[Physics] How toak interactions not conserve strangeness if the SM always conserves energy

quarksstandard-modelweak-interaction

I have read these questions:

Weak Interaction and Strangeness transformation

Weak decay iff or if strangeness changes?

Understanding type of force interaction in particle decays

The decay of the strange quark via weak interactions?

As I understand, currently all experimental data support the SM as being the accepted theory. Both weak interactions and strangeness and strange quarks are part of the SM model.

As I understand, energy is always conserved in the SM, and all other forces, EM, gravity and strong all conserve both energy and strangeness.

If the SM is supported by all experimental data, and it always conserves energy, then how is it possible that some weak interactions do not conserve strangeness?

Where does the energy go? How can the energy be conserved by not strangeness?

In our modern understanding, strangeness is conserved during the strong and the electromagnetic interactions, but not during the weak interactions. Consequently, the lightest particles containing a strange quark cannot decay by the strong interaction, and must instead decay via the much slower weak interaction. In most cases these decays change the value of the strangeness by one unit. However, this doesn't necessarily hold in second-order weak reactions, where there are mixes of
K0
and
K0
mesons. All in all, the amount of strangeness can change in a weak interaction reaction by +1, 0 or -1 (depending on the reaction).

Consequently, the lightest particles containing a strange quark cannot decay by the strong interaction, and must instead decay via the much slower weak interaction.

It is talking about this strangeness conservation braking as if it was only for composite particles, that contain strange quarks. But what about the strange quark itself? Is the strange quark stable, or can the strange quark as elementary particle decay via weak interaction?

Question:

  1. If energy is conserved during all weak interactions, then how can strangeness not be conserved? Is strangeness equal to energy asymmetry?

  2. Can strangeness not be conserved for (interactions/decay of) non-composite particles?

Best Answer

Strangness is a quantum number as peterh explained in his comment. Every particle has a strangeness number $S = -(n_s - n_\overline{s})$, where $n_s$ and $n_\overline{s}$ are the number of strange quarks and anti-quarks - the minus sign in the front looks arbitrary, the important thing is that it is the difference between the particles and anti-particles. There are equivalent quantum numbers for other flavours, like Bottomness.

The CKM quark mixing matrix shows how the weak interaction mixes quarks - it arises due to the mass eigenstates not being the same as flavour eigenstates. The charged weak interaction is able to change the flavour of a quark, e.g. beta decay - $d \rightarrow W^- + u, \Delta S = 0$. In the same way, you can have a strange quark decaying into an up quark $s \rightarrow W^- + u, \Delta S = 1$ or say a top quark decaying into s, $t \rightarrow W^+ + s, \Delta S = -1$. The probability of these interactions are proportional to the square of the CKM matrix elements - $|V_{ij}|^2$.

Cosmas Zachos covers the answer about isolated quarks.

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