The Higgs Boson

On 4th July 2012 the two experiments CMS and ATLAS at the Large Hadron Collider LHC at CERN presented groundbreaking results in their search for new particles.

The results were based on the data collected from the LHC in 2011 and 2012. To prevent any possible interference, the two experiments had kept their data apart. When the results were released they agreed with each other: both experiments noticed excess events at a mass of 125-126 GeV with 5 sigma confidence level.  The probability that such a result is due to a fluctuation is about 1 in 3 million. 

At that time more subtle characteristics of this new particle could only be determined with limited accuracy. Within this accuracy they are compatible with the predictions of the standard model for the Higgs boson.

The CMS spokesman Joe Incandela (on the right, next to the CERN General Director Rolf Heuer) at the press conference at the presentation of the results: "This is a new particle. It has to be a boson and it is the heaviest boson ever observed."
At the Institute for High Energy Physics in Vienna the physicists eagerly watched the presentation of the results via live stream.

The current state of research

In 2013, last year's results were confirmed. The measurement of the mass of the new particle now has an accuracy of 3 per mille. The result of the CMS experiment is

m = 125.7 ± 0.3 (stat.) ± 0.3 (syst.) GeV

For the detailed investigation of decay properties no deviations from the predictions made by the Standard Model have been observed.

In the next measurements in 2015, the higher center of mass energy and the higher beam intensity will enable more accurate measurements of the decay properties. This accuracy will allow any deviations from the Standard Model to be detected or it will exclude any possible new physical effects.

More details of this discovery is given on the following pages:

The Discovery
The Theory
The Challenge
The Standard Model
Austrian Contributions