The baryon has quark content

PHYSICS · Subjective · Fermi University Physics · Quantum Mechanics · Particle Physics & Quantum Fields · Particles, interactions and experiment

Particle Physics, Ch Hadrons: baryons, mesons and their quark content

Problem

The

\Sigma^{*+}

baryon has quark content

uus

, spin

3/2

and measured mass

1382.8\,\mathrm{MeV}/c^2

. Someone argues: "Colour is only needed when all three quarks are identical, as in

\Delta^{++}

. In

\Sigma^{*+}

only two of the three quarks, the two

u

quarks, are the same flavour, so at most two colours are needed, not three, and the

s

quark can stay uncoloured. Also, using

m_u c^2 = 2.2\,\mathrm{MeV}

and

m_s c^2 = 95\,\mathrm{MeV}

, the sum

2.2+2.2+95 = 99.4\,\mathrm{MeV}/c^2

is close enough to the measured mass once rounding is allowed for. Finally, since

\Sigma^{*+}

has baryon number

1

and strangeness

-1

, any reconstructed peak with those two properties must be

\Sigma^{*+}

." Identify every error in this argument and give the correct statement in each case.