A Proposal for a Phased Execution of the International Linear Collider Project

In March 2012, the Japan Association of High Energy Physicists (JAHEP) accepted
the recommendations of the Subcommittee on Future Projects of High Energy
Physics(1) and adopted them as JAHEP's basic strategy for future projects. In July
2012, a new particle consistent with a Higgs Boson was discovered at LHC, while inDecember 2012 the Technical Design Report of the International Linear Collider(ILC) will be completed by a worldwide collaboration.
On the basis of these developments and following the subcommittee's
recommendation on ILC, JAHEP proposes that ILC be constructed in Japan as aglobal project with the agreement of and participation by the international
community in the following scenario:(1) Physics studies shall start with a precision study of the "Higgs Boson", and thenevolve into studies of the top quark, "dark matter" particles, and Higgs selfcouplings, by upgrading the accelerator. A more specific scenario is as follows:(A) A Higgs factory with a center-of-mass energy of approximately 250 GeV shallbe constructed as a first phase.
(B) The machine shall be upgraded in stages up to a center-of-mass energy of~500 GeV, which is the baseline energy of the overall project.
(C) Technical extendability to a 1 TeV region shall be secured.
(2) A guideline for contributions to the construction costs is that Japan covers 50%of the expenses (construction) of the overall project of a 500 GeV machine. The
actual contributions, however, should be left to negotiations among thegovernments.

October, 2012

The Japan Association of High Energy Physicists

Reference(1) http://www.jahep.org/office/doc/201202_hecsubc_report.pdf
The subcommittee’s recommendations are attached in the next page.

Reference: The recommendations of the Subcommittee on Future Projects of High Energy Physics

Recommendations
The committee makes the following recommendations concerning large-scale
projects, which comprise the core of future high energy physics research in Japan.
• Should a new particle such as a Higgs boson with a mass below
approximately 1 TeV be confirmed at LHC, Japan should take theleadership role in an early realization of an e+e- linear collider. In particular,
if the particle is light, experiments at low collision energy should be started at
the earliest possible time. In parallel, continuous studies on new physics shouldbe pursued for both LHC and the upgraded LHC version. Should the energy
scale of new particles/physics be higher, accelerator R&D should be
strengthened in order to realize the necessary collision energy.
• Should the neutrino mixing angle θ13 be confirmed as large, Japan should
aim to realize a large-scale neutrino detector through international
cooperation, accompanied by the necessary reinforcement of accelerator
intensity, so allowing studies on CP symmetry through neutrino oscillations.
This new large-scale neutrino detector should have sufficient sensitivity to allow
the search for proton decays, which would be direct evidence of Grand UnifiedTheories.
It is expected that the Committee on Future Projects, which includes the High Energy
Physics Committee members as its core, should be able to swiftly and flexibly update
the strategies for these key, large-scale projects according to newly obtained knowledge
from LHC and other sources.
It is important to complete and start the SuperKEKB including the detector, asscheduled. Some of the medium/small scale projects currently under consideration havethe implicit potential to develop into important research fields in the future, such as
neutrino physics and as such, should be promoted in parallel to pursue new physics invarious directions. Flavour physics experiments such as muon experiments at J-PARC,
searches for dark matter and neutrinoless double beta decays or observations of CMB
B-mode polarization and dark energy are considered as projects that have suchpotential.