Patrick Janot edited Conclusions.tex  over 10 years ago

Commit id: 276ed2bfabdc87887170bfd0161edf37568613c5

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Beyond the HL-LHC, it is now generally accepted that it is important to choose the right machine, as not to mortgage the future of the discipline with a suboptimal choice (given the cost of these machines). To cut a long story short, the right machine must bring orders of magnitude with respect to what can be achieved at LHC, both in precision measurements and in discovery potential. It has been shown in this article that the ILC project has neither of these capabilities, with both too small a luminosity and too small a centre-of-mass energy.  Instead, a large $\epem$ circular collider seems to be the best complement to LHC, with {\it (i)} a per-mil precision on Higgs couplings; {\it (ii)} an unbeatable precision on EWSB parameters and on the strong coupling constant; {\it (iii)} a measurement of the number of active neutrinos to better than 0.001; {\it (iv)} a unique search programme for rare Z, W, Higgs, and top decays; and {\it (v)} a very competitive cost. Circular colliders have also the most mature technology: they are supported by progress of $\epem$ factories for 20 years, and it turns out that SuperKEKB, with parameters similar to TLEP, will be a precious demonstrator. Based on this experience, the cost, the power, and the luminosity predictions will be reliable. Most importantly, TLEP is also a first step towards a 100 TeV pp collider and a unique long-term vision for high-energy physics.  The design study of TLEP has now started, in close collaboration with the VHE-LHC design study, with worldwide collaboration from Asia, USA and Europe, and with full support from the CERN Council. The study is now acted in the approved CERN Medium-Term Plan (2014-2018). The first proposed step is a design study report in 2015, towards a conceptual design report and a detailed cost estimate in 2018-2019, for an informed decision to be taken in full knowledge of the LHC results at 13-14 TeV. A solid backbone exists for both the design and the rich, albeit demanding, physics case of TLEP.     We aim for physics in 2030.