Smash particles together in your browser. An electron and a positron counter-rotate around a particle accelerator and cross at the interaction point; the collision sprays particles into a detector, where every charged track curves in the magnetic field — its radius reads off the momentum, and opposite charges bend opposite ways. Slide the collision energy √s to change what can be produced — back-to-back muons, jets of hadrons, or two photons — and crank it to 91 GeV to light up a real Z⁰ boson. It's the same force that steers our charged particle in a magnetic field, turned into a collider.
Collide beams · slide the energy · snap to the Z⁰ at 91 GeV
e⁻ beame⁺ beammuonhadron jetphoton
Collision energy √s30 GeV
Dominant channelhadron jetsjets
Event rate
On Z⁰ peak?1%
Last event—
Total events fired0
Cross-section σ vs √s (log scale, drawn from the Breit-Wigner formula) — the Z⁰ resonance spikes at 91 GeV; the dot is your current energy
A collider turns energy into matter, then reads the debris by how it bends. Einstein's E = mc² runs in reverse here: pour enough energy into a head-on e⁺e⁻ collision and it materializes as new particles — but only those light enough that √s clears twice their mass. What flies out is identified in the detector by its track: charged particles curve in the field with radius r = p/(|q|·B), so the bend measures momentum and its direction measures the sign of the charge, while neutral particles leave no track and show up only as energy in the calorimeter. Tune √s to 91 GeV and a real Z⁰ boson appears as a sharp spike in the collision rate — the resonance that early electron–positron colliders were built to study.
Reading the simulation
What the counter-rotating bunches, the curving tracks and the resonance curve are telling you.
1
The ring and the crossing point
On the left, an electron (blue) and a positron (red) counter-rotate around the accelerator ring, held on track by the bending-magnet ticks and topped up each lap at the pulsing RF marker. Because they carry opposite charge, one machine steers both beams. Twice per lap they meet at the interaction point and collide — every crossing flashes the beamline and fires a fresh event into the detector on the right. Turn Auto-collide off and use Collide now to fire them one at a time.
2
Tracks curve by momentum and charge
Products fan out from the centre of the detector. Each charged track is turned by the detector's magnetic field so it bends with radius r = p/(|q|·B): high-momentum tracks run almost straight, low-momentum ones curl tightly, and a + charge and a − charge bend opposite ways — which is exactly how a real detector reads off momentum and sign. Neutral particles feel no force, so photons and neutral hadrons fly dead straight and leave no track, showing up only as a deposit in the outer calorimeter ring.
3
√s selects the channel
The collision energy √s decides what can be made — a particle needs √s above twice its mass. The Dominant channel badge and the lower σ-vs-√s curve track this together: across most of the range the cross-section falls as 1/s and hadron jets dominate, but slide toward 91 GeV and the curve spikes at the Z⁰ resonance. There the On Z⁰ peak? readout climbs to about 99%, and nearly every collision makes a real Z⁰ boson that decays to jets or muon pairs.
How It Works
Accelerate, collide, and read the debris — the three jobs of a real collider experiment.
1
Accelerate on the ring
The two beams gain energy every lap and are steered by the same ring of bending magnets — opposite charges, opposite sense of rotation, one machine. The energy each beam carries fixes the centre-of-mass energy √s available when they meet, and that is the single knob you set here. Real storage rings replace the energy radiated each turn with radio-frequency cavities, the pulsing marker at the top of the ring.
2
Energy becomes matter
When the bunches cross, E = mc² runs in reverse: the collision energy materializes as new particles. A channel is drawn from the real possibilities at that √s — back-to-back muons, a spray of hadron jets, or two photons — with relative rates that shift as thresholds open. Near 91 GeV a real Z⁰ resonance makes collisions vastly more likely, the sharp spike you see in the cross-section curve.
3
Read the detector
Each charged track has its velocity rotated by the exact gyro-angle every sub-step — a Boris-style update for the detector's uniform field — so its curvature is genuine, not sketched: r = p/(|q|·B). Fast tracks run almost straight, slow ones curl, + and − bend opposite ways, and neutral particles fly straight to light only the calorimeter. Telling curved-in-the-tracker from straight-to-the-calorimeter is exactly how experiments identify what came out.
Is this really how a particle collider works?
This particle collider is an accelerator plus event-display simulator, and the visible mechanics are real. Two counter-rotating beams are held on a ring by bending magnets and brought together at an interaction point; the products fan out into a layered detector and their tracks curve in a magnetic field so the curvature reveals each particle's momentum and charge. What a canvas cannot do is compute the quantum probabilities of what comes out — that is quantum field theory. So the choice of channel each collision (muons, hadron jets or photons) is sampled from realistic relative rates rather than derived from first principles, while everything you watch happen to the particles obeys the real physics.
Why do the two tracks curve in opposite directions?
Because the detector's magnetic force on a moving charge, q·v×B, points the opposite way when the charge flips sign. A positive particle and its negative antiparticle fly out back-to-back to conserve momentum, and the same field then bends one clockwise and the other counter-clockwise. The bending radius is r = p/(|q|·B): the higher a particle's momentum, the gentler its curve — which is exactly how real detectors measure momentum from the curvature of a track. It's the same steering you can explore in the charged-particle lab.
What happens at √s ≈ 91 GeV, and what is the Z⁰ boson?
The Z⁰ is the neutral carrier of the weak force, with a mass of about 91 GeV. When the collision energy √s is tuned to that value the electron and positron can annihilate into a real Z⁰, and the production rate spikes by a huge factor — a resonance whose shape is described by the Breit-Wigner curve, about 2.5 GeV wide. The rate meter in the simulator climbs steeply as you slide toward 91 GeV. The Z⁰ then decays almost at once, most often into a spray of hadron jets and sometimes into a pair of muons — the same channels the continuum produces, but far more of them. This is essentially what an electron–positron collider does with its energy sitting right on the Z⁰ resonance.
Why do the photons leave no curving track?
Photons are electrically neutral, so the magnetic force q·v×B is zero for them — nothing bends their path and they travel in a straight line. They also leave no trail in the tracking layers, which only sense charge. Instead a photon dumps its energy in the calorimeter, the outer ring, producing a localized deposit rather than a track. Telling neutral particles from charged ones this way — straight-and-only-in-the-calorimeter versus curved-in-the-tracker — is one of the core jobs of a real detector.
Learn More
Authoritative references to go deeper than the simulation.
Particle accelerator· Wikipedia How real accelerators work, from linear accelerators to circular storage rings.
W and Z bosons· Wikipedia The carriers of the weak force, including the Z⁰ and its mass of about 91 GeV.
Particle Data Group· pdg.lbl.gov The definitive reference tables for particle masses, lifetimes and properties.
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Classroom activity
A ready-to-assign lab using the simulation above. Free to use — nothing to install or sign up for, and no student data leaves the browser.
High school, College10–20 minInteractive simulation
Learning objectives
Apply conservation of energy and momentum to collisions.
Explain how new particles are created from collision energy.
Connect kinetic energy to mass via E = mc².
Variables to change
Collision energy
Particle types
Beam configuration
Procedure
Collide particles at low energy and observe the products.
Increase the collision energy and observe heavier products appear.
Compare head-on collisions with fixed-target collisions.
Observations
Record what products appear as collision energy increases.
Questions
What is conserved in every collision?
Where do new, heavier particles come from?
Why do physicists build higher-energy colliders?
Why are head-on collisions preferred over fixed targets?
What does E = mc² tell us here?
Explanation
In a collider, particles smash together conserving energy and momentum. Their kinetic energy can convert into mass (E = mc²), creating heavier particles — so higher collision energies, especially head-on, reveal more massive and exotic particles.
Answer key (for instructors)
1. Total energy and total momentum (and charge and other quantum numbers).
2. From the collision’s kinetic energy, converted to mass via E = mc².
3. Higher energy can create more massive particles, probing new physics.
4. They put more energy into creating particles rather than into the motion of the products.
5. Mass and energy are interconvertible, so energy can become new matter and vice versa.
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