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Director's Corner

Strategy for linear colliders

| 22 August 2013

Discussions during the recent Snowmass meeting in Minneapolis. Image: Reidar Hahn, Fermilab.

After last summer’s preparation for the European Strategy process – in the meantime successfully concluded into an approved document by the CERN Council – this summer has been dedicated to the Snowmass process in the US, as well as hectic ILC preparations and discussions in Japan. In all regions linear collider projects are high on the priority lists, and a lot of work of the linear collider community has gone into preparing input documents for these processes. No major surprises seem to emerge – as far as I can tell. The physics motivation for a linear collider based on ILC technology primarily aimed at mapping out the Higgs sector, and the further physics potential of a higher energy machine using CLIC technology remain convincing.

The same can be said for the full exploitation of the LHC including luminosity upgrades in the future. It may seem obvious, but it should be reiterated as it is a large and demanding programme on its own, and most of us hope that more than the Higgs will ultimately emerge from the LHC programme and that we can finally and truly move beyond the Standard Model.

Even though most of the LCC directorate’s attention is firmly on the ongoing political and site selection process in Japan related to ILC, I will concentrate on some of the discussions and developments that have followed the European Strategy process. Already in May this year the CERN Council approved the 2014 CERN budget, the first budget after the approval of the European Strategy. Can we see an implementation taking shape? After all strategy papers are fine but real action is more convincing.

The LHC luminosity upgrade programme is the major next CERN construction project and the first priority item in the European Strategy. A shift in gear is visible in the planning and preparation – and budget allocations. Discussions with funding agencies concerning their planning and contributions are underway. The long shutdown at CERN, a pre-requisite to any upgrades, is progressing according to schedule with an impressive effort.

The second and third items in the Strategy are the most relevant for the linear collider activities. The energy frontier options with hadrons and leptons, either a higher-energy LHC in the existing tunnel or in a new 80-100 kilometer tunnel, or a linear collider based on CLIC technology, are supposed to be developed as options towards the next European Strategy update. This requires that one can compare performance, parameters, costs and schedules of these machines, and also their capabilities for various types of beyond-the-Standard-Model physics. Such common efforts are just starting up and my hope is that we can see them becoming structured over the next half a year or so. For the CLIC collaboration plans are made for next period (2013-2018) that fit into the new CERN resource planning, while the high-energy hadron options are at an earlier stage of planning in most areas. However, since the LHC is already running very well there are many aspects of the energy-upgrade machine that can be extrapolated from the current machine. Common physics studies will be important but have yet to be organised in a serious way.

For the ILC the European Strategy is positive, welcoming further development in Japan. We are closely following the exiting processes in Japan and there will clearly be more open discussions about how the European region could participate in such a project, including the near-future developments if Japan decides to put more resources into the project as a result of the ongoing national discussions. There is still a “wait-and-see” attitude but the European communities are looking into opportunities for future support. For the common work between CLIC and ILC more firm plans are being drawn up for cooperation in certain areas and I hope that by the end of the year some activities will become true linear collider activities where the same people cover specific studies for both machines. There are good candidates among the areas where there are already combined ILC-CLIC working groups, and where common work is already ongoing.

So overall we are slowly moving forward. For the linear collider community these strategy processes have been mostly positive. For CLIC the framework for project developments is relatively well defined in the next period. For ILC the developments in Japan are evolving quickly and we are all hoping that a clear road ahead towards implementation will emerge during the second half of this year.

Steinar Stapnes

Steinar Stapnes is Associate Director for the Compact Linear Collider Study in the Linear Collider Collaboration.
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