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Higgs mass constrained (Fermilab 26 July report)


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"The bottom line is that CDF and D0 can now exclude (at 95% confidence level) the existence of a Standard Model Higgs particle over a fairly wide mass range in the higher mass part of the expected region: from 158 to 175 GeV. If the SM Higgs exists, it appears highly likely that it is in the region between 114 GeV (the LEP limit) and 158 GeV."

http://www.math.columbia.edu/~woit/wordpress/?p=3073 New Higgs Results from the Tevatron

 

Press release from Fermilab:

http://www.fnal.gov/pub/presspass/press_releases/Higgs-mass-constraints-20100726.html

 

So either the Higgs of the Standard Model does not exist or its mass is probably somewhere in the range of 114-158 GeV. That seems like progress.

The Fermilab ring collider is now quite old but still producing results. Has not, as yet, been made totally redundant by the new LHC.

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...So either the Higgs of the Standard Model does not exist or its mass is probably somewhere in the range of 114-158 GeV....

 

The Higgs boson was introduced as a patch of an otherwise massless gauge theory, roughly speaking. It is not a God's particle. I will not be surprised if it does not exist.

 

The "gauge principle" is not physical at all either. It does not come alone in QED but with renormalizations. No wonder if such a way of theory "development" fails. I am for a phenomenological way, with a deep physical phenomenology though.

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This is something I've somewhat been expecting. Looks like its about time for physicists to start thinking up new ideas again!

Why so?

 

It [the gauge principle] does not come alone in QED but with renormalizations.

I'm not quite getting your point here. We probably agree that the electromagnetic field exists and interacts with charged particles. So what is special about gauge invariance?

 

No wonder if such a way of theory "development" fails.
The particle physicists tend to consider their Standard Model a great success and are very proud of it. Where do you see the big fail?
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I'm not quite getting your point here. We probably agree that the electromagnetic field exists and interacts with charged particles. So what is special about gauge invariance?

Yes, we agree, no doubt. If we speak of E and B, there is no even a notion of gauge invariance, is there? So which physics may be encompassed with the gauge principle?

 

The particle physicists tend to consider their Standard Model a great success and are very proud of it. Where do you see the big fail?

It is a subject of another thread. I just wanted to say here that there are many other ways of constructing theories, apart from gauge (unphysical) principle.

Edited by Bob_for_short
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This was to be expected, since our electroweak precision tests were already indicate that it should be lighter.

 

Without the LEP constraint, the precision tests tell us the Higgs mass would have to be 80+30-23GeV.

 

With the LEP constraint this changes to 119+14-4GeV.

 

(Note that these are the figures not including the new data.)

 

So the new exclusion is not surprising (though it is interesting and worthwhile).

Edited by Severian
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There is no problem with renormalization, but there is an issue of naturalness, often called the hierarchy problem. The divergence behaves like the cut-off squared, and although the divergence can still be subtracted off as usual, it means that the bare mass has to be fine-tuned to get the physical mass right. Solving this is one of the principle motivations for supersymmetry,

Edited by Severian
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There is no problem with renormalization, but there is an issue of naturalness, often called the hierarchy problem. The divergence behaves like the cut-off squared, and although the divergence can still be subtracted off as usual, it means that the bare mass has to be fine-tuned to get the physical mass right. Solving this is one of the principle motivations for supersymmetry...

Bravo, you repeated Zinn-Justin's words! But whether the supersymmetry is observed physically or it is just another patch of a nice theory?

Edited by Bob_for_short
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That's why we are building the LHC - to find out.

 

I used to work with supersymmtries and supergravity in particular when I was a student (1979-80). Supergravity was motivated by canceling infinities in some loops, not by any physical observations. I think nothing has changed since.

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At the risk of going off topic the gauge principle seems to me to be very natural. It basically says that "physics should not depend on exactly how we chose to present it".

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I think nothing has changed since.

 

I think that is a fair comment. Progress is very slow, especially when you need to reach such high energies. But I think you can see from the Higgs mass limits that we are now homing in on exciting stuff.

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I think that is a fair comment. Progress is very slow, especially when you need to reach such high energies. But I think you can see from the Higgs mass limits that we are now homing in on exciting stuff.

I am afraid the excitement may well turn into disappointment with SM when no signs of Higgs are observed. To me Higgs "mechanism" is a highly theoretical (speculative) construction, not phenomenological one (in particle physics at least). I think the right direction is to proceed from non-elementary, permanently coupled things and they are not described with gauge approach.

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I am afraid the excitement may well turn into disappointment with SM when no signs of Higgs are observed.

 

I think if "no signs of Higgs are observed" everyone will get very excited because our theory will break down. The SM without a Higgs boson would violate unitarity, and this would be visible in WW scattering, causing the cross-section to rise too fast with energy. Since it obviously can't really violate unitarity (we can't have probabilities greater than one) there would need to be a mechanism to slow down the rise (the Higgs boson previously took this role). One possibility would be W-bosons that feel the strong interaction at higher energies, which would be quite revolutionary.

 

To me Higgs "mechanism" is a highly theoretical (speculative) construction, not phenomenological one (in particle physics at least).

 

I disagree. It is very phenomenological. We even have indirect evidence for the Higgs boson, since it should contribute to the scattering of other particles by being present in loops. Indeed we find that the SM without the Higgs boson is a poor fit compared to the SM with the Higgs boson, and this even allows us to place limits on the Higgs mass that I mentioned in an earlier post.

Edited by Severian
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I think if "no signs of Higgs are observed" everyone will get very excited because our theory will break down.

 

I agree that all particle physicists will be very exited, but what about the general public?

 

In the financial crisis we are in now, coupled with scaremongering over the LHC, as well as low confidence and suspicion of science via climate change issues, GM, stem cell research etc not finding the Higgs could be a nightmare. Sections of the public could see it as scientists don't have a clue what they are talking about and are only interested in getting money from governments for their own personal gain. We don't want people to think that the Higgs is just a scam to keep scientists employed. I have heard that said, by a nut job conspiracy theorist mind you.

 

Maybe I over worry...

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I agree that all particle physicists will be very exited, but what about the general public?

 

I think the public like revolutions. If we find something unexpected, I think they will be happy.

 

I would worry more about what would happen if we had either of the following scenarios:

 

1. No Higgs boson, but the WW scattering cross section turns over and we can't find a reason. (This is obviously very exciting for physicists but convincing the public it is might be difficult.)

 

2. We find the SM Higgs boson and nothing else. Critics of future research would say "Physics is done".

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I all ways worry about how effective communication with the general public really can be, especially when asking for lots of money. Your situations 1) and 2) at the moment both seem plausible. I hope whatever happens at the LHC the public engagement will be done carefully.

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I think if "no signs of Higgs are observed" everyone will get very excited because our theory will break down. The SM without a Higgs boson would violate unitarity, and this would be visible in WW scattering, causing the cross-section to rise too fast with energy. Since it obviously can't really violate unitarity (we can't have probabilities greater than one) there would need to be a mechanism to slow down the rise (the Higgs boson previously took this role). One possibility would be W-bosons that feel the strong interaction at higher energies, which would be quite revolutionary.

Unfortunately we see the things via pattern of our theories. And our theories have tendencies to be TOE because it is our aspiration and ambition. If Higgs does not exist, that will mean W-boson and all that do not exist either, at least in a way it was meant to be - as gauge fields.

 

I disagree. It is very phenomenological. We even have indirect evidence for the Higgs boson, since it should contribute to the scattering of other particles by being present in loops. Indeed we find that the SM without the Higgs boson is a poor fit compared to the SM with the Higgs boson, and this even allows us to place limits on the Higgs mass that I mentioned in an earlier post.

When a model is complicated and contains many "free" parameters, some experimental data can be "predicted" (fitted) and this creates an illusion that the model is right. With years we become hostages of our beliefs in our models and close eyes on obvious failures.

 

For example, the idea of elementarity is contradictory to the idea of interaction because there are "elementary" things that are in permanent interaction (non separable). It is better to speak of a compound complex system with elementary excitations rather than of elementary and separable particles (electron and photon, quark and gluon, etc.). The corresponding mathematics is known but different from "gauge" concept. So absence of Higgs will signify more then just new properties of W-boson at high energies, I think.

Edited by Bob_for_short
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