Wednesday, December 14, 2011

Searching for the Higgs boson - new LHC results

Some of you may have heard that 2 of the experiments at CERN (the European particle collider built to find the Higgs boson).

So, what is the Higgs boson?  Well, in the standard model of particle physics, the Higgs boson is the particle which couples to everything else and gives those particles mass.  It is a strange notion of quantum field theory and may be difficult to understand.  Basically, the language of particle physics is quantum field theory.  Quantum field theory tells us interactions between particles are mediated by bosons.  For a more concrete example, electromagnetic interactions are mediated by photons (the interaction (or gauge) boson of quantum electrodynamics - the quantum field theory that describes electromagnetic interactions).  So, when two like charges repel each other - they two charges are exchanging a bunch of photons to accomplish that interaction.  I hope that helps in some way.

Here is a summary of particle interactions in the standard model:

There is a great video put out by Fermilab (a US particle physics lab) on searching for the Higgs and how it is done:

So, recent results by two different experiments at CERN, ATLAS and CMS, both have constrained the mass of the Higgs to a much smaller region.  CMS gives the limits of 115-127 GeV/c² and ATLAS gives the limits of 116-131 GeV/c². 

For those with a little more interest here are some plots from Sean Carrol's blog (he borrowed from others, so follow the trail down the rabbit hole if you like!).

 Here are the ATLAS preliminary results:
And the CMS preliminary results:
The way you read these plots is this: Any time the black dotted line dips below 1 on the vertical scale, these mass regions for the Higgs are excluded.  Anytime the black line dotted line rises above the yellow shaded region, there is increased confidence the Higgs may be hiding in there.

ATLAS is seeing a peak at approximately 126 GeV/c², while CMS is observes a peak at about 124 GeV/c².

Guido Tonelli, the Spokesperson for CMS said this at the CERN Higgs Seminar:
"…we observe in our data a modest excess of events between 115 and 127 GeV that appears, quite consistently, in five independent channels. The excess is most compatible with a SM Higgs hypothesis in the vicinity of 124 GeV and below, but the statistical significance (2.6 sigma local and 1.9 sigma global after correcting for the LEE in the low mass region) is not large enough to say anything conclusive."

While Fabiola Gianotti, the ATLAS Spokesperson said this (also at the CERN Higgs Seminar):
"We observe an excess of events around m_H ~ 126 GeV:   local significance of 3.6 sigma, with contributions from the  H –>2 gammas (2.8 sigma), H –> ZZ –>4l (2.1 sigma), H –> WW –> lvlv (1.4 sigma), SM Higgs expectation: 2.4 sigma local –> observed excess compatible with signal strength, the global significance (taking account Look-Elsewhere-Effect) is ~2.3 sigma"

So, the big take away is that the LHC is closing in on the Higgs, but there is still a lot of data to collect next year.  It should also be noted that the LHC just finished the 2011 runs about 6 weeks ago.  So these results are very preliminary, but also very promising!

No comments:

Post a Comment

Related Posts Plugin for WordPress, Blogger...