Energy calibrated histogram/spectrum

ROOT
1

I am trying to create a multiple histograms in one plot with data from the attached file. Actually I am trying to apply an energy callibration on the x-axis values which are channels i.e.

where a=2.7361 and b=-64.608 while channels = the old values and energy=the new values.

I am creating the histograms using the following code

[code]#include “Riostream.h”
#include “TArrow.h”
#include “TLatex.h”

void MgB2(){

gROOT->SetStyle("Plain");
gStyle->SetOptStat(0000);
gStyle->SetOptFit(1111);
gStyle->SetOptTitle(0);

TPaveText *t = new TPaveText(0.005, 0.995, 0.85, 0.925, "brNDC");//left-up
t->AddText("Experimental and Simulated Spectra from MgB_{2}");
t->SetBorderSize(1);
t->SetFillColor(gStyle->GetTitleFillColor());

TCanvas *c = new TCanvas("c", "c");
c->SetFillColor(5);
c->SetFrameFillColor(10);

TString dir = gSystem->UnixPathName(gInterpreter->GetCurrentMacroName());
dir.ReplaceAll("MgB2.C","");
dir.ReplaceAll("/./","/");
ifstream in;
in.open(Form("%sMgB2.dat",dir.Data()));

Float_t x,y,z,w,k,l,m;
Int_t nlines = 0;
Int_t channels=1027;


Double_t xlow = 1.0;
TH1F *h1 = new TH1F("h1", "Total", channels, xlow, (channels + xlow));
TH1F *h2 = new TH1F("h2", "#alpha background", channels, xlow, (channels + xlow));
TH1F *h3 = new TH1F("h3", "#alpha background", channels, xlow, (channels + xlow));
TH1F *h4 = new TH1F("h4", "#alpha background", channels, xlow, (channels + xlow));
TH1F *h5 = new TH1F("h5", "#alpha background", channels, xlow, (channels + xlow));
TH1F *h6 = new TH1F("h6", "#alpha background", channels, xlow, (channels + xlow));
    
while (1) {

in >> x >> y >> z >> w >> k >> l >> m;
if (!in.good()) break;
if (nlines == 10) printf(“x=%8f, y=%8f, z=%8f\n”,x,y,z);
h1->Fill((x -64.608) / 2.7361 + xlow - 0.5, y);
h2->Fill((x -64.608) / 2.7361 + xlow - 0.5, z);
h3->Fill((x -64.608) / 2.7361 + xlow - 0.5, w);
h4->Fill((x -64.608) / 2.7361 + xlow - 0.5, k);
h5->Fill((x -64.608) / 2.7361 + xlow - 0.5, l);
h6->Fill((x -64.608) / 2.7361 + xlow - 0.5, m);
nlines++;
}
printf(“Found %d points\n”,nlines);

in.close();

h1->SetLineColor(8);
h1->Draw();
h1->GetXaxis()->SetTitle("Energy[keV]");
h1->GetYaxis()->SetTitle("Events"); 

h2->SetLineColor(kBlue);
h2->Draw("same"); 

leg = new TLegend(0.1,0.7,0.48,0.9);
leg->AddEntry("h1","with #delta E");
leg->AddEntry("h2","without #delta E");
leg->Draw();

t->Draw();

}[/code]

My output is the following

You can see that there are some “lost” bins in the plot. Any idea why is this happening and how to fix it?
Thank you very much in advance!
MgB2.dat (152 KB)

2

The way to solve this is to define the number of channels, the callibration parameters and the minimum bin that appears on the file.

Int_t channels=1027; Double_t xlow = 1.0; Double_t a=2.7361; Double_t b=-64.608;

Then one has to create the histogram in a correct way. This means that the mumber of channels remains the same, but the minum and maximum values have to change according to the callibration.

Then, in order to fill the histogram, one has to modify the values that are parsed in the code, from the external ascii file. While y values remain the same, x values have to change