---
title: "Particles, detectors and the rules of matter"
description: "How did a track in a photograph become a new particle? Follow the discoveries from cathode rays to the Higgs boson, and try the experiments that connect motion, decay and collision data."
canonical_url: "https://sandboxphysics.com/stories/particle-evidence/"
language: "en"
page_type: "story"
alternate_languages:
  zh-CN: "https://sandboxphysics.com/zh/stories/particle-evidence/"
last_modified: "2026-10-24"
---

27 readings · 3 paths · English and Chinese

# Particles, detectors and the rules of matter

How did a track in a photograph become a new particle? Follow the discoveries from cathode rays to the Higgs boson, and try the experiments that connect motion, decay and collision data.

A track gives a direction. Several tracks together can reveal a parent particle.

A particle is too small to watch directly. What reaches the experimenter is a trail of droplets, a pulse on a wire or a pair of particles flying apart. The discovery begins when someone asks what could have left that particular pattern. These readings follow that question from the apparatus to the result.

Start with Wilson’s chamber if you want to see how a track is made. Follow Anderson’s lead plate to learn how a new particle was identified. The symmetry path starts with a familiar question about mirrors, then builds towards quarks and the origin of elementary-particle masses. Each article explains the terms it needs along the way.

## Change one thing and watch the result

These teaching models use simulated events. The articles link to the original experiments and their published records.

1. ### [Build a mass peak](https://sandboxphysics.com/labs/particle-collider/)

   Select frozen muon pairs and compare the background.

2. ### [Reverse the nuclear spin](https://sandboxphysics.com/labs/weak-decay-parity/)

   Watch the electron preference reverse with the polarization.

3. ### [Follow a decaying kaon](https://sandboxphysics.com/labs/neutral-kaon-interferometer/)

   Compare flavour mixing, survival and the two-pion channel.

4. ### [Scatter an electron](https://sandboxphysics.com/labs/deep-inelastic-scattering/)

   Connect a scattering angle to momentum transfer and internal structure.

P1

## Detecting a passing particle

How a flash, droplet or wire pulse becomes a measurement.

1. ### [Lenard lets cathode rays out of the tube](https://sandboxphysics.com/stories/particle-evidence/lenard-cathode-ray-window/)

   How could a ray made in a nearly empty tube be studied in ordinary air?

2. ### [Thomson finds a common particle in cathode rays](https://sandboxphysics.com/stories/particle-evidence/thomson-electron-charge-mass/)

   How did a glowing discharge tube reveal a particle smaller than an atom?

3. ### [Wilson turns ionisation into a visible track](https://sandboxphysics.com/stories/particle-evidence/wilson-cloud-chamber/)

   Why does a passing particle leave a thin trail of cloud?

4. ### [Bothe and Geiger ask whether two signals belong together](https://sandboxphysics.com/stories/particle-evidence/bothe-coincidence-method/)

   When two counters respond, how can we tell whether they recorded the same event?

5. ### [Blackett and Occhialini let a particle take its own photograph](https://sandboxphysics.com/stories/particle-evidence/blackett-counter-controlled-cloud-chamber/)

   How did two counters turn rare cloud-chamber tracks into a dependable stream of photographs?

6. ### [The pion leaves a second track in photographic emulsion](https://sandboxphysics.com/stories/particle-evidence/powell-pion-emulsion/)

   How did microscopic silver grains reveal that two different particles had passed through a plate?

7. ### [Glaser makes a particle trail start the boiling](https://sandboxphysics.com/stories/particle-evidence/glaser-bubble-chamber/)

   Why can a hot liquid remain clear, then grow bubbles along a particle’s path?

8. ### [Alvarez’s group finds short-lived particles in combinations of tracks](https://sandboxphysics.com/stories/particle-evidence/alvarez-resonance-events/)

   How can a particle be discovered when it decays before it can leave a visible track?

9. ### [Cherenkov follows the blue light to a moving charge](https://sandboxphysics.com/stories/particle-evidence/cherenkov-light-cone/)

   How can a particle outrun light in water without outrunning light in vacuum?

10. ### [Charpak turns a particle’s position into an electrical signal](https://sandboxphysics.com/stories/particle-evidence/charpak-multiwire-chamber/)

    How did a plane of fine wires make particle tracks readable without developing a photograph?

P2

## Finding a new particle

A new track is a clue. Charge, mass and decay reveal what made it.

1. ### [The lead plate that revealed a positron](https://sandboxphysics.com/stories/particle-evidence/anderson-positron-lead-plate/)

   How did Anderson tell a positive electron from an ordinary electron moving the other way?

2. ### [Why Yukawa expected a particle between the electron and proton](https://sandboxphysics.com/stories/particle-evidence/yukawa-meson-range/)

   How can the short reach of the nuclear force suggest the mass of a new particle?

3. ### [Finding the antiproton among thousands of pions](https://sandboxphysics.com/stories/particle-evidence/chamberlain-antiproton/)

   How did the Berkeley team identify a rare negative particle as an antiproton?

4. ### [Two experiments met at the same narrow particle peak](https://sandboxphysics.com/stories/particle-evidence/november-revolution-jpsi/)

   Why did the J and psi observations in 1974 change particle physics so quickly?

5. ### [The tau appeared through an electron, a muon and missing energy](https://sandboxphysics.com/stories/particle-evidence/perl-tau-missing-energy/)

   How could two visible particles reveal a short-lived particle that escaped direct observation?

P3

## Testing the rules of matter

Follow the measurements that revealed quarks, broken symmetries and the Higgs field.

1. ### [What symmetry tells us about a particle](https://sandboxphysics.com/stories/particle-evidence/wigner-symmetry-principles/)

   Why do mass and spin label particles seen from many different viewpoints?

2. ### [Wu’s cobalt experiment showed a preference for one direction](https://sandboxphysics.com/stories/particle-evidence/wu-parity-experiment/)

   What did unequal electron counts have to do with the symmetry of a mirror?

3. ### [The rare kaon decay that broke CP symmetry](https://sandboxphysics.com/stories/particle-evidence/cronin-fitch-kaon-cp/)

   Why did a small number of two-pion decays matter in a long-lived kaon beam?

4. ### [How quarks brought order to the particle families](https://sandboxphysics.com/stories/particle-evidence/gell-mann-quark-classification/)

   Why did combining a few fractionally charged constituents explain so many particles?

5. ### [Electrons found compact constituents inside the proton](https://sandboxphysics.com/stories/particle-evidence/slac-deep-inelastic-scattering/)

   What in the SLAC scattering data suggested that a proton contains smaller charged objects?

6. ### [Why quarks look almost free in a hard collision](https://sandboxphysics.com/stories/particle-evidence/qcd-asymptotic-freedom/)

   How can quarks be tightly bound in a proton yet respond almost independently at short distances?

7. ### [How electromagnetism and weak decay came to share one theory](https://sandboxphysics.com/stories/particle-evidence/electroweak-unification/)

   How can a long-range electric force and short-range weak decay come from one framework?

8. ### [W and Z particles emerged from the collider debris](https://sandboxphysics.com/stories/particle-evidence/ua1-ua2-w-z/)

   How did UA1 and UA2 recognize heavy force carriers that decayed before leaving a track?

9. ### [How quantum corrections made electroweak theory precise](https://sandboxphysics.com/stories/particle-evidence/electroweak-quantum-corrections/)

   Why did a theory that predicted W and Z still need a new way to calculate?

10. ### [A symmetric law can have an asymmetric ground state](https://sandboxphysics.com/stories/particle-evidence/nambu-spontaneous-symmetry/)

    How can a system acquire a preferred state without changing the symmetry of its equations?

11. ### [Why a third quark generation opened a way to CP violation](https://sandboxphysics.com/stories/particle-evidence/kobayashi-maskawa-generations/)

    What changed when quark mixing had three generations instead of two?

12. ### [Two mass peaks brought the Higgs field within reach](https://sandboxphysics.com/stories/particle-evidence/higgs-discovery-mass/)

    What did the 2012 particle discovery reveal about the mechanism behind W and Z masses?

## The experiments in time

Dates below mark the work discussed in each article. Nobel Prize years appear separately on the article pages.

1. 1894 [Lenard lets cathode rays out of the tube](https://sandboxphysics.com/stories/particle-evidence/lenard-cathode-ray-window/)
2. 1897 [Thomson finds a common particle in cathode rays](https://sandboxphysics.com/stories/particle-evidence/thomson-electron-charge-mass/)
3. 1911 [Wilson turns ionisation into a visible track](https://sandboxphysics.com/stories/particle-evidence/wilson-cloud-chamber/)
4. 1925 [Bothe and Geiger ask whether two signals belong together](https://sandboxphysics.com/stories/particle-evidence/bothe-coincidence-method/)
5. 1932 [The lead plate that revealed a positron](https://sandboxphysics.com/stories/particle-evidence/anderson-positron-lead-plate/)
6. 1932 [Blackett and Occhialini let a particle take its own photograph](https://sandboxphysics.com/stories/particle-evidence/blackett-counter-controlled-cloud-chamber/)
7. 1934 [Cherenkov follows the blue light to a moving charge](https://sandboxphysics.com/stories/particle-evidence/cherenkov-light-cone/)
8. 1935 [Why Yukawa expected a particle between the electron and proton](https://sandboxphysics.com/stories/particle-evidence/yukawa-meson-range/)
9. 1939 [What symmetry tells us about a particle](https://sandboxphysics.com/stories/particle-evidence/wigner-symmetry-principles/)
10. 1947 [The pion leaves a second track in photographic emulsion](https://sandboxphysics.com/stories/particle-evidence/powell-pion-emulsion/)
11. 1952 [Glaser makes a particle trail start the boiling](https://sandboxphysics.com/stories/particle-evidence/glaser-bubble-chamber/)
12. 1955 [Finding the antiproton among thousands of pions](https://sandboxphysics.com/stories/particle-evidence/chamberlain-antiproton/)
13. 1957 [Wu’s cobalt experiment showed a preference for one direction](https://sandboxphysics.com/stories/particle-evidence/wu-parity-experiment/)
14. 1960 [Alvarez’s group finds short-lived particles in combinations of tracks](https://sandboxphysics.com/stories/particle-evidence/alvarez-resonance-events/)
15. 1961 [A symmetric law can have an asymmetric ground state](https://sandboxphysics.com/stories/particle-evidence/nambu-spontaneous-symmetry/)
16. 1964 [The rare kaon decay that broke CP symmetry](https://sandboxphysics.com/stories/particle-evidence/cronin-fitch-kaon-cp/)
17. 1964 [How quarks brought order to the particle families](https://sandboxphysics.com/stories/particle-evidence/gell-mann-quark-classification/)
18. 1967 [How electromagnetism and weak decay came to share one theory](https://sandboxphysics.com/stories/particle-evidence/electroweak-unification/)
19. 1968 [Charpak turns a particle’s position into an electrical signal](https://sandboxphysics.com/stories/particle-evidence/charpak-multiwire-chamber/)
20. 1969 [Electrons found compact constituents inside the proton](https://sandboxphysics.com/stories/particle-evidence/slac-deep-inelastic-scattering/)
21. 1972 [How quantum corrections made electroweak theory precise](https://sandboxphysics.com/stories/particle-evidence/electroweak-quantum-corrections/)
22. 1973 [Why a third quark generation opened a way to CP violation](https://sandboxphysics.com/stories/particle-evidence/kobayashi-maskawa-generations/)
23. 1973 [Why quarks look almost free in a hard collision](https://sandboxphysics.com/stories/particle-evidence/qcd-asymptotic-freedom/)
24. 1974 [Two experiments met at the same narrow particle peak](https://sandboxphysics.com/stories/particle-evidence/november-revolution-jpsi/)
25. 1975 [The tau appeared through an electron, a muon and missing energy](https://sandboxphysics.com/stories/particle-evidence/perl-tau-missing-energy/)
26. 1983 [W and Z particles emerged from the collider debris](https://sandboxphysics.com/stories/particle-evidence/ua1-ua2-w-z/)
27. 2012 [Two mass peaks brought the Higgs field within reach](https://sandboxphysics.com/stories/particle-evidence/higgs-discovery-mass/)

## Keep these words nearby

Track

A line of detector signals left by a charged particle.

Invariant mass

The mass calculated from the combined energy and momentum of a chosen group of particles.

Parity

The comparison between a process and its spatially inverted version.

CP symmetry

A comparison that exchanges particles with antiparticles and reverses spatial directions.

Cross section

A measure of how often a specified interaction occurs for a given incident beam and target.

## The neighbouring neutrino story

[Fermi’s beta-decay theory](https://sandboxphysics.com/stories/neutrinos/fermi-beta-decay-theory/) [The neutral-current discovery](https://sandboxphysics.com/stories/neutrinos/gargamelle-neutral-currents/) [The tau neutrino after the tau lepton](https://sandboxphysics.com/stories/neutrinos/donut-tau-neutrino/) [How a detector turns an interaction into a record](https://sandboxphysics.com/stories/neutrinos/neutrino-detector-measurement-chains/)