March 3, 2010

Large Hadron Collider: The Search for the God Particle

Print More

A lot of weird science is happening along the French Swiss border near Geneva these days at the Large Hadron Collider, run by the European Organization for Nuclear Research (CERN). In the eyes of the popular press, the LHC and CERN are many things. In the fictional novel Angels and Demons by Dan Brown, a religious super-sleuth discovers CERN scientists producing antimatter in a plot to destroy the Vatican. Meanwhile, the interwebs are all abuzz about the LHC’s capacity to produce Earth-devouring black holes. Meanwhile we hear talk of dark matter, “supersymmetry” and “the god particle,” as thousands of scientists toil endlessly deep underground, cranking up the power on what has become the largest, most expensive physics experiment in human history.

Will the LHC destroy the Earth? The Universe? Or just Europe? Will the LHC create new particles? What about dark matter? Does antimatter exist?

Many of these wild rumors are false. But then again, some of the craziest rumors are completely true.

The LHC will not create black holes. Probably. A few speculative theories insist such black holes are possible (in the sense that it’s possible all the water in your cup could jump to the left side of the glass), but fortunately these black holes are so tiny, they’d “evaporate” out of existence almost instantly. It’s worth noting that cosmic rays from outer space bombard our planet at LHC-like energies all the time, and so far we’ve had no world-ending black holes to show for it.

The ‘God Particle’

It’s been centuries since Isaac Newton first introduced us to an intelligent discussion about gravity, mass and forces. Therefore it seems ironic that the most high tech experiments in existence today are still attempting to answer very basic questions about these concepts.

The “Standard Model” of particle physics is one of the most successful modern theories of physics. Every particle predicted by the theory has been observed, from mundane electrons and photons (light), to the top quark, discovered well after you and I were born. These particles perform all sorts of tasks, from making electricity and magnetism work to holding together protons in atomic nuclei. But there are a couple (embarrassingly ubiquitous) phenomena this standard model can’t explain. One of these questions: What gives matter mass?

The Higgs Boson was postulated, along with a Higgs Field, to account for the mass of particles. One of the Large Hadron Collider’s chief tasks is to discover this elusive particle. This massive particle is remarkable for many reasons, but certainly not “divine.” So why all this “god particle” talk? Nobel Laureaute Leon Lederman gave the Higgs this exceedingly illustrious nickname. Much to the disappointment of many top scientists, the term has stuck in the popular press.

Want to make your own Higgs Boson? Just take two batches of protons (readily available in any atomic nucleus) and slam them into each other. Out pops an array of exotic particles, eventually including the elusive Higgs boson.

Now for a caveat: Higgs bosons are predicted to be quite massive compared to other elementary particles. This is where Einstein’s famous E = mc2 equation comes into play. To create Higgs Bosons, the collisions need to pack an extreme punch. Normal protons chilling in an atomic nucleus don’t provide that punch.

So to make this transformation happen, you need to give the protons more energy, by giving the protons speed — speed approaching the ultimate upper-limit of fast: the speed of light (c).

To do this, physicists build particle accelerators: tubes filled with magnets, to guide and accelerate charged protons, electrons and other small particles.

As the search broadened to find more elusive particles, predicted by ever-more complicated theories, devices got bigger and bigger, like the half-mile ring here at Cornell, dug into the bedrock beneath Alumni Fields. The 4-mile diameter Tevatron near Chicago held the record for highest-energy collisions prior to the LHC.

Cornell Scientists and the LHC

While CERN is a decidedly European affair, many Cornell physicists provide strong contributions to the collaboration. With seven faculty and dozens of students and postdocs working for the LHC, Cornell is one of the largest American contributors to the experiment. The LHC features four main detectors, each worked on by separate research teams. The two largest detector groups are Atlas and the Compact Muon Solenoid (CMS). The two enormous detection devices are very similar and the two groups compete against each other, to ensure quality and help verify detections. With two separate research groups spotting the same data with different equipment, CERN scientists can be sure they have actually spotted a Higgs Boson and not just a glitch in the hardware.

Professor Julia Thom, physics, contributes analysis software to CMS, crucial to developing accurate data analysis methods for the detection of new particles.

“We’ve been studying, using simulations, what may happen, to get our software ready to jump on the first data and analyze it,” she explained.

Inside the detectors, where collisions of protons occur, quantum mechanics dictates the vast assortment of particle reactions that may occur. This system is inherently probabilistic, and many reactions flood the detection devices with data. Thom’s simulations reproduce these myriad reactions, and help determine what they expect the detection software to see with the device running. The “fake” data produce by these simulations can be fed into real analysis pipelines, to see if the detection software is powerful enough to spot the elusive new particles.

When asked how soon the LHC can be expected to spot new physics, Thom noted it all depends on the physics of these undiscovered particles.

“It is possible that the clues are extremely subtle, and physicists may take a long time to prove anything conclusively,” she said. “It is also possible that new particles have certain characteristics that allow fast detection.” These particles may only present themselves two years from now, when the LHC cranks up from half-power to full-power.

“It’s possible that, given we can go to these high energies, you can see some really glaring, obvious differences [from the standard model],” Thom said. However, she noted that, even at half-power, where the LHC’s power is comparable to the Tevatron, new discoveries are possible. “Things at the LHC are sufficiently different, so you can see interesting new things.”

Dark Matter and Supersymmetry

The Higgs Boson is not the only new particle the LHC wishes to find to help explain fundamental problems.

When astronomers began looking at how stars orbit around the centers of galaxies, they noticed something odd. The speeds at which these stars orbit seemed to suggest there was much more mass in the galaxy than they could see with any telescopes. In essence: A lot of heavy stuff seems to be hiding in the dark corners of every galaxy. They called this missing matter “dark matter.”

But, researchers tell us, this matter isn’t simply everyday matter, lurking in the shadowy places of the universe. Dark matter escapes the view of telescopes because it fails to interact with light or any electromagnetic forces: It is truly invisible. In fact, dark matter could be flowing straight through you right now, and you’d have no natural ability to detect its presence.

Many theorists believe that for every normal particle in existence, a twin-particle exists. They call these particles “supersymmetric,” and these new particles could explain the mysterious dark matter.

Sound farfetched? At least take comfort knowing this approach to new particles is not historically unprecedented. When theorists first attempted to combine special relativity and quantum mechanics, the equations kept on producing negative-energy solutions. This led to the prediction of antimatter: electrons and protons had oppositely charged twins, called positrons (anti-electrons) and antiprotons. These bizarre particles have not only been observed, today we use them in medical applications like PET scans (positron-emission tomography).

So it seems while the LHC will probably fail as a black-hole production facility, or the source of world-domination weaponry, the Large Hadron Collider is set to explore uncharted waters of modern physics. And despite being being such a technical endeavor the LHC has definitely managed to capture public attention, if not always in scientifically-accurate ways.

“Physicists roll their eyes at some of this stuff,” said Thom. “But it has turned out to be great publicity. And you have to have the public on board for this kind of large endeavor.”

Original Author: Munier Salem