What are the "x" marks in a bubble chamber image?

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They’re “stereo fiducials”: marks used to calibrate from the distances on the (somewhat deformable film image) to accurate 3D positions during the scanning process. On the chambers I'm familiar with, they were precision scribe marks on the inner side of the windows.

In the chamber in the Question photo they're found in pairs, with one on the front window and a nearby one on the back. They’ve been very accurately measured independently of the camera and scanning optics.

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shai horowitz
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shai horowitz

Updated on June 29, 2020

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  • shai horowitz
    shai horowitz over 3 years

    Upon looking at a decent number of bubble chamber images I noticed an x shape fermilab bubble chamber trail. What particles are producing these trails?

    • DJohnM
      DJohnM over 5 years
      The Xs may be reference marks on the window of the bubble chamber? Do you have consecutive pictures from the same chamber?
    • dmckee --- ex-moderator kitten
      dmckee --- ex-moderator kitten over 5 years
  • anna v
    anna v over 5 years
    :) . scanning is the discovery of interesting events process, which was done by scanning girls with the instructions for the sought topology by physicists, on scanning tables. Then the film went to the measuring machine, where the chosen events were measured, ie the fiducial marks and points on the tracks were measured and recorded on magnetic tapes, for further analysis.
  • Bob Jacobsen
    Bob Jacobsen over 5 years
    @annav Depends on location and era, I think. The Berkeley convention was to call the device "Scanning and Measuring Projector" (SMP); I was trained to set up fiducials at the beginning. These eventually became the flying spot scanners that led to automated kinematics (which is where I came in). See asprs.org/wp-content/uploads/pers/1964journal/sep/… Berkeley ended up making an undergrad lab out of this, see experimentationlab.berkeley.edu/sites/default/files/pdfs/… but we decommissioned that a couple years ago because we needed the space.
  • anna v
    anna v over 5 years
    I am talking Europe 1960~70s . We had an ENETRA meauring machine and 6 scanning tables given by CERN. Maybe that is why they gave us the machines, they were getting automated :)