Higgs keeps mum about universe's secrets – for now

  

The Higgs boson will not open the door to exotic new physics anytime soon. The last remaining quirk in the particle's known properties has vanished from the data of one of the two experiments responsible for detecting the boson.

The Large Hadron Collider at CERN near Geneva, Switzerland, doesn't see the Higgs directly, but instead looks for the slew of particles it decays into. Back in July, when the ATLAS and CMS experiments, both at the LHC, announced the particle's discovery, they reported a number of anomalies, including almost twice as many pairs of photons among the decay debris as is predicted by the standard model of particle physics.

Since the standard model still can't explain everything, including dark matter and gravity, many hoped these anomalies would provide a clue as to how to extend the model.

Rumour confirmed

But, as more LHC data has accumulated, the quirks have vanished, leaving only the photon excess. Now even this looks unlikely to stick around. Last week, ATLAS published its most recent analysis, which failed to shed light on whether the excess was real or not.

CMS, meanwhile, has remained silent on the matter since July – though a rumour that surfaced on Twitter last week suggested that the experiment's excess of photons, also referred to as gamma rays, might have decreased, bringing it closer to the predictions of the standard model.

CMS has now confirmed that this is the case. "The new signal strength measurement from CMS in the two-gamma channel has a central value near to 1 – closer to the standard model value," Joe Incandela, spokesperson for CMS, told New Scientist.

Christophe Ochando of CMS presented the results at the Moriond meeting in La Thuile, Italy,last month

Although the CMS results don't point to any deviation from the standard model, as some had hoped they might, Incandela emphasises that this doesn't mean that the Higgs found at the LHC is the one predicted by the standard model

Options open    


   

Though an excess of photons would provide constraints on how to extend the standard model, the lack of an excess simply leaves the options for extensions wider open, says Albert De Roeck, also of CMS.

A rate of photon decay close to the standard model "is still new physics and there are a great deal of models that can come with such a number", De Roeck says.

Physicist and blogger Matt Strassler points out on his blog that ATLAS still hasn't ruled out the photon excess, leaving the possibility that the Higgs really does decay into more photons than predicted by the standard model.

But he adds that we won't know if this is the case for a while, since the results presented at Moriond represent the full data set collected so far, and the LHC has now shut for two years.

"Sorry, but if there's anything about this Higgs particle that is dramatically different from a Standard Model Higgs (the simplest possible type of Higgs particle), we'll have to look elsewhere in the 2011-2012 data to find it. Or we'll have to wait till 2015," Strassler writes.