Question Video: D Meson Decay | Nagwa Question Video: D Meson Decay | Nagwa

# Question Video: D Meson Decay Physics

The following equation shows a D meson decaying into a kaon and two pions, D⁰ (c𝐮) ⟶ K⁺ (u𝐬) + 𝜋⁺ (u𝐝) + 𝜋⁰ (u𝐮). What is the total charm before this interaction takes place? What is the total charm after this interaction takes place?

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### Video Transcript

The following equation shows a D meson decaying into a kaon and two pions. What is the total charm before this interaction takes place? What is the total charm after this interaction takes place?

The equation we see shows us a D meson, made up of a charm quark and an up antiquark, decaying into a positively charged kaon, made of an up quark and a strange antiquark, a positively charged pion, made of an up quark and a down antiquark, and then lastly a neutral pion, made of an up quark and an up antiquark. It’s important to know what quarks make up each of these particles because that will help us answer these questions about the total charm in the interaction.

We can recall that this property called charm is determined by the number of charm quarks and charm antiquarks a particle may possess. Every charm quark contributes a charm of positive one, while every charm antiquark contributes a charm of negative one. Any quarks that are not of this type do not contribute to the charm of the particle overall.

Knowing this, we can figure out the answer to the first part of our question by computing the charm of our D meson. This is the only particle that exists before the interaction. And we see that it’s made up of one charm quark, that contributes a charm of positive one to the meson, and one up antiquark. This particle makes no contribution to the overall charm. The overall charm of the D Meson, then, is positive one. This is the total charm in this equation before the interaction takes place.

The second part of our question asks about the total charm after the interaction has taken place. At this point, the D meson has decayed into the kaon and the two pions. So now, we want to calculate the total charm for these three particles combined. We’ll do this by adding together the charm of each individual particle. First, we consider the kaon. The quarks that make it up are the up quark and the strange antiquark. Neither of these impacts the charm of the particle overall, which means that its charm is zero.

Considering next our positive pion, we see this is made of an up quark and a down antiquark. These also have no impact on charm. So therefore, the charm of this particle is zero too, and so is the charm of our neutral pion because this also is not made up of any charm quarks or charm antiquarks. The way we figure out the total charm after the interaction has taken place is by adding together the charm of what we could call the products. Zero plus zero plus zero is zero. So, that is the total charm after the interaction. And note that in this interaction, charm is not conserved. It started out as one and ended up as zero.

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