This is the executive summary of the Science Council of Japan (SCJ)’s report on the International Linear Collider, released on 19 December 2018. This is an unofficial translation by KEK from the original Japanese.
Background
The International Linear Collider (ILC) is an international project in the field of elementary particle physics to construct a straight accelerator (linear accelerator) to perform high-energy electron-positron collision experiments, and thereby advance research on the Higgs particle.
In response to the receipt of “Regarding Deliberations on International Linear Collider (Requests)” by the President of the Science Council of Japan from the Ministry of Education, Culture, Sports, Science and Technology on July 20, 2018, the “Review Committee on the Revised Version of the International Linear Collider Project” and “Technical Verification Subcommittee” were established. Since the ILC is a major international project requiring huge long-term investment and international cooperation, the committees deliberated on the project itself, including its academic significance and technical feasibility, as well as the status of preparations for the organization and management systems at relevant research institutions both in Japan and abroad, and for international cost-sharing.
Response
- Regarding the academic significance of research at the ILC project (revised plan), and the position of the ILC project (revised plan) in elementary particle physics
In the current view of elementary particle physics, there is no doubt that the search for “new physics beyond the Standard Model” is the most important task. There are various experimental approaches using both accelerator- and non-accelerator-based methods to search for “new physics beyond the standard model”. In the high-energy particle physics community, consensus has been reached that the research topic of precise measurement of Higgs couplings is extremely important. However, the community has not yet reached the stage of discussing how to allocate personnel and budget to various research projects in the particle physics field. - On the position of the ILC project (revised plan) in academia as a whole
The ILC project is far more expensive than the large number of big research facilities which have until now been proposed and examined for the Science Council of Japan’s master plan formulation, and will span a period of 30 years from the start of construction to the end of research. It is a long-term ultra-large-scale project. Before proposing such a project to the public, the committee considers that it is necessary to have broad understanding and support within academia. More extensive discussion is necessary regarding the position of the ILC in a broader perspective, including not only the elementary particle physics field but also large research projects in other disciplines. - On the significance to the public and society of implementing the ILC project (revised plan) in Japan
As with much other purely academic research, the ILC project arouses the public’s intellectual interest in the sense of knowledge exploration. In addition, if it develops into a hub at which advanced researchers, who will later spread out across the world, develop in an environment where top-class scientists from around the world are working hard and competing, then the project’s significance is substantial.
On the other hand, with regard to the technical and economic ripple effects other than its pure academic significance, the effects of the ILC are unclear at the moment and are considered to be limited. More in-depth dialogue with the general public, and residents in the vicinity of the potential site in particular, is needed to communicate not only the scientific significance of the ILC project but also its potential merits, advertised in the context of regional development, and potential environmental impacts from civil construction and the production of radioactive material, based on accurate information provided by the scientific community. - Status of preparations for implementing the ILC project (revised plan) and various conditions such as the securing of budget and human resources necessary for construction and operation
Considering the scale of the budget and human resources necessary for the implementation of the ILC project, it is obvious that it is not feasible unless it is based on unprecedentedly strong international cooperation. At present, there is no clear prospect for appropriate international cost-sharing. Moreover, the prospect of securing the human resources required for the construction of the ILC accelerator facilities is unclear. In Japan there is presently a lack of researchers and engineers associated with accelerators in particular. Although it has been explained that this issue will be addressed by developing new human resources and participation from overseas, the related uncertainties are large.
Overall Assessment
The 250-GeV ILC project will require a large budget both for construction and operation over a long period of time. On the other hand, the major expected outcome is that it has the potential to suggest the future direction of elementary particle physics if a deviation from the Standard Model is found in the precision measurements of the Higgs coupling constants. This review committee, however, did not reach a recognition that the expected scientific achievements, which are to suggest the future direction, are sufficient to justify the major part of the huge project cost that Japan is expected to bear. Regarding the technical feasibility of the 250 GeV ILC, various issues still need to be resolved. Although project proponents claim that these issues can be addressed during the preparation period, the committee cannot help but point out that there are still some concerns regarding the project’s implementation. A further concern is that the prospects for appropriate international sharing of the huge investment required to implement the project over the long 30-year period are not clear.
Judging from the information so far presented regarding the current state of the project and its preparation, the Science Council of Japan cannot reach a consensus to support hosting the 250-GeV ILC project in Japan. The committee considers that the government should be cautious regarding a decision to announce its commitment to host the ILC in Japan.
Elementary particle physics has until now been exploring the basic composition of the natural world, and has produced excellent results by means of a collaboration between theoretical research and experiments using accelerators, resulting in the pillar known as the “Standard Model.” At present, an important issue is the quest for “physics beyond the Standard Model,” which the ILC project also aims to address. It is considered that a desirable way to proceed with accelerator-based high-energy elementary particle experiments in the near future is to realize, somewhere in the world, both a hadron collider pursuing the energy frontier (currently the LHC and its future upgrade), and a complementary high luminosity lepton collider. On the other hand, in view of the limited resources of mankind, it is thought that not only high-energy physics but also other research fields whose approach requires huge experimental facilities will eventually reach a limit of sustainability. The future path for big science is an issue that should be considered by the academic world as a whole.
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