Rivet analyses
Measurement of differential cross-section of FSR photons in Z decays
Experiment: CMS (LHC)
Inspire ID: 1346843
Status: VALIDATED
Authors: - Andrew Kubik - Michael Schmitt
References: - arXiv: 1502.07940
Beams: p+ p+
Beam energies: (3500.0, 3500.0)GeV
Run details: - pp → μ+μ−γ+X 7 TeV. These cross sections are given for the fiducial region defined as follows - Leading muon pT > 31 GeV and abs(eta) < 2.4 - Trailing muon pT > 9 GeV and abs(eta) < 2.4 - Photon pT > 5 GeV - Photon abs(eta) < 2.4 but not 1.4 < abs(eta) < 1.6 - Separation between photon and closest muon 0.05 < DeltaR < 3.0 - Di-muon invariant mass 30 < M_mumu < 87 GeV
The differential cross sections for the production of photons in Z to mu+ mu- gamma decays are presented as a function of the transverse energy of the photon and its separation from the nearest muon. The data for these measurements were collected with the CMS detector and correspond to an integrated luminosity of 4.7 inverse femtobarns of pp collisions at sqrt(s) = 7 TeV delivered by the CERN LHC.
Source
code:CMS_2015_I1346843.cc
// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/ChargedLeptons.hh"
#include "Rivet/Projections/NeutralFinalState.hh"
#include "Rivet/Projections/PromptFinalState.hh"
namespace Rivet {
/// Differential cross-section of FSR photons in Z decays
class CMS_2015_I1346843 : public Analysis {
public:
/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(CMS_2015_I1346843);
/// Book histograms and initialise projections before the run
void init() {
Cut c_photons = Cuts::pT >= 5*GeV && Cuts::abseta < 2.5 && !(Cuts::absetaIn(1.4, 1.6));
PromptFinalState photons(Cuts::abspid == PID::PHOTON && c_photons, TauDecaysAs::PROMPT, MuDecaysAs::PROMPT);
declare(photons, "PHOTONFS");
Cut c_muons = Cuts::pT > 9*GeV && Cuts::abseta < 2.4;
PromptFinalState muons(Cuts::abspid == PID::MUON && c_muons);
declare(muons, "MUFS");
book(_h["pho_et"] ,1, 1, 1); // photon transverse energy
book(_h["pho_et_wide"] ,1, 2, 1); // photon transverse energy (0.5 < dr < 3.0)
book(_h["pho_et_close"] ,1, 3, 1); // photon transverse energy (0.05 < dr < 0.5)
book(_h["pho_et_lqt"] ,1, 4, 1); // photon transverse energy (q_T < 10)
book(_h["pho_et_hqt"] ,1, 5, 1); // photon transverse energy (q_T > 50)
book(_h["pho_dr"] ,2, 1, 1); // delta_R
book(_h["pho_dr_lqt"] ,2, 2, 1); // delta_R (q_T < 10)
book(_h["pho_dr_hqt"] ,2, 3, 1); // delta_R (q_T > 50)
}
// Perform the per-event analysis
void analyze(const Event& event) {
const Particles muons = apply<PromptFinalState>(event, "MUFS").particlesByPt();
if (muons.size() < 2) vetoEvent;
if (muons[0].pT() < 31*GeV) vetoEvent;
if (muons[0].charge()*muons[1].charge() > 0) vetoEvent;
const double mZ = (muons[0].momentum() + muons[1].momentum()).mass();
if (!inRange(mZ, 30*GeV, 87*GeV)) vetoEvent;
const Particles photons = apply<PromptFinalState>(event, "PHOTONFS").particlesByPt();
// We want the photon with the highest pT that does not come from a decay
for (const Particle& p : photons) {
const double dR = std::min(deltaR(p, muons[0]), deltaR(p, muons[1]) );
if (!inRange(dR, 0.05, 3.0)) continue;
// Calculate the three-body (mu,mu,gamma) transverse momentum
const double qT = (muons[0].mom() + muons[1].mom() + p.mom()).pT();
// Fill the analysis histograms
_h["pho_et"]->fill(p.pT()/GeV, 1.0);
_h["pho_dr"]->fill(dR, 1.0);
_h[(dR <= 0.5 ? "pho_et_close" : "pho_et_wide")]->fill(p.pT()/GeV, 1.0);
if (qT / GeV < 10.) {
_h["pho_et_lqt"]->fill(p.pT()/GeV, 1.0);
_h["pho_dr_lqt"]->fill(dR, 1.0);
}
if (qT / GeV > 50.) {
_h["pho_et_hqt"]->fill(p.pT()/GeV, 1.0);
_h["pho_dr_hqt"]->fill(dR, 1.0);
}
break; // Exit the loop since we found the highest pT lepton already
}
}
/// Normalise histograms etc., after the run
void finalize() {
scale(_h, crossSection()/picobarn / sumOfWeights());
}
private:
map<std::string,Histo1DPtr> _h;
};
RIVET_DECLARE_PLUGIN(CMS_2015_I1346843);
}