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Baryon

Key Stage 5

Meaning

A baryon is a type of hadron made of three quarks.

About Baryons

Baryons are affected by the:
Baryon Quark-composition Charge/e Strangeness Baryon Number Lepton Number

Proton

\(uud\) \(Q=+1\) \(S=0\) \(B=+1\) \(L=0\)

neutron

\(udd\) \(Q=0\) \(S=0\) \(B=+1\) \(L=0\)

Determining Baryon Composition

NB: You only need to memorise the names and quark composition of the proton and the neutron. However, you should be able to determine the quark composition given the charge and strangeness of a given baryon and by remembering the properties of the up-quark, down-quark and strange-quark.

Baryons can be represented by the following diagram:
BaryonHexagon.png
The composition of these baryons can be determined given their charge and strangeness.

Examples

This table is for referencing the properties of the quarks.
Quark Charge/e Strangeness

Up-quark

\(q=+\frac{2}{3}\) \(S=0\)

Antiup-quark

\(q=-\frac{2}{3}\) \(S=0\)

Down-quark

\(q=-\frac{1}{3}\) \(S=0\)

Antidown-quark

\(q=+\frac{1}{3}\) \(S=0\)

Strange-quark

\(q=-\frac{1}{3}\) \(S=-1\)

Antistrange-quark

\(q=+\frac{1}{3}\) \(S=+1\)


Determine the composition of the Σ+ Determine the composition of the Ξ-

Strangeness

Σ+ has a strangeness of -1, therefore it contains a strange-quark.

Charge

\(+1 = -\frac{1}{3} + x + y\)

\(+\frac{4}{3} =x + y\)

Σ+ has a positive charge. This can be achieved with its strange-quark with a charge of \(-\frac{1}{3}\)e and two quarks with a charge of \(+\frac{2}{3}\)e (an pair of up-quarks).

Since \(+1 = -\frac{1}{3} + \frac{2}{3} + \frac{2}{3}\)

Therefore \(Σ^+ = s + u + u\)

Sigma Baryon = suu

Strangeness

Ξ- has a strangeness of -2, therefore it contains two strange-quarks.

Charge

\(-1 = -\frac{1}{3} + -\frac{1}{3} + x\)

Ξ- has a negative charge. This can be achieved with its two strange-quarks with a charge of \(-\frac{1}{3}\)e each and another charge of \(-\frac{1}{3}\)e (a down-quark).

Since \(-1 = -\frac{1}{3} + -\frac{1}{3} -\frac{1}{3}\)

Therefore \(Ξ^- = s + s + d\)

Xi Baryon = ssd