Shelley Marie DeWyer
PHY525
Analysis of Particle Tracks Key
PAIR PRODUCTION
1. The evidence indicating that a gamma ray was present in the cloud chamber diagram
includes the splitting of two equally opposite charged particle tracks. The fact that each of
the two particles curve in opposite directions indicates that they have opposite charges. In
particle collisions electric charge is conserved therefore the original particle must have
been neutral (a gamma ray is neutral).
2. The curvature of the particle tracks is evidence for the presence of a magnetic field.
3. The electrons have opposite signs because their particle tracks curve in opposite
directions indicating an opposite electric charge. Also the conservation of charge
indicates that the sum of the charges on the particles must be zero.
4. The path of the gamma ray is deduced through the conservation of momentum saying
that in every interaction, the total momentum of the particles involved must be conserved.
5. The electrons were moving slower than the gamma ray due to the conservation of
momentum. It is also apparent that they are slowing down because their particle track is
a solid line.
6. The path of the electrons are spiral because they are losing momentum (reducing their
radius of curvature) by colliding with Hydrogen atoms. These collisions cause the
electrons to slow down through the loss of some of their mass.
7. - was produced with higher energy because its particle track has a radius of curvature
that is straighter (or bigger) than that of +.
PI – MESON DECAY
8. The pi meson is traveling into the page because the spiral indicates the loss of energy
(momentum). It is unlikely that the energy necessary to create a pi meson would come
from the center of the spiral.
9. The electron and the pi meson have the same sign because their particle tracks curve in
the same direction.
10. In the decay of the pi meson a muon is produced along with another particle due to the
conservation of momentum. This particle must be a neutrino because no particle track is
observed indicating its neutral charge.
11. Direct evidence indicating that the electron has a smaller mass than the muon from which
it came is that the radius of curvature in the particle track of the muon is much straighter
than that of the electron. Also, the electron comes form the decay of the muon indicating
that the electron is part of the muon and therefore smaller.
12. The muon must be negative because it curves in the same direction of the electron which
has a negative charge. The conservation of charge also indicates that the electric charge
of the muon must be negative because the pi meson is negative.
13. The pi meson has a longer half-life than the muon because its particle track is longer.
K-LAMBDA ASSOCIATED PRODUCTION
14. The incoming proton collided with a larger charged particle. After the collision the proton
continues to the left while the particle breaks into three separate particles, two neutral
and one +.
15. The proton tracks are not straight but appear to be because they are moving with a high
velocity and have a large mass. The particle tracks of the protons have a large radius of
curvature.
16. The law of conservation of energy indicates that both the  and lambda particles must be
neutral because the + and - produced are opposite in charge. Another factor indicating
that they are neutral is that their particle tacks do not appear in the magnetic field.
17. It is evident that these particles exist even though they leave no particle tracks because
two new particles are produced as each of them decay. Also the particles appear to
emerge form the original event therefore, particles must be produced to conserve energy.
18. The proton and the pi-minus meson created in the decay of the lambda particle have
equal and opposite charges because their particle tracks curve in opposite directions.
19. The lifetime of the lambda particle is longer than that of  because its particle track is
longer.