Rivet analyses referenceLHCB_2012_I1208102Differential cross-sections of $\mathrm{Z}/\gamma^* \to e^{+}e^{-}$ vs rapidity and $\phi^*$Experiment: LHCb (LHC) Inspire ID: 1208102 Status: VALIDATED Authors:
Beam energies: (3500.0, 3500.0) GeV Run details:
Measurement of the $pp \to \mathrm{Z}^0$ cross-section in the $\mathrm{Z}/\gamma \to e^{+}e^{-}$ mode at $\sqrt{s} = 7$ TeV. Daughter electrons are required to have $p_T > 20$ GeV/$c$, $2 < \eta < 4.5$ and the dielectron invariant mass in range 60-120 GeV/$c^2$. The cross-section is given as a function of $Z$ rapidity and an angular variable ($\phi^*$) closely related to $Z$ transverse momentum (derived from the lepton pseudorapidity and azimuthal angle differences). For event generators implementing cross-section QCD corrections only at LO the distributions are normalized to the cross-section measured in data $76.0 \pm 0.8 \pm 2.0 \pm 2.6 \pm 0.4$ pb, where the first uncertainty is statistical, the second is systematic, the third is due to luminosity uncertainty and the fourth to FSR corrections. Source code: LHCB_2012_I1208102.cc 1// -*- C++ -*-
2#include "Rivet/Analysis.hh"
3#include "Rivet/Projections/DileptonFinder.hh"
4
5namespace Rivet {
6
7
8 /// Differential cross-sections of $\mathrm{Z}/\gamma^* \to e^{+}e^{-}$ vs rapidity and $\phi^*$
9 class LHCB_2012_I1208102 : public Analysis {
10 public:
11
12 /// Constructor
13 RIVET_DEFAULT_ANALYSIS_CTOR(LHCB_2012_I1208102);
14
15
16 /// @name Analysis methods
17 /// @{
18
19 /// Book histograms
20 void init() {
21 DileptonFinder zeefinder(91.2*GeV, 0.1, Cuts::etaIn(2.0, 4.5) && Cuts::pT > 20*GeV &&
22 Cuts::abspid == PID::ELECTRON, Cuts::massIn(60*GeV, 120*GeV));
23 declare(zeefinder, "ZeeFinder");
24
25 book(_h_sigma_vs_y, 2, 1, 1);
26 book(_h_sigma_vs_phi, 3, 1, 1);
27 }
28
29
30 /// Do the analysis
31 void analyze(const Event& e) {
32 const DileptonFinder& zeefinder = apply<DileptonFinder>(e, "ZeeFinder");
33 if (zeefinder.empty()) vetoEvent;
34 if (zeefinder.bosons().size() > 1)
35 MSG_WARNING("Found multiple (" << zeefinder.bosons().size() << ") Z -> e+ e- decays!");
36
37 // Z momenta
38 const FourMomentum zee = zeefinder.bosons()[0].momentum();
39
40 if (zeefinder.constituents().size() < 2) vetoEvent;
41
42 const Particle pozitron = zeefinder.constituents()[0];
43 const Particle electron = zeefinder.constituents()[1];
44
45 // Calculation of the angular variable
46 const double diffphi = deltaPhi(pozitron, electron);
47 const double diffpsd = deltaEta(pozitron, electron);
48 const double accphi = M_PI - diffphi;
49 const double angular = tan(accphi/2) / cosh(diffpsd/2);
50
51 // Fill histograms
52 _h_sigma_vs_y->fill(zee.rapidity());
53 _h_sigma_vs_phi->fill(angular);
54 }
55
56
57 /// Finalize
58 void finalize() {
59 const double xs = crossSection()/picobarn;
60 scale(_h_sigma_vs_y, xs/sumOfWeights());
61 scale(_h_sigma_vs_phi, xs/sumOfWeights());
62 }
63
64 /// @}
65
66
67 private:
68
69 /// @name Histograms
70 /// @{
71 Histo1DPtr _h_sigma_vs_y, _h_sigma_vs_phi;
72 /// @}
73
74 };
75
76
77 RIVET_DECLARE_PLUGIN(LHCB_2012_I1208102);
78
79}
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