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EchoReflection t1_iwm2kcx wrote

How exactly do the detectors in the LHC at CERN detect? How are all the different sizes, speed, and masses of particles detected? What is the science behind it?

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physicswizard t1_iwmas17 wrote

There are several different types of detectors in use, with each one specialized to detect specific particles or measure specific quantities, so the answer varies. Look up "silicon trackers", "hadronic/electromagnetic calorimeters", and "muon detectors" for some examples.

In general, the particles radiated by the collisions register "hits" with multiple detectors, and based on the trajectory of these hits and the energy deposited at each one, you can figure out the properties of the particle that made them (e.g. charge, momentum).

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Pharisaeus t1_iwmiris wrote

That's a complex question:

  • Charged particles passing through certain materials can induce electrical charge, so if you create a grate (lots of crossed strips, once a particle hit one you can see the voltage change) you can figure out where particle hit it. Now you can place multiple of those one after another, and this allows you to see how the particle trajectory was changing (eg. that it was curved)
  • Now you can create electrical field between those grates, you can figure out how much this electrical field is bending the particle trajectory (which is proportional to the particle momentum) and in which direction (which is related to the charge)
  • Finally you can make impenetrable shield at the very end which will completely stop the particle, and by measuring the impact you can figure out how much energy was this particle carrying.
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mfb- t1_iwnt52b wrote

> Now you can create electrical field between those grates, you can figure out how much this electrical field is bending the particle trajectory (which is proportional to the particle momentum) and in which direction (which is related to the charge)

A magnetic field.

> Finally you can make impenetrable shield at the very end which will completely stop the particle, and by measuring the impact you can figure out how much energy was this particle carrying.

Calorimeters are most important for uncharged particles (especially photons and neutral kaons) as we can't measure their energy in other ways. For charged particles the tracking system is typically more precise.

They are not the outermost detectors as muons still pass through and get detected in specialized muon chambers outside.

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pM-me_your_Triggers t1_iwmsbd1 wrote

Depends. One of the common sorts of detectors is called a scintillation detector, basically it’s a big hunk of special plastic/glass with a camera attached to it. When particles decay inside the material, they release photons of specific energies. These photons are then detected by the “camera” and the intensities of the photons can be used to figure out what particles decayed and what the energy/mass of the particle was.

Another kind of detector relies on a semi conductive tube with a thin wire passing through it and an inert gas filling the space (proportional tube particle detector). The exterior tube is grounded relative to the wire, which is held at a high voltage to induce a steep electric gradient inside the tube. Decays and electrically charged particles passing through the tube will create a pulse along the wire, which can be measured.

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