Help! Quick Question on Calculating Quark Jet Branching Ratios

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In summary, the book says that the branching ratios of quark jets come from the equation (1/3)^2*(2/3)^2=5/9. The notation the book uses is σ(ee-->dd*)/σ(ee-->mu mu) which is the same as the equation for the total number of quark jets created. If you neglect the effect of the color of the quarks, then the probability of creating a red-antired d,dbar pair is the same as a green-antigreend,dbar pair, and so on.
  • #1
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.
 
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  • #2


quarks carry different charges than charged leptons -> This changes the magnitude of the coupling-strength

also please use better names for your topics "help" is not a good title...
 
  • #3


Cheers, i won't use that title again.

Am i right in saying that Up, Charm and Top quarks have 2/3 charge and Down Strange and bottom have -1/3 charge so this is where these fractions come from - the relationship you mentioned with coupling constants and charge?

If that is the case, you say leptons are different so would they have to be treated differently?
 
  • #4


venomxx said:
Cheers, i won't use that title again.

Am i right in saying that Up, Charm and Top quarks have 2/3 charge and Down Strange and bottom have -1/3 charge so this is where these fractions come from - the relationship you mentioned with coupling constants and charge?

If that is the case, you say leptons are different so would they have to be treated differently?

The electromagnetic force couples to the product of charges of the particles in the interaction vertex, so leptons have integer charges and quarks 3rds of integers therefore you must treat them "different"

You have neglect one thing, that quarks have one additional quantum number, the color, which affects the cross-section (not the interaction itself) by a factor of 3.

The probability to create a red-antired d,dbar pair is the same as a green-antigreend,dbar pair, and so on.
 

1. What are quark jet branching ratios?

Quark jet branching ratios refer to the likelihood that a quark will split into different types of particles during a high-energy collision. These branching ratios are typically used in calculations to predict the observed particles in a particle accelerator experiment.

2. How do you calculate quark jet branching ratios?

To calculate quark jet branching ratios, you need to use the theory of quantum chromodynamics (QCD) and the Feynman diagrams to determine the probabilities of different quark splitting processes. This requires a combination of mathematical equations and computer simulations.

3. What factors can affect quark jet branching ratios?

Quark jet branching ratios can be affected by several factors, including the type of quark involved, the energy of the collision, and the type of particle being produced. The strong force, which binds quarks together, also plays a significant role in determining branching ratios.

4. Why are quark jet branching ratios important?

Quark jet branching ratios are important because they help us understand the fundamental building blocks of matter and the interactions between them. By studying these ratios, we can gain insights into the behavior of quarks and the strong force, which is crucial for understanding the universe at a subatomic level.

5. Can quark jet branching ratios be experimentally measured?

Yes, quark jet branching ratios can be experimentally measured using particle accelerators such as the Large Hadron Collider (LHC). By analyzing the particles produced in high-energy collisions, scientists can determine the branching ratios and compare them to theoretical predictions to test the validity of the underlying theories.

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