Charge conservation
Charged particles that travel far enough to be seen in
the bubble chamber have a charge that is equal or opposite to that of the
proton.This makes checking
charge conservation in
high energy processes a matter of simple counting.
From the physics point
of view we need to know that:
-
A moving charge is a current; if the charge is positive, the current is in
the same direction as the motion; for a negative charge, the current is in
the opposite direction to its motion.
- A current in a magnetic field experiences a force; so if a moving positive
charge is turned one way by a magnetic field, a moving negative charge
will be turned the other way.
-
In an interaction (some prefer to use the word `collision’) of a
beam particle with a proton in hydrogen, the total charge in the initial
state is
either 0 (if the beam is negative) or 2 (if the beam is positive); so,
in such interaction, total final state charges must be 0 or 2.
-
Apart from being involved in collisions, particles undergo other interactions
called `decays’ (very much like radioactive decays). Here again, charge
is conserved: the total charge of the decay products must equal the charge
of the original particle – which is -1 (eg. K- decay), 0 (eg. K0
decay) or +1 (eg. pi+ decay). Note: for decays,there is only one particle
in the initial
state.
Look at the following picture in which a beam of K- particles enters the CERN
2-metre bubble chamber, filled with liquid hydrogen. (VG: gal02_015 picture
only)
Verify that there is one collsion and that charge is conserved.
Verify that
there is one decay, and what is the charge of the decaying particle?