Particle Interaction Equations (Edexcel A Level Physics): Revision Note

A reaction that is proposed to create antiprotons in a laboratory is shown below: 

${}_1{}^{1}p+{}_1{}^{1}p\to {}_1{}^{1}p+{}_1{}^{1}p+{}_1{}^0\pi ^{+}+{}_{-1}{}^{-1}\overline{p}$

Determine whether this reaction is permitted. 

Answer:

Step 1: Determine conservation of charge Q

• There are two protons on the left hand side

• There are two protons on the right hand side, with a positively charged pion (Q = +1) and an antiproton (Q = –1)

• Therefore charge is conserved, because:  

1 + 1 = 1 + 1 + 1 + (– 1)

Step 2: Determine conservation of baryon number, B

• There are two baryons on the left hand side, each with a baryon number B = +1 (protons are baryons) 

• On the right hand side

  • Two protons each with baryon number +1

  • One pion, with a baryon number 0 (it is a meson)

  • One anti-proton with a baryon number –1 

• Therefore baryon number is not conserved, because:  

1 + 1 = 1 + 1 + 0 + (– 1)

Step 3: Conclude whether this reaction is permitted

• This reaction is not permitted

• Because baryon number is not conserved

The equation for β^– decay is

Using the quark model of beta decay, prove that the charge is conserved in this equation.

Answer:

Note:

• Quantum numbers for any exotic particles will be given in the question

• Additional information can always be deduced using the information provided