New twist in antimatter mystery

By | March 2, 2012

lhcbPhysicists have taken a step forward in their efforts to understand why the Universe is dominated by matter, and not its shadowy opposite antimatter.

A US experiment has confirmed previous findings that hinted at phenomena outside our understanding of physics.

The results show that certain matter particles decay differently from their antimatter counterparts.

Such differences could potentially help explain why there is so much more matter in the cosmos than antimatter.

The findings from scientists working on the CDF experiment have been presented at a particle physics meeting in La Thuile, Italy.

CDF was one of two multi-purpose experiments at the now-defunct Tevatron particle smasher in Illinois.

Physicists think the intense heat of the Big Bang should have forged equal amounts of matter and its “mirror image” antimatter. Yet today we live in a Universe composed overwhelmingly of matter.

Antimatter is relatively uncommon, being produced at particle accelerators, in nuclear reactions or by cosmic rays. Getting to the bottom of where all this antimatter went remains one of the great endeavours of particle physics.

The latest results support findings from the LHCb experiment at the Large Hadron Collider, which were announced in November 2011.

Both CDF and LHCb have been looking at the process by which sub-atomic particles called D-mesons decay – or transform – into other ones. For example, D mesons are made up of particles known as charm quarks, and can decay into kaons and pions.

Our best understanding of physics so far, known as the Standard Model, suggests the complicated cascades of decay of D-mesons into other particles should be very nearly the same – within less than 0.1% – as a similar chain of antimatter decays.

But the LHCb team reported a difference of about 0.8%, and the team from CDF have now presented data showing a difference of 0.62%.

Getting such a similar measurement as LHCb was “a bit of a surprise”, according to CDF’s spokesperson Giovanni Punzi, because it is a “very unusual result”.

He told BBC News: “That two separate experiments have found this using different methods – different environments – is very interesting.”

Prof Punzi, from the University of Pisa and Italy’s National Nuclear Physics Institute (INFN), said this was likely to “change the minds of many people about this being just one of those effects, to something that will be considered a confirmed observation – because of this independent result”.

He explained that when the results from CDF and LHCb are combined, the statistical significance almost reaches the four sigma level of certainty. This equates to roughly a one in 16,000 chance that the observation is down to some statistical quirk in the data.

Dr Tara Shears, a particle physicist from Liverpool University, who works on the LHCb experiment, told BBC News: “We don’t know yet if we are seeing the first signs of new physics, or are starting to understand the Standard Model better. …

via BBC News – New twist in antimatter mystery.

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