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What's the Matter with Antimatter?

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.

The Spokesman for the LHCb experiment, T. Nakada, describes a model of the experiment to the then Russian Science Minister, M. Kirpichnikov, during his first visit to CERN. F. Grishaev of Russian Mission in Geneva accompanied him.

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.

Assembly of one LHCb hadron calorimeter module for tests at CERN.

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