Harma’s Rig veda search

Dec. 13: Tantalising hints of a predicted but unseen subatomic particle, the last piece of an elegant theory of physics, have emerged for the first time through independent search experiments but uncertainty over what has been spotted persists.

Physicists exploring the debris of more than 470 trillion proton-proton collisions using two particle detectors in a laboratory near Geneva have observed events that may be caused by the particle called the Higgs boson or God particle.

But they still cannot rule out the possibility that what they have observed was nothing more than the antics of other subatomic particles created and destroyed during those collisions in the giant underground particle accelerator called the Large Hadron Collider (LHC).

Researchers at the European Organisation for Nuclear Research, or CERN, today revealed that two detectors in the LHC called ATLAS and CMS have independently observed events that suggest the Higgs boson has a mass 124 to 126 times the mass of a hydrogen atom.

But scientists caution that their data is not strong enough for any conclusion.

“Now more than ever, we have to be extremely careful,” said Aleandro Nisati, an Italian physicist with the ATLAS team. “These are exciting times, but we should not rush to any conclusion for which we do not have enough evidence yet,” Nisati told The Telegraph.

A graphic showing the collision of particles at the CMS experience at CERN on Tuesday in Geneva. (AFP)

The Higgs boson is a predicted member of a class of subatomic particles named after the 20th-century Calcutta physicist Satyendra Nath Bose, and proposed by the British physicist Peter Higgs and others in the 1960s as a mechanism to explain the origin of mass.

It also remains the last missing nugget of the Standard Model, a theory of physics that explains the behaviour of all subatomic particles observed so far and all forces in nature except gravity.

“It’s intriguing that both CMS and ATLAS are seeing a signal at nearly the same mass level,” said Vivek Sharma, an India-born physicist at the University of California, San Diego, who is also head of the CMS Higgs search group at CERN.

The latest results from the CMS group exclude with 95 per cent confidence the existence of the Higgs boson over a wide range of masses: 127 GeV to 600 GeV where 1 GeV is nearly the mass of a hydrogen atom.

The Higgs boson has only a fleeting existence and is predicted to decay through multiple channels that create other subatomic or fundamental particles. Physicists at CERN are hoping to catch a glimpse of the boson by spotting events, or snapshots, of its decay channel products.

The CMS team, using five independent decay channels, has observed excess of events within a mass range of 115 GeV to 127 GeV — the excess that is most compatible with a Higgs boson lies in the vicinity of 124 GeV, but has low relatively statistical significance.

“The rate at which we see the excess is consistent with Higgs bosons being produced, but there is still uncertainty because fluctuations in the background may also produce the same signal,” Sharma told The Telegraph. “But we can now say with confidence that if the Higgs boson exists, it is somewhere between 115 GeV and 127 GeV — I call this our corridor of uncertainty,” he said.

The signals that the CMS and ATLAS teams have seen are akin to tantalising snapshots of something that looks like a chameleon in a forest. Researchers will continue to refine their analyses in the coming months to resolve the uncertainty.

“We need to see what we’ve seen many more times before we can be sure of what we are really observing,” said Sudeshna Banerjee, a physicist at the Tata Institute of Fundamental Research, Mumbai, and a member of the CMS group.

But despite the similarities in the observations by CMS and ATLAS, Banerjee said, there are also some mismatches in the results that need to be resolved.

“Unaccounted background may also explain the signals observed,” said Manjit Kaur, a physicist at Panjab University, Chandigarh, who had helped build the CMS and is now involved in keeping track of the background events in the proton-proton collisions.

The ATLAS group has observed events that look like a Higgs boson with a mass of 126 GeV independently decaying into a pair of photons and four leptons and the analysis suggests that there is a 1 per cent chance that these events are caused by background.

“This is interesting but not enough to claim a discovery,” said Nisati. “For a conclusive determination we need more data to show that the probability that the observed signal is due to background is 3 in 10 million.”