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Question 19M.3.HL.TZ1.6a

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Date May 2019 Marks available [Maximum mark: 3] Reference code 19M.3.HL.TZ1.6a
Level HL Paper 3 Time zone TZ1
Command term Show that Question number a Adapted from N/A
a.
[Maximum mark: 3]
19M.3.HL.TZ1.6a

The particle omega minus ( Ω ) decays at rest into a neutral pion ( π 0 ) and the xi baryon ( Ξ ) according to

Ω π 0 + Ξ

The pion momentum is 289.7 MeV c–1.

The rest masses of the particles are:

Ω : 1672 MeV c–2

π 0 : 135.0 MeV c–2

Ξ : 1321 MeV c–2

(a)

Show that energy is conserved in this decay.

[3]

Markscheme

momentum of xi baryon is also 289.7«MeVc−1» ✔

total energy of xi baryon and pion is 289.7 2 + 1321 2 + 289.7 2 + 135.0 2 = 1672 «MeV» ✔

which equals the rest energy of the omega ✔

Allow a backwards argument, assuming the energy is equal.

Examiners report

Energy conservation in a decay. This relativistic mechanics question was very challenging. Only a few candidates were able to calculate the total energy of the baryon and pion, despite being able to recognize the correct momentum of the baryon.