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Here’s a question I have that maybe somebody in this thread can help me with: what is the positive case for a new particle collider at much higher energies than

Here’s a question I have that maybe somebody in this thread can help me with: what is the positive case for a new particle collider at much higher energies than the LHC? It seems to me that particle physics post-LHC is just the same as it was pre-LHC. We verified the existence of the Higgs, which is great, but that meant no revisions to the Standard Model were needed as it already assumed the Higgs. And no exotic or unexpected new particles have turned up. You can definitely argue that the technology spin-offs from the LHC have been great; but is that really an argument for another collider specifically, or just Big Science in general? To put it another way, what’s the argument for a collider that goes beyond “provide employment for hundreds of high-energy physicists, and throw some unprecedented engineering and logistical challenges at then”? Is there a pitch that’s based on the science rather than the technology?

magicalhippo 6y ago
The current standard model can't explain a number of observations. There was a rather detailed post over on PhysicsForums[1] detailing a number of issues. The LHC hasn't really shown us where to look, the hope is that a larger collider can give a more clear indication. That said, I have this feeling that we're approaching the limits of "going big". There was a very interesting talk[2] over at Perimeter Institute recently about larger colliders and their feasibility. [1]: https://www.physicsforums.com/threads/what-are-the-most-important-phenomena-that-the-standard-model-cant-explain.992129/post-6376780 https://www.physicsforums.com/threads/what-are-the-most-impo... [2]: http://pirsa.org/20100056/ http://pirsa.org/20100056/
magv 6y ago
> verified the existence of the Higgs As a related tangent: we have verified the existence of the Higgs, but only partially. What was so far measured was the interaction strength between Higgs and W bosons, Z bosons, and the top quarks: these are the main channels of Higgs production at the LHC, and they fit the theory prediction within 20%. Yes, 20%. Not precise at all. What about interaction between Higgs and the other 5 kinds of quarks? Electrons? Muons? Tau? Itself? The data ranges from +-100% to none at all. In particular the measurement of Higgs-Higgs interaction is an important one: the assumption Standard Model makes about the strength of this interaction is not unique, and others are possible. We don't know yet: not enough data. Moreover models with multiple Higgs particles are possible. Again, we don't know yet, not enough data. This is why some cautious researchers claim that we have discovered "a scalar particle", "believed to be Higgs", but further measurement is needed to determine all of its properties. This is one of the main activities at LHC and among the theoreticians at the moment: measuring Higgs interactions with other particles. There is still way to improve precision with more data from LHC, but ultimately there is only so much it can do without increasing the energy.

magicalhippo 6y ago

The current standard model can't explain a number of observations. There was a rather detailed post over on PhysicsForums[1] detailing a number of issues. The LHC hasn't really shown us where to look, the hope is that a larger collider can give a more clear indication. That said, I have this feeling that we're approaching the limits of "going big". There was a very interesting talk[2] over at Perimeter Institute recently about larger colliders and their feasibility. [1]: https://www.physicsforums.com/threads/what-are-the-most-important-phenomena-that-the-standard-model-cant-explain.992129/post-6376780 https://www.physicsforums.com/threads/what-are-the-most-impo... [2]: http://pirsa.org/20100056/ http://pirsa.org/20100056/

magv 6y ago

> verified the existence of the Higgs As a related tangent: we have verified the existence of the Higgs, but only partially. What was so far measured was the interaction strength between Higgs and W bosons, Z bosons, and the top quarks: these are the main channels of Higgs production at the LHC, and they fit the theory prediction within 20%. Yes, 20%. Not precise at all. What about interaction between Higgs and the other 5 kinds of quarks? Electrons? Muons? Tau? Itself? The data ranges from +-100% to none at all. In particular the measurement of Higgs-Higgs interaction is an important one: the assumption Standard Model makes about the strength of this interaction is not unique, and others are possible. We don't know yet: not enough data. Moreover models with multiple Higgs particles are possible. Again, we don't know yet, not enough data. This is why some cautious researchers claim that we have discovered "a scalar particle", "believed to be Higgs", but further measurement is needed to determine all of its properties. This is one of the main activities at LHC and among the theoreticians at the moment: measuring Higgs interactions with other particles. There is still way to improve precision with more data from LHC, but ultimately there is only so much it can do without increasing the energy.