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Based on this article

the accelerator has smashed together approximately 16 million billion protons since 2015, when it reached its current energy of 13 trillion electron volts. Planned improvements before the machine restarts in 2021 will bring the energy up to 14 trillion electron volts

I'm all for improvements and there are probably limits to how fast they can get the protons moving based on the size of the circular tunnel, so I'm all for the upgrade, but it still seems to me that going from 13 to 14 is a very narrow window to find something new.

My question is whether there's any hints or good reasons to believe that the increase to 14 trillion electron volts and/or increasing the number of proton-proton collisions is expected to discover something new, or if they've reached close to the limit of what CERN is likely to discover and perhaps start discussions of building a bigger one?

My guess is the latter (more collisions) might find something, but the increase from 13 to 14 is a narrow window and probably not.

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    $\begingroup$ One of the purposes of any experiment is not just to look for something you expect, but to make sure there isn't anything you don't expect e.g. even if you expected nothing you still have to check there is nothing. $\endgroup$ – StephenG Jan 1 '19 at 11:29
  • $\begingroup$ @StephenG That's a very good point. It makes a lot of sense to test their way up through the range, which obviously includes the 13 to 14 range. That leads me to another question, what the maximum ev collision that CERN can generate is, but I'll do some research on that before I ask. The article above implies that 14 trillion might be around to the limit, but it doesn't say that directly. $\endgroup$ – userLTK Jan 1 '19 at 22:28
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    $\begingroup$ 14 TeV is the design energy, which hasn't yet been reached due to a number of setbacks. Running at lower energy wasn't really deliberate, and there's no real advantage in doing it for the majority of the physics programme: particularly direct searches for exotic particles. The 'ultimate' collision energy that the LHC might be capable of (without replacing all the dipole magnets) is 15 TeV, but that requires some work. $\endgroup$ – dukwon Jan 2 '19 at 1:17
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    $\begingroup$ Maybe something is unexpected to be found. $\endgroup$ – my2cts Jan 16 '19 at 12:55
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but it still seems to me that going from 13 to 14 is a very narrow window to find something new.

It is normal for people when units go from GeV to TeV , just a little letter change, to see it as a small change, but the difference it makes to capabilities can be a step function, because 1000 GeV make a TeV , and any particles we have seen up to now are counted in GeV at the moment.

Let me give you a real life example:

LEP, the e+e- collider in the same tunnel:

The collider's energy eventually topped 209 GeV in 2000.

I was involved in the almost discovery of the Higgs at the time, with the ALEPH experiment:

Near the end of the scheduled run time, data suggested tantalizing but inconclusive hints that the Higgs particle of a mass around 115 GeV might have been observed, a sort of Holy Grail of current high-energy physics. The run-time was extended for a few months, to no avail. The strength of the signal remained at 1.7 standard deviations which translates to the 91% confidence level, much less than the confidence expected by particle physicists to claim a discovery

If the colliding energy could have gone maybe to 220 GeV the Higgs might have been discovered early in the 2000sands, as we were really looking for it.

Maybe the five events we saw were connected with the existence of the Higgs , probably not ( as the Higgs is supposed to have a width of 4MeV), but for sure an increase in beam energy would have revealed the real Higgs.

One must not forget that standard models are just that, mathematical models , not molders of nature, and maybe nature has unexpected surprises around the corner.For example, it was better fitted with a new emergent quark model, than with the famous parton model of Feynman, dominant at that time.

My question is whether there's any hints or good reasons to believe that the increase to 14 trillion electron volts and/or increasing the number of proton-proton collisions is expected to discover something new,

So as I argue above, there were no hints that the real Higgs would be just 10 GeV larger in mass than LEP reached. The LHC was planned as the next window in energy for discovering what was there, with a map from theories flexible enough where it could have been at 1 TeV instead of 125. And there are a lot of predictions for supersymmetric or even GUTS predictions for heavy particles, which have not materialized, and are sought as the window of accessible masses enlarges. There is nothing to exclude that the next new resonance is only a few hundreds of GeV away, and the higher energy will reveal it.

That is what experimenting is about. Experimentalists should always use models as medieval maps: here there be dragons.

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    $\begingroup$ I'm not sure you're answering the question at all. Perhpas it would have made more sense to argue in this way before the construction of the LHC. But the question is about a not-so-significant increase in energy (and luminosity, though that can be significant with time). Can't we say with large significance that we don't expect any 5sigma discovery ... given the fact that there's not a single little 3sigma fluctuation right now that could grow? Just by extrapolation? $\endgroup$ – xi45 Jan 16 '19 at 10:24
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    $\begingroup$ @xi45 you are prophesizing the model of non existing data. When the psi was discovered en.wikipedia.org/wiki/J/psi_meson nobody expected how sharp it would be from the previous data and models. In the example of the ALEPH higgs the sum of all experiments gave no fluctuations, and it was just a few gev higher in energy. There is only the map of existing theories and the expectation that something new will be over the horizon, which need not be in TeV distance is all I am saying. $\endgroup$ – anna v Jan 16 '19 at 10:39

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