## Friday, November 10, 2017

### Japanese planned ILC collider shrinks to half

In 2013, I discussed the Japanese competition choosing the host of the International Linear Collider

The folks in the Sefuri mountains who created this catchy music video lost and Tohoku won instead – those had more credible, respected, and boring physicists behind themselves, not to mention a 5 times longer video with the 20 times smaller number of views. ;-)

Yesterday, Nature announced that physicists shrink plans for next major collider. How much did it shrink? A lot. By 50%.

In March 2013, the electron-positron collider was supposed to collide 250+250=500 GeV beams, and later even 500+500=1000 GeV beams, in a 33.5-kilometer long tunnel.

Well, the length of the tunnel was shrunk to some 20 km now and the particles colliding should only have 125+125=250 GeV. The price would be shrunk by 40% or so, to some \$7 billion in total.

The total center-of-mass energy is a special number because this energy is enough for the Higgs boson pair production – the Higgs boson mass happens to be 125 GeV, too. I am not sure whether they pay any attention to this special phenomenon happening at this energy, whether they will try to amplify this particular pair creation event or allow it. The collider should be sufficiently energetic to probe the energies slightly below as well as slightly above this threshold, I think.

Update: Tristan is telling me that the pair production "hh" is only visible at higher energies and this one relies on "Zh" only.

Note that the total energy is small compared to the LHC's 6,500+6,500=13,000 GeV but the electron-positron collisions are much cleaner and new physics should be more visible.

Well, this downward trend is disappointing. Chinese are great but in the grand scheme of things, because of the political systems etc., I would probably still prefer such big projects to be run by the Japanese.

This collider could probe the properties of the Higgs boson in detail and precisely but I am not sure whether this task would make me excited by itself. It sounds like physics of the sixth place of decimals to me.