A subatomic particle has been
found to switch between matter and antimatter, according to Oxford physicists
analyzing data from the Large Hadron Collider. It turns out that an
unfathomably tiny weight difference between two particles could have saved the
universe from annihilation soon after it began.
Antimatter is kind of the “evil
twin” of normal matter, but it’s surprisingly similar – in fact, the only real
difference is that antimatter has the opposite charge. That means that if ever
a matter and antimatter particle come into contact, they will annihilate each
other in a burst of energy.
To complicate things, some
particles, such as photons, are actually their own antiparticles. Others have
even been seen to exist as a weird mixture of both states at the same time,
thanks to the quantum quirk of superposition (illustrated most famously through
the thought experiment of Schrödinger’s cat.) That means that these particles
actually oscillate between being matter and antimatter.
And now, a new particle has joined
that exclusive club – the charm meson. This subatomic particle is normally made
up of a charm quark and an up antiquark, while its antimatter equivalent
consists of a charm antiquark and an up quark. Normally those states are kept
separate, but the new study shows that charm mesons can spontaneously switch
between the two.
What ultimately gave away the
secret was that the two states have slightly different masses. And we mean
“slightly” in the extreme – the difference is just
0.00000000000000000000000000000000000001 grams.
This incredibly precise
measurement was fished out of data gathered during the Large Hadron Collider’s
second run, by physicists at Oxford University. Charm mesons are produced at
the LHC in proton-proton collisions, and normally they only travel a few
millimeters before they decay into other particles.
By comparing the charm mesons that
tend to travel further versus those that decay sooner, the team identified
differences in mass as the main factor that drives whether a charm meson turns
into an anti-charm meson or not.
An illustration highlighting the
difference in mass between two versions of the charm meson CERN
This absolutely tiny find could
have gigantic implications for the universe. According to the Standard Model of
particle physics, the Big Bang should have produced matter and antimatter in
equal amounts, and over time that all would have collided and annihilated,
leaving the cosmos a very empty place. Obviously that didn’t happen, and
somehow matter came to dominate, but what caused that imbalance?
One hypothesis that the new
discovery raises is that particles like the charm meson will transition from
antimatter to matter more often than they turn from matter to antimatter.
Investigating whether that’s true – and if so, why – could be a major clue that
busts open one of the biggest mysteries of science.
The study has been submitted to
the journal Physical Review Letters, and is currently available on the preprint
server arXiv.
Sources: Oxford University, CERN
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