Higgs boson signals fade at Large Hadron Collider

leave a comment »

Cern scientist says he sees ‘no striking evidence of anything that could resemble a discovery’ in hunt for Higgs boson

Screens show data from a collision at the Large Hadron Collider. Photograph: Denis Balibouse/Reuters

Ripples of excitement swept through the physics community last month when Cern scientists reported what looked like glimpses of the long-sought Higgs boson. But the hopes have been dashed as it was revealed that the tantalising hints had all but faded away.

Researchers at the Large Hadron Collider (LHC) near Geneva noticed intriguing signals in their data in July that they thought might be caused by the elusive sub-atomic particle. But the latest analyses, based on nearly twice as much data, saw those signals weaken considerably. The news was broken at the Lepton-Photon conference in Mumbai.

“We see no striking evidence of anything that could resemble a discovery,” Guido Tonelli, spokesman for the Compact Muon Solenoid (CMS) detector group at Cern, told the Guardian.
One of the main objectives of the collider is to discover what gives mass to elementary particles, something many physicists credit to the Higgs boson. The LHC has two large, multipurpose detectors, Atlas and CMS, and last month both teams independently reported signals that suggested the Higgs boson might weigh between 120 and 140 GeV (gigaelectronvolts), the units of mass used in particle physics. One GeV is roughly equivalent to the mass of a proton, a subatomic particle found in atomic nuclei.

But in Mumbai both teams said the signals had faded, although it was too early to completely rule out a Higgs particle in that mass range. In particle colliders, it is common for signals to come and go because of statistical blips or fluctuations.

“We might be very close to a depressing moment in which we conclude those fluctuations were statistical jokes, but there is also the possibility of seeing them grow with more data. The exciting part is that after 20 years of preparation and work, I would say this will be decided by Christmas,” Tonelli said.

Results so far suggest that if the most simple version of the Higgs boson is real (some theories call for multiple Higgs particles), it must have a mass between 114GeV and 145GeV.

Particle physicists rank their confidence in new results on a scale in which a “three sigma” signal counts as an “observation”, and a more robust five sigma signal claims a concrete discovery.

A five sigma signal means the chance of the result being a statistical fluke is less than one in three million. Since July, the Higgs-like signals seen by the CMS group have fallen from around 2.8 to 2.3 sigma. Those seen by the Atlas group have dropped from around 2.8 to less than two.

“We need to be patient. We need to take data and analyse them and understand them,” said Fabiola Gianotti, head of the Atlas detector group. “At the same time, we are super-excited, because we are very close. We are months, away from really solving one of the major mysteries in fundamental physics. It’s so close I feel I can touch it with my hand.”

She added: “If the Higgs boson is not there, then a completely new scenario opens up, there must be something else that plays the role of the Higgs boson.”

Written by physicsgg

August 22, 2011 at 11:17 am

Posted in High Energy Physics

Tagged with , ,

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.

%d bloggers like this: