Reviewing 2013: Finally Higgs Boson

The massive CMS detector in the LHC (CERN/LHC/CMS)

The massive CMS detector in the LHC (CERN/LHC/CMS)

The hunt for the Higgs Boson, the “last” component of the Standard Model of physics, came to an end in March when physicists analyzing data from the Large Hadron Collider, near Geneva, Switzerland, confirmed that the particle had been discovered. This concluded the “99 percent certainty” discovery announcement of July 2012 that the particle was, without a shadow of a doubt, the Higgs boson. The Higgs boson is the “exchange particle” that mediates the Higgs field, endowing all matter in the universe with mass. The discovery quickly led to the original Higgs boson theoretical physicists — Francois Englert of Belgium (pictured here, left) and Peter Higgs of the United Kingdom (right) — being awarded the 2013 Nobel Prize for Physics.

From Higgs field theory in the 1960s, to the construction of the most complex machine humans have ever conceived (the LHC), to the boson’s ultimate discovery, it’s one of the biggest discoveries and most fascinating physics journeys of our time.

The discovery of a particle consistent with the Higgs boson has been announced by physicists from the Large Hadron Collider’s CMS and ATLAS detectors.

The discovery was detailed at a major conference to update the world on the continuing efforts by CERN scientists to find the last remaining piece of the Standard Model that underpins the foundations of our Universe. The Higgs boson mediates the “Higgs field” that ultimately endows all matter with mass — finding the Higgs is therefore imperative for physicists to understand what gives the Universe substance.

“We have observed a new boson.” – Joe Incandela, CMS lead physicist
When reports first surfaced that Peter Higgs — one of the six physicists who, in the 1960s, developed the theory behind Higgs boson — had been invited to CERN for this morning’s announcement, the event became hard to ignore: something historic was about to happen.

And sure enough, at 9 a.m. in Geneva, Switzerland (3 a.m. EST), the news we had all been waiting for was spelled out by Joe Incandela, lead scientist of the CMS experiment: “We have observed a new boson.”

This “new boson” revealed itself in the CMS data as a “bump” at 125 GeV/c2, a value that places it at over 130 times more massive than a proton.

After combining all the results gathered over many different channels in the CMS, the level of certainty — 4.9-sigma — came tantalizingly close to the “Gold Standard” (5-sigma) for subatomic particle discovery. This means there is a one-in-2 million chance of the result being a random fluctuation, or noise. For all intents and purposes, this is a discovery of a particle that acts very much like a Higgs boson.

“This is very preliminary result, but it’s very strong,” added Incandela.

Following the CMS announcement, ATLAS’ Fabiola Gianotti said: “We observe in our data clear signs of a new particle, at the level of five sigma, in the mass region around 126 GeV.” A 5-sigma result represents a one-in-3.5 million chance of the result being noise. This is undeniable proof that a boson, with very Higgs-like qualities, has been discovered by the two detectors.

However, more work needs to be done to figure out if this is indeed a Higgs boson or some unexpected renegade particle that just acts like the Higgs (although the latter is highly unlikely). Also, if it is a Higgs boson, is it a part of a larger Higgs family of particles?

In this high-stakes game of quantum mechanics, statistics and landmark particle discoveries, it can be hard to pronounce a definitive discovery of any subatomic particle, especially if it happens to be a particle that underpins the Universe’s very existence.

The ATLAS and CMS detectors are located at strategic locations around the 17-mile (27-kilometer) circumference ring of superconducting electromagnets of the LHC. Both detectors are looking for, amongst a myriad of other things, evidence for the Higgs. And both, according to this announcement, have found that evidence to a very high degree of statistical certainty.

During all the excitement of a round of LHC results announced in December 2011, physicists pointed to an “excess” of particles around the predicted energy range for one type of theoretical Higgs boson. The energy range was 115 to 130 GeV/c2 and the statistical certainty was 2.4-sigma. 2.4-sigma means that there is a 98 percent chance that the signal is real and not caused by experimental error.

HOWSTUFFWORKS: What is the Higgs boson?

Interestingly, on Monday, physicists of the DZero and CDF experiments at the Fermilab’s now-retired Tevatron particle accelerator announced a 2.9-sigma “bump” around the 115 to 135 GeV/c2 energy range (that’s a 99.998 percent chance that the signal is real and not caused by experimental error).

Not only are different detectors in the same particle accelerators capturing signals that relate to the theoretical energy of the Higgs, different detectors in different accelerators are suggesting the same thing!

“I think we have it,” said CERN Director-General Rolf Heuer. “We have discovered a particle that is consistent with a Higgs boson.”

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