Preparations for a balloon flight - EUDET's new magnet has been to space.

The self-sustained magnet in a lab at KEK.

A magnet used in a stratospheric antimatter experiment in Japan is on its way to DESY where it will play an important role in R&D for the ILC detectors. Tobias Haas from DESY reports.

In 1928 Paul Dirac wrote down a most peculiar equation. It was the result of his attempt to combine the two most successful theories of his times, namely Einstein's theory of Special Relativity and Bohr's theory of Quantum Mechanics. The problem was: combining the two theories only made sense if you doubled all known particles. Antimatter was born. Dirac proposed that for each particle there would be an anti-particle—particles that look like exactly like pieces of known "regular" matter, but differ by the sign of their electric charge. When particles and anti-particles meet they annihilate and new particles form out of pure energy. Only four years later the American experimentalist Carl Anderson discovered the positron, the anti-partner of the electron. Dirac's mysterious equation turned out to be a huge success that even got him the Nobel Prize. Today, we create antimatter routinely in the lab. For example, day after day, positrons circulate inside the HERA storage ring. At CERN anti-hydrogen is being generated on a regular basis, though in very small amounts.

Still antimatter keeps puzzling us. At the Big Bang, matter and antimatter should have been produced in roughly equal amounts, but we have not seen antimatter from outer space. How do you look for anti-matter from space? Obviously, you have to look outside the atmosphere since any anti-particle would immediately annihilate when hitting Earth's outer layers. This means that, at the border between the atmosphere and outer space you have to position a spectrometer which distinguishes particles from anti-particles. The heart of such a spectrometer is a strong magnet that bends the particles' paths into one direction and those of anti-particles into the other direction. Normally, such magnets weigh many tons and are highly unsuited for a trip to space. Physicists and engineers at KEK in Japan, however, have developed special magnets that are light enough to be flown with a giant balloon and thus can search for antimatter from outer space. The magnets are superconducting and weigh around 400 kg. They can be operated in a self-sufficient way: before the flight they are filled with helium and are charged using an external power source. During the flight they keep running without any outside connections, producing fields of up to 1.2 Tesla inside the coil.

Recently, researchers from DESY and other European laboratories discovered that these magnets are useful not only for antimatter searches but also for the detector R&D programme to develop detector prototypes for the International Linear Collider, called EUDET. It brings together 31 institutes from 12 countries that are developing and building a highly flexible test beam infrastructure for future detector prototypes for the ILC. For the benefit of worldwide cooperation this infrastructure should be flexible and movable to any location around the globe, hence the need for a light self-sufficient highly mobile magnet. The European Union is supporting the project with 7 Mio Euros over 4 years. The KEK laboratory is one of the collaborators in EUDET and contributes one of its magnets as a loan for the duration of the project. In a first step, the magnet will be brought to DESY to be installed on one of the DESY-III test beams in hall 2. Later on the magnet may also travel to other labs.

On the trip from Japan to Germany the magnet with the awkward name "PCMAG" travels not by balloon but by plane. Delivery at DESY is expected this month. Once arrived, it will be commissioned by the Japanese engineers together with their DESY colleagues. First detector tests will be performed next year.

More information on the antimatter balloon experiment is available online.

-- Tobias Haas

Tobias Haas is a physicist in the ZEUS collaboration at DESY and coordinator of a EUDET workpackage.