Patrick Janot edited Conclusions.tex  over 10 years ago

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The discovery of the H(126) particle at the LHC has focused studies for the next machine needed for high-energy physics. While brand-new ideas are emerging for future Higgs factories, the prospects for the next decade already look quite promising: the HL-LHC is indeed an impressive Higgs factory, with great potential for Higgs boson coupling measurements to a few per-cent accuracy. The run at 13-14 TeV may discover something else, unfortunately likely to be beyond the ILC reach.  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 As alluded to  in this article article, it turns out  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.