10 ms·

C³: A "cool" route to the Higgs boson and beyond

99 points by noslenwerdna 5y ago

knzhou 5y ago
This is a new proposal, fresh on the arXiv today, from a group of U.S. particle physicists. The introduction is very readable and lays out the mission clearly: > 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.
- 01100011 5y ago
  Where are we at with femtosecond laser driven accelerators? It seemed like there were promises of table-top accelerators in the near future.
  - naasking 5y ago
    I was just thinking that laser-driven plasma wakefield accelerators have produced some promising results recently. Particle physicists still seem stuck in the big accelerator mentality when maybe there are better uses for that money, even in their own field.
    - bettysdiagnose 5y ago
      I would say that 8km is actually quite small, and besides, LPWA has its own problems.
      - naasking 5y ago
        Of course it has its own problems, the question is whether a novel approach is likely to yield more novel insights than the standard approach for the past 50 years. Answer seems kind of obvious.
- spullara 5y ago
  I dropped out of my theoretical particle physics Ph.D. program when the SSC was cancelled. Experimental results for the stuff I worked on was delayed 20 years.
  - rob_c 5y ago
    Don't worry the legacy of the LHC is likely that the SSC would not have given us much. (Unless there are funny resonances at 20TeV+)
    - scrubs 5y ago
      Agree. Had much the same thought. Ssc maybe have found higgs as predicted but nothing new. Now, that's not to give the CERN ppl a hard time. They tried and are trying very hard to go beyond SM but mom (mother nature) isn't making it easy for them. In the US I'm hoping neutrino work will give us the edge there
- jamesmaniscalco 5y ago
  I would expand on this to say that they propose to use an innovative cavity shape. Normal-conducting cavities can reach higher accelerating fields than superconducting cavities, but at much lower duty factors and with high voltage breakdown events. This new design would allow for lower power dissipation than typical normal-conducting structures, ultimately allowing higher RF duty factors. 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.
milliams 5y ago
Could the title be changed to: C³: A "Cool" Route to the Higgs Boson and Beyond
- drfuchs 5y ago
  Or at least corrected to $C^3$, though downloading the source file shows: \def\CCC{C$^{3}$~}
  - blowski 5y ago
    I will confess I thought someone was using Excel to look for it.
- dang 5y ago
  Sure. Done.
ISL 5y ago
Generally when papers like this come out, there are a couple of decades' history behind them. (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?
chroem- 5y ago
Has the LHC produced technological advances that are used outside of particle physics? I am struggling to think of any.
- mhh__ 5y ago
  Is it not the case that a lot of machine learning research was done to make the data processing at LHC possible? 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.
- ampdepolymerase 5y ago
  It has created a ton of jobs for instrumentation engineers and PhDs. It has also brought many economic benefits to Switzerland.
  - LegitShady 5y ago
    creating jobs is not a positive argument in and of itself.
    - mhh__ 5y ago
      Better than selling ads I guess
      - LegitShady 5y ago
        that makes jobs too right?
  - noslenwerdna 5y ago
    Yes, building an accelerator would have economic benefits for whatever location is chosen as the site. This could be built in Japan (as the paper mentions, it may build the ILC) or even the US.
- MauranKilom 5y ago
deleted 5y ago
[deleted]
avz 5y ago
The paper describes a design for a linear accelerator that would reach 250GeV in center of mass frame and that may be extended to 550GeV (see section 2) and even multi-TeV (see section 5). 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? [1]: https://en.wikipedia.org/wiki/Large_Hadron_Collider https://en.wikipedia.org/wiki/Large_Hadron_Collider
- tobias2014 5y ago
  The difference is that the LHC is a proton-proton collider, and the proton constituents (partons) that participate in the "hard" collision only have a fraction of the total energy, given by some probability distribution (parton distribution functions). For an e+e- machine you essentially use the full energy in the hard collision.
- prof-dr-ir 5y ago
  Good question, and the answer is not easy. 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.
- quantum_mcts 5y ago
  https://physics.stackexchange.com/q/53558/386 https://physics.stackexchange.com/q/53558/386
tambourine_man 5y ago
“with a compact 8 km footprint”
- T-A 5y ago
  Relatively speaking: https://accelconf.web.cern.ch/napac2016/talks/mob2co03_talk.pdf https://accelconf.web.cern.ch/napac2016/talks/mob2co03_talk....
roca 5y ago
It would probably read better if they focused on the science benefits and were less overtly "need jobs for particle physicists or no-one will go into our field".
eximius 5y ago
> It is now common to describe the SM as an “effective” theory that should be derived from some more fundamental theory at higher energies. 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.
- Koshkin 5y ago
  Well, it’s not that you need higher energies to invent a new theory (even though you do, on a personal level), the problem is that it takes a discovery of a new particle to see which of these theories may be correct (and which of them aren’t), and new particles are only expected to be found as products of an interaction between particles at higher and higher energies.
- andreareina 5y ago
  Interactions at lower energies are very well predicted by the Standard Model, so deviations are either so small they're hard to find (but see the muon g-2 experiments), or at energies higher than what we've probed. 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.
- galcerte 5y ago
  We believe we should have new physics at higher energies because treating the SM as an effective field theory introduces additional terms in the Lagrangian which are suppressed (~ divided) by some energy scale. These additional terms are the ones allowing lepton flavor violation (so a muon decaying to an electron and a photon, for example) but we know from experiments that these events are incredibly rare. This tells us that the energy scale of new physics is very high. However, we could also have new physics at lower energy scales, as is the case with axions.
rob_c 5y ago
"compact 8km..." Gotta love particle physics :)
quantum_mcts 5y ago
This proposes a linear e+e- collider with beam energies of about 250 GeV. 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 https://inspirehep.net/literature/166246

99 points by noslenwerdna 5y ago

This is a new proposal, fresh on the arXiv today, from a group of U.S. particle physicists. The introduction is very readable and lays out the mission clearly: > 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.

01100011 5y ago
Where are we at with femtosecond laser driven accelerators? It seemed like there were promises of table-top accelerators in the near future.
- naasking 5y ago
  I was just thinking that laser-driven plasma wakefield accelerators have produced some promising results recently. Particle physicists still seem stuck in the big accelerator mentality when maybe there are better uses for that money, even in their own field.
  - bettysdiagnose 5y ago
    I would say that 8km is actually quite small, and besides, LPWA has its own problems.
    - naasking 5y ago
      Of course it has its own problems, the question is whether a novel approach is likely to yield more novel insights than the standard approach for the past 50 years. Answer seems kind of obvious.
spullara 5y ago
I dropped out of my theoretical particle physics Ph.D. program when the SSC was cancelled. Experimental results for the stuff I worked on was delayed 20 years.
- rob_c 5y ago
  Don't worry the legacy of the LHC is likely that the SSC would not have given us much. (Unless there are funny resonances at 20TeV+)
  - scrubs 5y ago
    Agree. Had much the same thought. Ssc maybe have found higgs as predicted but nothing new. Now, that's not to give the CERN ppl a hard time. They tried and are trying very hard to go beyond SM but mom (mother nature) isn't making it easy for them. In the US I'm hoping neutrino work will give us the edge there
jamesmaniscalco 5y ago
I would expand on this to say that they propose to use an innovative cavity shape. Normal-conducting cavities can reach higher accelerating fields than superconducting cavities, but at much lower duty factors and with high voltage breakdown events. This new design would allow for lower power dissipation than typical normal-conducting structures, ultimately allowing higher RF duty factors. 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.

milliams 5y ago

Could the title be changed to: C³: A "Cool" Route to the Higgs Boson and Beyond

drfuchs 5y ago
Or at least corrected to $C^3$, though downloading the source file shows: \def\CCC{C$^{3}$~}
- blowski 5y ago
  I will confess I thought someone was using Excel to look for it.
dang 5y ago
Sure. Done.

ISL 5y ago

Generally when papers like this come out, there are a couple of decades' history behind them. (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?

chroem- 5y ago

Has the LHC produced technological advances that are used outside of particle physics? I am struggling to think of any.

mhh__ 5y ago
Is it not the case that a lot of machine learning research was done to make the data processing at LHC possible? 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.
ampdepolymerase 5y ago
It has created a ton of jobs for instrumentation engineers and PhDs. It has also brought many economic benefits to Switzerland.
- LegitShady 5y ago
  creating jobs is not a positive argument in and of itself.
  - mhh__ 5y ago
    Better than selling ads I guess
    - LegitShady 5y ago
      that makes jobs too right?
- noslenwerdna 5y ago
  Yes, building an accelerator would have economic benefits for whatever location is chosen as the site. This could be built in Japan (as the paper mentions, it may build the ILC) or even the US.
MauranKilom 5y ago

deleted 5y ago

[deleted]

avz 5y ago

The paper describes a design for a linear accelerator that would reach 250GeV in center of mass frame and that may be extended to 550GeV (see section 2) and even multi-TeV (see section 5). 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? [1]: https://en.wikipedia.org/wiki/Large_Hadron_Collider https://en.wikipedia.org/wiki/Large_Hadron_Collider

tobias2014 5y ago
The difference is that the LHC is a proton-proton collider, and the proton constituents (partons) that participate in the "hard" collision only have a fraction of the total energy, given by some probability distribution (parton distribution functions). For an e+e- machine you essentially use the full energy in the hard collision.
prof-dr-ir 5y ago
Good question, and the answer is not easy. 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.
quantum_mcts 5y ago
https://physics.stackexchange.com/q/53558/386 https://physics.stackexchange.com/q/53558/386

tambourine_man 5y ago

“with a compact 8 km footprint”

T-A 5y ago
Relatively speaking: https://accelconf.web.cern.ch/napac2016/talks/mob2co03_talk.pdf https://accelconf.web.cern.ch/napac2016/talks/mob2co03_talk....

roca 5y ago

It would probably read better if they focused on the science benefits and were less overtly "need jobs for particle physicists or no-one will go into our field".

eximius 5y ago

> It is now common to describe the SM as an “effective” theory that should be derived from some more fundamental theory at higher energies. 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.

Koshkin 5y ago
Well, it’s not that you need higher energies to invent a new theory (even though you do, on a personal level), the problem is that it takes a discovery of a new particle to see which of these theories may be correct (and which of them aren’t), and new particles are only expected to be found as products of an interaction between particles at higher and higher energies.
andreareina 5y ago
Interactions at lower energies are very well predicted by the Standard Model, so deviations are either so small they're hard to find (but see the muon g-2 experiments), or at energies higher than what we've probed. 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.
galcerte 5y ago
We believe we should have new physics at higher energies because treating the SM as an effective field theory introduces additional terms in the Lagrangian which are suppressed (~ divided) by some energy scale. These additional terms are the ones allowing lepton flavor violation (so a muon decaying to an electron and a photon, for example) but we know from experiments that these events are incredibly rare. This tells us that the energy scale of new physics is very high. However, we could also have new physics at lower energy scales, as is the case with axions.

rob_c 5y ago

"compact 8km..." Gotta love particle physics :)

quantum_mcts 5y ago

This proposes a linear e+e- collider with beam energies of about 250 GeV. 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 https://inspirehep.net/literature/166246