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Physicists show strengthened signals of Higgs-like particle in publications

Protons collide in the CMS detector at 8 TeV, forming Z bosons which decay into electrons (green lines) and muons (red). Such an event is compatible with the decay of a Standard Model Higgs boson. Image: CMS

The CMS and ATLAS experiments at CERN’s Large Hadron Collider released papers Tuesday confirming their earlier simultaneous, independent discovery of a particle that resembles the Standard Model Higgs boson.

The ATLAS paper reports the observance of a Higgs-like particle with a 5.9 sigma confidence level, up from the 5.0 sigma reported on July 4.

The CMS paper likewise reports a Higgs-like particle, with a 5-sigma level of confidence.

“We believe that what we have observed will be shown to be an elementary spinless particle,” CMS Spokesperson Joe Incandela said. “This is something we have never seen before and really important to study in detail. We are going to see a lot of creativity in trying to get at a better understanding of its properties. It’s a great achievement for the field and an important milestone in human intellectual history.”

The Higgs boson, when created in a particle collision, can decay into different combinations of lighter particles. The CMS paper uses data from 2011 and 2012 to examine the new particle in five decay channels; the ATLAS paper examines five channels with 2011 data and three main channels with 2012 data. Analysis with 2012 data of the third of these channels, in which the particle decays to two W bosons, is new for the ATLAS paper.

Both collaborations found the mass of the heavy new particle to be about 125 to 126 GeV, more than 134 times the mass of a proton.

Last week Fermilab’s CDF and DZero collaborations released a joint paper with their updated Higgs search results. The Tevatron experiments report evidence, with a significance of about 3 sigma, for a particle in the same mass region using the decay channel in which the particle decays to a bottom quark and its antiparticle, which is produced differently at the Tevatron than at the LHC..

“The [LHC] discovery was even more exciting than I had imagined,” said Andrew Lankford, deputy spokesperson for the ATLAS collaboration. “Now, while the sense of excitement persists, it is being overtaken by the many new questions to be addressed.”

Until the collaborations can carefully measure the properties of the new boson, it is not clear whether it is the Standard Model Higgs or a more exotic version of the particle.

Both the CMS and ATLAS collaborations showed their appreciation to every contributor by dedicating their papers to their colleagues who passed away before the discovery was made.

Editor’s note: This article has been updated since it was first published to correct inaccuracies in the number of channels each collaboration used in the published analyses and to clarify the Tevatron's results.