Question on errors.

From: Patricia Fachini (pfachini@physics.wayne.edu)
Date: Tue Mar 28 2000 - 19:58:01 MEST 

Hi,

I define my histograms as:

  typedef TH1D StHbt1DHisto;
  mNumerator = new StHbt1DHisto(TitNum,theTitle,nbins,MinvLo,MinvHi);
  mDenominator = new StHbt1DHisto(TitDen,theTitle,nbins,MinvLo,MinvHi);
  mDifference = new StHbt1DHisto(TitDif,theTitle,nbins,MinvLo,MinvHi);

  mNumerator->Sumw2();
  mDenominator->Sumw2();
  mDifference->Sumw2();

  mNumerator->Scale(1./NEvents);
  mDenominator->Scale(1./NEvents);
  mDifference->Scale(1./NEvents);

and after running my macro:

root4star [17] hh2->GetBinContent(50)
(Stat_t)8.04982038234593347e+02
root4star [18] hh2->GetBinError(50)
(Stat_t)1.26884362824517383e+00

root4star [19] hhh2->GetBinContent(50)
(Stat_t)7.85032637287047692e+03
root4star [20] hhh2->GetBinError(50)
(Stat_t)3.96240501355956098e+00

You see that the error in the bin is not the square root of the bin
contents, as I would expect... What am I missing here?

Thank you,
Patricia

__________________________________________________________________
Patricia Fachini, Ph.D.                   1-313-577-5419 -> WSU
Universidade de Sao Paulo                 1-631-344-7635 -> BNL
Wayne State University                  pfachini@physics.wayne.edu

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