Episode 3: Physics - Feynman Diagrams

[amorenobr]

The Feynman package allows to draw Feynman diagrams using matplotlib. This could be included in this episode in order to show more examples and applications

[welcome]

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[amanmdesai]

I have a couple of scripts here (for Higgs-strahlung)

https://github.com/amanmdesai/Feynman-Diagrams/blob/master/higgs_strahlung.py

or this one if you want to show decays of Higgs

https://github.com/amanmdesai/Feynman-Diagrams/blob/master/higgs_cc.py

[amorenobr]

Yes Aman, that would be the idea...

[amanmdesai]

How about adding this:

import matplotlib.pyplot as plt
from feynman import Diagram

fig = plt.figure(figsize=(10.,10.))
ax = fig.add_axes([0,0,1,1], frameon=False)

diagram = Diagram(ax) 
diagram.text(.5,0.9,"Higgs Strahlung with H -> cc~ and Z decay to l+ l-", fontsize=20)
in1 = diagram.vertex(xy=(.05,.75), marker='') #quark starting point (left up); xy- vertex coordinates (x,y); marker
in2 = diagram.vertex(xy=(.05,.25), marker='') # anti-quark starting point (left down) 
v1 = diagram.vertex(xy=(.30,.5)) # Z boson starting point (left) 
v2 = diagram.vertex(xy=(.60,.5)) # Z boson starting point (right)
higgsout = diagram.vertex(xy=(.8,.65)) # higgs boson
zhout = diagram.vertex(xy=(.8,.35),marker='')  # produced Z boson in association with Higgs
c1 = diagram.vertex(xy=(.9,.75),marker='') # charm quark 
c2 = diagram.vertex(xy=(.9,.55),marker='') # charm antiquark
l1 = diagram.vertex(xy=(.9,.25),marker='') # lepton 1
l2 = diagram.vertex(xy=(.9,.45),marker='') # lepton 2

q1 = diagram.line(in1, v1) #quark 1; line joining the points 
q2 = diagram.line(v1, in2) #quark 2 
wz1 = diagram.line(v1, v2, style='wiggly',nwiggles=6) # wiggles to represent Z boson 
wz2 = diagram.line(v2, zhout, style='wiggly',nwiggles=6)
higgs = diagram.line(v2, higgsout, arrow=False, style='dashed') # dashed line to represent the higgs
charm1 = diagram.line(c1,higgsout)
charm2 = diagram.line(higgsout, c2)
lep1 = diagram.line(zhout, l1)
lep2 = diagram.line(zhout, l2)

# Text command adds text near the line

q1.text("q",fontsize=30)
q2.text(r"$\bar{\mathrm{q}}$",fontsize=30)
wz1.text("$Z$",t=0.5,y=0.1,fontsize=30)
wz2.text("$Z$",t=0.5,y=-0.15,fontsize=30)
higgs.text("H",fontsize=30)
charm2.text("c",fontsize=30)
charm1.text(r"$\bar{\mathrm{c}}$",fontsize=30)
lep2.text(r"$\mathcal{l}^{\pm}$",t=0.5,y=0.1,fontsize=30)
lep1.text(r"$\mathcal{l}^{\mp}$",t=0.5,y=-0.1,fontsize=30)
diagram.scale(0.6)
diagram.plot()
plt.savefig('zh_hcc.eps', format='eps')

Here is the code with comments

https://github.com/amanmdesai/Feynman-Diagrams/blob/master/higgs_ZH_production_hcc.py

[amorenobr]

That looks great Aman. I think it is important to make everything clear, as much as we can.

I don't know if you have had any problem with that, but in my case Feynman runs with python 2.

[amanmdesai]

I am using Python 3.10.4

[klieret]

Hi @amanmdesai @amorenobr Thanks a lot for starting this! I think we were discussing this a long time ago in one of our training meetings. I'm a bit wary of pushing too many "walls of code" on the students and I think that this will be more of a special use case of matplotlib.
But I think it would indeed be a fun bonus episode that can be included depending on the time budget of the workshop or for students who want more :)

[amorenobr]

I agree with you @klieret. Maybe we could add these codes in hidden sections right below every diagram in this episode, so if anybody is interested in learning something fun can take a look :)

[klieret]

Ah, I also really like that idea :)

[amanmdesai]

The idea sounds good. Codes to the Feynman diagrams could be found here:

https://github.com/GkAntonius/feynman/tree/master/examples/Particle_Physics

1 . plot_VBF.py
2. plot_VH.py
3. plot_ggF_SM.py
4. plot_ttH.py

[klieret]

We could simply wrap it in a HTML details element like so:

<details>
  <summary>See More</summary>
  This text will be hidden if your browser supports it.
</details>

So feel free to open a PR for that.

For consistency, please format your code with black