DP Physics (last assessment 2024)

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

Date	May 2019	Marks available	[Maximum mark: 2]	Reference code	19M.3.HL.TZ1.6b
Level	HL	Paper	3	Time zone	TZ1
Command term	Calculate	Question number	b	Adapted from	N/A

[Maximum mark: 2]

19M.3.HL.TZ1.6b

The particle omega minus ( ${\Omega ^ - }$ ) decays at rest into a neutral pion ( ${\pi ^0}$ ) and the xi baryon ( ${\Xi ^ - }$ ) according to

^{${\Omega ^ - } \to {\pi ^0} + {\Xi ^ - }$}

The pion momentum is 289.7 MeV c^–1.

The rest masses of the particles are:

${\Omega ^ - }$ : 1672 MeV c^–2

${\pi ^0}$ : 135.0 MeV c^–2

${\Xi ^ - }$ : 1321 MeV c^–2

(b)

Calculate the speed of the pion.

[2]

Markscheme

$\gamma « = \frac{{\sqrt {{{289.7}^2} + {{135.0}^2}} }}{{135.0}} » = 2.367$ ✔

$v «= \sqrt {1 - \frac{1}{{{{2.367}^2}}}} c » = 0.903c$ ✔

Award [2] for bald correct answer.

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. The same for the speed of the pion in b), most of the attempts demonstrated by candidates were not relevant.

Syllabus sections

Option A: Relativity

Option A: Relativity » Option A: Relativity (Additional higher level option topics) » A.4 – Relativistic mechanics (HL only)

Option A: Relativity » Option A: Relativity (Additional higher level option topics)

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

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