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Panel probes new particle results

17 June 11 00:49
Tevatron particle accelerator
By Paul Rincon
Science Editor, BBC News Website

The head of the US' biggest particle physics lab has appointed an expert committee to establish whether or not a new, unanticipated sub-atomic particle has been detected by scientists.

Such a discovery, hinted at by experts in April, would mark one of the most radical changes to physics in years.

But separate science teams at the Tevatron accelerator are at loggerheads over the matter.

The Tevatron is the US rival to Europe's Large Hadron Collider (LHC).

The American machine is operated by the Fermi National Accelerator Laboratory (Fermilab) in Batavia, Illinois.

Two separate multi-purpose detectors - or experiments - analyse data from particle collisions at the Tevatron: DZero and CDF.

Each can cross-check the other team's discoveries.

The committee, set up by Fermilab director Pier Oddone, will aim to resolve the differences between scientists working on the CDF and DZero experiments.

The panel members will "compare notes", aiming to determine the cause of the signal seen by CDF team members, but not by DZero physicists.

Professor Giovanni Punzi, co-spokesperson for the CDF team, told BBC News: "DZero did not confirm our result, but it is not clear they reject it either. So we need to do more work and look at more data."

He said the estimated size of the "excess" - the possible signal of a new particle - seen by CDF was affected by a large statistical uncertainty. Because of this, he said, "it is quite likely that the disagreement [between the CDF and Dzero analyses] is not nearly as large as it appeared at first glance".

Comparing notes

The CDF team was analysing data from collisions between protons and their anti-matter counterparts antiprotons. In these collisions, particles known as W bosons are produced, along with a pair of "jets" of other particles.

It was in these jets that the unexpected "bump" in the team's data came to light, potentially representing a particle that the widely accepted theory of particle physics - known as the Standard Model - does not anticipate.

Confirmation of the CDF results would have signalled a radical change in physics. But last week, an independent analysis of the data carried out by the DZero team failed to find support for the observation.

Professor Stefan Soldner-Rembold, spokesperson for the DZero collaboration, commented: "The probability that the CDF effect is really new physics is very low."

He told BBC News that the data bump might have been caused by the procedure used to to remove the "background" from the soup of interactions produced by particle collisions in the Tevatron.

However, he added: "We would also be open to other possible explanations."

As spokespeople for the CDF and DZero collaborations respectively, Professor Punzi and Professor Soldner-Rembold will sit on the committee.

Fermilab theoreticians Estia Eichten and Keith Ellis have also been appointed to the panel.

There is currently no timeline for the committee to report back, but one source said they hoped the matter would be resolved soon.

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