Friday, January 04, 2008

The Higgs Mass

In the Standard Model of particle physics, all particles are massless, unless they interact with a special field, called the Higgs field. We know of course that electrons and quarks and Z bosons have masses, so, taking the Standard Model at face value, the Higgs field should be real, and there should be particles associated with the Higgs field, the Higgs bosons. The Higgs boson in the Standard Model is expected to have a high mass, which, however, cannot be predicted within the current theoretical framework. Thus, the Higgs mass is a parameter that has to be determined by experiment.

As it comes out, no experiment so far has seen direct traces of the Higgs boson. This should be not too big a deception, since the Higgs mass is big - and, as it seems, too high for the Higgs to be produced in today's particle colliders. However, there are indirect means to estimate a probable range for the mass of the Higgs boson. The current expectations about the Higgs mass are encoded in the following figure:

A least-square fit to a number of precisely known data in electroweak physics using the Standard Model as theoretical framework and the Higgs mass as a free parameter yields an expectation value for the Higgs mass around the minimum of the parabola. [Source: Precision Electroweak Measurements and Constraints on the Standard Model by the LEP Collaborations and the LEP Electroweak Working Group, arXiv: 0712.0929v2, Figure 5.]

For while the Higgs mass could not be measured directly so far, it's a parameter which, within the framework of the Standard Model, influences all kinds of measurable quantities. An example of this reasoning is the analysis of the Z pole, the resonance peak of the Z boson in the cross section for the production of particles in electron-positron annihilation. There are many details of the Z pole that have been determined very precisely in experiment, for example the width, shape, asymmetry, or background slope - about a dozen or so parameters altogether. On the other hand, all these measured parameters can also be calculated within the Standard Model. In these calculations, there are five quantities that have to be assumed as input parameters: the coupling constants of QED and QCD at the Z pole, α(m²Z) and αs(m²Z), the masses of the Z boson and the top quark, and the Higgs mass.

Now, one can search for those values of these five parameters that reproduce best the data measured in experiment. To do so, one minimises the squares of the differences between measured data and calculated values, weighted by the experimental error. This quantity to be minimised as a function of the free parameters is called χ² ("chi-square"). It is given in general by the formula


where Xi and &sigmai are the experimental data and their respective errors, while the fi are the theoretical predictions, depending on the free parameters p1 ... pN. In this case, there are five free parameters. Fixing the values for the coupling constants and the Z and top quark masses (parameters p1 ... p4) at their best fit values, one can then check how χ² changes if the Higgs mass (parameter p5) is varied.

This yields the plot above: The parabolic curves show, as a function of the Higgs mass mH, the corresponding χ² above its minimum at a mass of about 80 GeV/c². Note that the Higgs mass is shown on a logarithmic scale. The blue band represents theoretical uncertainties within the Standard Model calculations, and the dashed and dotted parabolas correspond to a different parametrisation for the running of the coupling constant α and the inclusion of more data into the fit, respectively. The area marked in yellow corresponds to Higgs masses which can be excluded by available experimental data: A Higgs boson with a mass below 114.4 GeV/c² would have been discovered at the Large Electron-Positron Collider LEP at CERN before it was shut down to give place for the construction of the Large Hadron Collider LHC.

Now, supposing that the Standard Model is the correct theory to describe electroweak data such as the Z pole, the fitting procedure predicts the Higgs mass to be around the minimum of the χ² curve. Together with the experimentally excluded mass range, this yields an upper limit on the Higgs mass of 182 GeV/c² at a 95% confidence level, meaning that if the Standard Model is right, there is a 95% probability that the mass of the Higgs boson is between 114 and 182 GeV/c².

This is a predictions that will be easy to check checked at the LHC.




The Higgs mass plot is taken from the preprint Precision Electroweak Measurements and Constraints on the Standard Model by the The LEP Collaborations: ALEPH Collaboration, DELPHI Collaboration, L3 Collaboration, OPAL Collaboration, the LEP Electroweak Working Group, arXiv: 0712.0929v2. More plots and details can be found on the web site of The LEP Electroweak Working Group (LEP EWWG), which "combines the measurements of the four LEP experiments ALEPH, DELPHI, L3 and OPAL on electroweak observables, such as cross sections, masses and various couplings of the heavy electroweak gauge bosons, properly taking into account the common systematic uncertainties" to confront "theories such as the Standard Model of particle physics."

Details of the fitting procedure (Which data have been fitted, actually? What are the fitting parameters?) are described in Section 8 (see specifically 8.5 and 8.6) of the paper Precision Electroweak Measurements on the Z Resonance by the ALEPH Collaboration, the DELPHI Collaboration, the L3 Collaboration, the OPAL Collaboration, the SLD Collaboration, the LEP Electroweak Working Group, the SLD electroweak, heavy flavour groups, arXiv:hep-ex/0509008v3, Physics Reports 427 (2006) 257.

χ² minimisation is done using the software package MINUIT. Different minimisation techniques and the χ² minimisation are described in a tutorial (PDF file).

Results of the direct Higgs search at CERN before the decommission of the LEP which have established the lower bound for the Higgs mass at 114.4 GeV/c² are described in Search for the Standard Model Higgs Boson at LEP by G. Abbiendi, et al., arXiv: hep-ex/0306033v1, Phys. Lett. B565 (2003) 61-75.

Physics World has a portrait of Peter Higgs, after whom the Higgs field has its name.




This post is a latecomer to our A Plottl A Day series.

37 comments:

Anonymous said...

The upper limit on the Higgs mass from the electro weak precision data is shaky territory. First off, b/c the value is quite sensitive to experimental adjustements of various values and their uncertainties. The value has already changed noticeably in the last 7 years or so.

Secondly, b/c its hard to believe that the SM exists and absolutely *nothing* else. Of course all bets are off under that circumstance.

Regardless, more fundamental theory bounds (triviality, stability, unitarity, etc) places an upper limit on typical SM higgs scenarios firmly within LHC ranges, so its a moot point.

Of course the leading candidates for beyond the SM physics (SuSY etc) tend to predict or strongly favor light Higgs.

-Haelfix

Phil Warnell said...

Hi Bee and Stefan,

Has the higgs field not only just been tied to mass but also our inflationary expansion theories? That is, the potential energy connected with this field is thought to be what contributed to the early universes exponential initial expansion. With the current observed expansion rate being larger then first anticipated, has this had any affect on the higgs boson energy calculation? This current expansion rate in present thinking is assigned to what is referred to as dark energy (as to say that we are not sure what it is). Could any of this be explained by residual potential energy still to be found in the higgs field? If so, then would this still leave the energy range of the higgs particle within what’s achievable by the LHC?

muon said...

Hi,

this is a very nice explanation of the famous "blue-band" plot, and I am happy to see it as one of your excellent "A Plot a Day" series. :)

Your very last statement is not quite true, however. Discoverying a standard model-like Higgs boson will not be easy at the LHC if its mass is below 130 GeV. In a sentence: the backgrounds at lower masses are much worse than at higher masses, so a greater integrated luminisity is required to establish a significant signal. The details are debatable, and researchers at ATLAS and CMS are working hard to find better search strategies, but it is clear that a Higgs boson of mass 160 GeV would show up much quicker than one with mass 115 GeV.

As it turns out, searches at the Tevatron cover the range below 130 GeV most successfully, so there is a nice complementarity in the capabilities of the experiments at both facilities, in principle.

I am planning to explore this aspect of LHC searches in future posts at my blog - it is great to have your post as the perfect starting point. :)

Michael

Bee said...

Hi Phil:

There are several people playing around with the ideas you mention, but afaik nothing very convincing has come out of it so far. The Higgs is a scalar field that acquires a non-zero vacuum expectation value, and it is tempting trying to connect it to the mysterious vacuum energy, the inflaton, or the cosmological constant respectively, instead of trying to explain them by separate features. I would agree that there is something about the vacuum that we don't quite understand but I find it very unlikely that some 'residual point energy' explains these features 'naturally', given that this residuum would have to be tiny but nonzero, the usual cc problem, and all tracking solutions for dark energy I find similarly constructed and unconvincing - so far that is.

Best,

B.

Neil' said...

Has anyone played with what fraction of the Planck mass the Higgs mass should be? The PM is the one mass we can construct from other parameters (not counting factors about the universe as a whole) so the ratio should be interesting I presume.

Bee said...

Hi Neil':

See here Fifth crime, point two. Best,

B.

Uncle Al said...

The simple, direct path is "no Higgs." The Higgs mechanism is a desperate attempt to salvage the Standard Model from being a heuristic. Quantum gravitation is also a disaster. As we more closely examine our theories toward unification, convenient but defective constructions will burst at the seams.

Grab a second bucket. Theory is internally OK. Founding postulates are set to weep.

stefan said...

Hi Haelfix,

thanks for your comment! Yeah, if data and their error bars change, the χ² estimate for the Higgs mass changes also... The LEP EW group has the "blue band" plot for the Higgs mass back to 1997 on its site - it seems to me that the upper limit from this estimate has mainly been dropping since then?

As for Beyond the SM, SUSY etc, can this least-square fit business be carried over to these theories, or are there just to many parameters then to make any serious attempts to fit the electroweak data? Do you know details about this, and maybe a reference?

Best, Stefan

stefan said...

Hi Michael,


thanks that you like the post, and that we didn't get it too wrong ;-)... The "blue band plot" had featured prominently on our list for the "plottl of the day" right from the beginning, but since we both had been not so sure about what is actually plotted there, we had to have a closer look at the literature first, and so it was postponed, and postponed...

I have changed the last sentence of the post about the LHC, thanks for the correction! Being not an experimentalist myself, it's difficult to judge the actual amount of hard work to extract the Higgs signal from the raw data. Moreover, naively I would have thought that the Higgs is the easier to detect the lower its mass.

What is this background that keeps dropping at higher energies? Is it because the cross section for jet production in proton-antiproton collisions drops quite strong with energy?

BTW, what will happen if there is no Higgs? I've heard about ideas for Higgsless Theories, but don't know any details. Is there any "Plan B" to check these theories in the experiments if the Higgs does not show up at the LHC?


Best, Stefan

Dick said...

There are lots of scalar fields (e.g., elevation above sea level), but no known scalar particles. Suppose the Higgs field exists but is not a particle field (e.g., a fluctuation in the elevation profile is not what we usually think of as a particle). Will the experiments planned for the LHC find it? If not, then we can't conclude that it doesn't exist just because the LHC sees zero signal.

Anonymous said...

Hi Stefan, the answer is a limited yes. Under some circumstances you can still use that general gist with say (example) a few extra heavy particles included. People use things called the S-T-U formalism to conveniently paramatrize those sorts of ideas (Spires search for Peskin + Takeuchi).

These parameters are sensitive to the radiative corrections in W and Z propagators from new physics and are useful in some *limited* circumstances.

For the more complicated leading models, theres just too many unknown parameters for the use of that ew data, and usually theory provides better bounds anyway (eg naturalness makes the MSSM prefer light higgs, hopefully not much larger than 115 GEV)
~Haelfix

Phil Warnell said...

Hi Bee,

Thanks for the reply. It is at least nice to know that a few real physicists come up with the same crazy notions that I have at times. I also understand that you say that so far it hasn’t worked out and doesn’t look promising. With that now understood, if the higg’s field did have this additional (residual) energy would it have any significant effect on the plot values you indicate. It seems that with this dark energy component being so much larger then what was originally expected that if such a notion were true it potentially could set the anticipated values higher. What makes me think that this could be a possibility relates to the surprise we’ve had in the case of neutrino energies over the last several years. That’s with them morphing from one type to the other (oscillating potential). Perhaps the higg’s field also has an oscillating potential, yet rather over very large time spans. The consequence of this is that expansion rates would also vary over time and reciprocally so would the perceived energy content. Then again this may simply relate to dark energy and dark matter being described as constituting 96% of the universe. That is perhaps in being part of the remaining 4% has left me feeling somewhat insecure :-)

a quantum diaries survivor said...

Hi Stefan,

I wish to pay a tribute to your nice post here and answer the question you pose about the counter-intuitive trend of discovery reach at the LHC versus Higgs mass (for a given integrated luminosity), waiting for Michael's posts on the Higgs.

The problem is that as the Higgs mass changes, the mixture of possible final states it decays into changes dramatically. So, while at 160 GeV the Higgs is best sought in its decay to a pair of real W bosons (which weigh 80 GeV each), and in that case backgrounds are small because the signature is very distinctive, at 115 GeV the Higgs mostly decays to a pair of b-quark jets. Seeing a bump in the jet-jet mass distribution is utterly out of the question because in that case backgrounds are HUGE. So one has to rely on very rare decays such as H->gamma gamma - which still is plagued by large backgrounds.

The Higgs search is not one, but ten different analyses, depending on the unknown parameter M_h. Each analysis has its own problems. The higher the Higgs mass, the smaller the number of produced events; but as M_h changes, the signature varies from invisible to highly distinctive. Above 180 GeV, a Higgs can be seen with no trouble in the ZZ final state, when four muons are a gold-plated signature. It is not by chance that CMS was originally conceived as a compact muon solenoid: muons are all you need, at high mass, for the Higgs.

Cheers,
T.

Phil Warnell said...

Hi T,

That was an enlightening explanation as to the complexities involved in the search of the higg’s boson. I also wait with great anticipation to what you and the others may find. I am always impressed that so much can be discovered in such a complex process. That is, to use the old analogy to compare what you do as to smashing a couple of pianos into each other and by observing in an instant what flies out that one learn what they may be made of and subsequently how they work. One thing it has given me is a different perspective on when I observe a child smashing something intricate and delicate against the wall. I used to think it was simply an act of bad behavior. Now I understand it may be their instinctive first application of this methodology in fundamental research :-)

Best,

Phil

Phil Warnell said...

Hi Bee and Stefan,

Not to be a pest, yet in looking at the parabola you supplied I’m curious if the slope increases exponentially (vertically) or that it approaches linear (straight line) characteristics? Of course this in the effort of my attempt to understand what the likelihood of being able to construct a collider that would find the higgs in the unfortunate event that the current machine fail.

Best,

Phil

Mark said...

Usually, nature has her way. If the Higg does exist it is probably sits in the huge background cloud that would be at 115 GeV. So far she has not made it easy for us and for all the money thrown at the problem it will unlikely be presented on an easy "golden platter" (or grail) for our ecstasy.

stefan said...

Hi haelfix,


thanks for the explanations and for pointing out to me the STU paramatrisation and the Peskin & Takeuchi papers!

Searching for these, I stumbled upon this discussion on what's behind the precision electroweak fits that are discussed so often at the Fermilab web site, which seems to be agood start for further reading...


Hi Tommaso,

thanks a lot for your comment - that's a very plausible explanation! I wasn't aware that the Higgs search is that complicated...


Best regards, Stefan

Bee said...

Hi Phil,

No, the value of the CC is about 15 orders of magnitude below the vacuum expectation value (vev)of the Higgs. It is irrelevant if you add this to the above estimate. That gap between the scales actually is a big part of the problem. But either way, I think you are mixing up two different issues here. The relevant thing about the Higgs isn't only that its vev is non-zero, but that it couples to the matter fields we know, causing a mass-like term after symmetry breaking - it does so in a setting entirely without any gravitational field. The problem with the CC is that there is 'something' (that can be interpreted as a residuum of quantum vacuum energy, but not necessarily) that couples to the gravitational field. Best,

B.

Bee said...

Hi Tommaso, Mark, Haelfix and Muon:

Thanks for your interesting comments!

I was wondering what you think about this scenario:

The Higgs Decay Width in Multi-Scalar Doublet Models

arXiv: 0709.1505 [hep-ph]

Where the Higgs decay looks significantly different, and wouldn't show up at the LHC as expected. I am actually not sure how artificial this construction is - made for the case 'IF' - or whether it is natural in some sense? Best,

B.

Mark A. Thomas said...

I am really ignorant of the Higgs physics processes but does the paper suggests that we need to know the new physics (what they say it predicts) before we recognize what is going to be a very difficult signature? And does this suggest that if the Higgs is light we may have already seen the Higgs at say the Tevatron buried in the data.

muon said...

Hi,

I'm happy to see this discussion continue!

Tommaso gave a nice answer to Stefan's question, and I won't expand upon it here.

Concerning the non-observation of a Higgs boson - that would be extremely important. First, the standard model says there must be a Higgs boson with certain properties, and the LHC definitely will see it, if it exists, given enough time (ie, integrated luminosity). So ruling out a SM-like Higgs boson will rule out the SM, and much of low-energy supersymmetry, too. Second, a scalar field is basic to electro-weak symmetry breaking in nearly all models of physics beyond the SM (the scalar fields may differ in their specific properties, though), so the non-observation of any kind of Higgs-like particle means that we really don't understand the origin of particle masses - that our current theoretical notions are really wrong. It would be like finding out that QED fails to give the right answer for hyper-fine splitting. Finally, the non-observation of a Higgs boson at the LHC would overthrow the current culture of theory guiding experiment - it would be as almost as surprising as the discovery of the J/psi (though I admit that one can't really place the non-observation of an expected particle at the same level as the discovery of a real one).

There are theoretical scenarios in which give electro-weak symmetry breaking without a fundamental scalar (Higgs) field, or which give one with properties that make it impossible to observe at the LHC. In this sense the cat-and-mouse game of experiment and theory can continue even if no Higgs boson is observed. But the tone and basis for the particle physics discussions will change, for sure. I do know people who hope for precisely this outcome...

If no Higgs signal is seen at the LHC, including not in any of the standard variants, then people will put a lot of effort into the more exotic scenarios, such as a light scalar missed so far at the Tevatron (or even LEP). By the way, a high-energy e+e- collider is able to find a Higgs boson independently of how it decays, which is one reason why many people are enthusiastic about the ILC. Alas, prospects for building an ILC seem very dim right now.

Stefan and Bee, I really like your concept of the Plottl a Day - maybe you could continue this at the level of a Plottle a month or something like that?

-- Michael

Phil Warnell said...

Hi Bee,

Thanks again for the response. This clears things up somewhat. Are you in essence saying that the higgs field (not boson) is oblivious to the gravitational one or again do I have something wrong? It seems strange that a field that is supposed to be responsible for mass is not coupled to the field that reacts to part of what it is responsible for. So that gravity is not actually reacting to mass but rather the total energy content of the particles including that of the higgs. That is to say that the higgs only serves as a marker (so to speak) for a certain manifested form of this total energy content. Then to continue this line, if all the particles in the universe (excluding the higgs boson) were converted to energy (photons), then the only way the higgs boson would be evident is through its reaction to gravity (and of course the affects demonstrated by its own mass). In a way though it does serve to demonstrate why gravity makes no distinction between mass and energy. That is of course except perhaps for that dark (energy) stuff which it does seem oblivious to. It is not to wonder then why your coffee bills run so high 

Best,

Phil

Bee said...

Hi Phil,

No, that was not what I said. I didn't say the Higgs is oblivious of gravity, I said the mass generation via the Higgs-mechanism doesn't have anything to do with the presence or absence of gravity (at least in the standard picture). The Higgs couples to gravity as everything else does. Regarding the vacuum energy problem in quantum field theories, you might find this or this helpful. What I was trying to say is that one shouldn't confuse the one with the other: the mass generation through the Higgs, and the tiny but non-zero gravitational vacuum energy that we have observational evidence for. Best,

B.

Phil Warnell said...

Hi Bee,

Sorry about me getting it all wrong again. How do you put up with us novices? Anyway, as you advised I will look over the material you suggest and let you get back to your chalk board.

Best,

Phil

Bee said...

Hi Phil: No need to apologize. Best - B.

stefan said...

Hi Michael,

thanks again for the enlightening comments!

Actually, the idea of the "plottl a month" is not a bad one, we will think about that! It's good to hear that some of our readers have appreciated and enjoyed the series so far :-).

Best, Stefan

Phil Warnell said...

Hi Bee,

Thanks so much for pointing to those two previous posts that you put up. Some of this I am aware of and yet some indeed is new to me. The confusion resultant of the theoretical expectation of the vacuum energy and the observed I found particularly enlightening. It also serves to make it clear (for me) that even if the higgs is discover (despite the energy level) that this will give little guidance to theorists in terms of a unified theory; beyond of course that this would further reinforce that the standard model will have to be accommodated within such a scheme. I continue to be impressed by your ability to express yourself in a way that can be understood by a larger sector of those who may be interested, without loosing the required accuracy of what’s being explained. Strangely enough this benefits the professional as often it does the novices of the world. The most poignant example of this is David Albert’s book, Quantum Mechanics and Experience. Albert in this book explains the topic in a straight forward manner and then proceeds to sort out the chalk from the cheese, so to speak. The two articles you posted accomplished the same in terms of the subject matter you were covering.

With all this said, have you ever entertained the thought of applying for the Director of Outreach for Perimeter? I suppose your immediate reaction is that it would lead you away from research. I wonder though, have you considered that in the act of clarifying things for others that this could also serve to expand and solidify the central issues for yourself. That is, besides the technical difficulties of developing a TOE, the other challenge being that as a consequence of the scope of the problem the solution must account for everything that has been firmly established already. This is perhaps where the two streams meet. One thing for sure, that from the communicative, clarity and the zeal for the subject aspects, you have demonstrated to be a worthy candidate for such a position.

Regards,

Phil

Low Math, Meekly Interacting said...

Thanks for another wonderful post!

A question: It appears that the VEV of the Higgs field (which seems to have a very precise value from theory) and the mass of the Higgs boson have little to do with one another, besides the fact that nothing would have mass without a non-zero VEV.

Could you elaborate a little (i.e., hand-wave enough so that my head doesn't explode) on where this VEV comes from, and what, if any, other relation to the Higgs mass it might have beyond its non-zero-ness?

Thanks so much!

Bee said...

Hi Low Math:

Theoretically, these two values have nothing to do with each other. In the Mexican hat potential for the Higgs (μ^2 φ^2 + λ φ^4) there are two free parameters. They are related to the VEV and mass as v = \sqrt(- μ^2/λ), and M_h= v^2 λ (up to factors of order one), but they remain two independent parameters. v can be expressed through the (measured) parameters of the EW model. The mass of the Higgs boson is constrained by a variety of other experimental data, as well as theoretical consideration. Best,

B.

Alan Gillis said...

Hi Bee and Stephan,

Perhaps the Higgs question is a moot one. When astrophysicists suggest that 96% of the Universe is dark energy and dark matter, with no provision in the Standard Model for them, what's the use of a $10 billion experiment at the LHC, largely focused on finding the Higgs?

Certainly we're going to find something or nothing that can be analyzed. Don't forget that CERN is filtering its data to managable proportions, from a stack of CDs to the Moon for a year, to some thousands of DVD's.

There are also the safety issues. Can anything so gargantuan and complex, whether or not it produces black holes or strangelets, be without risk, when ATLAS is a stone's throw from the Geneva Airport? I once worked at the largest ever cryogenic facility, an LNG (Liquid Natural Gas) plant and we were in an emergency situation about every 2 weeks. But if anything really went wrong, all we'd wind up doing is blowing up about 2 billion dollars and a lovely stretch of sandy beach in Algeria.

On the physics side, I'd like to hear what you think of possible dangers at the LHC. The point is the unparalled energies involved, 14 TeV for the proton collisions, and 1,150 TeV for the lead ion collisions in the ALICE experiment. CERN plays down the energy used, and points to the miniscule amounts of hadrons employed. But energy does transform into matter under the conditions imposed by the LHC. The former LEP employed only 200 GeV collision energies and the RHIC, the most powerful collider today, 1.9 TeV.

For another view of the LHC and big science, see my writer's blog, http://bigsciencenews.blogspot.com

-Alan Gillis

Alan Gillis said...

Hi again Bee and ph=f,

A correction and another question. It's the Tevatron at Fermilab with the greatest collision energies so far, at 1.9 TeV.

The other point is something of a minor or major revelation. Depends on what happens at the LHC. I've been studying this installation for months to produce a definitive guide that unphysicists can follow, though as serious science journalism.

What finally bothered me about the LHC is 60 tonnes of superfluid helium coolant, well contained within the ring even if spilled, and in the detectors themselves where the lines are much more fragile, like tiny refrigerator freezer piping. Helium will leak and fuse if the proton fireball is big enough.

I've posted a new article on this in "The Science of Conundrums" at http://bigsciencenews.blogspot.com called "The Almost Thermonuclear LHC".

Bee, you've blogged about the moral questions of building a "$10 billion (experiment) or whatever it is," says Brian Cox. The safety issues are much bigger.

-Alan Gillis

Phil Warnell said...

Alan,

I left a comment that addresses your concern on your blog. I notice that all comments are first viewed by you before they are posted. If you actually release it to be read, I will at least be less skeptical as to your understanding, motives and tactics.


Hi Bee,

Sorry Bee, as this is your blog and should you decide to remove my comment I will understand.

Best,

Phil

Alan Gillis said...

Regarding Phil Warren's comment: Although he suggests that his comment sent to me "addresses your concerns", it is nothing more than a 2 line insult without any critique of data or analysis, so not worth publishing.

As regarding LHC potential dangers, you need look no further than some of CERN's own concerns. Steve Myers, who is the head of accelerators and beams at CERN was interviewed and quoted by physicsworld.com/cws/article/print/26015--in October 2006: "The LHC is the first accelerator ever built that has the ability to self-destruct."

-Alan Gillis

Bee said...

Alan, Phil: I currently don't have the time to read whatever you are talking about. If you want to continue this discussion, please do it elsewhere, or I will just delete everything.

Alan, I can't find any comment at the post you mentioned above, but given that Phil is one of the most polite commenters we've ever had at this blog, I find it hard to believe all he said was a two line insult (and then leave a pointer here to inform everybody of his alleged content free hickup?).

B.

stefan said...

Hi Alan,


I hadn't noticed your comment before, sorry... I don't think this is the right place for a discussion about this, but let me just comment on the physics points you have mentioned.

Hmm, the energy equivalent to 100 kg of TNT mentioned by Steve Myers in the Physics World article, or the 400 tonne train travelling at 150 km/h (CERN Safety at the LHC), that's indeed a lot - but we should keep in mind that this energy is distributed uniformly over the 30 km or so of the tunnel. If something goes wrong, that may wreck the billion euro installation in the tunnel - worse enough - but it would not result in a 007 like explosion of Dr Blofelds underground lab.

More energy than in the beam is stored in the magnets, and a sudden loss of superconductivity (a so-called quench) would release this energy. That's a real hazard for the installation, but as far as I know, there is a safety system that is supposed to avoid big damage (see LHC magnet quench protection system).

I can't quite share your concerns about the helium - at least, it wouldn't burn in case of a leakage, other than natural gas. And I don't see at all how you could possibly expect nuclear fusion to set in: The extremely high temperature produced at the collision points exists only for extremely short times, the amount of actual matter in the beam is tiny, and, most important, there is no confinement at all for the hot plasma, so it will expand and cool before an energy-producing fusion reaction sets in.


There is indeed research going on looking for nuclear fusion induced in accelerators by heavy-ion collisions. You may have a look at the site of US Heavy-Ion Fusion Science Program. But the accelerators used in such programs have properties very unlike the LHC (not to mention that this kind of fusion never has work in practice so far) - energy alone is not the decisive criterion. There has to be a lot of dense matter in the first place - helium gas from a leakage even at 100s of atmospheric pressure won't even think about fusion. And colliding nuclei are less stopped at higher energies than at lower energy, for example. I can imagine that the people at the LBL/LLNL could give you a more detailed answer about the fusion problem.

Best, Stefan

Phil Warnell said...

Hi Stefan & Bee,

Stefan you essentially gave Alan the professional opinion which I suggested he should have sought prior to posting his blog (the comment he held back). This kind of opinion he should have sought before he wrote his blog, alerting and I suspect more to worry those would might read his piece to suggest that the LHC was some sort of doomsday machine. He hints that all the bright minds and experts that have planned and constructed it, had somehow overlooked what this unstudied and unqualified person had realized.

My concern was not that it wouldn’t be addressed knowledgably and professional here as you have, yet rather he would write such a thing before thoroughly investigating it. I fear the effects of publicized pseudo science designed to promote irrational fear far more then anything that the people at LHC could have missed. I would not have left a comment here at all, if Alan was not in the practice to use censorship on his site to distort and thereby elevate the soundness and urgency of his message. I only left a message here since I was certain he would not publish my criticism of his post as to the lack of responsibility he did in doing so. However, I would again challenge Alan to copy your reply along with my comment into his posting. As I stated before please feel free to delete my comments as I will understand and I apologize for any annoyance it may have caused.

Best,

Phil

Alan Gillis said...

Hi Stefan,

I like your 007 analogy. Megalomaniacs like Blofeld in Goldeneye are amusing, but physicists in the real world who spend $10 billion on a potentially dumb and dangerous experiment should be given even more scrutiny. Keep in mind too that writers like the late Arthur C. Clarke, H.G. Welles and Jules Verne were visionaries too.

There are many potential dangers at the LHC. What Steve Myers said about the beam dump is only a part of the story. A general failure during an experiment would release far more energy from the magnets. First of all the beam would release not 100 kg but 157 kg TNT equivalent (Wikipedia, LHC articles edited by CERN), plus 2 metric tonnes from the ring magnets, plus for instance, another 4 metric tonnes if CMS were on line, from its colossal solenoid, or more than 6 tonnes of TNT in all. Perhaps it can all be safely discharged, but from my experience in the field, a crash down of an terribly expensive system as a test is never performed. You don't want to risk everything to prove you're safe. Bits and pieces are all you test. And there have been failures here too. See SciAm articles.

Other safety issues are discussed on my blog, http://bigsciencenews.blogspot.com

Two other cautionary quotes from people in the know, from http://discovermagazine.com/2007/aug/the-biggest-thing-in-physics/

From Peter Limon at Fermilab: "It is the most complicated thing that humans have ever built." And from Yves Schutz, a French physicist at LHC ALICE: "We don't know what to expect. We're in a domain of energy that nobody has ever experienced." Including possible proton fusion and a 4 Tesla field to contain it in CMS.

My initial question was about the wisdom of proceeding with the LHC, since there is apparently, according to astrophysicists, a missing 96% of the Universe of dark matter and dark energy that doesn't fit in with the collection of pieces of Standard Model theories, one missing piece, the Higgs theory that the LHC is trying to confirm. Are physicists fiddling while Rome is burning? Another look at the big picture wouldn't hurt. Another Theory of Everything might be better than SM Monopoly.

And where are all the ethics in all of this? An unnecessary, extremely costly experiment to keep some particle physicists in business. Perhaps a $100 million is cheap after all for a Bond film that explores our humanity or lack of it. Or cautions us. Or might even predict the future.

-Alan Gillis