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venomxx

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**Quick question - Help!**

Im working on branching ratios of quark jets, the book is pulling fractions out of nowhere and I am wondering how its getting them!

for example with a beam of e+ and e- colliding you get quark jets, the book says the ratio of the crossections of the collsions going to dd* compared to muons (where* designates the anti-particle) is (1/3)^2 and the ratio given for uu* created is (2/3)^2.

Therefore total = 5/9

The notation the book uses is σ(ee --> dd*)/σ(ee -->mu mu) = (1/3)^2

As the centre of mass energy increases other heavier quarks can become possible...

Can anyone shed light on where these fractions come from? I am sure there easily calculated.