The LHC is set to embark on another year of discovery.  (Source: Claudia Marcelloni / CERN)

Scientists hope, over the next two years, to find dark matter and the legendary Higgs boson. Along the way they'll be looking to evaluate the predictions of key physics theories, such as the string theory.  (Source: Google Images)
Record-setting physics test-bed is back for a second season

Physicists around the world are gearing up for another season of hard, but exciting work as CERN's Large Hadron Collider (LHC) begins its spring runs.

Like most great works of science, the $10B USD LHC had less than glorious beginnings -- its 2009 debut was marked by misinformed public outcry over the possibility that the LHC might create "micro-black holes" (turns out such holes would be harmless) and costly malfunctions that set the collider's startup back a year.

But in 2010, the reactor sprung to life, successfully completely proton beam collisions with a net energy of 7 TeV -- a new world record.  Data collected during those runs by the LHC's cutting edge instruments confirmed decades worth of work from lower power colliders and even provided what might be the first hints of dark matter.

Over the weekend the collider came back online.  Researchers fired 3.5 TeV proton beams around the 17-mile (27-km) circular track, located beneath the Swiss-French border.  CERN spokesman James Gillies stated that proton beam collisions could resume within a week.

i. Alone in the Dark Matter

Next on the agenda for the LHC is to definitively identify dark matter and perhaps dark energy.  To do that, scientists must essentially detect the invisible -- particles that don't emit or respond to light.

Dark matter particles are thought to be composed on one higgsino, the superpartner of the Higgs boson, and two Gauginos, superpartners of the gauge fields.  Gauge fields produce the particles that govern interactions in our universe, including the photon, which is responsible for electromagnetic phenomena (and allows us to view the world as we know it).  Lesser-known products of gauge fields include gluons, responsible for the strong atomic force, and W/Z bosons, responsible for the weak atomic force.

ii. Hunt for the Higgs boson

Speaking of the Higgs boson, the legendary "God particle" is also on the physicists to-do list (or perhaps "to detect" list) for the year.  The Standard Model of particle physics has yet to explain how the W and Z bosons (responsible for radioactivity) have lots of mass, while other vector bosons (photons, gluons) have virtually no mass.  According to one current theory, the Higgs boson is a special component of the W and Z bosons that lends them mass.

If the Higgs boson indeed exists and is a component of the bosons responsible for the weak force, physicists say that it should be detectable at collision speeds under 1.4 TeV.  This would mean that Fermilab's Tevatron (soon to close) and the LHC should both be capable of detecting the particle, though it may take some time to spot one.

According to top physicists, if the Higgs boson is not detected by the LHC by the end of 2012, it will, in effect be verified not to exist.  That would mean that much of the Standard Model of particle physics is broken.  If this is the case, it's back to the drawing board. Physicists know a number of particles that exist; if the Standard Model is broken, researchers will have to come up with new theories to categorize and explain these particles' existence.

Argonne National Laboratory's Thomas LeCompte, who serves as the physics coordinator for the LHC's ATLAS detector told MSNBC in an interview that the task of sifting through the collected data accurately is daunting.  Mr. LeCompte compares it to oil prospecting, stating, "You might strike oil, but you haven't explored the whole field."

He acknowledges that the detection of the Higgs boson is by no means a sure thing.  He comments, "We know the Standard Model is wrong at some level. We know that something lies beyond that. The Higgs is the simplest and most elegant way to push it to the next level, but nature may have something else in mind."

While not finding the Higgs boson would be fundamentally import to physics and fascinating to theoreticians, it might spell public relations disaster for the LHC.  

University of Maryland physicist Nicholas Hadley, who works with the Compact Muon Solenoid detector, summarized at a recent press meeting, "If we don't see it, we will be very excited, because it means that there's something very brand-new. But to say we looked and we didn't find anything ... we'll probably volunteer to have other people stand up here in front of you if that day comes."

iii. Real Gains

Regardless of whether they mysteries of the elusive dark matter or the Higgs boson are solved, CERN researchers are already offering up profound and intriguing discoveries.

At the American Association for the Advancement of Science's annual meeting in Washington, the CERN physicist supervising the LHC's ALICE detector, Yves Schutz, announced the creation of the hottest, densest form of matter on Earth yet.  States Mr. Schultz, "We have produced in the laboratory the hottest matter ever, the densest matter ever."

Nicknamed Quark Soup (officially know as Quark-Gluon Plasma or QGP), the exotic form of matter created by bombarding lead ions with proton beams.  Quark Soup had only been successfully created once before on Earth ever, at the Relativistic Heavy-Ion Collider in New York.

Many physicists had challenged the RHIC's data as the Quark Soup behaved like a super-dense liquid -- an unexpected result for some.  Some physicists had theorized that Quark Soup would act as a gas at hotter temperatures.  But it did not.  Instead the Quark Soup remained a "perfect liquid, which flows without resistance and is completely opaque."

The properties of the Quark Soup precisely match those predicted by a particular superstring theory variant, dubbed AdS/CFT correspondence.  AdS/CFT addresses such arcane mysteries as quantum gravity and higher dimensions.

String theories predict 11 dimensions, including the familiar three dimensions of space and the fourth dimension, time.  Under most string theory models, the titular strings are what compose matter.  These vibrating vector trails snake through space weave complex nets and giving rise to matter, fundamental forces, and everything else in the universe.  

Traditional physicists have attacked string theory as being overly hypothetical and unverifiable in its vague predictions.  But certain refined string theories, such as AdS/CFT could lend credibility to the field, by offering discrete, testable conclusions.

The fact that the LHC verified one of those conclusions is noteworthy.  Mr. Schultz remarks, "I'm surprised that [string theorists] can make a prediction and that it matches what we measured."

iv.  Back to Earth -- Looking Ahead

If string theory, dark matter, and Higgs bosons are enough to make your head spin, take comfort in some more straightforward news from the LHC.

CERN recently announced [press release] that it would be putting off the proposed year long shutdown and update to the LHC until the end of 2012, in lieu of the collider's success.  The reactor will complete yearlong runs this year and next.

At the end of 2012, it will be shut down and repairs will begin.  These repairs will allow the collider to operate at 7 TeV per beam -- the original intend power for the LHC.

While most of the desired subatomic particles should be detectable at the current power, the higher power should make certain kinds of particles easier to detect.  It also should allow for the creation of even hotter particle mixes, further confirming or denying various theories of physics.

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