ALPHA Collaboration

From Wikipedia, the free encyclopedia

ALPHA Logo

The ALPHA Collaboration (Antihydrogen Laser PHysics Apparatus) consists of scientists from a number of scientific institutions whose goal it is to trap neutral antimatter in the form of antihydrogen in a magnetic trap, and to subsequently conduct experiments with the trapped antiatoms. The ultimate goal of this endeavour is to test CPT symmetry through comparison of the atomic spectra of hydrogen and antihydrogen. The ALPHA collaboration consists of some former members of the ATHENA collaboration (the first group to produce significant amounts of cold antihydrogen, in 2002), as well as a number of new members.

The challenges posed by these goals are manifold. Magnetic traps - wherein neutral atoms are trapped using their magnetic moments - are notoriously weak; only atoms with kinetic energies equivalent to less than a kelvin may be trapped. The cold antihydrogen created first in 2002 by the ATHENA and the ATRAP collaborations was produced by merging cold plasmas of positrons (antielectrons) and antiprotons. While this method has been quite successful, it seems to create antiatoms with kinetic energies too large to be trapped. Furthermore, to do laser spectroscopy on these antiatoms it is important that they are in their ground state, something which does not seem to be the case for the majority of the antiatoms created thus far.

Antiprotons are received from CERN's Antiproton Decelerator and are 'mixed' with positrons from a specially-designed positron accumulator in a versatile Penning-Malmerg trap. This is surrounded by a superconducting octupole magnet to form a 'minimum-B' magnetic trap.