August 1, 2012
Scientists Debate The Likelihood That The Higgs Boson Particle Has Been Found
Brett Smith for redOrbit.com - Your Universe Online
After years of theories and speculation, the Higgs boson particle discovery was announced on July 4, or was it?
Several caveats swirled around the somewhat anti-climactic announcement, and almost a month later many scientists familiar with the CERN project are still reluctant to definitively say what they found was the so-called ℠God Particle´.
A new report by the Atlas team working at the Large Hadron Collider that cited a "5.9 sigma" level of certainty is the closest thing the scientific community has come to a ℠Eureka´ moment. Another team, called CMS, claimed results between 4.9 and 5 sigma.
The recognized threshold for claiming the detection of a particle is a 5-sigma level, which equals a one-in-3.5 million chance it does not exist. A 5.9 level means that the Atlas team has calculated the odds of statistical flukes resulting in a ℠false positive´ particle is one-in-300 million.
In the original July 4 announcement, Atlas had claimed a 5-sigma level, but after a more comprehensive analysis, the team has now reached the 5.9 level of significance, according to their report published in the journal Physics Letters B.
Meanwhile, the CMS team has maintained their more conservative 5-sigma level, according to their report submitted to the same journal.
When the LHC smashes together particles at extreme energies in an attempt to create a Higgs particle, the results exist only for fraction of a second before decaying into other particles or flashes of light that can be calculated, caught, and counted.
The Atlas team based their sigma upgrade on the analysis of these "decay channels", which a Standard model Higgs boson will select based on probabilities dictated by the Standard Model theory.
The decay channels involve several particles, including W bosons, Z bosons, photons, and many types of fermions. The more often the created particle decays into these particles at the Higgs-predicted rates, the more readily physicists can proclaim they have found the elusive particle.
“We discovered this new boson through its decays to pairs of photons and pairs of Z bosons (with some indication now that it also decays to W bosons),” wrote team Atlas scientist Jon Butterworth in a recent Guardian op-ed.
“The fact that it decays to Zs and probably also Ws at roughly the expected rate is strong evidence that whatever we have found, it is connected to electroweak symmetry breaking. So I am comfortable calling it a Higgs boson.”
The latest report reinforces a declaration of the existence of a new particle, but even Butterworth has some lingering questions as to whether the particle is indeed the actual Higgs boson, as the many announcements have been carefully phrased to describe a "Higgs-like" particle.
“(W)e have not yet seen the boson decay to fermions” as the Standard Model predicts, wrote Butterworth.
“The most common decay of the Higgs in fact is to fermions - to a b quark/antiquark pair. But there are many other ways such pairs can be produced, and the experiments have trouble extracting the signal from background noise.”
He concludes that “when we see the Higgs decaying in these two channels at roughly the predicted rates, I will probably start calling this new boson the Higgs rather than a Higgs.”