Anti-hydrogen atoms are neutral

Anti-hydrogen atoms were trapped in a magnetic field and were kicked about by an electric field pulse.

The European Organization for Nuclear Research (CERN) houses the world’s most powerful particle collider, the Large Hadron Collider, and often we hear news of the discoveries made through experiments being carried out using this collider. There is also another experiment which is part of CERN, where experiments on antimatter are being carried out. Scientists at this facility, ALPHA, have succeeded in showing that an atom of anti-Hydrogen is charge neutral to a never-before degree of precision, according to a paper published recently in the journal Nature .

The experiment used anti-hydrogen atoms trapped in a magnetic field, which were kicked about by an electric field pulse. If the anti-hydrogen atom should have a charge, it would react to the electric field, and escape from the trap and disintegrate. Using this technique, the scientists have estimated to the highest precision possible till now that anti-hydrogen atom is neutral. They have in fact improved the accuracy by a factor of twenty compared to earlier known value, and this placed an improved limit on the value.

This is important for several reasons. One is that since the neutrality of matter atoms is known, they would expect to see something different in antimatter atoms that would explain why nature prefers matter over antimatter. There is also the question of whether the universe is charge neutral and whether the sum of all positive charges is equal in magnitude to that of all the negative charges. For normal matter this is known to be true to an accuracy of one part in 10

²¹ . Whether it is true for antimatter also is the question. Also, since the charge of an antiproton is known to a high degree of accuracy, this measurement places an improved limit on the charge of the positron.

Every particle has an antiparticle which has equal mass and opposite charge. The antiparticle of an electron is the positron which has a mass equal to electron’s mass and positive charge. Similarly, the proton’s antiparticle is the antiproton, which has an equal mass as the proton but negative charge. Antimatter is made up of antiparticles — hydrogen is made up of a positively charged nucleus, consisting of one proton, bound to a negatively charged particle, the electron, orbiting it. Therefore, anti-hydrogen consists of just the opposite — a negatively charged nucleus, consisting of the antiproton, bound to a positron orbiting it.

But we do not see these antimatter atoms freely occurring in nature. As the Standard Model of particle physics would have, at the beginning of the universe, that is, at the instant of the Big Bang, there were equal proportions of matter and antimatter present.

However, this symmetry was broken and now we see only stable matter particles in our universe. The Standard Model does not explain how this symmetry has been broken.