Higgs Territory Continues To Shrink

PhysicsDavid writes "Announced this morning by Fermilab, the possible territory for the Higgs boson has shrunk even further. Combined results from the CDF and DZero experiments at the Tevatron have ruled out the existence of the Higgs with a mass between 160 and 170 GeV/c^2 with 95% confidence. At 90% confidence the Higgs is ruled out between about 157 and 185 GeV/c^2. Here is Fermilab's press release. If the Higgs is to be found at the lighter end of the currently allowed range of 114 GeV/c^2 to 185 GeV/c^2, its detection will be harder than at the heavier end due to the kinds of signals that the Large Hadron Collider and the Tevatron will see. Some physicists think that a lighter Higgs will be easier to spot at the Tevatron as the background processes which obscure the faint signal are not as prevalent in those experiments."

Comments

Re:Boring...

[Hordeking]

It isn't a fact at all in fact. I don't think we can say we know everything that is left to know about high energy physics except the big Higgs.

Nah, when they find H, they'll start looking for something else. That is, if they find H. There's no guarantee the model that predicts it is even correct. That's what experimental physics is all about. And usually the answer to your question is another question.

Easier vs. Harder

[n0mad6]

Its not a matter of "some thinking"-- the backgrounds that swamp a Higgs signal for a low mass Higgs are simply more prevalent at the energies of the LHC. The LHC makes up for that by being able to accumulate much more data than the Tevatron in a shorter amount of time. Of course, up to probably early next year, we at the Tevatron are in a superior position in that any data is greater than the zero the LHC will have accumulated.

Re:Easier vs. Harder

[geekoid]

"...any data is greater than the zero the LHC will have accumulated."

BURN!

Re:So ... worst-case scenario?

[n0mad6]

No, there's no guarantee a *Standard Model* Higgs Boson (which is what this search is) even exists. We know some mechanism exists for the symmetry that's broken between the Electromagnetic and Weak forces, but that doesn't necessarily have to be in the form of a standard model Higgs.

Wow!

[Bruce Perens]

This is so cool! I get a hadron just thinking about it :-)

Not boring!

[Roger W Moore]

The fact that this is all that's left of high energy physics says a lot.

The fact that you say this shows that you do not know a lot about high energy physics. Even if the Higgs does exist somewhere in the gap shown there is a huge problem trying to explain why it has such a small mass compared to the scale where gravity is important and the Standard Model has to break down. The chances of this occuring by pure chance are about the same as you winning the UK national lottery for about 5 weeks in a row - if you did that people would not be thinking 'wow you are incredibly lucky' they would be wondering how on earth you cheated the system. Similarly we need to figure out how the universe 'cheated' and made the Higgs mass so light.

There are also several other questions we need to solve: what is all the dark matter?, what is all the dark energy?, why is there no anti-matter in the Universe?, is the neutrino its own anti-particle?, how does quantum gravity work? etc. etc. You need to remember that so far all of science has been based on the 4% of the Universe made of atoms. 96% of the Universe is made of stuff we do not understand so thinking that the Higgs is all that is left is just crazy talk!

Re:Not boring!

[bcrowell]

The GP would have been more accurate to say something more limited, like referring to "high-energy physics from the LHC" rather the just "high-energy physics." The painful truth is that the LHC may end up finding essentially nothing of interest. It's possible that Fermilab will discover the Higgs, and absolutely nothing else that's very exciting will ever be found using the general type of accelerator and detector technology represented by these systems.

It's unlikely that physics in general will ever become a a completely understood subject. However, certain subfields of physics do go extinct. A century ago, a Nobel prize was awarded in physics for the invention of a certain type of lighthouse, and many grad students were still doing their PhD theses on subjects like the motion of a certain type of top on an inclined plane. More recently, low-energy nuclear structure physics is an example of a field that is arguably just a corpse, because the techniques used to study it (such as arrays of HPGe gamma-ray detectors) have reached the point of diminishing returns. It's quite plausible that the same kind of stagnation will now happen in high-energy accelerator physics as currently practiced.

[...] we need to figure out how the universe 'cheated' and made the Higgs mass so light. [...] There are also several other questions we need to solve: what is all the dark matter?, what is all the dark energy?, why is there no anti-matter in the Universe?, is the neutrino its own anti-particle?, how does quantum gravity work? etc. etc. You need to remember that so far all of science has been based on the 4% of the Universe made of atoms. 96% of the Universe is made of stuff we do not understand so thinking that the Higgs is all that is left is just crazy talk!

There's a strong possibility that all of these questions will turn out to be ones that can't be answered by LHC-style accelerator experiments. Some of them almost certainly can't be. For instance, the LHC doesn't come anywhere near the Plank energy scale, so there's virtually no chance that it will give any insight into quantum gravity. Dark matter and dark energy probably aren't going to give up their mysteries to particle accelerator experiments, either; that's more likely to happen with astronomy or cosmic ray observations. The only thing that was really guaranteed to happen at LHC energies was that there had to be either a Higgs mechanism or some other, similar mechanism occurring in that energy range, because the standard model sans Higgs is provably not self-consistent in this energy range.

Re:Not boring!

[Roger W Moore]

The GP would have been more accurate to say something more limited, like referring to "high-energy physics from the LHC"....It's possible that Fermilab will discover the Higgs

Not true. The Tevatron will not get to a 5 sigma discovery significance unless the LHC is delayed by several years more - the best they can hope for is 'evidence' of the Higgs, and event that is somewhat doubtful. However there are very good theoretical arguments that the LHC should be able to reach the Dark Matter scale as well as finding some evidence to explain the Higgs low mass. These are certainly not certainties but they are certainly well motivated possibilities.

There's a strong possibility that all of these questions will turn out to be ones that can't be answered by LHC-style accelerator experiments.....For instance, the LHC doesn't come anywhere near the Plank energy scale, so there's virtually no chance that it will give any insight into quantum gravity.

Sorry but you are also wrong here. There are extremely good arguments regarding thermal production of dark matter that suggest the particle cannot have more than ~1TeV mass unless it is not thermally produced. As such it is likely that we will produce it at the LHC and, if not the LHC, it could be produced in a higher energy accelerator since these recreate the conditions just after the Big Bang where the Dark Matter has to be produced (unless you believe a certain amount of Dark Matter was one of the starting conditions of the Big Bang).

Regarding the Planck scale you only think that it is unreachable because gravity is so weak. If there are extra dimensions of space then the Planck scale might only be a few TeV and then we can do quantum gravity at the LHC. Personally I find this far less likely than finding Dark Matter but it is certianly a possibility. Plus, while the neutrino questions need fixed target or underground experiments to answer these are still particle physics, and there is more to particle physics than the LHC!

The trap you seem to be falling into is that because there is no guarentee that something will be seen there is no chance of seeing it. While it is certainly true that there is no strong guarentee of seeing more than just the Higgs (or whatever else it might be) there are good theoretical motivations to expect to solve some of these other problems. You cannot say whether it is a strong or weak possibility because we do not know enough to assign any meaningful chance. All we can say is that there is a possibility and there is some good theoretical motivation for such a possibility based on reasonable assumptions. Sometimes those assumptions can of course be wrong...but not always in a 'bad' way.

Best case scenario!

[Roger W Moore]

What are the implications for NOT finding the Hggs Boson?

Not finding the Higgs is the BEST scenario because it means that what we think we know is all wrong and that means that the Universe does things a different way and once we figure out what that is there will be a whole realm of new and exciting possibilities to explain some of the other stuff that we do not understand.

What is great about the LHC is that we have to start seeing evidence either for either the Higgs or something else. The Standard Model literally breaks down and starts to make no sense at all arounf 1TeV in energy: without the Higgs it predicts certain interactions will happen more than 100% of the time! Hence we either have to see the Higgs or something else if the Higgs does not exist.

Re:Boring...

[vadim_t]

How the hell are we supposed to know?

When electricity was discovered, did anybody imagine computers or even electric motors or light bulbs?

When Babbagge was working on his Difference Engine, did he talk about PCs or the Internet to his investors?

When Hero of Alexandria made his Aeropile in the 1st Century, it was just a toy that was used to open temple doors. Only a thousand years later the steam turbine was found to have practical uses.

Nobody probably expected CDs as an application for a laser. Back when one was made probably the best justification for laser research would have been spectroscopy and interferometry, applications that are obscure and hard to understand to normal people.

I imagine that the discovery will initially confirm or disprove some theories, but not have much practical application at first. But who knows if it'll lead to hovercars some years later, or turn out to be of interest only in specialized areas of physics research.