Time projection chamber and energy

[florianb]

Hi all !

I'm currently studying time projection chambers and I am wondering how the energy of the incident particle (the one that ionizes the gas in the drift chamber) is calculated from the measured signals.

Does anyone have some hints for me ?

Thanks a lot for your answers.
Best regards

[wolverine]

Hi

It is quite simple:

- You have access to a number of charges (electrons) collected by the anode in your TPC when a ionizing particule came in
- you may know the energy needed to create a electron/ion pair in your gaz (in eV)

- so you can infer the energy lost by the particule in the gaz

- you know the energy lost (dE) fot a length (dx) of gaz

- you just assume (in first approximation) that your particule lost her E in a continue way

- then, by using Bethe-Block formulae, you have the incident E of you particule (cos' you already know the A,Z,rho,I of your gaz..)

You may be able to find better way to find it, but I think it works (by asking my memories ...)

Thus ...

[florianb]

Thanks a lot Wolverine !

I came to the same conclusions, but I was still quite unsure about it (I'm not used to Bethe-Bloch, so this looked fuzzy to me).

All the best !

[vanesch]

- then, by using Bethe-Block formulae, you have the incident E of you particule (cos' you already know the A,Z,rho,I of your gaz..)

Thus ...

This doesn't work for high energy particles, because the B-B formula levels off to a constant value (called the "minimum ionizing particle limit") when the particle is highly relativistic. The usual way the energy is inferred with a tracker such as a TPC is by putting the whole thing within a uniform magnetic field. The particles ionize along a track, and you can find those tracks back in a TPC. From the curvature of the track, you can infer the momentum (which equals the energy in the relativistic domain).

cheers,
Patrick.