FILE 01 / MATTER & QUANTUM
Capture the charged particles
PENNING TRAPS / ANTIPROTONS + POSITRONS
How do you hold antimatter without letting it touch the chamber?
Antiprotons carry negative charge; positrons carry positive charge. In the laboratory, electric and magnetic fields confine these particles in vacuum so they do not meet the walls. ALPHA collects and prepares the two populations separately before bringing them together. The colored swarms and field traces in this scene make that separation legible; they are not measurements of individual paths or a scale drawing of CERN’s hardware.
A Penning trap works for charged particles because those fields can act on their charge. The question becomes harder once a positron binds to an antiproton: the resulting antihydrogen atom has no net electric charge. The same electric confinement cannot simply hold the neutral atom.
FILE 02 / MATTER & QUANTUM
Make an antiatom
RECOMBINATION / NEUTRAL ANTIHYDROGEN
What changes when two antiparticles become one atom?
ALPHA cools and merges prepared antiprotons and positrons so some can form antihydrogen, the antimatter counterpart of hydrogen. In this view, the cyan and amber marker groups move into an overlapping region; a few small pale markers then stand for newly formed neutral antiatoms. They do not travel back and forth between separate clouds. The colors, quantities, and motions are illustrative rather than observed particle tracks or a calculation of the formation rate.
The transition matters because a neutral atom no longer responds to the electrodes in the way its charged components do. Most antiatoms produced in a trap are difficult to keep away from ordinary matter. In real experiments, cooling and the details of the field geometry are essential to the small population that can be studied.
FILE 03 / MATTER & QUANTUM
Hold the neutral atom
MAGNETIC MINIMUM / A DIFFERENT TRAP
If electric confinement is gone, what keeps antihydrogen off the wall?
Antihydrogen is electrically neutral, but it has a small magnetic moment. ALPHA uses a specially shaped magnetic field to confine suitable antiatoms away from the material boundary. The blue loops in this view stand for that distinct magnetic environment. They are a schematic field motif, not a computed field map or a reconstruction of the ALPHA-g magnet.
This is why “an antimatter trap” cannot be explained with one cage and one switch. Penning traps confine charged antiprotons and positrons; a magnetic minimum trap can confine neutral antihydrogen. Keeping those steps separate reveals what the actual apparatus has to solve.
FILE 04 / MATTER & QUANTUM
Release and detect
ALPHA-g / THE GRAVITY TEST
What did the experiment measure when the trap weakened?
Gravity pulls downward, but it does not require every moving antiatom to strike the lower wall. ALPHA-g gradually weakened the magnetic trap and recorded where escaping antihydrogen annihilated on the chamber boundary. The atoms had motion of their own while the confining fields changed. Some could therefore leave above even when gravity biased the overall outcome below.
For the release conditions, simulations for ordinary matter predicted roughly 80% of exits below and 20% above. ALPHA’s repeated antihydrogen trials were consistent with a downward gravitational pull within the precision of the experiment. The markers here make that downward bias visible; their number and paths are illustrative, not the observed counts or a replay of the data. The result does not solve why the observable universe contains so much more matter than antimatter.
