After a false start in 2008, the Large Hadron Collider (LHC), the glitzy new atom smasher at CERN (the European laboratory for particle physics) near Geneva, is finally due to start its experiments this October. The LHC may or may not end up spewing out dark matter, mini black holes or other exotica. But whichever way, figuring what's coming out will be a tremendously hard task. A controversial approach to analyzing data could help physicists make sure they don't miss any of the good stuff.
The LHC and other accelerators such as the Tevatron at the Fermi National Accelerator Laboratory in Batavia, Ill., push protons or other particles to near light speed and smash them together. Thanks to Albert Einstein's E = mc2, some of that collision energy turns into rare, heavy particles that almost immediately decay into hundreds of more mundane particles (of which many dozens of different types are known). The LHC's huge detectors will record the passage of this debris and produce data at a staggering rate, equivalent to one CD-ROM per second.
Physicists will rummage through the information for particular combinations of decay products that would suggest a new particle has been created. They will be looking for signs of the Higgs boson, the long-sought particle that is supposed to give other particles their masses, and also for entirely new particles that could give a first glimpse of the laws of physics at higher energies.
But some fear that this traditional approach akin to running a computer algorithm through a text searching for the letters H-I-G-G-S could end up missing interesting new signatures that no one had foreseen. At Fermilab, Bruce Knuteson and Stephen Mrenna have for some years advocated a more "holistic" approach called global search. Instead of looking for particular signatures, they wrote software that analyzes all the data and compares them with predictions of the so-called Standard Model, which comprises the known set of laws of particle physics. The software then flags any deviations from the Standard Model as potential new particles. It is a bit like having an algorithm that, instead of searching a text for a particular word, matches every single word against the dictio nary of known words and flags the ones that sound as if they might belong to a foreign language.
To limit false positives sometimes mundane particles will interact and mimic the behavior of other, more interesting particles physicists can set a threshold for the minimum number of times a strange event may occur before alerting the experimenters of something possibly new. "We take into account the fact that we look at a lot of different places," Knute son says.
Knuteson, Mrenna and their collaborators put their method to work on old Tevatron data. In principle, exotic particles could have been lurking where no targeted searches had looked before. The team found nothing of particular statistical relevance, so they made no claims of new discoveries. But that effort at least showed that global searches do not necessarily lead to many false positives, as some physicists feared. The results, which appear in the January Physical Review D, also constitute the Standard Model's most stringent test to date, says Knuteson, who has since left active research.
Physicist Louis Lyons of the University of Oxford says the team's statistics were sound. But Pekka Sinervo, a University of Toronto physicist who is involved in both Tevatron and LHC experiments, remains unconvinced. "The authors had to sweep a lot of poorly understood effects 'under the carpet' and not address them directly," Sinervo states, meaning that the search generated an abundance of hard-to-interpret signals. Still, global searches could have some utility, he concedes, as long as they do not distract researchers from searches targeted at specific phenomena, adding that he is "not convinced that one would be able to use such a search for an early discovery at the LHC."
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Add CommentRegarding this kind of research, ideally the objective should be to spin off some kind of practical benefit, beyond the mere understanding of how this reality is put together. In the case of the LHC, we should address the issue of where all the matter in the Universe came from and how it is generated, and that out of this research make possible the deliberate creation of mass from the photon background, to be harnessed as the energy which that mass represents, for our own use. In a sense, that will be the ultimate intent of the relentless pursuit of the Higgs boson, which, even though it probably does not exist, will surely bring us closer to this goal. Given the huge global investment in particle physics research, it is apparent that we are not so much trying to understand God, as to be Him. It is a valid quest.
Reply | Report Abuse | Link to thisBaudrunner is wrong to say that ideally the object of LHC physics should be to produce results of practical benefit. It is to understand matter, forces, space and time. It is almost certain that practical benefits will come (they already do) from pushing the limits of technology, but that is not the object. Astronomers learnt to understand the interior of stars in much detail; important knowledge but of no practical application. As for dreaming that finding a Higgs boson might lead to new ways of energy or mass generation, forget it. That's not the point.
Reply | Report Abuse | Link to thisThanks for the "colliding philosophy", albrow. Frankly, I don't see how studying particle collisions helps us to understand the interior of stars. The current paradigm regarding the nature and composition of the sun, for example, is one based on very early theory developed well before the age of space exploration and contemporary solar research, one that colossal organizations like NASA find great difficulty in shaking (re: http://www.thesurfaceofthesun.com/ for a comprehensive and detailed explanation of why that paradigm demands a major rethinking). I find it difficult to justify the expenditure of such vast sums of money just to satisfy our curiosity, with no other goal in mind. The fact is that the more we know and understand, the greater ouropportunity to benefit materially from our knowledge and understanding. The trend is inevitably toward the development of some practical benefits. That's just how the world works. As to just how that benefit might be represented is anybody's guess, but I suggest that ultimately the concept of power generation will likely be addressed. Furthermore, the productive application of our perceived understanding of what happens at the quantum scale serves as proof to support theory. Science without proof is not true science.
Reply | Report Abuse | Link to thisOK Baudrunner, my point was not that particle collisions help us understand the interior of stars (although they actually do), but that both endeavours are curiosity- driven research and worth doing by a civilisation such as ours for that reason alone. And we are not talking vast sums of money, mor like a cup of decent coffee per person per year. Build a couple less stealth bombers and you can pay for it all. But I agree with you that research in particle physics is likely to have benefits in power generation, probably through the application of accelerators (such as sending high power proton beams into radiactive waste (thorium, uranium etc.). Many other benefits too, including advanced computing (and the invention of www), medical imaging, cancer therapy, high field superconducting magnets (to be used in transportation one day, and in MRI scanning today), fast and dense electronics, etc etc etc. Many of these spin-offs only happened because some thousands of physicists, driven by curiosity, needed to push the limits of technology to, e.g., look for a Higgs boson. Not to find it, but to see if it is or is not there.
Reply | Report Abuse | Link to thisNot arguing with you albrow, but the fact remains that for the price of a cup of coffee a day you could help an impoverished orphan in the third world see some of the same benefits of civilisation as we in the first world do.
Reply | Report Abuse | Link to thisI am absolutely for the peaceful pursuit of scientific research and wish altruistically that all of this world's military expenditures be directed toward the effort toward an understanding of the fundamental nature of reality, whether it be through space exploration or the unravelling of subatomic particles.
Let it not go unsaid that all military endeavors by the U.S. to date have been to protect and profit from American interests abroad. Were it otherwise, then she would find herself embroiled in the affairs of most of the rest of the world's second and third world nations, but her cause in actuality is not a moral one, but a money-centric one. That , again, is how the world works. Not taking issue there, that's just the way that things are.
But I digress. Just how do particle collisions help us understand the interior of stars?
Right, I think we're on the same wavelength. But you ask: "Just how do particle collisions help us understand the interior of stars?"
Reply | Report Abuse | Link to thisA: the energy emitted by stars as heat and light essentially comes from fusion reactions in the core. Not, by the way, the d+t reaction they try to make in a Tokamak, but others. These reactions emit neutrinos, which can pass right through the sun and reach the Earth, where they can be detected in deep underground detectors. The neutrino fluxes were measured and found (by Reines) to be only about 1/3 what was expected (by Bahcall). Was the understanding of the centre of the Sun that wrong? Bahcall didn't think so. The mystery was eventually solved, and accelerator experiments played a role, by there being 3 different types of neutrino (e, mu and tau). Only e-types come from the Sun's reactions, but the neutrinos "mix" among themselves (proving they must have some mass) and by the time they reach Earth they are a mix of 3 types. Reines only detected the e-type so he saw 1/3 of what Bahcall predicted. Mystery solved, and a magnificent confirmation that we understand the nuclear reactions in the core of the Sun very well. Beams of neutrinos made at accelerators are now studying this "neutrino mixing" in detail. What is amazing is that for maybe 20 years there was this discrepancy between what Bahcall predicted and what Reines found, but they checked and double checked and stuck to their guns, and it turned out they were both right, and the factor of 3 discrepancy is just the number of neutrino types!!!
And the big neutrinos detectors can actually see the Sun shining right through the Earth at night, as a bright patch in the "neutrino sky".
Great example, albrow! It shows that we are on the right track in rationalising how reality is put together, as well as the forces that contribute to its persistence.
Reply | Report Abuse | Link to thisNow if we can just get away from believing in Higgs bosons or gravitons. Fundamental particles do not lie at the root of all physical phenomena.
E =mc� is not Einstein's formula. This is a fairy tale.Poincare, Hasenoehrl and others have discovered it in 1904. Many reviewed publications have shown that. The most famous paper on this has been written by Herbert Ives at Bell Telephone Laboratories in 1952, it had appeared in the Journal of the Optical Society of America, vol. 42, No. 8, pp. 540-543. The last sentence in the Ives paper reads "E=mc� was not derived by Einstein"
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