Pythia and differential cross sections

dilekulas

Dear Users,

I would like to ask you how can I plot d_sigma/d_Pt graph for proton proton collisions using pythia event generator. I am also using root macro which plot d_N/d_Pt graph for pion and I have also attached this for you. I would be garetful if you could tell me how can I convert this example for my aim or any other example related to this.

Any ideas would be appreciated.

Kind regards.

Attached Files

pythiaExample.txt (6.8 KB, 93 views)

Timo

I am not familiar with Pythia (but with competiting programs) but I don't quite get what you want to do? Does the example given work or do you have problems getting it to work? What, i,.e. which particle(s), do you want to plot the differential cs of? The file attached seems to call Pythia and plot the diff. cs for created pi+ (specified by "#define PDGNUMBER 211"). If you want other particles, you have to change at least this number (dunno if Pythia automatically figures out which processes lead to the desired particle in the final state or if you have define that yourself somewhere else).

dilekulas

Dear Timo,
Thank you for your reply. The file I've attached give the transverse momentum distribution of pi+. What I want to plot is differential cross section distribution of pi+.I remember (but I am not sure) if d_N/d_pt divided by luminosity this should give the d_sigma/d_Pt distribution. I could not find any example macro to do this. I hope you could help me.

Cheers,

drpsycho

dilekulas, so your question is "how to go from the number of events to the cross section"?
You don't need to look for macros for that, just look in your textbook (or in wikipedia) what is the relation between cross section and luminosity!

Anyway I will help you, since I remember by hearth: if you know the integrated luminosity L (i.e. the luminosity integrated with time), N = sigma * L.
Now do the algebra and obtain sigma as a function of N ;)
You will have to scale the histogram accordingly. In case you don't know how to scale an histogram in root, have a closer look to your example macro and you will probably understand how to do :)

dilekulas

drpscho, yes, you are right. now I am sure if momentum distribution divided by L, this gives the cross section distribution. Ok, this is a good way. But if I don't know the luminosity what should I do?

drpsycho

This is a free parameter of the problem. Ask the person who told you to plot this distribution.

Anyway, are you sure that what this macro is plotting is dN/dpt and not already dSigma/dpt?
In fact, pythia or any other generator, will calculate a cross section and THEN turn it into a number of events in an histogram. So, probably this macro is already doing the inverse of what you want to do.
(I didn't looked at it in detail.)
I suggest you to use this macro as a way to understand the root syntax, and by modifying it you will certainly learn something, both about root and about physics :)
Have a nice work.