Antimatter may be the stuff of science fiction, but to physicists
it poses a serious question. Why is there not more of it around?
At the Big Bang, matter and antimatter should have been created
in equal amounts, yet today we seem to live in a Universe entirely
made of matter. So where has all the antimatter gone?
When matter and antimatter meet, they annihilate leaving behind
nothing but energy, so it seems strange that there is anything
left at all. It is possible that whole regions of space exist
filled only with antimatter, and experiments are planned in space
to look for them. But most scientists believe that there is a
subtle difference between the way nature treats matter and antimatter,
and that is why a tiny fraction of the matter has survived to
build the Universe we inhabit. If they are right, then just one
proton surviving for every billion to have annihilated with antiprotons
would be enough.
In 1966 the Russian physicist Andrei Sakharov outlined three
necessary conditions for our matter-dominated universe to have
evolved. Among these is a way for nature to favour matter over
antimatter, an effect physicists call 'CP violation'. Experiments
have been trying to measure this difference ever since. The LHCb
experiment is set to provide the definitive answer.
LHCb will watch the production and decay of particles,
called 'B mesons'. These will be produced in abundance at the
LHC and will be studied using a highly specialised detector. The
geometry of the LHCb detector will be quite different to that
of the other LHC experiments.
Rather than surrounding the collision point, the LHCb detector
will look very closely at particles emerging in one direction.
It will reach down to very low angles close to the beamline where
most B mesons will be produced.
Two of the largest components of the LHCb experiment are its
energy-measuring calorimeter and its muon detector. Physicists
from Romania, Russia, and Ukraine are involved in designing the
calorimeter. Meanwhile physicists from Russia's PNPI are working
alongside colleagues from Rio de Janeiro in Brazil in a truly
world-wide collaboration to develop LHCb's muon detection system.