C³: A "cool" route to the Higgs boson and beyond
arxiv.org
arxiv.org
> We can now confidently claim that the “Standard Model” of particle physics (SM) is established. At the same time, we are more and more strongly persuaded that this SM is incomplete. [...] It is now common to describe the SM as an “effective” theory that should be derived from some more fundamental theory at higher energies. But we have almost no evidence on the properties of that theory.
> Our successes have become a liability in reaching this goal. Scientists from other fields now have the impression that particle physics is a finished subject. They question our motivations to go on to explore still higher energies. The scale of an energy frontier collider is also challenging to the young people in our field. They need to see qualitatively new capabilities realized during their active scientific careers. [...] That is where the urgency lies.
> [T]he entire C3 program could be sited in the United States. With the cancellation of the Superconducting Super Collider and the end of Tevatron operations the US has largely abandoned construction of domestic accelerators at the energy frontier. C3 offers the opportunity to realize an affordable energy frontier facility in the US. This may be crucial to realize a Higgs factory in the near term, and it will also position the US to lead the drive to the next, higher energy stage of exploration.
The main innovation is that they propose to use non-superconducting cavities, which allow much higher accelerating fields, cooled to increase their quality factor. The resulting shorter length dramatically decreases the cost, to an estimated $4 billion, which is 80% to 90% less than other proposals. Of course, $4 billion is no small amount of money, but for perspective that's about equal to the monthly budget of the National Institutes of Health, a third of the cost of the James Webb Space Telescope, or 2% of the total cost of the space shuttle.
There are still some downsides/tradeoffs compared to superconducting structures, including a much smaller beam aperture (5 mm diameter vs. ~100 mm for superconducting cavities), which disrupts the quality of the beam. Superconducting machines can also be run in continuous wave mode (100% duty factor), and state-of-the-art niobium cavities have been driven at ~50 MV/m in CW.
(Disclaimer: I'm an experimental physicist, but don't have domain knowledge in the subtleties of modern accelerator-cavity design, which is both an art and a science. Most modern accelerators, including LHC, are driven with superconducting niobium cavities.)
Since essentially every author is at SLAC, I suspect that there is a strong cold-copper research group there.
Can anyone with domain-knowledge summarize the generally-accepted strengths/weaknesses/risks of cold-copper accelerator designs?
I was curious how this compares against LHC which Wikipedia [1] says reached record 13TeV total collision energy. However, it isn't clear whether Wikipedia cites energy in center of mass frame that could be directly compared.
Does anyone know how the two accelerators would compare in this respect? In particular, would the proposed C³ accelerator actually achieve higher total collision energy than LHC or is it instead hoped that future extensions of a C³ accelerator would exceed LHC's capabilities?
It looks like the proposed accelerator smashes electrons and positrons together which are nice and clean elementary particles (as far as we know), so much of the collision energy is directly usable to create, say, Higgs bosons with a mass of 125GeV.
At the LHC they smash protons into each other which at this scale are a bit like a soupy mess of quarks and gluons. So its 13 TeV c.o.m. energy actually gets spread out over multiple elementary particles, which might not even hit each other straight on. Because of this the number of high-energy collisions between elementary particles is significantly lower.
This is just my lay-physicist perspective by the way; an accelerator specialist can probably provide more details.
Now if you shine a laser light on these electron beams, then the back-scattered photons will carry ~80% of the electrons' energy. So you'll have 200 GeV photons. And, since photons do not repel from each other, you can focus them much better - meaning that you might achieve even higher luminosities, despite conversion losses.
This is the idea of a Photon Linear Collider (PLC), that a bunch of my profs came up with in 1981: https://inspirehep.net/literature/166246
I'm curious why the more fundamental theory should be at higher energies.
In some sense I know part of the answer is 'because we haven't found it at low energies yet', another being 'because it takes sufficiently high energy to produce additional particles (e.g., Higgs)'.
Still, it is backwards from my intuition.
This isn't like the discovery of quantum mechanics where we knew there were things in the "everyday" regime we couldn't predict (e.g. blackbody spectra), more like general relativity where we have an otherwise extremely successful theory that breaks down in an extremal regime. Except we don't even have an example like the precession of Mercury's orbit to point at and say, "this is where it breaks down".
"We haven't found it at low energies yet" understates how much they've looked and how much hasn't been found.
However, we could also have new physics at lower energy scales, as is the case with axions.
https://accelconf.web.cern.ch/napac2016/talks/mob2co03_talk....
But fundamental research like this does not have short-term prosperity or technological breakthroughs as main priority anyway, so I'm not sure why you're so concerned about that.
There is literally civilizations worth of knowledge generated by projects like this, not all of it exactly commercially useful but if you bump into it and they've solved your problem or written your tutorial better than you it's very nice to have.
(0): https://white-rabbit.web.cern.ch/
(1): https://www.eurex.com/ex-en/support/initiatives/archive/high...
I'm especially looking at where it says "typical distances of 10 km between network elements"
Other things are work on grid/cloud technology as well as supercomputing, computer visualisation, research on industrial automation (something I personally used for work, directly related to challenges of building and running LHC), etc. etc.
Here is an exchange between physicist Robert Wilson and senator John Pastore in 1969, about establishing Fermilab.
Pastore: Is there anything connected with the hopes of this accelerator that in any way involves the security of the country?
Wilson: No sir, I don't believe so.
P: Nothing at all?
W: Nothing at all.
P: It has no value in that respect?
W: It has only to do with the respect with which we regard one another, the dignity of man, our love of culture. It has to do with: Are we good painters, good sculptors, great poets? I mean all the things we really venerate in our country and are patriotic about. It has nothing to do directly with defending our country except to make it worth defending.
Consumption is not bad (up to ecological damage). Wealth hoarding and concentration is bad.
It's also subsidizing the high precision research and development that private companies do to be able to provide the tools used by these research facility (thought to a much lower extend than military programs), which in turns should lower the cost of producing high precision doodads you put on your wrist or your pocket.
In the modern world, much of our economic growth is driven by innovation - new scientific understandings result in new technologies that result in new products and services that introduce new capabilities into the world that never existed before, and which are in demand because they improve people's lives.
Scaling production and volume lowers prices making them more accessible to everyone. That's the wealth creation pipeline at work, a modern miracle that brought humanity out of the permanent dark ages and repeating Malthusian cycles.
For example, much of modern technology - silicon chips, mobile phone networks, etc, would not have been possible without a deeper understanding of quantum physics.
However, continuing this growth and wealth generation process depends on continuing to deepen our understanding of the fundamental building blocks of matter and energy. Stop or slow the latter and we stop or slow the former. To date, particle accelerators are key component of doing that. And even if someone discovers a better way, we'll still have to invest in that. Either way we still have to invest in the process of unveiling the deep structure of matter.
What?
Yes, I recall at the time that when news articles talked about the SSC, flat panel displays were mentioned in multiple articles. Now this was certainly a case of one article influencing the others, with the original information source buried in obscurity.
We're really bad at projecting the technological outcomes of any specific science research project, and asking scientists or their funding agencies to do so is just an invitation for them to make up some bullshit. I'd prefer that they are just honest with their expectations.
If we have not found any applications, its probably because we have not tried enough / invested enough.
C³: A "Cool" Route to the Higgs Boson and Beyond
\def\CCC{C$^{3}$~}