# Question Video: Determining the Strangeness of a Phi Meson Physics

A phi meson is a particle that is made up of a strange quark and a strange antiquark. What is the strangeness of a phi meson?

01:52

### Video Transcript

A phi meson is a particle that is made up of a strange quark and a strange antiquark. What is the strangeness of a phi meson?

Let’s say we represent this particle using the Greek letter Φ. Now, because this particle is a meson, we can recall that that means it’s made up of one quark and one antiquark. And indeed we’re told that this particle is made up of a strange quark and a strange antiquark. We then want to figure out what is the strangeness of a phi meson.

Strangeness, we can recall, is a property of particles as well as nuclear interactions. The strangeness of an interaction comes from the number of strange quarks and strange antiquarks involved. The rule for determining strangeness is, for every strange quark involved, a strangeness of negative one is contributed. And then every strange antiquark has a strangeness of positive one.

Now, the fact that the strangeness of a strange quark is negative one and that of a strange antiquark is positive one might seem a little strange, get it? But the reason for this comes down to the historical fact that the concept of strangeness preceded the discovery of quarks.

Anyway, we can now use these rules to figure out the strangeness of our phi meson. Before we count up any of the quarks involved, let’s say that our particle has an overall strangeness of zero. We can consider this our starting value. And then as we take into account this strange quark, our rule tells us that that contributes a strangeness of negative one. At this point then, that’s the strangeness of our particle overall. But then we consider the contribution of our strange antiquark. And going back to our rule, this contributes a strangeness of positive one. So our strangeness overall is negative one plus one, or simply zero. And this is the strangeness of our phi meson. The strangeness of the strange quark and that of the strange antiquark canceled one another out.