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Indian duo find neutrino fault - Scanner on faster-than-light claim

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  • Published 25.12.11

New Delhi, Dec. 24: Two Indian physicists have identified a problem in the experimental observations earlier this year that appeared to show that subatomic particles called neutrinos can travel faster than light, defying Albert Einstein’s special theory of relativity.

The physicists Ramnath Cowsik and Utpal Sarkar, collaborating with Shmuel Nussinov from Tel Aviv University, have used the laws of conservation of energy and momentum to show that the neutrinos claimed to be faster than light contradict the very observations that spotted them.

Scientists from the European Organisation for Nuclear Research (CERN) had reported earlier this year that neutrinos produced in high-speed proton-proton collisions in an underground laboratory near Geneva had travelled 730km to Italy about 60 billionths of a second faster than light.

Their findings had stunned the physics community because special relativity theory, which has survived every experimental test since Einstein proposed it a century ago, dictates that nothing can travel faster than light.

Cowsik, Sarkar, and Nussinov applied principles of conservation of energy and momentum to the neutrino production process in CERN. Their calculations, based on equations taught in masters-level physics courses, show that if the neutrinos detected in Italy had indeed travelled faster than light, they would have had much lower energies than observed. A paper pointing out this problem is published today in the journal Physical Review Letters.

“The conservation of energy and momentum laws are fundamental to physics. If we assume they apply to these neutrinos, the experiment should not be seeing the neutrino energies that it did,” Cowsik, professor of physics at the Washington University, St. Louis in the US, said.

The CERN neutrinos are produced in a step-wise process. The proton-proton collisions create subatomic particles called pions which decay into neutrinos and another type of particles called muons. The energy balance calculations show that if the neutrinos that are produced through such pion decays travelled faster than light, the neutrinos would carry a smaller fraction of energy that is shared between the neutrinos and the muons.

The calculations emerged from an informal chat about the CERN results the three physicists had when Nussinov and Sarkar, a senior physicist at the Physical Research Laboratory, Ahmedabad, were visiting Cowsik’s office in St Louis about a month ago.

“This is a strong paper with well-articulated arguments,” said Amitava Raychaudhuri, Palit professor of theoretical physics at Calcutta University. “Their calculations show that faster-than-light neutrinos are inconsistent with the neutrino energies seen.”

Cowsik and his colleagues checked their calculations by analysing the neutrino energies seen in an observatory called IceCube buried in Antarctic ice that has been tracking neutrinos created when cosmic rays strike the Earth’s atmosphere. These neutrinos are also produced from the decay of pions and mimic the CERN production process. “The contradictions are exacerbated in the Antarctic experiment — we see neutrinos with extreme high energies,” Cowsik said.

The scientific teams from CERN and the neutrino detector laboratory in Gran Sasso in Italy, aware of the significance of their observations first reported in September this year, have thus far declined to speculate on the theoretical interpretation of their results.

In October, two US-based physicists Andrew Cohen and Sheldon Glashow had published a paper in the journal Physical Review Letters, in which they had shown that faster-than-light neutrinos would rapidly radiate energy in pairs of electrons and positrons.

“But even very strong theoretical calculations can be questioned because they make some assumptions,” Raychaudhuri said. “The feeling within the physics community is that we need another test — we’re all waiting for a second independent experiment to see how neutrinos behave.”

Cowsik said he has “great respect” for the experimental teams in CERN and Gran Sasso. “When physicists encounter such experimental results and they don’t find any obvious errors in their observations, they are compelled to publish and report their findings.”

But, he said, the theoretical calculations suggest that the experimental details need to be reexamined.