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## Sunday, 21 August 2011

### Physics GRE - #20

According to the Standard Model of elementary particles, which of the following is not a composite object?

• Muon
• Pi-meson
• Neutron
• Deuteron
• Alpha particle

Solution :

The answer is muon. A muon is an elementary particle (a lepton).

Pi - mesons are a quark with an antiquark.
A neutron is made of two down quarks and an up quark.
A deuteron is a proton and a neutron (a proton is two up quarks and a down quark).
An alpha particle is two protons and two neutrons.

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