df106_HiggsToFourLeptons.py File Reference

Detailed Description

The Higgs to four lepton analysis from the ATLAS Open Data release of 2020, with RDataFrame.

This tutorial is the Higgs to four lepton analysis from the ATLAS Open Data release in 2020 (http://opendata.atlas.cern/release/2020/documentation/). The data was taken with the ATLAS detector during 2016 at a center-of-mass energy of 13 TeV. The decay of the Standard Model Higgs boson to two Z bosons and subsequently to four leptons is called the "golden channel". The selection leads to a narrow invariant mass peak on top a relatively smooth and small background, revealing the Higgs at 125 GeV. Systematic errors for the MC scale factors are computed and the Vary function of RDataFrame is used for plotting. The analysis is translated to an RDataFrame workflow processing about 300 MB of simulated events and data.

See the corresponding spec json file.

 
import ROOT
import os
 
# Enable Multi-threaded mode
ROOT.EnableImplicitMT()
 
# Create the RDataFrame from the spec json file. The df106_HiggsToFourLeptons_spec.json is provided in the same folder as this tutorial
dataset_spec = os.path.join(ROOT.gROOT.GetTutorialsDir(), "dataframe", "df106_HiggsToFourLeptons_spec.json")
df = ROOT.RDF.Experimental.FromSpec(dataset_spec)  # Creates a single dataframe for all the samples
 
# Add the ProgressBar feature
ROOT.RDF.Experimental.AddProgressBar(df)
 
# Access metadata information that is stored in the JSON config file of the RDataFrame.
# The metadata contained in the JSON file is accessible within a `DefinePerSample` call, through the `RSampleInfo` class.
df = df.DefinePerSample("xsecs", 'rdfsampleinfo_.GetD("xsecs")')
df = df.DefinePerSample("lumi", 'rdfsampleinfo_.GetD("lumi")')
df = df.DefinePerSample("sumws", 'rdfsampleinfo_.GetD("sumws")')
df = df.DefinePerSample("sample_category", 'rdfsampleinfo_.GetS("sample_category")')
 
# We must further apply an MC correction for the ZZ decay due to missing gg->ZZ processes.
ROOT.gInterpreter.Declare(
    """
float scale(unsigned int slot, const ROOT::RDF::RSampleInfo &id){
                return id.Contains("mc_363490.llll.4lep.root") ? 1.3f : 1.0f;
}
"""
)
 
df = df.DefinePerSample("scale", "scale(rdfslot_, rdfsampleinfo_)")
 
# Select events for the analysis
ROOT.gInterpreter.Declare(
    """
using ROOT::RVecF;
using ROOT::RVecI;
bool GoodElectronsAndMuons(const RVecI &type, const RVecF &pt, const RVecF &eta, const RVecF &phi, const RVecF &e, const RVecF &trackd0pv, const RVecF &tracksigd0pv, const RVecF &z0)
{
    for (size_t i = 0; i < type.size(); i++) {
        ROOT::Math::PtEtaPhiEVector p(0.001*pt[i], eta[i], phi[i], 0.001*e[i]);
        if (type[i] == 11) {
            if (pt[i] < 7000 || abs(eta[i]) > 2.47 || abs(trackd0pv[i] / tracksigd0pv[i]) > 5 || abs(z0[i] * sin(p.Theta())) > 0.5) return false;
        } else {
            if (abs(trackd0pv[i] / tracksigd0pv[i]) > 5 || abs(z0[i] * sin(p.Theta())) > 0.5) return false;
        }
    }
    return true;
}
"""
)
 
# Select electron or muon trigger
df = df.Filter("trigE || trigM")
 
# Select events with exactly four good leptons conserving charge and lepton numbers
# Note that all collections are RVecs and good_lep is the mask for the good leptons.
# The lepton types are PDG numbers and set to 11 or 13 for an electron or muon
# irrespective of the charge.
 
df = (
    df.Define(
        "good_lep",
        "abs(lep_eta) < 2.5 && lep_pt > 5000 && lep_ptcone30 / lep_pt < 0.3 && lep_etcone20 / lep_pt < 0.3",
    )
    .Filter("Sum(good_lep) == 4")
    .Filter("Sum(lep_charge[good_lep]) == 0")
    .Define("goodlep_sumtypes", "Sum(lep_type[good_lep])")
    .Filter("goodlep_sumtypes == 44 || goodlep_sumtypes == 52 || goodlep_sumtypes == 48")
)
 
# Apply additional cuts depending on lepton flavour
df = df.Filter(
    "GoodElectronsAndMuons(lep_type[good_lep], lep_pt[good_lep], lep_eta[good_lep], lep_phi[good_lep], lep_E[good_lep], lep_trackd0pvunbiased[good_lep], lep_tracksigd0pvunbiased[good_lep], lep_z0[good_lep])"
)
 
# Create new columns with the kinematics of good leptons
df = (
    df.Define("goodlep_pt", "lep_pt[good_lep]")
    .Define("goodlep_eta", "lep_eta[good_lep]")
    .Define("goodlep_phi", "lep_phi[good_lep]")
    .Define("goodlep_E", "lep_E[good_lep]")
    .Define("goodlep_type", "lep_type[good_lep]")
)
 
# Select leptons with high transverse momentum
df = df.Filter("goodlep_pt[0] > 25000 && goodlep_pt[1] > 15000 && goodlep_pt[2] > 10000")
 
# Reweighting of the samples is different for "data" and "MC". This is the function to add reweighting for MC samples
ROOT.gInterpreter.Declare(
    """
double weights(float scaleFactor_1, float scaleFactor_2, float scaleFactor_3, float scaleFactor_4, float scale, float mcWeight, double xsecs, double sumws, double lumi)
{
    return scaleFactor_1 * scaleFactor_2 * scaleFactor_3 * scaleFactor_4 * scale * mcWeight * xsecs / sumws * lumi;
}
"""
)
 
# Use DefinePerSample to define which samples are MC and hence need reweighting
df = df.DefinePerSample("isMC", 'rdfsampleinfo_.Contains("mc")')
df = df.Define(
    "weight",
    "double x; return isMC ? weights(scaleFactor_ELE, scaleFactor_MUON, scaleFactor_LepTRIGGER, scaleFactor_PILEUP, scale, mcWeight, xsecs, sumws, lumi) :  1.;",
)
 
# Compute invariant mass of the four lepton system
ROOT.gInterpreter.Declare(
    """
float ComputeInvariantMass(RVecF pt, RVecF eta, RVecF phi, RVecF e)
{
    ROOT::Math::PtEtaPhiEVector p1{pt[0], eta[0], phi[0], e[0]};
    ROOT::Math::PtEtaPhiEVector p2{pt[1], eta[1], phi[1], e[1]};
    ROOT::Math::PtEtaPhiEVector p3{pt[2], eta[2], phi[2], e[2]};
    ROOT::Math::PtEtaPhiEVector p4{pt[3], eta[3], phi[3], e[3]};
    return 0.001 * (p1 + p2 + p3 + p4).M();
}
"""
)
 
df = df.Define("m4l", "ComputeInvariantMass(goodlep_pt, goodlep_eta, goodlep_phi, goodlep_E)")
 
# Book histograms for the four different samples: data, higgs, zz and other (this is specific to this particular analysis)
histos = []
for sample_category in ["data", "higgs", "zz", "other"]:
    histos.append(
        df.Filter(f'sample_category == "{sample_category}"').Histo1D(
            ROOT.RDF.TH1DModel(f"{sample_category}", "m4l", 24, 80, 170),
            "m4l",
            "weight",
        )
    )
 
# Evaluate the systematic uncertainty
 
# The systematic uncertainty in this analysis is the MC scale factor uncertainty that depends on lepton
# kinematics such as pT or pseudorapidity.
# Muons uncertainties are negligible, as stated in https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/MUON-2018-03/.
# Electrons uncertainties are evaluated based on the plots available in https://doi.org/10.48550/arXiv.1908.00005.
# The uncertainties are linearly interpolated, using the `TGraph::Eval()` method, to cover a range of pT values covered by the analysis.
 
# Create a VaryHelper to interpolate the available data.
ROOT.gInterpreter.Declare(
    """
using namespace ROOT::VecOps;
 
class VaryHelper
{
    const std::vector<double> x{5.50e3, 5.52e3, 12.54e3, 17.43e3, 22.40e3, 27.48e3, 30e3, 10000e3};
    const std::vector<double> y{0.06628, 0.06395, 0.06396, 0.03372, 0.02441, 0.01403, 0, 0};
    TGraph graph;
 
public:
    VaryHelper() : graph(x.size(), x.data(), y.data()) {}
    RVec<double> operator()(const double &w, const RVecF &pt, const RVec<unsigned int> &type)
    {
        const auto v = Mean(Map(pt[type == 11], [this](auto p)
        {return this->graph.Eval(p); })
        );
        return RVec<double>{(1 + v) * w, (1 - v) * w};
    }
};
 
VaryHelper variationsFactory;
"""
)
 
# Use the Vary method to add the systematic variations to the total MC scale factor ("weight") of the analysis.
df_variations_mc = (
    df.Filter("isMC == true")
    .Vary("weight", "variationsFactory(weight, goodlep_pt, goodlep_type)", ["up", "down"])
    .Histo1D(ROOT.RDF.TH1DModel("Invariant Mass", "m4l", 24, 80, 170), "m4l", "weight")
)
histos_mc = ROOT.RDF.Experimental.VariationsFor(df_variations_mc)
 
# We reached the end of the analysis part. We now evaluate the total MC uncertainty based on the variations.
# No computation graph was triggered yet, we trigger the computation graph for all histograms at once now,
# by calling 'histos_mc["nominal"].GetXaxis()'.
# Note, in this case the uncertainties are symmetric.
for i in range(0, histos_mc["nominal"].GetXaxis().GetNbins()):
    (
        histos_mc["nominal"].SetBinError(
            i, (histos_mc["weight:up"].GetBinContent(i) - histos_mc["nominal"].GetBinContent(i))
        )
    )
 
# Make the plot of the data, individual MC contributions and the total MC scale factor systematic variations.
 
# Set styles
ROOT.gROOT.SetStyle("ATLAS")
 
# Create canvas with pad
c1 = ROOT.TCanvas("c", "", 600, 600)
pad = ROOT.TPad("upper_pad", "", 0, 0, 1, 1)
pad.SetTickx(False)
pad.SetTicky(False)
pad.Draw()
pad.cd()
 
# Draw stack with MC contributions
stack = ROOT.THStack()
 
# Retrieve values of the data and MC histograms in order to plot them.
# Draw cloned histograms to preserve graphics when original objects goes out of scope
# Note: GetValue() action operation is performed after all lazy actions of the RDF were defined first.
h_data = histos[0].GetValue().Clone()
h_higgs = histos[1].GetValue().Clone()
h_zz = histos[2].GetValue().Clone()
h_other = histos[3].GetValue().Clone()
 
for h, color in zip([h_other, h_zz, h_higgs], [ROOT.kViolet - 9, ROOT.kAzure - 9, ROOT.kRed + 2]):
    h.SetLineWidth(1)
    h.SetLineColor(1)
    h.SetFillColor(color)
    stack.Add(h)
 
stack.Draw("HIST")
stack.GetXaxis().SetLabelSize(0.04)
stack.GetXaxis().SetTitleSize(0.045)
stack.GetXaxis().SetTitleOffset(1.3)
stack.GetXaxis().SetTitle("m_{4l}^{H#rightarrow ZZ} [GeV]")
stack.GetYaxis().SetLabelSize(0.04)
stack.GetYaxis().SetTitleSize(0.045)
stack.GetYaxis().SetTitle("Events")
stack.SetMaximum(35)
stack.GetYaxis().ChangeLabel(1, -1, 0)
 
# Draw MC scale factor and variations
histos_mc["nominal"].SetFillColor(ROOT.kBlack)
histos_mc["nominal"].SetFillStyle(3254)
h_nominal = histos_mc["nominal"].DrawClone("E2 same")
histos_mc["weight:up"].SetLineColor(ROOT.kGreen + 2)
h_weight_up = histos_mc["weight:up"].DrawClone("HIST SAME")
histos_mc["weight:down"].SetLineColor(ROOT.kBlue + 2)
h_weight_down = histos_mc["weight:down"].DrawClone("HIST SAME")
 
# Draw data histogram
h_data.SetMarkerStyle(20)
h_data.SetMarkerSize(1.2)
h_data.SetLineWidth(2)
h_data.SetLineColor(ROOT.kBlack)
h_data.Draw("E SAME")  # Draw raw data with errorbars
 
# Add legend
legend = ROOT.TLegend(0.57, 0.65, 0.94, 0.94)
legend.SetTextFont(42)
legend.SetFillStyle(0)
legend.SetBorderSize(0)
legend.SetTextSize(0.025)
legend.SetTextAlign(32)
legend.AddEntry(h_data, "Data", "lep")
legend.AddEntry(h_higgs, "Higgs MC", "f")
legend.AddEntry(h_zz, "ZZ MC", "f")
legend.AddEntry(h_other, "Other MC", "f")
legend.AddEntry(h_weight_down, "Total MC Variations Down", "l")
legend.AddEntry(h_weight_up, "Total MC Variations Up", "l")
legend.AddEntry(h_nominal, "Total MC Uncertainty", "f")
legend.Draw()
 
text = ROOT.TLatex()
text.SetTextFont(72)
text.SetTextSize(0.04)
text.DrawLatexNDC(0.19, 0.85, "ATLAS")
text.SetTextFont(42)
text.DrawLatexNDC(0.19 + 0.15, 0.85, "Open Data")
text.SetTextSize(0.035)
text.DrawLatexNDC(0.21, 0.80, "#sqrt{s} = 13 TeV, 10 fb^{-1}")
 
c1.Update()
 
# Save the plot
c1.SaveAs("df106_HiggsToFourLeptons_python.png")
print("Saved figure to df106_HiggsToFourLeptons_python.png")

|>                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |   [Elapsed time: 0:13m  processing file: 7 / 9  processed evts: 1000 / 556693  7.41e+01 evt/s 2:04:58h  remaining time (per file being processed)]   
|================================================================================================================================================================================================================================>                                                                                                                                                                                                                                          |   [Elapsed time: 0:14m  processing file: 9 / 9  processed evts: 449000 / 912535  2.24e+05 evt/s 0:02m  remaining time (per file being processed)]   
|===========================================================================================================================================================================================================================================================================================================================================================================================================================================================>               |   [Elapsed time: 0:15m  processing file: 9 / 9  processed evts: 883000 / 912535  2.93e+05 evt/s 0:00m  remaining time (per file being processed)]   
 
 
[Total elapsed time: 0:15m  processed files: 9 / 9  processed evts: 912535 / 912535]   
Saved figure to df106_HiggsToFourLeptons_python.png

Date

March 2020, August 2022, August 2023

Authors

Stefan Wunsch (KIT, CERN), Julia Mathe (CERN), Marta Czurylo (CERN)

Definition in file df106_HiggsToFourLeptons.py.