MadAnalysis 5

forward-backward asymmetry

Asked by Zboson

Can you please suggest a way for me to plot the forward backward asymmetry of a process, for example p p~ -> mu+ mu- , as a function of the CM energy (which i call s_hat)?

I know how to modify the user.cpp file in the Build directory, but I am having a difficult time collecting subsamples for each s_hat:

I would like to collect a set of events with the *same* s_hat, and separate these events into those where theta < pi/2 and theta > pi/2.

Then of course, I can calculate the asymmetry.

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Benjamin Fuks (fuks) said : 		#1

Hi,

I am not sure to understand the question. It is easy to obtain the theta from MA5 basic methods. Then, the rest is a matter of c++. You can implement two global variables dsigma_plus and dsigma_,minus and compute the AFB in the Finalize method of user.cpp.

Cheers,

Benjamin

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Zboson (911876gev) said : 		#2

Dear Benjamin,

Thanks a lot for replying! here's the relevant part of what I'm currently doing (something similar to what you said):

Within 'Execute':

    for (ind[0]=0;ind[0]<_P_muPTorderingfinalstate.size();ind[0]++)
    {
      float thetavar = _P_muPTorderingfinalstate[ind[0]]->theta();
     if (thetavar >= 0 && thetavar <= 0.5*(3.14159))
        sf->Fill(PHYSICS->SqrtS(event.mc()),1);
        sf2->Fill(PHYSICS->SqrtS(event.mc()),1);
      if (thetavar >= 0.5*(3.14159) && thetavar <= 3.14159)
        sb->Fill(PHYSICS->SqrtS(event.mc()),1);
     }

Within 'Finalize':

  //Asymmetry calculation
  sf->Add(sb,1);
  sf2->Add(sb,-1);
  sf2->Divide(sf);

So sf2 would be my AFB histogram.

Revision history for this message
Benjamin Fuks (fuks) said : 		#3

I am not too sure to understand why you would need any histogram here. Why can't this work with just double-precision numbers?

Cheers,

Benjamin

> On 3 Dec 2017, at 14:02 , Zboson <email address hidden> wrote:
>
> Question #661360 on MadAnalysis 5 changed:
> https://answers.launchpad.net/madanalysis5/+question/661360
>
> Status: Answered => Open
>
> Zboson is still having a problem:
> Dear Benjamin,
>
> Thanks a lot for replying! here's the relevant part of what I'm
> currently doing (something similar to what you said):
>
> Within 'Execute':
>
> for (ind[0]=0;ind[0]<_P_muPTorderingfinalstate.size();ind[0]++)
> {
> float thetavar = _P_muPTorderingfinalstate[ind[0]]->theta();
> if (thetavar >= 0 && thetavar <= 0.5*(3.14159))
> sf->Fill(PHYSICS->SqrtS(event.mc()),1);
> sf2->Fill(PHYSICS->SqrtS(event.mc()),1);
> if (thetavar >= 0.5*(3.14159) && thetavar <= 3.14159)
> sb->Fill(PHYSICS->SqrtS(event.mc()),1);
> }
>
> Within 'Finalize':
>
> //Asymmetry calculation
> sf->Add(sb,1);
> sf2->Add(sb,-1);
> sf2->Divide(sf);
>
> So sf2 would be my AFB histogram.
>
> --
> You received this question notification because you are an answer
> contact for MadAnalysis 5.

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