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Does this increase the likeliness that we need a bigger collider to finally reach new physics?

jug 8y ago
I wonder if it’s harder to get funding for that. With the LHC they at least expected the Higgs boson. And hopes for super symmetry signs that seem to have failed to materialize. With only hand waving and hopes for hypotheses left, and ever increasing costs... :-/
- ISL 8y ago
  The easy ask now is for a precision electron-positron collider to study the Higgs itself. Lepton/anti-lepton colliders are as clean as an experiment can be, in stark contrast to hadron colliders, which are as clean as a car accident. With the improved understanding of the Higgs that we have now, an e+/e- machine can be custom-built to study it in great detail. The Higgs is the newest fundamental particle to physics, and the first/only known scalar. We should expect that it has more to tell us than simply its own existence. Even when the LHC was being planned, LHC was the discovery machine, and precision experiments were to follow. In my opinion, only when those measurements are complete should we consider a huge leap toward higher energy, unless new accelerator technology emerges.
  - wolfgke 8y ago
    > The Higgs is the newest fundamental particle to physics, and the first/only known scalar. A question to physicists: Is there (strong) evidence that there might exist other scalars (if yes: at which energy level?). If not: Do there exist attempts of theories that predict why there is only one scalar?
    - ISL 8y ago
      I'm unaware of a particular compelling argument for another scalar. Scalars are easier for theorists to use when trying out a new theory, so they abound in theoretical physics. At some level, it is something of a surprise to have found that there is just one particle responsible for the Higgs mechanism, and it is indeed spin-0, as Nature hasn't given us one of those before. Prior to the discovery of the Higgs, perhaps the majority of physicists were betting on something Higgs-like, but not quite the pure vanilla Standard Model Higgs. I would not bet any money on it, but if one were looking for another scalar, one might find it in whatever mechanism underlies dark energy. Many theoretical models for dark energy use scalars, again, because they are easier...
ISL 8y ago
It means that another way in which the standard model could have been broken doesn't appear, at first glance, to be broken. Improved colliders, and improved experiments generally, tend to increase the number of ways in which we can search for a departure from the plan. What we may need, at least as much as new colliders, is the right insight to open a new way forward. The standard model is large and complicated -- there aren't that many people who really understand its complexity enough to find something analogous to Gell-Mann's eightfold way.
- erickj 8y ago
  At roughly what scale would new colliders need to increase by to open new paths? Are proposal estimating new efforts at 100's of km? 1000s?
  - chriswarbo 8y ago
    The problem is that it's very difficult to rule out most hypotheses, since they can be tweaked to avoid whatever a particular experiment said. Usually this means that colliders can't rule out a hypothesis; they can only put a limit, like "no effect is observed below energies of 14TeV". Rather than trying to rule out a hypothesis completely, it's easier to place limits outside of which a hypothesis is essentially useless. IIUC, if the LHC didn't spot the Higgs mechanism below 14TeV then that wouldn't work as an explanation of other particles' mass. At that point there might have still been a Higgs mechanism at higher energies, but we wouldn't really care either way since the whole point of coming up with the Higgs mechanism was to explain the mass of other particles: if it can't do that, it becomes inconsequential. That's why the LHC was so important for the Higgs: we would either find it, and hence have a better explanation of particles' mass; or we would know that particle mass doesn't follow the Higgs mechanism. At the moment we have a bunch of hypotheses which predict effects that larger colliders might see, but I don't think we have (feasible) limits which let us discard these hypotheses. Hence new colliders don't have a goal to aim at: it's just a case of going as big as possible to have the highest chance of seeing new effects. Yet we might see nothing, and that wouldn't actually tell us much, since the predictions could just be tweaked again.
gboudrias 8y ago
I've been told it's physically impossible to make a bigger collider (any physicists around?), which is partly why the LHC was such a big deal, it's the end of a technological path. We can make different types of colliders though. Edit: Nope I'm wrong.
- InclinedPlane 8y ago
  Where'd you hear that? It's absolutely not true. The LHC itself has been upgraded several times during its life and there are several designs for next generation colliders (such as the Future Circular Collider).
  - dukwon 8y ago
    There has only been one upgrade to the LHC by my count (splice consolidation in LS1).
    - InclinedPlane 8y ago
      There was a major upgrade in 2013-2015 which doubled the energy (from 3.5 TeV per beam to 6.5 TeV per beam), but the luminosity was increased in 2016 and 2017 as well.
      - dukwon 8y ago
        > There was a major upgrade in 2013-2015 which doubled the energy (from 3.5 TeV per beam to 6.5 TeV per beam) Yeah, that was the splice consolidation. > but the luminosity was increased in 2016 and 2017 as well. From what I know, that's through conditioning, repairs and improved techniques (BCMS, ATS, anti-levelling). The increase from 2015 to 2016 was because they didn't finish the intensity ramp in 2015 as the scrubbing campaign lasted so long. 2016 had the TIDVG dump problem as well as outgassing from the injection kickers. 2017 was marred by 16L2.
walrus1066 8y ago
To guarantee new physics, you'd need a 10^16 TeV collider, so literally one-thousand-trillion times more powerful than the LHC which is at 14 TeV! Context: at 10^16 TeV you start probing the planck energy scale, where gravity becomes strong enough to influence particle interactions. In nature, these energies are reached only inside black holes and just after the big bang. The standard model does not describe gravity, so it has no predictive power at this scale, which is why the above phenomena are a complete mystery to us. The standard model gets away with this at LHC energy scale because gravity is so weak it can literally be neglected in the calculations. It's of course possible we'd see some new physics before then, but it's not guaranteed, building a collider 10 times would be a bit of a stab in the dark.

jug 8y ago

I wonder if it’s harder to get funding for that. With the LHC they at least expected the Higgs boson. And hopes for super symmetry signs that seem to have failed to materialize. With only hand waving and hopes for hypotheses left, and ever increasing costs... :-/

ISL 8y ago
The easy ask now is for a precision electron-positron collider to study the Higgs itself. Lepton/anti-lepton colliders are as clean as an experiment can be, in stark contrast to hadron colliders, which are as clean as a car accident. With the improved understanding of the Higgs that we have now, an e+/e- machine can be custom-built to study it in great detail. The Higgs is the newest fundamental particle to physics, and the first/only known scalar. We should expect that it has more to tell us than simply its own existence. Even when the LHC was being planned, LHC was the discovery machine, and precision experiments were to follow. In my opinion, only when those measurements are complete should we consider a huge leap toward higher energy, unless new accelerator technology emerges.
- wolfgke 8y ago
  > The Higgs is the newest fundamental particle to physics, and the first/only known scalar. A question to physicists: Is there (strong) evidence that there might exist other scalars (if yes: at which energy level?). If not: Do there exist attempts of theories that predict why there is only one scalar?
  - ISL 8y ago
    I'm unaware of a particular compelling argument for another scalar. Scalars are easier for theorists to use when trying out a new theory, so they abound in theoretical physics. At some level, it is something of a surprise to have found that there is just one particle responsible for the Higgs mechanism, and it is indeed spin-0, as Nature hasn't given us one of those before. Prior to the discovery of the Higgs, perhaps the majority of physicists were betting on something Higgs-like, but not quite the pure vanilla Standard Model Higgs. I would not bet any money on it, but if one were looking for another scalar, one might find it in whatever mechanism underlies dark energy. Many theoretical models for dark energy use scalars, again, because they are easier...

ISL 8y ago

It means that another way in which the standard model could have been broken doesn't appear, at first glance, to be broken. Improved colliders, and improved experiments generally, tend to increase the number of ways in which we can search for a departure from the plan. What we may need, at least as much as new colliders, is the right insight to open a new way forward. The standard model is large and complicated -- there aren't that many people who really understand its complexity enough to find something analogous to Gell-Mann's eightfold way.

erickj 8y ago
At roughly what scale would new colliders need to increase by to open new paths? Are proposal estimating new efforts at 100's of km? 1000s?
- chriswarbo 8y ago
  The problem is that it's very difficult to rule out most hypotheses, since they can be tweaked to avoid whatever a particular experiment said. Usually this means that colliders can't rule out a hypothesis; they can only put a limit, like "no effect is observed below energies of 14TeV". Rather than trying to rule out a hypothesis completely, it's easier to place limits outside of which a hypothesis is essentially useless. IIUC, if the LHC didn't spot the Higgs mechanism below 14TeV then that wouldn't work as an explanation of other particles' mass. At that point there might have still been a Higgs mechanism at higher energies, but we wouldn't really care either way since the whole point of coming up with the Higgs mechanism was to explain the mass of other particles: if it can't do that, it becomes inconsequential. That's why the LHC was so important for the Higgs: we would either find it, and hence have a better explanation of particles' mass; or we would know that particle mass doesn't follow the Higgs mechanism. At the moment we have a bunch of hypotheses which predict effects that larger colliders might see, but I don't think we have (feasible) limits which let us discard these hypotheses. Hence new colliders don't have a goal to aim at: it's just a case of going as big as possible to have the highest chance of seeing new effects. Yet we might see nothing, and that wouldn't actually tell us much, since the predictions could just be tweaked again.

gboudrias 8y ago

I've been told it's physically impossible to make a bigger collider (any physicists around?), which is partly why the LHC was such a big deal, it's the end of a technological path. We can make different types of colliders though. Edit: Nope I'm wrong.

InclinedPlane 8y ago
Where'd you hear that? It's absolutely not true. The LHC itself has been upgraded several times during its life and there are several designs for next generation colliders (such as the Future Circular Collider).
- dukwon 8y ago
  There has only been one upgrade to the LHC by my count (splice consolidation in LS1).
  - InclinedPlane 8y ago
    There was a major upgrade in 2013-2015 which doubled the energy (from 3.5 TeV per beam to 6.5 TeV per beam), but the luminosity was increased in 2016 and 2017 as well.
    - dukwon 8y ago
      > There was a major upgrade in 2013-2015 which doubled the energy (from 3.5 TeV per beam to 6.5 TeV per beam) Yeah, that was the splice consolidation. > but the luminosity was increased in 2016 and 2017 as well. From what I know, that's through conditioning, repairs and improved techniques (BCMS, ATS, anti-levelling). The increase from 2015 to 2016 was because they didn't finish the intensity ramp in 2015 as the scrubbing campaign lasted so long. 2016 had the TIDVG dump problem as well as outgassing from the injection kickers. 2017 was marred by 16L2.

walrus1066 8y ago

To guarantee new physics, you'd need a 10^16 TeV collider, so literally one-thousand-trillion times more powerful than the LHC which is at 14 TeV! Context: at 10^16 TeV you start probing the planck energy scale, where gravity becomes strong enough to influence particle interactions. In nature, these energies are reached only inside black holes and just after the big bang. The standard model does not describe gravity, so it has no predictive power at this scale, which is why the above phenomena are a complete mystery to us. The standard model gets away with this at LHC energy scale because gravity is so weak it can literally be neglected in the calculations. It's of course possible we'd see some new physics before then, but it's not guaranteed, building a collider 10 times would be a bit of a stab in the dark.