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CMS_2015_I1346843

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: Beams: p+ p+
Beam energies: (3500.0, 3500.0) GeV
Run details:
  • $p p \to \mu^+ \mu^- \gamma$+X 7 TeV. These cross sections are given for the fiducial region defined as follows - Leading muon $p_T > 31$ GeV and abs(eta) < 2.4 - Trailing muon $p_T > 9$ GeV and abs(eta) < 2.4 - Photon $p_T > 5$ 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
 1// -*- C++ -*-
 2#include "Rivet/Analysis.hh"
 3#include "Rivet/Projections/FinalState.hh"
 4#include "Rivet/Projections/ChargedLeptons.hh"
 5#include "Rivet/Projections/NeutralFinalState.hh"
 6#include "Rivet/Projections/PromptFinalState.hh"
 7
 8namespace Rivet {
 9
10
11  /// Differential cross-section of FSR photons in Z decays
12  class CMS_2015_I1346843 : public Analysis {
13  public:
14
15    /// Constructor
16    RIVET_DEFAULT_ANALYSIS_CTOR(CMS_2015_I1346843);
17
18    /// Book histograms and initialise projections before the run
19    void init() {
20
21      Cut c_photons = Cuts::pT >= 5*GeV && Cuts::abseta < 2.5 && !(Cuts::absetaIn(1.4, 1.6));
22      PromptFinalState photons(Cuts::abspid == PID::PHOTON && c_photons, TauDecaysAs::PROMPT, MuDecaysAs::PROMPT);
23      declare(photons, "PHOTONFS");
24
25      Cut c_muons = Cuts::pT > 9*GeV && Cuts::abseta < 2.4;
26      PromptFinalState muons(Cuts::abspid == PID::MUON && c_muons);
27      declare(muons, "MUFS");
28
29      book(_h["pho_et"]           ,1, 1, 1);  // photon transverse energy
30      book(_h["pho_et_wide"]      ,1, 2, 1);  // photon transverse energy (0.5 < dr < 3.0)
31      book(_h["pho_et_close"]     ,1, 3, 1);  // photon transverse energy (0.05 < dr < 0.5)
32      book(_h["pho_et_lqt"]       ,1, 4, 1);  // photon transverse energy (q_T < 10)
33      book(_h["pho_et_hqt"]       ,1, 5, 1);  // photon transverse energy (q_T > 50)
34      book(_h["pho_dr"]           ,2, 1, 1);  // delta_R
35      book(_h["pho_dr_lqt"]       ,2, 2, 1);  // delta_R (q_T < 10)
36      book(_h["pho_dr_hqt"]       ,2, 3, 1);  // delta_R  (q_T > 50)
37    }
38
39
40    // Perform the per-event analysis
41    void analyze(const Event& event) {
42
43      const Particles muons = apply<PromptFinalState>(event, "MUFS").particlesByPt();
44
45      if (muons.size() < 2) vetoEvent;
46      if (muons[0].pT() < 31*GeV) vetoEvent;
47      if (muons[0].charge()*muons[1].charge() > 0) vetoEvent;
48      const double mZ = (muons[0].momentum() + muons[1].momentum()).mass();
49      if (!inRange(mZ, 30*GeV, 87*GeV)) vetoEvent;
50
51      const Particles photons = apply<PromptFinalState>(event, "PHOTONFS").particlesByPt();
52      // We want the photon with the highest pT that does not come from a decay
53      for (const Particle& p : photons) {
54
55        const double dR = std::min(deltaR(p, muons[0]), deltaR(p, muons[1]) );
56        if (!inRange(dR, 0.05, 3.0)) continue;
57
58        // Calculate the three-body (mu,mu,gamma) transverse momentum
59        const double qT = (muons[0].mom() + muons[1].mom() + p.mom()).pT();
60
61        // Fill the analysis histograms
62        _h["pho_et"]->fill(p.pT()/GeV, 1.0);
63        _h["pho_dr"]->fill(dR, 1.0);
64
65        _h[(dR <= 0.5 ? "pho_et_close" : "pho_et_wide")]->fill(p.pT()/GeV, 1.0);
66
67        if (qT / GeV < 10.) {
68          _h["pho_et_lqt"]->fill(p.pT()/GeV, 1.0);
69          _h["pho_dr_lqt"]->fill(dR, 1.0);
70        }
71
72        if (qT / GeV > 50.) {
73          _h["pho_et_hqt"]->fill(p.pT()/GeV, 1.0);
74          _h["pho_dr_hqt"]->fill(dR, 1.0);
75        }
76
77        break; // Exit the loop since we found the highest pT lepton already
78      }
79    }
80
81
82    /// Normalise histograms etc., after the run
83    void finalize() {
84      scale(_h, crossSection()/picobarn / sumOfWeights());
85    }
86
87
88  private:
89
90    map<std::string,Histo1DPtr> _h;
91
92  };
93
94
95  RIVET_DECLARE_PLUGIN(CMS_2015_I1346843);
96
97}