Particles, detectors and the rules of matter

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. 01

   Build a mass peak

   Select frozen muon pairs and compare the background.

2. 02

   Reverse the nuclear spin

   Watch the electron preference reverse with the polarization.

3. 03

   Follow a decaying kaon

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

4. 04

   Scatter an electron

   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

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

2. Thomson finds a common particle in cathode rays

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

3. Wilson turns ionisation into a visible track

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

4. Bothe and Geiger ask whether two signals belong together

   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

   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

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

7. Glaser makes a particle trail start the boiling

   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

   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

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

10. Charpak turns a particle’s position into an electrical signal

    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

   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

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

3. Finding the antiproton among thousands of pions

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

4. Two experiments met at the same narrow particle peak

   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

   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

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

2. Wu’s cobalt experiment showed a preference for one direction

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

3. The rare kaon decay that broke CP symmetry

   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

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

5. Electrons found compact constituents inside the proton

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

6. Why quarks look almost free in a hard collision

   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

   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

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

9. How quantum corrections made electroweak theory precise

   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

    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

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

12. Two mass peaks brought the Higgs field within reach

    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. 1894Lenard lets cathode rays out of the tube
2. 1897Thomson finds a common particle in cathode rays
3. 1911Wilson turns ionisation into a visible track
4. 1925Bothe and Geiger ask whether two signals belong together
5. 1932The lead plate that revealed a positron
6. 1932Blackett and Occhialini let a particle take its own photograph
7. 1934Cherenkov follows the blue light to a moving charge
8. 1935Why Yukawa expected a particle between the electron and proton
9. 1939What symmetry tells us about a particle
10. 1947The pion leaves a second track in photographic emulsion
11. 1952Glaser makes a particle trail start the boiling
12. 1955Finding the antiproton among thousands of pions
13. 1957Wu’s cobalt experiment showed a preference for one direction
14. 1960Alvarez’s group finds short-lived particles in combinations of tracks
15. 1961A symmetric law can have an asymmetric ground state
16. 1964The rare kaon decay that broke CP symmetry
17. 1964How quarks brought order to the particle families
18. 1967How electromagnetism and weak decay came to share one theory
19. 1968Charpak turns a particle’s position into an electrical signal
20. 1969Electrons found compact constituents inside the proton
21. 1972How quantum corrections made electroweak theory precise
22. 1973Why a third quark generation opened a way to CP violation
23. 1973Why quarks look almost free in a hard collision
24. 1974Two experiments met at the same narrow particle peak
25. 1975The tau appeared through an electron, a muon and missing energy
26. 1983W and Z particles emerged from the collider debris
27. 2012Two mass peaks brought the Higgs field within reach

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