I have never been comfortable
with the name of ‘antimatter’ and this work conforms to that opinion. We are still dealing with large structures in
the particle universe and while destructive pairing is plausible and well
demonstrated, the idea that we have a mirror image is useful but still
speculative. This work shows us that the
mirror image postulate is quite questionable.
Of course, we will push mirror
image models simply because they will allow us some form of progress. Yet is also feel we are largely blind to an
awful lot of the content of particle physics simply because we can not measure
it all. Sort of why we call it dark
matter.
I presently have a pretty clear
conception of what dark matter really is and that naturally leads to a much
richer particle universe than we have actually been able to observe.
New twist in antimatter mystery
By Paul RinconScience editor, BBC News website
29 February 2012 Last updated at 12:40 ET
CDF was one of two multi-purpose experiments at the US Tevatron
accelerator near Chicago
Physicists 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
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%.
LHCb is an enormous detector designed to examine CP violation
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".
Statistics of a 'discovery'
Particle physics has an accepted definition for a
"discovery": a five-sigma level of certainty
The number of standard deviations, or sigmas, is a measure of how
unlikely it is that an experimental result is simply down to chance rather than
a real effect
Similarly, tossing a coin and getting a number of heads in a row may
just be chance, rather than a sign of a "loaded" coin
The "three sigma" level represents about the same likelihood
as tossing more than eight heads in a row
Five sigma, on the other hand, would correspond to tossing more than 20
in a row
With independent confirmation by other experiments, five-sigma findings
become accepted discoveries
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.
"What we've seen is a hint that's worth looking into. And the fact
that CDF see the same effect as LHCb is confirmation that this is really worth
doing."
These views were echoed by Giovanni Punzi: "This effect is
definitely much larger than anything that had been predicted. So there will be
discussions between the theoreticians, asking: 'Is this really new physics, or
did we get our calculations wrong?'"
The dominance of matter in the Universe is possible only if there are
differences in the behaviour of particles and anti-particles.
Physicists had already seen such differences - known as called "CP
violation". But these known differences are much too small to explain why
the Universe appears to prefer matter over anti-matter.
One other experiment has shown a significant "asymmetry" of
matter over antimatter. In June 2010, physicists working on the Tevatron's
DZero experiment reported seeing
a 1% difference in the production of pairs of muon (matter) particles
and pairs of anti-muons (antimatter).
The Tevatron was shut down in September last year, after the American
government rejected a proposal to fund it until 2014, but scientists continue
to analyse data gathered up to the end of operations.
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