Archives For particle physics

particle decay at the lhc

Once upon a time, we looked at an explanation for dark matter involving a theory about how all matter around us could decay over 6.6 × 10^33 years and noted that there’s a controversy as to whether protons actually decay. To help settle this, astronomers took advantage of the fact that telescopes are relativistic time machines, and peered through them at a galaxy known as PKS 1830-211 — a name only a scientist could love — that just so happens to be a gravitational lens allowing us to see some 7 billion years back. To be a bit more precise, it lets us look at clouds of alcohol molecules formed eons ago in deep space and compare their spectrum to that of booze analyzed in a lab right here on Earth. Don’t worry, no hard liquor was harmed in the process as the alcohol in question is methanol, the kind used in fuel and manufacturing, and which causes blindness if ingested, not the ethanol in which we can indulge. But even if no buzz was killed for the sake of science, what exactly does looking at the light spectra of alcohol tell us about how our universe formed and its possible fate many quadrillions of years from now?

Well, the spectrum of a molecule depends on μ, the ratio of proton to hydrogen mass. That’s an extremely important metric because it lets us measure the strong force, one of the fundamental interactions of matter as we know it responsible for building atomic nuclei. Because the masses involved are created by interactions of elementary particles representing the strong force, if μ falls below or exceeds 1,836.15267245(75) and the difference is reproducibly recorded, we can say that something changed the effect of this fundamental force on matter. Hence, if the 7 billion year old methanol emits an appreciably different spectrum from methanol we create today, this would mean that one of the fundamental forces has changed as the universe grew and matter is decaying on cosmic time scales. Lucky for us, turns out that atoms are very much stable since the spectrum of methanol was for all intents and purposes identical over 7 billion years, which is just over half of the way back to the Big Bang itself.

This tells us a couple of things about the fate of the universe. First is that the Standard Model of physics is still accurate and can make viable predictions about atomic structure and decay. The second is that matter will continue to be matter at the end of the universe or decays so slowly it would only matter on time scales far exceeding the lifetimes of supermassive black holes. Finally, it allows us to rule out overly exotic explanations for the origins of dark matter involving decay of particular subatomic elements or quirky behavior of the strong force since these results match a number of previous experiments designed to find out the same thing. In a universe flying apart, churning with explosions, collisions, and radiation, it’s nice to know that you can rely on matter that makes you and the planet on which you live isn’t also slowly decaying on you like a ticking cosmic time bomb. And while space may be out to get you through GRBs, asteroids, and huge galactic train wrecks, it will at least spare the very fabric of your existence.

See: Bagdonaite, et. al. (2012). A stringent limit on a drifting proton-to-electron mass ratio from alcohol in the early universe Science DOI: 10.1126/science.1224898

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cern_detector_600

Apologies for the long silence but it looks like life and work has been interfering with the blogging. Oh well, all yours truly can do is grin and bear it, and take a moment when he can to write a post. Luckily for me, there’s a really big event that makes for excellent post fodder; the apparent discovery of the Higgs boson, the linchpin of mass for all known matter in the universe. The short version of all the press releases boils down to a bump in particle decay data showing a very heavy particle fitting right in the predicted range of masses and lifespan for the long-sought Higgs, a bump which hasn’t just been detected at the LHC, but replicated by the Tevatron with a lesser but still significant degree of certainty, indicating that this time, we’re really on to something huge and really heavy. Yes, pun intended. Of course not having a Higgs lurking in the data would make things exciting, but with it finally making a brief appearance means that the Standard Model of particle physics is as airtight as it could possibly be from a scientific standpoint and we can now proceed to study the boson in more depth.

So what can we find out when we study this boson? Well, by lucky coincidence, Just as we’re figuring out that our ides of how the universe works are along the right path, astrophysicists found a filament of dark matter shaping galaxy nodes and a thorough knowledge of the Higgs could provide us with clues about the ultimate makeup and fate of the cosmos. We may also study how the Higgs affects quantum particles to answer a few of our pressing questions about quantum mechanics. Practical applications like creating a relativistic rocket by canceling out the Higgs boson’s effects on matter with a finely calibrated device, allowing our spacecraft to cross the vast distances between stars within years rather than eons, are probably too far fetched at this point to consider seriously. However, who knows what we could accomplish when we understand the origins of all mass? That’s the fun of science and technology. You never know what you can discover or create until you set your mind to it and try. The current confirmation of the Higgs shows us how far particle physics has come in a century; from barely being able to define atoms, it can now define and model entire particle zoos.

And which physics keeps studying the Higgs, I hope that the media will quickly forget the bosons’ unfortunate nickname since calling it The God Particle misrepresents Leon Lederman’s original intention to convey how hard it was to find the boson despite its perfect fit into every other experiment and equation, and by letting his publisher change his phrase “the goddamned particle” into a pseudo-religious euphemism he earned a lot of cold stares from his fellow scientists. Yes, it is a critically important particle and yes, it has very profound effects on matter as we know it, but it has nothing to do with theology or a deity, and ultimately, all the particles defined by the Standard Model are important because they all play a role in the makeup of our universe. To go out of your way to pin the responsibility for making the cosmos as it is on a single particle and endow it with a highly misleading supernatural epithet just because it resonates with the faithful, it just plain wrong. We need to name it in a way that gives credit to Peter Higgs’ lifetime of work since it was his labor that made the LHC’s discovery possible and enabled us to keep extending the Standard Model to the dawn of the cosmos itself.

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Say you need to communicate not just with someone or something far away, but someone or something very, very deep underground, or underwater, or on the other side of a planet. You could create satellite relays which will bounce the signal around to get to your target wherever it is in space, but that requires a lot of money and some very delicate arranging and aligning so the satellites can see each other. And when you need to send a message through water or rock, no satellite will help you there. The signal will just dissipate to nothing before reaching the receiver or slow down to the point where you’d have to transmit a simple message for hours just to make sure the other party can piece it together. What to do, what to do? How about just sending out a beam of neutrinos which will easily travel through solid objects and help ensure high fidelity where other signals will not reach or become totally impractical to use? A team of physicists at FermiLab just so happened to test how well this idea would work and managed to transmit a brief binary message through almost 780 feet of rock at an impressive 99% accuracy rate. Neat, huh? Definitely. But there are some major tradeoffs involved…

First off, if you want to download a movie or watch Netflix underground with your new neutrino wi-fi, you will be sorely disappointed since their more or less average transfer rate was 0.1 bits per second, peaking at a very much not blistering 2.2 bits per second. It’s not that the beam can’t carry more data, it’s that neutrinos interact so rarely with normal matter that this is what could be detected from the 2.5 × 10^14 particles sent. Speaking of detecting the messages sent with neutrino beams, if you want to use a neutrino wi-fi, you’d need a very big, very precisely calibrated modem that weighs around 170 tons, which would make it rather difficult to stuff in a backpack or launch into space for practical use. Finally, you need a very, very powerful beam to send all these neutrinos and aim it directly at your target, much the same way laser communication would work. Certainly, it should be possible to broadcast waves of neutrinos across a wide area in pulses, each pulse representing a binary symbol, but as the neutrinos disperse, they would become a lot harder to detect and that average data rate cited above would plummet by at least an order of magnitude if not two. And if you’re already using a very powerful neutrino beam with which it would still take almost five and a half days to download the illustration I used for this post, it’s very hard to imagine that a wide area broadcast would perform comparably.

But all that said, this is just a proof of concept and the whole point was to show that neutrino beams really can transmit data in a scenario where they’re needed to do just that. We shouldn’t expect this test to reach any real or useful data rate. However, it’s difficult to overlook the problems with detecting these neutrinos because any sort of reliable detection would not only involve a massive detector but hiding it somewhere only neutrinos will pass without any difficulty. Suddenly a satellite array looks like a much more practical solution since satellites be able to provide much faster data exchange, won’t have to accommodate enormous internal structures, and be buried underground or sink deep underwater to do their work. Unless we can come up with lightweight but accurate neutrino detectors, this proof of concept is very likely to remain just that, and given the difficulty in the amount of effort necessary to detect something that only rarely and very weakly interacts with matter, it’s not an easy task to put it mildly. At least we know it can actually be done and have a very good use for new detectors right away, thinking out of the box to harness exotic particles for our data needs. Even if we can get something close to a slow dial-up connection going, that would already be more than enough to use in emergencies and scenarios in which we need to talk with the outside world in very challenging and distant environments and a few brief words sent every once in a while would definitely make a real difference.

See: Stancil D., et al. (2012). Demonstration of communication using neutrinos Phys Let A arXiv: 1203.2847v1

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Few things in particle physics seem to be as elusive as the Higgs boson. After many years of smashing a lot of particles, we’ve been able to narrow its probable mass down to about 125 GeV, about five times less than predicted by a number of scientists at the beginning of the search. With CERN staying vague about whether it got even a smidgeon closer to finally finding the particle and its potential habitat getting smaller and smaller, so much so that at this point one starts to wonder if it’s actually too light to impart mass all by itself, maybe we should start considering a future without the boson as the linchpin of mass. What if it’s really not so much the definitive result of the standard model, but actually a placeholder for something far more complex? What if we have to look at the data collected by the LHC again, going over with a fine-tooth comb for anything anomalous or run new experiments which make sure that we detected every but of subatomic shrapnel blasting out of the high energy collision? Far from marking the LHC a failure, it would actually greatly boost its importance…

Here’s an important thing to keep in mind. An unfortunate truth with which scientists are often faced is that the public at large has been conditioned that every project has two possible outcomes. You set out to find or build something and you either succeed or fail. Projects are evaluated for how well they achieve a goal, not how the knowledge gained through attempting them can be applied elsewhere. Yet, in the research world, failure isn’t only an option, but sometimes, a very desirable one because the post-mortem of your attempt to prove a new hypothesis or test an old one can yield new ideas and new approaches. Patent offices are filled with all sorts of innovations that came from accidents, failures, or discarded efforts. Who cares if you didn’t prove that some plant in a distant rainforest can be used as an ingredient in a moisturizing skin cream if it turns out to have an aggressive effect against melanoma? Failure to create an artificial mind plagues the AI field, and yet we make complex signal processing algorithms and our questions have leaked over into fascinating new research into how the human brain actually works. We didn’t find the Higgs boson? Too bad, so sad. But now we have one very bizarre and complex mystery on the origins of mass and a few trillion data points to crunch.

All right, so if there’s no Higgs boson, what else could there be? Well, there’s a myriad of ideas out there and they range from the incredibly exotic, to hinting at some unification between quantum mechanics and our run of the mill standard model particles. In one scenario from a set of theories known as Technicolor Models, an interaction between W and Z bosons breaks symmetry and generates mass. This approach relies on what’s known as confinement, the idea that quarks are tied to each other by charges that prompt them to appear as jets of particles, clumping together into baryons and mesons, or ordinary particles and quark-anti-quark pairs in plain English. Since this symmetry breaks at around 250 GeV, roughly twice the new upper bound set for a wild Higgs to appear out of the particle showers, it would mean that we’ve already went below the point where the appearance of the said wild Higgs boson would falsify this hypothesis. It also gives us a new target area for further study should the Higgs fail to materialize completely, though how to evaluate confinement at such a small scale is something best left for a professional physicist to consider since the equations involved aren’t for the faint of heart to put it mildly, and the mechanics of the experiment are nothing to take lightly either.

But despite the fact that physics could jettison the Higgs if it fails to appear, one prominent tehologian across the pond adopted the search for the boson as his justification for belief in a deity, declaring that physics is filled with esoteric and exotic proposals like dark matter and dark energy, posits ideas that cannot be proven, and believes that the Higgs exists solely because it’s necessary to make their equations work. Of course our theologian in question, Alister McGrath, is woefully mistaken on all counts. If physicists really believed that the universe contains the Higgs boson in the same way theists believe in a deity, they wouldn’t build the LHC in a very complex and expensive attempt to prove whether it exists, and as pointed out above, there are other ways of making the standard model work on paper. Rather than simply looking to confirm their beliefs, scientists at the CERN labs are putting their theories to the test, and they’ll move on should they fail to summon the Higgs, rather than doing the same thing as McGrath; shrugging and declaring that some things just can’t be proven, but since the math works, then it must be correct and the Higgs boson must therefore exist because it makes the math work, using a textbook example of circular logic. Though explaining why they’re moving on would be an uphill fight against those stuck in a very black and white, I-want-to-believe kind of mindset…

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Heat is a relative term to those of us living on this planet. The highest natural temperature we’ve recorded is a downright uncomfortable 57.8 °C recorded in Libya, while the coldest is what the vast majority of us would call a bone-chilling -89.7 °C at Antarctica’s Vostok Station. In the lab, however, scientists can take temperatures to otherworldly extremes. On the cold end of the scale, they’ve come very close to absolute zero, a temperature at which entropy itself seems to stop and thought to be nearly impossible to happen naturally. But when you start dealing with heat, you can crank things up a lot more than a few hundred degrees in the desired direction and keep it up until matter itself starts to break down under the extreme conditions. And amazingly, the RHIC, the original doomsday atom-smasher, managed to push beyond that limit during a number of collisions.

One important thing to keep in mind is that the RHIC didn’t just reach the limits of known physics in one event, but instead, the measurements came as a result of crunching data gathered during years of collisions. So what was the record breaking temperature achieved in the atom smasher? Roughly 4 trillion degrees, close to twice the theoretical melting point of protons and neutrons, and several thousand times hotter than the core of a Type II supernova. Matter as we know it can’t exist in these conditions. Instead, we get a soup of quarks and gluons which flow like a frictionless liquid with zero viscosity. And it’s from this searing quark-gluon soup that the universe is thought to have emerged as the newly carved out cosmos expanded and cooled enough for baryogenesis to take place. Of course as with almost all research at the frontier of our knowledge, there were some surprises, mainly in the behavior of the elementary particles in this highly energetic state as was noted by Professor Steven Vigdor, who oversees the RHIC’s research program.

The temperature inferred from these new measurements at RHIC is considerably higher than the long-established maximum possible temperature attainable without the liberation of quarks and gluons from their normal confinement inside individual protons and neutrons. However, quarks and gluons in the matter we see at RHIC behave much more cooperatively than the independent particles initially predicted for QGP [or Quark-Gluon Plasma].

This certainly sets the bar for the researchers at LHC who could achieve even higher temperatures and come even closer to replicating the theoretical quark-gluon plasma which filled the early universe after the Big Bang. On another note, there’s money to be made from these experiments and scientists at Brookhaven patented a few potential commercial uses for what they expect to find from these energetic events, targeting energy efficiency and possibly potential applications for computing and electronics.

Quarks spin in different directions and understanding how and why they do so can help scientists harness the power. It may be possible to replicate this symmetrical spin in graphene, for example, said [RHIC theorist] Dmitri Kharzeev. Graphene is a so-called nanomaterial that scientists believe may replace silicon in super-fast and super-small devices.

So not only can we learn about the Big Bang and high energy physics, but we might get more efficient TVs and cameras, as well as faster computers. This is why when people ask me what’s the benefit of spending a few billion on smashing atoms, I always say that just because the applications of the science they do aren’t really obvious at first glance, it doesn’t mean that there aren’t any. After all, without a particle collider in the 1980s, it’s very likely that you wouldn’t be reading this blog, or any other science blog for that matter since the World Wide Web wouldn’t be around, or was limited to a very small group of people as it was before Tim Bernes Lee had an idea to use the internet to help physicists collaborate on their research. And there was also a matter of refining oncology treatments which come from a better understanding of how to work with particle beams…

[ illustration by Jean Didier ]

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Good news everybody. The LHC is up and running and already started colliding particles, thought they’re not as powerful as the collider can do when its revved up to full speed, just a measly 900 GeV. Now, I say measly not to be funny but because that’s slightly less than the energy of a lazy mosquito casually flying through the air, probably while doing the insect equivalent of yawning. And yet, because of all the impressive prefixes that have been attached to the energies to be produced by CERN’s experiments, some people are warning us of a potential particle of strange matter coalescing during a particularly powerful collision and changing everything around it into more copies of itself until the entire planet becomes a quivering ball of compact strange matter.

strange matter

Think of it as the death by micro black hole scenario, but with an exotic particle cast in the role of the insidious subatomic culprit. According to the idea, several collisions create stable strangelets, elementary particles of a substance thought by some physicists to live in the core of a neutron star. Strangelets are hadrons, much like protons and neutrons. However, instead of being made up of up quarks and down quarks like the matter we all know and love, it contains strange quarks. And unlike the aforementioned micro black holes which would evaporate in an instant, strangelets are supposed to be extremely stable and persist long enough to interact with nearby atomic nuclei, triggering protons and neutrons to rapidly decay into more strange matter. The new batch of strangelets will start to convert matter around itself into even more strange matter, and so on and so forth until the whole planet is just a dense, hot sphere of exotic particles in a classic ice-nine event.

Wait a second. Why does all this sound so familiar? Ah yes, the same worries were raised when the original doomsday collider, the RHIC, was built and I remember vivid animations showing a quark-gluon plasma that shoots out as two hadrons collide at 99.7% the speed of light, spawning a sinister black ooze referred to as a strangelet by the narrators. In reality, according to a paper written as the RHIC was in its planning stages by a quartet of physicists from Europe and the U.S., certain collisions would allow strangelets to form and gain a negative charge before they decay in just a fraction of a second. Of course rather than worry about the planet’s potential fate, the authors urge future detection systems of massive particle colliders to try and detect strange matter which should fall within certain energy and life expectancy parameters. After nearly a decade of work at the RHIC, no strangelets have been announced and as we can see, our planet is still here. As work began on the much more powerful LHC, the doomsday theories of the RHIC era were simply recycled by substituting an acronym and arguing that at higher energies, the fears are now justified.

However, remember when we translated 900 GeV into real world terms? Well, the maximum planned energy levels of the LHC at 7 TeV per beam isn’t exactly all that much energy either. In fact, it’s like flinging an ant at a little under two miles an hour at another ant in a similar predicament. The insects would probably just hit each other, get up, release a few choice chemical signals about the humans who turned them into projectiles, and go on their merry way. On a subatomic level, the end result would be a very violent and messy collision which throws out a stream of short lived particles that physicists will analyze to see if the interactions between these tiny bits of matter and their decay times match the mathematical models. And remember that most particles created this way have extremely low masses in the macro world and don’t stick around for long. Considering that even the longest lived strangelets hypothesized to appear in a relativistic ion collision would decay about 500 times faster than the blink of an eye, or 10^-5 seconds, there’s not a whole lot a damage they can do.

Even if scientists are wrong and by an amazing feat of physics strangelets don’t decay, we’re talking about an infinitesimal particle separated from atoms it can influence by distances billions of times greater than its own diameter. It would take ages to convert enough mass to even register at a level we would notice. This may be one of the reasons why the highly energetic collisions between atmospheric particles and cosmic rays which happen all the time right above our heads haven’t produced enough strangelets to turn our planet into a hyper- dense soup of searing hot strange matter. The other reason? The strange matter hypothesis might be wrong and strangelets don’t form in colliders due to the way quark-gluon plasmas behave…

See: Schaffner-Bielich, J., Greiner, C., Diener, A., & Stöcker, H. (1997). Detectability of strange matter in heavy ion experiments Physical Review C, 55 (6), 3038-3046 DOI: 10.1103/PhysRevC.55.3038

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Do you hear the rumble in the background? That’s the Large Hadron Collider getting ready to smash particles and either seal the standard model of particle physics for the foreseeable future, or overturn much of what we know about quantum mechanics. And of course, once again people are asking whether black holes will form as a result of smashing atoms at nearly the speed of light and if the world is about to be destroyed. Once the first collisions are imminent, don’t be surprised to hear doomsday chatter about micro black holes growing so large, they escape and devour the Earth as they either sink stealthily into the ground, or spectacularly blast the collider to pieces and unleash the kind of explosive doom on the word, it would move Michael Bay to tears.

smashed collider

Believe it or not, many physicists racked their brains about the possibility of micro black holes being made at the LHC and so far, all of them are sure that unless we’re completely way off base about the quantum world, a micro black hole couldn’t possibly harm us. The problem is mass. The smaller the black hole, the less pull it has, the more unstable it is and the faster it evaporates into nothing. Because its mass would be comparable to a few protons, it would evaporate so quickly, it wouldn’t have enough time to actually exist according to very basic calculations. On top of that, it’s radius would be smaller than Planck Length so it would also be way too small to register as a physical object. But again, those are just quick and dirty estimates. The reality of a micro black hole is much more complex and according to a recent paper, there is a chance it could be born and live long enough to be detected. Of course there’s a hitch. It would need five space-time dimensions to do it.

According to a five-dimensional construct of space and time known as the Randall-Sundrum model, there’s a dimension which experiences a gravity leak. Micro black holes would be anchored in this dimension and try to accrete matter faster than their predicted evaporation. Thus, they could last far longer than your quick and dirty estimate would allow them, but they would still evaporate within fractions of a second. To actually grow into an immense monster with which we’re familiar, would take longer than the lifetime of the entire universe. And it’s not guaranteed by any stretch of the imagination because this black hole would need optimal conditions and to be fed with enough matter in enough time and with the kind of precision that would put any atomic clock to shame. The worst possible case scenario in realistic terms? We’d get a micro black hole with the mass of a bacterium which would take countless eons to grow to a truly noticeable size. Considering that the sun would burn out well before that, a micro black that survived by being anchored to an extra dimension is the absolute least of our worries as far as the cosmos is concerned. And on top of that, we need to keep in mind that so far, the only place where the Randall-Sundrum model exists is in the realm of mathematics.

See: Casadio, R., et. al (2009). Theoretical survey of tidal-charged black holes at the LHC, arXiv: 0911.1884v1

[ illustration from the video game Dead Space, story tip by Dr. Ian O’Neill ]

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