PyROOT Exercise 1: Histogram Drawing

Exercise

Write a python macro ExerciseHist.py.

1. Open the Zmumu.root file and load the tree called physics.
2. Create two histograms with 40 bins ranging from 0 to 0.2 GeV to plot the muon masses.
3. Fill the histograms with leading and subleading muon mass from branches lep1_m and lep2_m.
4. Calculate the mean values and RMSs.
5. Calculate the integrals.

Bonus questions:

1. Are the integrals the same and why?
2. Write the histogram to a file.

Solution

import ROOT
%jsroot on

Welcome to JupyROOT 6.28/00

from ROOT import gStyle, TCanvas, TFile, TH1D

gStyle.SetOptStat(0)

file = TFile("Zmumu.root")
tree = file.Get("physics")

canvas = TCanvas("canvas", "", 800, 600)

hist_1 = TH1D("hist_1", "Leading lepton mass", 40, 0, 0.2)
hist_2 = TH1D("hist_2", "Subleading lepton mass", 40, 0, 0.2)
tree.Draw("lep1_m >> hist_1", "", "PLC")
tree.Draw("lep2_m >> hist_2", "", "PLC same")
canvas.Draw()

print(f"Leading muon mass: mean={hist_1.GetMean():.6f}; rms={hist_1.GetRMS():.6f}")
print(f"Subleading muon mass: mean={hist_2.GetMean():.6f}; rms={hist_2.GetRMS():.6f}")

print(f"Leading muon mass integral: {hist_1.Integral()}")
print(f"Subleading muon mass integral: {hist_2.Integral()}")

Leading muon mass: mean=0.105476; rms=0.007434
Subleading muon mass: mean=0.105479; rms=0.005120
Leading muon mass integral: 2495706.0
Subleading muon mass integral: 2496792.0

Last update: 06 March 2023