Thursday, March 7, 2013

We haven't wet ourselves yet--the Higgs Boson

"This Just in: Higgs Boson Still Boring"


Adam Mann

March 6th, 2013


Physicists from around the world are convening this week and next in Italy at the annual Rencontres de Moriond conference to discuss the latest in particle physics and cosmology. Scientists with the main Higgs-searching experiments, ATLAS and CMS, presented their most recent data and analysis on March 6. Aside from some tantalizing but tenuous hints, they showed few surprises.

“The new particle discovered at CERN last year is looking more and more like a Higgs boson,” wrote spokesman James Gillies in an update on CERN’s website. “However, more analysis is still required before a definitive statement can be made.”
The long-sought Higgs boson was the only missing piece in the Standard Model, which explains how all known particles and forces interact. Physicists with the LHC continue to be extremely cautious about calling the particle they found in July the Higgs boson. That’s because not all of the new particle’s characteristics have been fully analyzed, and it could yet turn out to be something unexpected.

But all information suggests that the Higgs-like boson spotted last year with a mass of 125 gigaelectron volts (GeV) — roughly 125 times heavier than a proton – is the actual real-life Higgs boson.

The main property that scientists are now probing is the particle’s spin, a quantum mechanical characteristic of all subatomic particles that determines how they intermingle with other particles. The Higgs-like boson appears to have a spin of zero, exactly what was predicted beforehand, though a spin of two can’t yet be ruled out. A spin of two would indicate that what scientists found was a new particle, an exciting scenario that would likely tell physicists something about the nature of gravity. But this seems less and less likely.

There are some interesting hints in the data already reported. ATLAS has seen an excess in a particular decay of the Higgs-like particle (to two photons) that might indicate exotic new physics. The excess had been noticed in previous data and it was thought it might disappear with further analysis. But it continues to show up. The result isn’t statistically significant enough to be considered a discovery but it is intriguing that it hasn’t gone away, said theoretical physicist Lisa Randall of Harvard University.

“I think the news so far has been as interesting as it could be, given what we knew already,” she said.

Other physicists haven’t exactly been thrilled by the news from Moriond.

“Big analysis of the new data on the Higgs boson, and – it’s looking pretty vanilla,” tweeted cosmologist Sean Carroll of CalTech.

“All in all, the story is that this is looking very much like a garden variety SM [Standard Model] Higgs,” wrote mathematician Peter Woit of Columbia University on his blog, Not Even Wrong. “The experiments will continue working on improving their analyses of this data, but it seems unlikely that the picture will change much.”

The situation is almost the exact opposite of the excitement and frenzy in July, when CERN physicists made a grand announcement about finding a particle that could very well be the Higgs boson. Back then the discovery was preceded by excited rumors, leaked videos, and great interest among the particle physics community and laymen alike.

Now some physicists are getting a bit nervous that no new particles have turned up at the LHC. In particular, scientists were hoping for a signature of a theory known as supersymmetry, which pairs all known particles with a heavier but nearly identical partner, of which there is still no clear evidence. Supersymmetry has been the favorite way to solve several problems in the Standard Model among particle physicists and is now starting to see more scrutiny as evidence remains scarce.

But many in the field remain hopeful that something will turn up when the LHC comes back online in late 2014. Then, it will be smashing protons together at much higher energies and could conceivably uncover new exotic physics.

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