• Question: How much impact does ambient radiation, such as cosmic rays, have on the data collected at CERN? Is the LHC located so far underground in order to minimise this impact?

    Asked by strangeness to Arttu, Ceri, James_M, Monica, Philip on 16 Jun 2011.
    • Photo: Philip Dolan

      Philip Dolan answered on 16 Jun 2011:

      I’m not sure about CERN, but we detect cosmic rays quite regularly in our nitrogen cooled spectrometer. It’s fairly easy to remove them from the data for us. It might be harder in CERN tho, I’m sure James knows more about it.

    • Photo: Ceri Brenner

      Ceri Brenner answered on 16 Jun 2011:

      Background radiation tends to be fairly constant and so you can normally take a background reading (take a measurement with no experiment happening) and then subtract this from your results (that’s what we do with our radiation diagnostics anyway).

    • Photo: James M Monk

      James M Monk answered on 16 Jun 2011:

      The LHC isn’t that far underground because of cosmic rays – other particle accelerators are on or near the surface. Cosmic rays are an issue though. They are used to calibrate the detector when there isn’t any beam, but you also have to make sure when you detect a particle that it didn’t come from a cosmic ray. There are a few ways of doing this: the cosmic ray generally won’t arrive at the same time as a beam collision; the cosmic ray won’t point back to the collision point; generally the cosmic ray will be a different shape (and more isolated) in the detector.