[ExI] antimatter asymmetries

[Damien Broderick]

[apologies for the baby talk]


New twist to matter-antimatter mystery

Thursday, 20 March 2008
by Ker Than
Cosmos Online


NEW YORK: A new particle-smashing experiment has 
uncovered surprising evidence that nature treats 
matter and antimatter differently.

The findings, detailed today in the U.K. journal 
Nature, suggests that a complete solution to the 
mystery of why the observable universe is 
dominated by matter, and not antimatter, may have 
to await the discovery of novel particles or the invention of new physics.

Antimatter is the weird twin of matter. For every 
particle of normal matter, there is a particle of 
equal mass but opposite electric charge. When a 
normal particle and an anti-particle collide, 
they annihilate one another in an explosion of pure energy.

Weird twin

According to the standard model of physics, 
matter and antimatter were created in equal 
quantities shortly after the Big Bang. The two 
types of particles should have thus cancelled 
each other out and the universe should be permeated by energy.

But as our existence attests, that did not 
happen. Experiments suggests the universe today 
is composed of about 75 per cent dark energy, 20 
per cent dark matter, and five per cent 
matter/antimatter, with the overwhelming bulk of 
the latter consisting of normal matter.

A major mystery of modern physics is why normal 
matter particles are the building blocks of the 
observable universe. Why are we not made of 
antimatter? Or pure energy? Scientists speculate 
that a tiny imbalance in the early universe 
allowed a small fraction of normal matter – one 
particle for every one billion – to avoid 
annihilation and survive to form stars, planets, and humans.

In recent years, experts have attempted to 
artificially recreate this primaeval imbalance 
using high-energy particle smashers. In this 
latest study, a consortium of international 
researchers called the Belle collaboration, led 
by Paoti Chang at the National Taiwan University 
in Taipei, used the high-energy KEK-B accelerator 
in Japan to collide electrons and their antimatter counterpart, positrons.

When these two particles smash together, they 
create a burst of pure energy which quickly 
materialises into particles called 'B mesons'. 
The experiment created four different types of B 
mesons: neutral B mesons; the antimatter 
counterpart of neutral B mesons, sometimes called 
anti-Bs; positive B mesons; and the antimatter 
counterpart of positive B mesons, called negative B mesons.

Twice the asymmetry

A study in 2004 showed that neutral B mesons 
break down, or "decay," into other subatomic particles faster than anti-Bs.

Scientists had previously assumed that the 
differences in makeup between different B mesons 
were minor. This led them to predict that 
positive B mesons should decay at the same rate 
as neutral B mesons (since both are normal matter 
particles), and that negative B mesons should 
decay at the same rate as anti-Bs (both are antimatter particles).

The new study reveals this isn't true. The team 
found that neutral B mesons decayed faster than 
anti-Bs, but positive B mesons decayed slower than their antiparticles.

"It's not just that there's a 
particle-antiparticle asymmetry. It's that there 
are two particle-antiparticle asymmetries that 
are different from one another," commented 
Michael Peskin, a theorist at Stanford University 
in California, U.S. who was not involved in the 
study. "That's the thing that tips you off 
there's something new that's going on."

The new results are similar to unpublished data 
recently gathered by another international team 
working at the Stanford Linear Accelerator Centre 
called BaBar, of which Peskin is a member.

Considered together, the teams' findings can't 
easily be explained by the standard model of 
physics, and could "hint of an entirely new 
mechanism for particle-antiparticle asymmetry," Peskin said.

http://belle.kek.jp/