Particle physics
Quantum chromodynamics (QCD)
Watch a high-energy photon convert into an electron–positron pair in a nuclear field and the spiraling tracks of both particles in the detector's magnetic field. Vary photon energy and field strength to verify the threshold MeV and the track radius scaling inversely with B.
Equipment
- Virtual detector chamber with magnetic field and nuclear Coulomb field
- Photon-energy slider (readout in MeV)
- Magnetic-field slider (readout in tesla)
- 'Change energy split' button sharing energy between the pair
- Pause button and two opposite helical tracks on the 3D canvas
Procedure
Create a pair above threshold
Pull the photon-energy slider below 1 MeV: the readout warns 'Eγ below the 1.022 MeV threshold' and no pair forms. Raise it to tens of MeV: the photon becomes an electron and a positron — the threshold is the rest energy MeV of the two particles.
Read track radius in the field
At fixed energy, watch the two tracks curl in opposite senses — electron and positron carry opposite charges. Lower the field slider B: the spirals widen since the radius is inversely proportional to B; this is how detectors measure charged-particle momentum.
Change the energy split and compare showers
Press 'Change energy split' to redivide the photon energy between the particles: the less energetic one curls tighter. Push Eγ to maximum and see secondary tracks multiply — hinting at the particle shower that QCD hadronizes from quarks and gluons in a real detector.