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Re: Bear Smear and Cross Sections [message #13894 is a reply to message #13893] Tue, 28 August 2012 01:32 Go to previous messageGo to previous message
Michael Kunkel is currently offline  Michael Kunkel
Messages: 53
Registered: June 2011
continuous participant
From: *hr.hr.cox.net
I do understand that my thoughts are hard to convey, I appreciate the time you are taking with this. I wanted to clarify a typo in my previous message.

Instead of
Michael Kunkel wrote on Mon, 27 August 2012 21:07

Is _f the density function? If so, wouldn't using
Input : _x s cos(theta), _y is differential cross section
      Output : cross section
suffice?


I wanted to say

Is _f the density function? If so, wouldn't using
Input : _x s cos(theta), _y is differential cross section
      Output : _f cross section
suffice?

What I am finding hard to conceive here is how the distribution is generated.

Moreover, I want to clarify what I am trying to do, and hopefully I can understand my mistakes after this.

I have 64 models I will be using. I was assuming I could implement this as


  model1->SetRange(1.77,1.8); 
...
...
...
  model64->SetRange(2.56,2.6);

  model1->AddHistogram(example1,"value = Eval(_x); _f =_y * value");
  makeDistributionManager()->Add(model1);
  ...
  ...
  ...
  model64->AddHistogram(example64,"value = Eval(_x); _f =_y * value");
  makeDistributionManager()->Add(model64);


In the above snipet I use 1 histogram for each model. Each histogram is derived from published data with
_x = Cos(theta)
_y = Differential Cross section

The histograms are extrapolated from TGraphs (see below);
c.m. 1.77 ->1.8 GeV
index.php?t=getfile&id=7103&private=0

c.m. 2.56 ->2.6 GeV
index.php?t=getfile&id=7104&private=0

As it can be seen from the plots above, the cross section depends on both the c.m. energy and Cos(theta);

I am trying to model this, however the example macro you provided states (lines 31 & 32):
    //Input:  _x is cos(theta), _y is the c.m. energy
    //Output: _f: cross section

model->AddHistogram(distribution,"value = Eval(_x); _f = _y * value");

But cross section, from a physics stand point is proportional to Cos(theta) / s, where s is square of c.m. energy.

This is my a source of my confusion and also not understanding how to use what I already have, cos(theta) vs. diff XSection, is the other part of my confusion.

Thanks

[Updated on: Tue, 28 August 2012 01:34]

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