Measurement of the Z boson cross-section in - Harvard University ...

Chapter 3: Luminosity Measurement at the LHC and in ATLAS 78
Figure 3.6: Image of an LHC beam spot produced with a scintillator screen and
viewed on a TV. This image was taken at the LHC Interaction Point 3 on September
10, 2008.
Wire scanners: Wire scanning involves shooting a thin wire through the beam.
As the beam particles hit the wire, secondary particles are emitted which lead to a
current in the wire. Measuring this current as a function of the wire position yields
a profile of the beam. Another way to map the beam profile is to measure the flux of
the secondary particles using scintillators and photomultipliers placed downstream of
the scanner. Wire scanners can be of two types: rotative scanners, in which the wire
is mounted on a fork attached to a rotating motor, and linear scanners, in which the
motor pushes or pulls the wire across the beam.
Wire scanners can be used over a wide range of beam energies, with resolutions
as good as a few microns [66]. The LHC uses them in IP4. Their principal use is for
absolute calibration of other profile monitors, but they can also be used as beam tail