Color flow

In my post Hadronization two days ago I tried to describe what happens when two quarks are created at high energy in the decay of a Z boson. The quarks escape the decay point with light speed, pulling a color string between them. Once energetically favourable, the color string breaks, creating a new quark-antiquark pair. The process continues until quarks and antiquarks recombine in colorless combinations - hadrons.

In the post, I included a picture that described the process and tried to bring home a few points. However, I was not completely happy with the technical correctness of that picture. So here I go again - I will try to make a more precise one.

This time, I will not use smileys for quarks. Instead, I will picture their travel in time and space with colored lines. Time increases going down (see the arrow), space is exemplified by the horizontal coordinate. Here is the picture:

 

The pair of red quarks emitted by the disintegrating Z boson at the top vertex of the figure above travel apart (one towards the left and one towards the right), until the quark on the right emits a red/antiyellow gluon, and becomes yellow. The gluon (the double line with red and yellow color) shortly thereafter splits into a quark-antiquark pair, a red quark and a yellow antiquark.

After a while, the original yellow quark emits a yellow-antiblue gluon, and it becomes blue. Later, also the original red antiquark emits a gluon - a blue-antired one, becoming blue.

In the end, all colors recombine, and quark-antiquark pairs are created which are colorless: hadrons! This fragmentation process has involved the emission of three gluons, the materialization of three quark-antiquark pairs, and the final production of four hadrons traveling away from the Z decay point.

One last bit to note: in the figure above, the energy stored in a string when two partons fly apart can be thought to be proportional to the area of the polygons. That is part of the reason why I like this one better than the one with smileys.

Addendum 2/28: if you think the four hadrons created at the bottom are respectively blue, red, yellow, and blue, you're missing the whole picture! Hadrons are colorless objects... They got those colors because, well, I haven't figured out how to paint with a anti-brush yet... Red+antired= no color, etcetera!

Comments

[Aaron]

Very nice diagram! You might try using complementary colors to represent anti-colors -- green for anti-red, orange for anti-blue, and purple for anti-yellow. Or maybe you could mark anti-color lines by making them dotted instead of solid.

p.s. I've always heard the color charges represented by red, green and blue rather than red, yellow, and blue. Is this just personal preference, or are different colors standard in different countries and institutions?

[Tommaso Dorigo]

True, I could use complementary colors, but then I think the message would be less easy to grasp.
Dotted lines... Maybe. I think the important thing though is clarity, and sometimes this fights with accuracy. Also, too much information in a graph like that tends to confuse the message.

Thanks for your suggestions though. For a undergrad course I would definitely use complementary colors...

And about colors, I know red green and blue is the common choice, but I prefer red, blue and yellow, since they are the true complementary colors.

Cheers,
T.