Last month rumors swirled that scientists at Fermilab's Tevatron particle accelerator found the Higgs Boson particle. Those reports were untrue, but we have made significant progress towards finding the elusive particle. Why is this such an important discovery?
What is the Higgs Boson?
The Higgs is one of the five bosonic elementary particles, each of which acts as a carrier of a fundamental property of nature. The other four bosons, known as the gauge bosons, are the carriers of the fundamental forces - photons carry electromagnetism, the W and Z bosons both carry the weak nuclear force, and gluons carry the strong nuclear force. (There's also another hypothetical gauge boson, the graviton, which unsurprisingly carries the gravitational force, but that one remains undiscovered.)
Now, the Higgs Boson is the carrier of mass in the universe. It does this by helping to form a Higgs field, a quantum structure through which all the other elementary particles pass. According to the Standard Model of physics, certain particles - such as the photon - pass through the field unaffected and remain massless, while others - such as the W and Z bosons - bring part of the field with them, giving them mass. This subatomic interaction with the Higgs field is what accounts for the existence of all the mass in the universe - at least, if the theory is correct. And the only way to confirm it is to find the Higgs Boson.
Why is the Higgs Boson so difficult to find?
It's a relatively massive subatomic particle, thought to be over a hundred times the mass of a proton. The problem is that the Higgs Boson is thought to exist at extremely high energy levels - so high that only the newly built Large Hadron Collider is thought to be capable of achieving them. And then it only survives for a few seconds before decaying into other particles. Then there's the fact that, despite some rather ingenious deductions of its nature using indirect evidence, we still don't really know exactly where we should be looking for the Higgs Boson.
Today we're getting closer to knowing the Higgs Boson mass
Scientists at Fermilab, home of the world's most powerful particle accelerator that isn't the LHC, have been able to significantly narrow down the possible masses of the Higgs.
Physicists use the unit of measurement GeV/c^2, or Gigaelectronvolts divided by the speed of light squared, to measure the mass of subatomic particles. An electronvolt is the amount of energy of, you guessed it, a single electron. Because of Einstein's iconic equation E=mc^2, dividing the electronvolt by the speed of light squared makes it a unit of mass. And because most subatomic particles are much, much bigger than the tiny electron, we have to bump up the unit of measurement we use from electronvolts to gigaelectronvolts, or a billion electronvolts. Protons have a mass of about one GeV/c^2.
Here's what the Fermilab scientists found - their experiments with the Tevatron particle accelerator have conclusively ruled out a Higgs Boson with a mass between 158 and 175 GeV/c^2. Since the previously known range extends from 114 to 185 GeV/c^2, that means nearly a quarter of the possible masses have been eliminated.
Those remaining higher masses may be soon to fall as well, says physicist Dmitri Denisov:
We are close to completely ruling out a Higgs boson with a large mass. Three years ago, we would not have thought that this would be possible. With more data coming in, our experiments are beginning to be sensitive to a low-mass Higgs boson.
But where is the Higgs Boson?
If the Higgs does exist, it's running out of possible hiding spots, says University of Manchester physicist Stefan Söldner-Rembold:
"Our latest result is based on about twice as much data as a year and a half ago. As we continue to collect and analyze data, the Tevatron experiments will either exclude the Standard Model Higgs boson in the entire allowed mass range or see first hints of its existence."
It was thought until recently that the Large Hadron Collider held the only practical hope of discovering the Higgs Boson, but now it looks as though Fermilab's Tevatron accelerator is back in the hunt as well. As Fermilab spokespeople point out, creating high energy environments may actually be less important than simply creating as huge an amount of collisions as possible. We haven't found the Higgs Boson yet, but we're fast approaching the moment of truth: either we will discover it and confirm the Standard Model in the process, or we will have to reluctantly head back to the drawing board and start building a Higgs-less universe.