New boson confirmed at around 126GeV
Published by marco on
NB: Don’t worry if you don’t understand this introductory paragraph; feel free to blow right through it and see how you fare with the alternate explanations and analogies below.
The news so far is that the scientists at CERN have announced that they have consistently been able to generate bosons at around 126GeV with a certainty of 5 sigmas. The Standard Model of physics predicts that this energy level is sufficient to generate the long–sought-after Higgs boson, which is the only predicted particle that has not yet been confirmed to have been detected.
That carefully worded description of the discovery is a good deal less hyperbolic than other headlines or articles you may have read. The media tended toward the less accurate and more down-to-Earth, spouting “God Particle Found!”, “Higgs Boson Discovered!” or “Scientists Find Particle Responsible for Why We Weigh so Much!” But what does it mean for you and me? I suppose the most important question for many will be: why should I care?
An Audiovisual Presentation
If you haven’t seen it already and you think you’ve got the scientific chops, the following video does a lovely job of explaining the discovery.
If you watched that and drifted off to check Facebook a couple of times before it finished…but would still like to know more, you’ll have to soldier on.
It’s hopeless, so don’t even try
Before we try to answer the question of why you should care (posed above), we’ll have to address the very realistic possibility that many people will, by dint of their experience or education, simply be wholly and entirely incapable of understanding what the hell happened and why it’s important in any but the most superficial of ways.
Explaining why this discovery is important may be doomed to failure for reasons best explained by one of the best explainers of physics who ever strode the Earth, Richard Feynmann, as cited in Diving deeper into the metaphorical molasses by Ben Zimmer (Language Log). In the video (cued to 06:09) and the transcript (included below), Feynmann tries to explain magnetism or, rather, he explains why it’s hopeless to even make an attempt at explaining magnetism to his interviewer. It’s not arrogant because it’s true.
“I can’t explain that attraction in terms of anything else that’s familiar to you. For example, if we said the magnets attract like as if rubber bands, I would be cheating you. Because they’re not connected by rubber bands. I’d soon be in trouble. And secondly, if you were curious enough, you’d ask me why rubber bands tend to pull back together again, and I would end up explaining that in terms of electrical forces, which are the very things that I’m trying to use the rubber bands to explain. So I have cheated very badly, you see. So I am not going to be able to give you an answer to why magnets attract each other except to tell you that they do. And to tell you that that’s one of the elements in the world − there are electrical forces, magnetic forces, gravitational forces, and others, and those are some of the parts. If you were a student, I could go further. I could tell you that the magnetic forces are related to the electrical forces very intimately, that the relationship between the gravity forces and electrical forces remains unknown, and so on. But I really can’t do a good job, any job, of explaining magnetic force in terms of something else you’re more familiar with, because I don’t understand it in terms of anything else that you’re more familiar with. (Emphasis added.)”
And that, right there, might be the long and the short of it. If you lack too much understanding—whether it’s a background in physics or the sciences or just familiarity with thinking about how things work and working from axiom to logical conclusions—you may very well have no hope of understanding this discovery. The explanation of what scientists at CERN just accomplished will sound like so much magic to you. It will be, to paraphrase the late, great Arthur C. Clarke, “a sufficiently advanced technology that is [to you] indistinguishable from magic”. You may, however, still be able to understand how it may affect you. Most people don’t understand how their cars or smart-phones or GPSs work, but they know that they can do more stuff because of them.
Pressing on nonetheless
If you fail to understand not only the news of the discovery but also have no idea of any of the dozens of levels of scientific underpinnings for it, how do you even stand a chance of ranking the importance of this news vis à vis other seemingly more pressing news, like Katie Holmes leaving Tom Cruise? In what way does this news differ from the latest discovery in crystal healing? How the hell can you tell the difference?
Does it mean that the next generation of smart-phones will be even faster? Are we getting jet-packs or hover-cars?
None of the above.
How science works
Conservation notice: the following section is a pretty pedantic, long-winded and largely self-congratulatory exercise in describing the scientific method. YMMV.
Well, what sort of magic can we look forward to, then?
None, I’m afraid.
The only conclusion we can reach so far is that CERN has produced promising results that are almost certain to provide evidence that the best model we have about how the universe is structured at the lowest level is not wrong. Therefore, the predictions made based on that model have a higher likelihood of being, if not correct, then useful.
The latest results from CERN are simply science doing what science does. Science is about (1) making guesses—hypotheses—about the way the world works; and (2) running experiments to test those hypotheses. If the experimental results agree with the prediction, it provides evidence that the guess might be correct. There is almost no way to prove that the guess is correct, although some theories have a tremendous amount of evidence to support them.
Take the theory of matter—that matter is composed of atoms—we have seen these atoms with electron microscopes, which seems to prove beyond a shadow of a doubt that atoms exist. Electron microscopes operate on other principles that contain assumptions about light, wavelength and so on. That the microscope works as expected—that any piece of technology works as expected—provides support for the various theories on which that technology is based. The existence of such functioning technology doesn’t prove the hypothesis, but it provides strong evidence for its usefulness—that other results and theories can be derived from and based on it.
The LHC (Large Hadron Collider) is an enormous piece of technology based on the same principles and theories on which much of our consumer electronic culture is based. Scientists predict that cell-phones will work and then, when we build them, they function as expected, which while not proving beyond a shadow of a doubt all of our theories about light and energy, it certainly shows that enormously useful results can be obtained from predictions based on unproven theories. Scientists came up with a model of how the universe works at the most basic level—the Standard Model—and they’ve spent decades searching for the particles that the theory predicts.
How do you find particles that you can’t see? How do you know when you’ve found one? How can you trust the particle detector? The LHC accelerates particles in opposite directions through dozens of miles and then collides them at very close to the speed of light to excite them into high-energy states that they hope will result in the particle that they’re looking for. Theory predicts the myriad ways in which these particles can decay into other particles. Theory predicts which particles are created initially and that the technology in the LHC will contain and accelerate those particles through the tubes. Theory predicts how the detector react to particles tearing through them and theory predicts that the computers will retain this information, crunch the numbers and display the results.
It’s all theory and it sounds like a Rube-Goldbergian contraption but the point is that scientists made many, many predictions about what they thought would happen, based on their new theories and using equipment built to specifications dictated by other theories—a veritable pyramid of millions, if not billions, of assumptions about how the world works, all having acquired the sheen of veracity simply because they have proved to be extraordinarily useful and reliable predictors of reality—and all of these experiments came out as expected, providing a lot of evidence to support these theories, particularly the Standard Model.
What if they hadn’t found the particle they were looking for at the energy-level at which they expected it? Before the recent discovery, there was already a lot of talk about throwing out the Standard Model and having to try again. In fact, some scientists were looking forward to being able to start from scratch because progress on closing the gaps and removing the hacks from the Standard Model has been so slow and seemingly hopeless.
Though we don’t know for certain (or with 5 sigmas of confidence) that the particle is the Higgs boson, we may soon. The odds of tossing out the Standard Model entirely went down significantly already; if the particles that the LHC is generating match the other expected parameters of the Higgs, those odds will drop again.
Models with a lot of evidence to support them are more reliable. They are a very good thing.
Thank you, science!
The article There is something and not nothing by Roger Ebert (Chicago Sun Times) waxes a bit philosophic about scientists and how the scientific method is “the awesome” and how we should be more than a bit in-awe of those among us who can hypothesize on such a grandiose and abstracted level. You know, instead of calling them nerds and pushing them until they cry. Or ignoring them completely and letting the world burn. But I digress.
“The mind of a theoretical physicist must be a wonderful place. It can consider things that for me are only words, and will always be words. It can make play with multiple dimensions. It can contemplate black holes. It can not only theorize the existence of the Higgs boson, but can devise an experiment to find it–an experiment that succeeds.”
“Here is where we get to the heart of the question. The scientific method has no interest in belief. What you believe is of interest only from an autobiographical viewpoint. Scientists (1) regard a phenomenon they would like to explain, (2) suggest a hypothesis to explain it, and (3) devise an experiment to test their hypothesis.”
Forget the “God” particle
Somehow the Higgs boson has earned the epithet “The God Particle”. This seems to be a name promulgated by those who don’t understand what’s going on at all.
It’s the highest-energy particle predicted by the Standard Model. That’s the reason it took so long to find. It’s not because it’s evidence of a God that has managed to remain hidden from our heathen eyes until the ruthlessness of science managed to prize it from God’s omnipotent—and yet still helpless-to-resist—hands.
The article Worth the Wait: A timeline of the Standard Model of particle physics (The Economist) includes the following chart that depicts how long it took to discover the other particles in the Standard Model:
Now that you’re better-versed in these matters, you may have noticed that they incorrectly indicated that the Higgs Boson has been discovered. Though it’s a strong possibility that 126GeV spike indicates the presence of the Higgs Boson, we’ll have to wait until CERN gathers more data and publishes results either at the end of this year or early next year to know for sure (or, to be more precise—because we’re scientists!—to know within 5 sigmas).
What does 5 sigmas mean?
“When physicists announce that they have a 5-sigma result, that means that there’s a 1 in 3.5 million chance that it was the result of a statistical fluctuation over the spectrum of experiments they performed. Particle physicists working on the CMS and ATLAS experiments are looking for “bumps” in their data that stand out from the background. When these bumps reach the 5-sigma level, they have very good reason to believe that they’ve discovered or observed a new particle.”
Alles klar? I hope so. Because it’s not going to get any easier than that.
Ok, fine. The CMS and ATLAS are other particle accelerators—like the LHC at CERN—that were also busily smashing particles together. The data from all of the machines are combined to create a huge pile of data which, hopefully, will provide enough collisions for the probabilistic noise to subside into the background and let the desired signal appear. In the form of an anti-climactic bump on a graph.
What is the Standard Model?
The article Gotcha! The hunt for physics’s most elusive quarry is over (The Economist) describes the model as follows:
“[T]he Standard Model [is] the best explanation to date for how the universe works—except in the domain of gravity, which is governed by the general theory of relativity. The model comprises 17 particles. Of these, 12 are fermions such as quarks (which coalesce into neutrons and protons in atomic nuclei) and electrons (which whizz around those nuclei). They make up matter. A further four particles, known as gauge bosons, transmit forces and so allow fermions to interact: photons convey electromagnetism, which holds electrons in orbit around atoms; gluons link quarks into protons and neutrons via the strong nuclear force; W and Z bosons carry the weak nuclear force, which is responsible for certain types of radioactive decay. And then there is the Higgs.”
If you never took chemistry and your understanding of neutrons, protons and electrons is already shaky—not to mention the particles of which they themselves are composed—the paragraph above means nothing. For you, the take-away is that there’s a theory called the Standard Model that predicts the building blocks of everything and we’ve been able to verify the existence of all of these particles save one: the Higgs boson. Batting 16 for 17 would, in most fields be considered quite good. For science, it’s only a good start.
Though the Higgs was predicted by the Standard Model, there are other theories—supersymmetry, extra dimensions, etc.—that stand ready to account for any deviations from the properties predicted by it, should any such deviations appear in the data. The official Higgs announcement thread (Reddit) includes the following rather cryptic description of some of these.
“If it’s really a Higgs, then we need to solve the Hierarchy problem or abandon the idea of naturalness. The problem is that the Higgs is “unaturally light”, since quantum corrections would “naturally” make the Higgs mass as big as the Planck scale (1019 GeV compared to the 126) and to make it light we need a an arbitrary cancellation that is heavily fine-tuned. The best candidates were supersymmetry and large extra dimensions, but it seems that both are very unlikely now.”
Supersymmetry and extra dimensions—both associated with most versions of string theory—something you may also have heard of if you watch The Big Bang Theory—were alternate ways of looking at the problem in an attempt to get around some of the less elegant ramifications of the Standard Model.
This is all getting into quite heady territory, though. We can just leave it at scientists getting all itchy when their theories of how the universe works involve too many “magic numbers” and hand-waving in order to work. It would be nicer if all explanations and proofs proceeded without any “hacks” or assumptions about optimal conditions.
Is it the Higgs boson or isn’t it?
You keep writing that CERN hasn’t yet determined that it’s the Higgs boson, but many sources—including the Economist above—are equating the discovery of a particle with the discovery of the Higgs boson.
The short answer is that the LHC has detected many particles at the energy level predicted by the Standard Model for the Higgs boson. Particles have other properties than just energy, though, so further data-mining will have to determine whether the detected particles match more than just the energy level of the Higgs boson.
A longer answer can be found in the official press release, CERN experiments observe particle consistent with long-sought Higgs boson (CERN):
“The results are preliminary but the 5 sigma signal at around 125 GeV we’re seeing is dramatic. This is indeed a new particle. We know it must be a boson and it’s the heaviest boson ever found […] The implications are very significant and it is precisely for this reason that we must be extremely diligent in all of our studies and cross-checks.”
That part should be pretty clear. We’ve definitely found something and it’s very promising, but easy does it with iggs-Hay oson-Bay.
“The results presented today are labelled preliminary. They are based on data collected in 2011 and 2012, with the 2012 data still under analysis.”
Data-mining proceeds apace, but there are petabytes of data to analyze. Cool your heels, world media. We’ve waited forty years; we can wait a few months more. The article CERN celebrates as Higgs signal reaches significance by John Timmer (Ars Technica) mentions that CERN is pushing onward as fast as it can to get more data:
“CERN has indicated it will extend this year’s LHC run by several months in order to get enough data to know more things about the newly discovered boson. This is the last chance they’ll get before the extended shutdown for upgrades, and they probably have some sense of what it will take to push key measurements into statistical significance now.”
So why is so hard to figure out if we found a Higgs or not? The particles are really, really small and exceedingly fleeting. That means the Higgs, when produced, decays almost immediately into other, more stable particles. These are the particles picked up by the detector. It’s the presence of these particles—as well as their energy levels, spins, etc.—from which scientists can construe that a particle with a certain energy had to have caused it.
A comment on Ars Technica by a scientist working at CERN provides more detail on the mechanics of the detectors:
“Basically each detector is made of sub-detector: “trackers” that sense electrically charged particles passing through and “calorimeter” that have enough material to stop particles (except muons and neutrinos) and measure their energy deposit. That’s the “raw data”, [on the] order [of a] few MB per collision, [a] few PB of data per year. These low-level informations are then processed to “reconstruct” the path of charged particles (their path in a magnetic field allows to measure their momentum) and the energies and properties of deposits in calorimeters.
“For the Higgs decaying in two photons, one would then require two energetic energy “blobs” in calorimeters with a shape that makes them look like photons and calculate the invariant mass. Unfortunately there are many other ways to produce two photons with no Higgs involved so other properties of the collision need to be used to reach a good sensitivity.”
As you can imagine, this is all bloody difficult. The article CERN celebrates as Higgs signal reaches significance by John Timmer (Ars Technica) talks about this a bit.
“Finding the Higgs was always a matter of probability. We can’t detect the particle directly, but the Standard Model tells us what its decay pathways will look like, provided we feed the equations a specific mass. So, for example, we can calculate that a Higgs boson weighing in between 115 and 135GeV (the range suggested by the Tevatron data) should decay into two photons with some frequency; two Z bosons with a different frequency, and other combinations of particles with additional probabilities.
“The challenge comes from the fact that the Standard Model also predicts that processes that don’t involve a Higgs will also produce similar looking patterns of particles. So, we’re left with probabilities. Do we see an excess of these events that can’t be accounted for by non-Higgs decays? How statistically significance is that excess?”
“Particle physicists have settled on a specific measure of significance called five sigma (or five standard deviations) before they’re willing to accept that we’ve spotted a new particle.”
So, not only do we have to play Sherlock Holmes with the detected data, it turns out that it’s not only a Higgs boson that can cause the Higgs-like pattern that theory predicts and that we’re looking for.
Imagine a forensic scientist who picks shards of pottery out of the wall and determines that something had blown up a bunch of pottery in that room. But she also knows that there were three cops in that room shooting like crazy and it stands to reason that there are pottery shards in the wall. There seem, however, to be more pottery shards than expected, which lends credence to her theory that there was a fourth shooter involved.
Now take the scenario and run it millions—or billions? trillions? I don’t even know—of times and see if the data consistently shows the presences of a fourth shooter. That’s how you get to five sigmas of certainty and that’s how you extract a signal from all of the noise.
And next? Imagine if she now had to figure out where the fourth shooter was standing and what color his pants were.
Does the Higgs make me fat?
The last thing that needs to be addressed are the wild claims—some accompanied by demonstrations with sand and ping-pong balls—that this particle imbues everything with mass. The post, Lets get this right: The Higgs Boson does *not* give “us” mass by Foolie (Reddit), takes the wind right out of the sails of that argument:
“99% of the proton mass (and similarly the neutron mass) is coming from the strong nuclear force and not the Higgs mechanism, and we have one electron per proton in the universe at 0.0005 GeV, compared to the proton mass of 1GeV. (The electron does get all of its mass from the Higgs mechanism, it’s just not very much).”
The strong nuclear force is one of the four known fundamental interactions (electromagnetism, weak nuclear force and gravitation are the others). It’s the one that binds protons to neutrons at the core of atoms. Again, if that doesn’t make any sense to you, then the take-away is that the Higgs mechanism imbues atoms with almost none of their mass. Your Sunday-morning talk show was misinformed.
The article CERN celebrates as Higgs signal reaches significance by John Timmer (Ars Technica) also takes a crack at describing the place that the Higgs occupies in the Standard Model.
“Physics’ Standard Model describes the fundamental particles that make up all matter, like quarks and electrons, as well as the particles that mediate their interactions through forces like electromagnetism and the weak force. Back in the 1960s, theorists extended the model to incorporate what has become known as the Higgs mechanism, which provides many of the particles with mass.”
Again, the particles to which the citation refers are some of the more exotic, ephemeral of the particles in the Standard Model and not the ones that our high-school physics courses are talking about. In other words, the Higgs has nothing to do with your weight. It’s the Twinkies.
The official press release, CERN experiments observe particle consistent with long-sought Higgs boson (CERN), also alludes to the effect that the Higgs boson is theorized to have on the mass of other particles.
“The next step will be to determine the precise nature of the particle […] Are its properties as expected for the long-sought Higgs boson […] Or is it something more exotic? The Standard Model describes the fundamental particles from which we, and every visible thing in the universe, are made, and the forces acting between them. All the matter that we can see, however, appears to be no more than about 4% of the total. A more exotic version of the Higgs particle could be a bridge to understanding the 96% of the universe that remains obscure.”
You see, discovery of the Higgs, while huge for scientists, is not so huge that they’re going to sit on their laurels. Instead, in the official press release, they’re already looking beyond what is a fantastic result, but a predicted one to see if they can figure out what’s up with all the dark matter?
What’s dark matter? That’s a discussion for another article. Or Wikipedia is just a few clicks away if your interest in the dark arts of physics has been piqued.
The post Higgs Boson Confirmed at 5-sigma Standard Deviations at 125 GeV (Reddit) put it like this:
“The discovery itself doesn’t change our understanding […]. It had already been predicted in theory and so the only thing that is changed by this “discovery” is that the theory has more evidence behind it, and is much more “confirmed”. As for cool star-trek-style science that the Higgs will allow us to do…well, it’s all sensationalism, really. Knowing about the higgs is like knowing about quarks and gluons; any practical application (as in, commercial uses) of the knowledge won’t manifest until decades later, if ever.”