC programmes following from CERN, Switzerland, last year. We have had joint technical working groups for more than two years at this point and the degree of mutual awareness of the capabilities and problems we both face was on show at both the plenary and parallel sessions. Both programmes were covered in detail to an audience keen to hear about all aspects of the technical programmes. During the opening plenary, in additional to the latest LHC news, Rolf Heuer delivered a strong message for integration in the total high-energy physics community and offered support for further consolidation of the global linear collider programme. This call for enhanced cooperation was echoed by Atsuto Suzuki on behalf of the International Committee for Future Accelerators. While describing the way forward to the realisation of a linear collider project, Suzuki had an implicit strand of global action running throughout his presentation.
On a more parochial front, one of the most impressive aspects in the technical sessions was the recent progress of the superconducting radiofrequency (SRF) cavity programme. The cavity high-gradient yield has improved dramatically within the past year with much better understanding of the reasons for performance limitations. With the knowledge and techniques to diagnose cavity problems and control processing to correct flaws, potentially post facto, it appears to me that a yield of 100% is plausible, especially when taking into account that the high-level radiofrequency system is now capable of handling a spread of gradients. At the start of the R&D programme in 2007, it was considered a somewhat speculative call to adopt a gradient specification of 35 megavolts per metre. Now it is starting to appear possibly conservative. The ILC SRF programme has been one of the highest priorities of the global R&D effort and it is especially gratifying to see this level of achievement. It doesn’t hurt that SRF is increasingly viewed as one of the fundamental accelerator technologies throughout the world and thus support is forthcoming, but the ILC programme has been in the forefront of these efforts and has continued to demonstrate the power of a well-conceived global approach. To quote Jim Kerby from one of the parallel sessions, “the past two years have been remarkable”.
In preparation for the Technical Design Report (TDR), the process of design integration was in full flow during the workshop. The Conventional Facilities and Siting (CFS) group has the not unreasonable desire to know where to put the tunnels and infrastructure and had joint meetings with most of the systems groups to firm up the baseline. I think this step more than anything demonstrates that we will present a mature project design for the TDR. This represents a crucial step towards determining the scope (and cost) of an ILC: a firm basis on which to proceed.
Throughout the workshop, the elephant in the corner of the room remained the CERN’s Large Hadron Collider (LHC) results. Both the machine and detectors are running well. In excess of 3 inverse femtobarns of luminosity has been delivered and most of it has been analysed. If either the Higgs boson or physics beyond the Standard Model are seen then the case for a linear collider will be strong and the energy and luminosity scales apparent. To date however, the underlying physics remains uncertain and thus so do the appropriate linear collider machine parameters. This situation may resolve itself by the end of the present LHC run in 2012, which will take proton beams to a centre-of-mass energy of 7 or 8 teraelectronvolts (TeV), but it may require the subsequent run at 14 TeV starting in 2015 to clarify the situation. Until the correct design energy is apparent, an ILC R&D programme post-TDR that considers various energies while maintaining SRF technology development, especially with regard to cost effectiveness, looks to be the appropriate way to proceed.
Back in the political arena: An important upcoming event will be the release of the European Strategy in early 2013. This is a five-year plan for the European Union high-energy physics programme and as such will have a major influence on the whole field. A plenary session with Brian Foster and Steinar Stapnes described how this process will unfold. A position paper from the complete linear collider community will be submitted for consideration by the study group. These deliberations will be concurrent with the ILC Global Design Effort reorganisation at the end of the TDR phase. The way forward is still uncertain. The future remains interesting.
One of the high points of the workshop was undoubtedly the visit to the Alhambra (thanks to Juan Fuster and the local organising committee). Such antiquities remind us of the unquenchable nature of the human spirit to provide a sign for posterity that “we were here and our values were such that we did this”. While the technology may have changed I like to think that to some degree we share these same principles in our chosen field. After the visit I noticed Vic Kuchler and John Osborne from the CFS group sharing notes. I can only assume that ILC experimental cavern will be a memorable artifact in its own right too.