Electrons and positrons have been smashed together before. It has been done at CERN before, too. The premise of this experiment is to do it at higher energy than has been done before.
The scientific goals of that experiment are somewhat more unclear, though. The LHC had a landmark scientific purpose, finding the last particle in the standard model. There is, as far as I can tell, no specific experiment that can be the headline for this new machine because the LHC pretty much did its job (modulo some error) and string theory et al need higher energy. There are a bunch of guesses about the higgs field and about dark matter that failed to materialize at the LHC, so now we want moar energy to see if that fixes our problems.
As to the theory they will be proving, maybe there are a few minor ones about the higgs field, but that's pretty much it at this point.
No, not quite. The electron-positron collision will allow more precise measurements. The goal is precision, not higher energy range, where a proton-proton machine would be much better. The goal is not to go beyond LHC in energy to see if something new shows up because of moar energy. The goal is to go to high energy with electron/positrons to measure stuff more precisely.
The FCC-ee is an intermediate goal, which will probe similar collisions as the LHC but at higher precisions. It is also a direct successor as the LEP which was housed in the LHC tunnel, so in this sense it is very much about "moar energy" than the previous electron-positron collider that CERN had. They're also hoping against hope that maybe they'll identify some rare collisions and even dark matter at the energy ranges that they couldn't probe before (at the LEP) with such high precision (at the LHC).
Then, when the tech for it is ready, the FCC-ee will be replaced by the FCC-hh, which is the successor of the LHC and can probe energy levels that are completely unaccessible at the moment - at about 5-6 times the energy level of the LHC. This is the true goal of the FCC project, and the biggest reason for building such a huge tunnel in the first place. But this requires significant advancements in magnets and other components which won't be available for several decades. So, they're filling in that time with the FCC-ee.
I lay out above, the IEEE article linked lays out, and you come across to me as having domain knowledge to understand that having electron-positron collisions at the same energy level of LHC lets us nail down the hints of what we saw at LHC -- persistent deviations in the standard model that require new theory.
When we get new theory, then we go hunting new particles, presuming its physically possible (as you point out with the incorrect idea that this might be being built to look for confirmation of string theory)
I understand the idea this won't find new particles, is it worth it?, but the idea this is unclear, confusing, misguided, or hoping for an outcome are trivially verifiable as false.
Things like:
- "The scientific goals...are unclear" (they are very clear!)
- "(modulo some error)" (reducing the error in the glimpses of deviation from the standard model is the interesting part, 5 sigma or bust, because that lets the theorists know how to progress. This isn't just "oh we'd like to reduce error bars, a less-entitled discipline would just get some grad students on SPSS", this is "holy shit...looks like we found something is fucky in our fundamentals here, but all we know is its off. we need to figure out by how much to give the theorists more data")
- "string theory et al" (I worry very much about the effectiveness of my communication if this is coming up, to be clear, no one is attempting to verify string theory, and it doesn't come up at all even in Sabine's arguments, no?
)
The IEEE article lays out this is not about discovering particles.
No one thinks new particles will be discovered.
The investment is not based on speculating new particles will be discovered.
The investment is not based on bad theory that new particles will be discovered.
The investment is not to find a sneaky way to hopefully accidentally find new particles.
Investments in colliders in general haven't been spectulatively looking for new particles in decades.
As both the IEEE, open source information, and my comment lay out above, they are specifically for nailing down these previously-assumed-settled values in the standard model. Because getting more data on the things theory can't explain leads to informed revisions in the theory. The next pendulum swing after that data would be theory to tell us a narrow band of energies to look at for any new particles theory needed to fix the standard model.
I don't care about Sabine and I'm not defending her. There are lots of other people who think this is a bad idea, and Nature has quoted "dozens" of them.
The error they saw isn't interesting unless it leads to something. There aren't even good theories about what it might lead to, other than some extra significant figures on some constants that nobody uses. Surely you can see there is a problem with doing science this way.
Theory precedes experiment. It always has, and you can't call what you're doing "science" unless that is true.
If it's just Dark Matter, and Matter/Anti-matter asymmetry, what theoretical framework is it going to explain it? Will it explain it, or will it just do "Your asymmetric partners are in another Order of Magnitude collider"? Or maybe there are actually 34 dimensions and not like four.
Blatantly false. Plenty of FCC docs from CERN itself mention the possibility that new particles could be discovered, from dark matter to axions. They even think they could help gather data to guide searches for supersymmetric partners.
> In addition to the dark matter examples given before, Volume 1 documents the extraordinary sensitivity to less-than-weakly coupled particles, ranging from heavy sterile neutrinos (see Fig. 5, right) down to the see-saw limit in a part of parameter space favourable for generating the baryon asymmetry of the Universe, to axions and dark photons.
> Future searches at lepton and proton colliders would further constrain any viable scenarios and put progressively tighter bounds to SUSY candidate particles. Searches could profit from data collected at the FCCs as they will allow better discrimination of the Standard Model backgrounds but also deliver more information for event reconstruction.
Supersymmetry is on its last legs after the LHC didn't find any supersymmetric particles. WIMPs and other dark matter particles are now no longer speculated to be on the menu because they are too light for this energy range.
There's lots of "could" in your own post and your sources. Very little "will" - as in "will test X theory."
The poster above was claiming, in several posts, that the people at CERN and experimental particle physicists more broadly are being unfairly represented by claims that they are including possible new particles in the case for building the FCC. They even found an IEEE publication about it that (apparently) made no such claims and stuck to well motivated physics.
I was merely showing that there is nothing unfair about it, as all materials about the FCC, at least from CERN, come with beliefs about the chance that new particles could be found. Sure, they don't make hard claims that they will be found. But even these claims that they could be found are unfounded. It's just as likely that I'll spot a WIMP in my oven if I look carefully while it's pretty hot as WIMPs being found at the FCC. This speculation has no place in serious discussions about this level of spending and human effort.
If this were an abstract discussion at a panel and someone was asking "what are some speculations about what we could see at the FCC", it would be perfectly fine to go on about SUSY and dark matter detection and axions and whatever else. But this has no place whatsoever in official documents about the scientific purpose of allocating billions of euros to this project. It is blatant speculation to pad out an otherwise pretty thin motivation. It's like writing a proposal for a new build system at your company and including speculation that it might detect security vulnerabilities automatically, or it might reduce build times a hundred fold.
The scientific goals of that experiment are somewhat more unclear, though. The LHC had a landmark scientific purpose, finding the last particle in the standard model. There is, as far as I can tell, no specific experiment that can be the headline for this new machine because the LHC pretty much did its job (modulo some error) and string theory et al need higher energy. There are a bunch of guesses about the higgs field and about dark matter that failed to materialize at the LHC, so now we want moar energy to see if that fixes our problems.
As to the theory they will be proving, maybe there are a few minor ones about the higgs field, but that's pretty much it at this point.