The Viewer Controls

The three-dimensional representation of the inner part of the detector (the vertex and drift chambers) is shown in the right hand panel of the screen. The tracks represent charged particles - neutral particles are not detected in this 'layer' of the detector.
Try using the slider bars to change your view of the event :

• The upper-right slider bar zooms in and out.
• The lower-right slider bar rotates the detector up and down.
• The bottom-right slider bar rotates the detector left and right.
• The bottom-left slider bar adjusts the strength of the magnetic field, which runs longitudinally along the cylinder.

The Magnetic Field

The strength of the magnetic field in the actual detector will be 1.5 tesla.

Why use a magnetic field?
You are probably familiar with the fact that the paths of charged particles in a magnetic field are circular, as quantified by the expression which equates the centripetal force to the force exerted on the particle by the magnetic field:

where

• m is the mass of the particle.
• v is the component of the velocity of the particle perpendicular to the magnetic field.
• r is the radius of the circle the particle moves along in the x-y plane.
• q is the charge of the particle.
• B is the magnetic field.

If we cancel a v on each side, and use the fact that the momentum, p = mv, we are left with

The radius of the circle is small and tight for particles with small momenta in the x-y plane or subject to large magnetic fields.

Note also that the direction of r depends on the sign of q, in other words, positively and negatively charged particles will bend in opposite directions.

These facts help us to identify the particles produced in the and decays.

When you have finished playing, click on the 'next' button to make some measurements.

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