[Phys-L] In Search of Anti-Matter Properties
The ALPHA-g experiment at Cern, Switzerland, was designed to test the effects
of gravity by containing antihydrogen in a vertical, two-metre tall trap.
Antihydrogen is created in the trap by combining its antimatter constituents:
the position and the antiproton.
Positrons are readily produced by some radioactive materials – we used
radioactive table salt. To create cold antiprotons, however, we had to use
immense particle accelerators and a unique decelerating facility that operates
at Cern.
Both ingredients are electrically charged and can be trapped and stored
independently as antimatter in Penning traps, which consist of electric and
magnetic fields.
Anti-atoms, however, are not confined by the Penning traps, and so we had an
additional device called a “magnet bottle trap”, which confined the anti-atoms.
This trap was created by magnetic fields generated by numerous superconducting
magnets.
These were operated to control the relative strengths of the different sides of
the bottle. Notably, if we weakened the top and bottom of the bottle, the atoms
would be able to leave the trap under the influence of gravity.
We counted how many anti-atoms escaped upwards and downwards by detecting the
antimatter annihilations created as the anti-atoms collided with surrounding
matter particles in the trap. By comparing these results against detailed
computer models of this process in normal hydrogen atoms, we were able to infer
the effect of gravity on the anti-hydrogen atoms.
Our results are the first from the ALPHA-g experiment and the first direct
measurement of antimatter’s motion in a gravitational field. They show that
antihydrogen gravitation is the same as that of hydrogen, it falls downwards
rather than rising, within the uncertainty limits of the experiment.
William BertscheReader in Particle Accelerators, UManchesterIntended for a
general scientific audience via "The Conversation" online.
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