Teaching Modern Physics - QuarkNet - Fermilab

Analyzing Bubble Chamber Decays Lab – Teacher’s Key
Goal: Find the mass of Λ ο using the equation E 2 = m 2 +p 2 .
Note: Do not forget to draw the appropriate work on the graph clearly and neatly.
Procedure:
1. Draw two chords on the curve, bisect, and find the radius of the curve for each resulting
particle. Using this radius (R), and the knowledge that a charged particle (q) with a
known mass (m) is moving in a uniform magnetic field (B) at a given velocity (v), write a
relationship that will relate q, v , B, m, and R in the space below.
FB=Fcentr.
q v B = m v 2
R
q B = m v
R
2. Given the above relationship and considering that we will ultimately need to find the
momentum (p), solve the above relationship for the momentum. (HINT: Think back to
the original formula for momentum and manipulate the above to solve for momentum.)
Write your answer below.
q B = m v
R
q B R = m v
q B R = p
3. You should be able to see that R is proportional to p; this means that if you know R you
“know” p.
Rp+ ~ pp+
173
R π- ~ p π-
4. For this experiment, the momentum = 2 x radius (in meters).
pp+: 0.320
p π-: 0.214