viernes, 6 de julio de 2012

Why Higgs Discovery Deserves the Hype

Physicists using the Large Hadron Collider announced yesterday their discovery of a particle consistent with the Higgs boson. The find was expected, but it's still a big deal.

Compact Muon Solenoid
A view through the heart of the Compact Muon Solenoid (CMS), one of the experiments used to detect the Higgs boson. The CMS detects protons smashed together with energies of 7 trillion electron volts.
Yesterday’s big news story about the discovery of a “Higgs-like particle” at Europe’s Large Hadron Collider (LHC) is about as surprising as astronomers finding a new exoplanet. A lot of experts have been expecting this Higgs discovery ever since LHC scientists presented preliminary evidence for the particle last year, and optimism was bolstered when researchers at Fermilab in the U.S. unveiled results that are consistent with those at the LHC.

But even if yesterday’s announcement was widely expected, it’s still a big deal, and I won’t be surprised if July 4, 2012, goes down in history as a landmark date in the human quest to understand the universe. 

Finding a particle with properties similar to those predicted for the Higgs boson is strong indication that our best theory for understanding the origin of mass is on the right track. “Mass” is one of the fundamental properties in the universe, and we owe our very existence to the fact that gravity can gather lots of particles with mass into large structures. This enables a variety of physical and chemical processes to organize those particles into complex structures such as galaxies, stars, planets, and people. Without mass, the universe would consist of a boring sea of elementary particles whizzing around at light speed but not doing anything interesting. If a species of intelligent creatures wants to understand how the universe works, it must attain an understanding of the origin of mass.

According to a theory developed by Peter Higgs and five other physicists in the early 1960s, particles acquire mass by interacting with a field (the Higgs field) that permeates all of space. Particles such as top quarks that interact strongly with this field have a high mass; those that interact weakly (such as electrons and neutrinos) have low mass. Massless particles such as photons don’t interact with the Higgs field at all. And just as an electromagnetic field has an associated particle (the photon), so does the Higgs field. As predicted in the early 1960s, if experimentalists could ever collide particles together with just the right amount of energy, the Higgs field would essentially spit out its own particle — the Higgs boson. 

ATLAS / Large Hadron Collider
This section was mounted close to the heart of the ATLAS experiment to detect the path of particles produced in proton-proton collisions. ATLAS was also involved in the Higgs boson detection.
The theory also predicts that the Higgs boson will decay almost instantaneously into a shower of elementary particles. This is what the LHC actually detected. After studying more than a trillion near-light-speed particle collisions at the LHC over the past several years, the lab’s two detectors (ATLAS and CMS) saw a slight excess of decay events at an energy of about 125 billion electron volts, or GeV for short. For comparison, a proton’s energy is about 1 GeV, meaning the Higgs boson is 125 times more massive than a proton. Theory didn’t predict a specific mass for the Higgs boson, but the measured mass is well within the range of what physicists expected.

According to LHC officials, there’s only about 1 chance in 3 million that the excess events at 125 GeV are a statistical fluke, assuming there are no systematic errors. (In the language of science, this makes it a 5-sigma detection.) People who run physics labs don’t want to end up with eggs splattered on their faces, so I have a very high level of confidence that the LHC team’s claims will stand the test of time. The fact that Fermilab also saw an excess signal around 125 GeV should give the public additional confidence in the discovery.

I’m not a particle physicist, but I read a lot about the field and have interviewed a number of experts over the years. For me, this is the take-home message of yesterday’s announcement:

  • Understanding the origin of mass is fundamental to understanding the nature of the universe, so this new result gives me a lot of confidence that we’re heading in the right direction. With all the weird stuff in relativity and quantum mechanics, physicists sometimes sound a tad bit crazy. But they can’t be too crazy.

  • It’s yet another demonstration of the predictive power of science. For more than a century, physicists have done a remarkable job of seeing patterns and relationships in known particles to predict new particles, and then creating them in laboratories.

    Here’s just a short list of particles that physicists have successfully predicted: neutrons, positrons, antiprotons, neutrinos, W bosons, Z bosons, gluons, six different types of quarks, and now Higgs bosons. This track record demonstrates the power of the human intellect to probe nature at a deep level.

  • In all likelihood, the discovery will point the way to new physics. Note that the LHC scientists called the 125-GeV particle a “Higgs-like particle.” The reason for their caution is that some theories predict more than one type of Higgs particle. The LHC will continue smashing particles, and will eventually crank up the energy of these collisions to twice the current level. This might bust open entirely new particles — perhaps other types of Higgs particles, perhaps particles responsible for dark matter, or perhaps something completely unexpected.

It’s this latter possibility that’s most tantalizing. For years, physicists have been finding particles predicted by their so-called Standard Model. But given the fact we have yet to identify the nature of dark matter and dark energy, and the fact we can’t reconcile general relativity with quantum mechanics, we know there’s a lot of important stuff going on in the universe beyond the Standard Model. Learning more about the particle announced yesterday (or finding new types of Higgs bosons) will rule out some theories and bolster others, enabling physicists to focus their collective mental energy on the most productive avenues of inquiry. That will lead to progress.

One final comment. It did not escape my attention that the mostly European LHC team made this announcement on July 4th. If the U.S. Congress had continued funding the Superconducting Super Collider in the 1990s, yesterday’s discovery would have been made a decade ago, and most of the glory would have gone to American scientists.

Don’t get me wrong: I’m glad to see the science get done. But Congress dropped the ball on a cutting-edge scientific project that barely made a dent in the federal budget, and for a long time to come we can expect the most important discoveries in physics to be made in other countries. University of Michigan physicist Gordon Kane also reminded me that if the U.S. Department of Energy had given Fermilab more funding, the Higgs discovery could have been made several years ago right here in the good ol’ U.S.A. 

Posted By Robert Naeye, July 5, 2012

SOURCE: sky and telescope 

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