Friday, March 15, 2013

CERN LHC: New results indicate that Higgs boson particle is discovered

Event display of a H -> 4mu candidate event with m(4l) = 124.1 (125.1) GeV without (with) Z mass constraint. 

The masses of the lepton pairs are 86.3 GeV and 31.6 GeV. 

The event was recorded by ATLAS on 10-Jun-2012, 13:24:31 CEST in run number 204769 as event number 71902630.

Zoom into the tracking detector. Muon tracks are coloured red. 

Credit: ATLAS Experiment © 2012 CERN

At the Moriond Conference today, the ATLAS and CMS collaborations at CERN's Large Hadron Collider (LHC) presented preliminary new results that further elucidate the particle discovered last year.

Having analysed two and a half times more data than was available for the discovery announcement in July, they find that the new particle is looking more and more like a Higgs boson, the particle linked to the mechanism that gives mass to elementary particles.

It remains an open question, however, whether this is the Higgs boson of the Standard Model of particle physics, or possibly the lightest of several bosons predicted in some theories that go beyond the Standard Model. Finding the answer to this question will take time.

Whether or not it is a Higgs boson is demonstrated by how it interacts with other particles, and its quantum properties. For example, a Higgs boson is postulated to have no spin, and in the Standard Model its parity -- a measure of how its mirror image behaves -- should be positive.

CMS and ATLAS have compared a number of options for the spin-parity of this particle, and these all prefer no spin and positive parity. This, coupled with the measured interactions of the new particle with other particles, strongly indicates that it is a Higgs boson.

"The preliminary results with the full 2012 data set are magnificent and to me it is clear that we are dealing with a Higgs boson though we still have a long way to go to know what kind of Higgs boson it is." said CMS spokesperson Joe Incandela.

"The beautiful new results represent a huge effort by many dedicated people. They point to the new particle having the spin-parity of a Higgs boson as in the Standard Model. We are now well started on the measurement programme in the Higgs sector," said ATLAS spokesperson Dave Charlton.

To determine if this is the Standard Model Higgs boson, the collaborations have, for example, to measure precisely the rate at which the boson decays into other particles and compare the results to the predictions.

The detection of the boson is a very rare event -- it takes around 1 trillion (1012) proton-proton collisions for each observed event. To characterize all of the decay modes will require much more data from the LHC.

The above story is reprinted from materials provided by CERN, the European Organization for Nuclear Research.

No comments:

Post a Comment