Particle Physics Questions
Q11.
(a) Complete the table comparing some of the properties of the positive pion, π+, and the proton
Name |
π+ |
Proton |
Relative charge |
+1 |
+1 ![](../../../graphics/symbols/nuclides/ticksmall.png) |
Baryon number |
0 ![](../../../graphics/symbols/nuclides/ticksmall.png) |
+1 ![](../../../graphics/symbols/nuclides/ticksmall.png) |
Quark composition |
u ̅d̅ ![](../../../graphics/symbols/nuclides/ticksmall.png) |
uud ![](../../../graphics/symbols/nuclides/ticksmall.png) |
![](../../../graphics/equations/dataSheet/quarks.png)
(b) When a positive pion interacts with a proton, a kaon can be produced, along with another strange particle, as shown in this equation
![](particlequestions_clip_image002.jpg)
What type of interaction is shown in this equation?
Strong nuclear interaction ![](../../../graphics/symbols/nuclides/ticksmall.png)
(1mark)
(c) Deduce the relative charge, baryon number and strangeness of particle X.
![](particlequestions_clip_image002.jpg)
conservation of charge:
+1 +1 → +1 + ?
charge of particle X must be +1 ![](../../../graphics/symbols/nuclides/ticksmall.png)
conservation of baryon number:
0 + 1 → 0 + ?
baryon number of particle X must be +1 ![](../../../graphics/symbols/nuclides/ticksmall.png)
conservation of strangeness:
0 + 0 → 1 + ?
strangeness of particle X must be -1 ![](../../../graphics/symbols/nuclides/ticksmall.png)
(3marks)
(d) Particle X can decay to produce a neutron and positive pion as shown in this equation
![](particlequestions_clip_image004.jpg)
What type of interaction is shown in this equation?
Weak nuclear interaction ![](../../../graphics/symbols/nuclides/ticksmall.png)
(1mark)
(e) Explain your answer.
The strangeness of X is -1, the strangeness of the pion and neutron are both zero so strangeness is not conserved.
This can only occur in weak interactions. ![](../../../graphics/symbols/nuclides/ticksmall.png)
(2 marks)
(f) The neutron and positive pion will then decay. The positive pion can decay into a positron and an electron neutrino.
Write down the equation for the decay of the neutron.
n → p
+ e- + ̅ν̅e ![](../../../graphics/symbols/nuclides/ticksmall.png)
(2 marks)
(g) Explain why no further decays occur.
The proton is a stable particle (in fact it is the only stable baryon!)
and the electron and antineutrino are stable fundamental particles
. None of them decay.
(2 marks)
(Total 16 marks)