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A discussion about the particle cloud chamber

Charged particles passing through a chamber filled with hydrogen-neon liquid leave bubbles along their paths Image: BEBC Subatomic particles are far too tiny to see, so over the years physicists have devised ingenious ways to detect and visualise them, often forming beautiful patterns and pictures in the process.

From early experiments with cloud chambers to state-of-the-art animations of Higgs-boson decays, data visualisation in particle physics has come a long way. Here are just a few of the most striking images of particle interactions - or "event displays" - from over the years.

Cloud chambers This photograph, taken in 1932 by American physicist Carl D Andersonshows a track left by the first positron ever identified.

  1. This could be done in groups, or you could give each photograph a number and pin them up around the room. And the images continue to become increasingly detailed.
  2. CERN Charpak and the move to digital Though spark chambers were faster than bubble chambers, they did not provide the detail — the resolution — that a bubble chamber could. In a spark chamber, particles pass through an inert gas such as neon, forming tracks.
  3. During the first half of the 20th century, experiments that looked at cosmic rays passing through cloud chambers revealed the existence of several fundamental particles, including the positron, the muon and the first strange particles.

The line across the centre of the image is a 6 millimetre lead plate separating the upper and lower halves of the chamber. Wikimedia Commons Some detectors can reveal subatomic particles by making their tracks visible to the naked eye. A cloud chamber is a box containing a supersaturated vapour.

  • Here are some possibilities;
  • A voltage is applied to plates on alternate sides of the chamber, causing a trail of sparks to flash across the gas;
  • As charged particles pass through, they ionise the vapour, which condenses to form droplets on the ions;
  • Watch people at work at a scanning table starting from 3:

As charged particles pass through, they ionise the vapour, which condenses to form droplets on the ions. The tracks of the particles become visible as trails of droplets, which can be photographed.

  • A cloud chamber is a box containing a supersaturated vapour;
  • After about five hours the particles have grown to sizes sufficient to begin to seed cloud droplets Image;
  • This could be the type of radiation, or it could be something more abstract like how easily they could explain what is happening, or how interesting the photograph looks.

During the first half of the 20th century, experiments that looked at cosmic rays passing through cloud chambers revealed the existence of several fundamental particles, including the positron, the muon and the first strange particles. The CLOUD chamber is used both to grow the aerosol particle seeds for cloud droplets and also to form the clouds themselves.

After about five hours the particles have grown to sizes sufficient to begin to seed cloud droplets Image: Glaser invented the bubble chamber 1952, for which he was awarded the 1960 Nobel prize in physics.

  1. It works on a similar principle to the cloud chamber, but the tracks are made visible as a trail of bubbles in a superheated liquid that is about to boil rather than in a vapour.
  2. The rarity of these events is an indication that the nucleus is much smaller than the atom. The computer system Megatek rendered the displays Video.
  3. The line across the centre of the image is a 6 millimetre lead plate separating the upper and lower halves of the chamber. Charpak's invention, for which he received the 1992 Nobel prize in physics, revolutionized particle detection.
  4. The rarity of these events is an indication that the nucleus is much smaller than the atom.
  5. The displays reflect this complexity but are useful since they can provide a visual summary of what happened; you can describe geography and a route with words, but sometimes nothing beats a map with a line marking the way. Photographs were no longer the only way to visualise particle tracks in detail; rather, event displays became visual representations of patterns of digital signals that corresponded to the particles produced in an interaction.

It works on a similar principle to the cloud chamber, but the tracks are made visible as a trail of bubbles in a superheated liquid that is about to boil rather than in a vapour. CERN's famous bubble chamber Gargamelle was instrumental in the 1973 discovery of weak neutral currents. The discovery confirmed the prediction of such currents by electroweak theory, which treated the weak force and the electromagnetic force as different facets of the same interaction.

This photograph of tracks in the Gargamelle bubble chamber provided the first confirmation of the weak neutral-current interaction. The Gargamelle collaboration announced the discovery of the weak neutral current in July 1973 Image: Other non-visual particle detectors triggered cameras to take photographs in the chamber, and these were later projected onto a special table for analysis. At CERN in the 1960s, people worked in shifts round the clock to analyse such images, sifting through many thousands to find the events that physicists found interesting.

They then measured the length and direction of the interesting particle tracks. Watch people at work at a scanning table starting from 3: Bubbles form at this point and the chamber must be recompressed to stop the bubble growth for a picture.

This limits the rate at which events can be collected. The spark chamber improved on the bubble chamber as interactions could be captured much more rapidly. In a spark chamber, particles pass through an inert gas such as neon, forming tracks. A voltage is applied to plates on alternate sides of the chamber, causing a trail of sparks to flash across the gas.

CERN Charpak and the move to digital Though spark chambers were faster than bubble chambers, they did not provide the detail — the resolution — that a bubble chamber could. Charpak's chamber was basically a gas-filled box with a large number of parallel detector wires, each connected to individual transistor amplifiers.

Now there was no need for a spark; a detector wire connected to an amplifier can detect a much smaller effect. Charpak's invention, for which he received the 1992 Nobel prize in physics, revolutionized particle detection.

It made data acquisition quick, automated and electronic.

Display of cloud chamber photographs

As a result, it also changed the nature of event displays. Photographs were no longer the only way to visualise particle tracks in detail; rather, event displays became visual representations of patterns of digital signals that corresponded to the particles produced in an interaction.

Moreover, the event display can be made to show only those tracks that physicists find interesting. So the display has become a visual representation of the most interesting part of what happened in the detector.

Seeing the invisible: Event displays in particle physics

As detectors became more complex and able to detect many more particles at a time, the amount of data associated with each event increased and event displays became correspondingly more intricate. Researchers developed software that could interpret the patterns of signals picked up by detectors and recreate them as images in 3D space.

  • Watch people at work at a scanning table starting from 3;
  • In collisions with nitrogen and other heavy atoms, the alpha particle sometimes bounces backwards, showing a collision with something more massive.

The advent of computer colour screens in the late 1970s allowed physicists for the first time to render event displays in full colour, leading to discussions about which were the most suitable hues to represent different particles. Coupled with computer systems such as the Megatek, these displays could even be manipulated in 3D. The computer system Megatek rendered the displays Video: The displays reflect this complexity but are useful since they can provide a visual summary of what happened; you can describe geography and a route with words, but sometimes nothing beats a map with a line marking the way.

CMS These days to create a display, experiment teams run software that converts the data into graphical objects. The details of the display — views, colours, what is shown and what is not — depend on the particular use-case.

Physicists at CERN use event displays for viewing geometry, developing algorithms and detector monitoring. The displays are also frequently used in communicating LHC science to the general public and to the media. And the images continue to become increasingly detailed. ALICE "These days thanks to advances in computing we're capable of so much more graphics-wise and can run on many different devices and platforms," says McCauley.

But one thing has not changed.