CERN Accelerating science

� How can you be so sure there is not antimatter around?
If there was antimatter here, around us, it would annihilate with matter and we would see light coming out. But we don't...

About the possibility of antimatter in space (antistars or antigalaxies), theorist have reasons to believe that the Universe is all made of matter. But we are not 100% sure, and that's way there are experiments, like AMS, which are going to look for it.

� If the only difference between a particle and its antiparticle is the charge, how do you distinguish a neutron from an antineutron ?
Neutrons are made of quarks, and antineutrons are made of antiquarks. Quarks and antiquarks have opposite charges, even though they sum up to zero in both cases.

And a very good way to recognize them is to put a neutron close to an antineutron and see how they immediately annihilate.

� What about antiphotons?
Photons have zero charge and do not contain inside objects that are charged, so a photon can not be distinguished from an antiphoton. Photon and antiphotons are the same thing, i.e. the photon is its own antiparticle.

� How do sound waves propagate in antimatter?
If there is a difference between matter and antimatter, it is very very tiny, that's why we are doing experiments here at CERN to investigate it. They are so similar that sound waves, that are vibrations of matter or antimatter, would be identical. An antimatter piano would sound exactly as a matter one.

� How does the gravitational field act on antimatter?
 The gravitational force depends from the energy of an object, and since matter and antimatter have both positive energy, gravitation acts on them in the same way.

This means that an object made of matter and one made of antimatter would both stand on the floor, the latter one not flying off the sky...

� How mach antimatter can you make in one accelerator cycle?
Here at CERN we can produce 50 millions antiprotons in each cycle (about once a minute), that allows us to make a few hundred antihydrogen atoms.

The number could be 10 times higher in particular configurations of the accelerator. This sounds a lot, but expressed in grams it is a billionth of a gram in a year.

� How much does it cost to produce antimatter?
If we count on the production CERN has done over the last 10 years (about 1 billionth of a gram), it has cost a few hundred millions Swiss francs.

� How long will it take to have "new results" out of the AD?
The experiments took about three years to set up, and now that they are ready, it will take a year or two to understand the production of antihydrogen and how to contain it. Then the first studies can be done, where we compare atoms and antiatoms, and this will be two or three years from now.