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CMS_2013_I1122847

Forward-backward asymmetry A\_FB in Drell-Yan lepton pairs at sqrt(s) = 7 TeV
Experiment: CMS (LHC)
Inspire ID: 1122847
Status: VALIDATED
Authors:
  • Markus Radziej
References: Beams: p+ p+
Beam energies: (3500.0, 3500.0) GeV
Run details:
  • Drell-Yan events with an electron or muon final state are necessary. High statistics as well as a NLO generator are recommended for a good agreement

This analysis measures the forward-backward asymmetry $A_{FB}$ in Drell-Yan events at a center-of-mass energy of 7 TeV. Both the individual and combined electron and muon pair channels are analyzed. In four rapidity regions, $A_{FB}$ is given as a function of the lepton mass. The data, recorded with the CMS detector, corresponds to an integrated luminosity of $5\,\textrm{fb}^{-1}$.

Source code: CMS_2013_I1122847.cc
  1// -*- C++ -*-
  2#include "Rivet/Analysis.hh"
  3#include "Rivet/Projections/FinalState.hh"
  4#include "Rivet/Projections/DileptonFinder.hh"
  5
  6namespace Rivet {
  7
  8
  9  class CMS_2013_I1122847 : public Analysis {
 10  public:
 11
 12    /// Constructor
 13    RIVET_DEFAULT_ANALYSIS_CTOR(CMS_2013_I1122847);
 14
 15
 16    /// Book histograms and initialise projections before the run
 17    void init() {
 18
 19      Cut cuts_mu = Cuts::abseta < 2.4 && Cuts::pT > 20*GeV;
 20      DileptonFinder zfinder_mu(91.2*GeV, 0.0, cuts_mu && Cuts::abspid == PID::MUON, Cuts::mass > 40*GeV);
 21      declare(zfinder_mu, "zfinder_mu");
 22
 23      Cut cuts_el = Cuts::pT > 20*GeV && Cuts::abseta < 2.4 && !Cuts::absetaIn(1.447, 1.57);
 24      DileptonFinder zfinder_el(91.2*GeV, 0.0, cuts_el && Cuts::abspid == PID::ELECTRON, Cuts::mass > 40*GeV);
 25      declare(zfinder_el, "zfinder_el");
 26
 27
 28      /// Histograms
 29      // dimuon
 30      book(_hist_mm_100_num, "TMP/mm_100_num", refData(1, 1, 1));
 31      book(_hist_mm_125_num, "TMP/mm_125_num", refData(1, 1, 2));
 32      book(_hist_mm_150_num, "TMP/mm_150_num", refData(1, 1, 3));
 33      book(_hist_mm_240_num, "TMP/mm_240_num", refData(1, 1, 4));
 34
 35      book(_hist_mm_100_den, "TMP/mm_100_den", refData(1, 1, 1));
 36      book(_hist_mm_125_den, "TMP/mm_125_den", refData(1, 1, 2));
 37      book(_hist_mm_150_den, "TMP/mm_150_den", refData(1, 1, 3));
 38      book(_hist_mm_240_den, "TMP/mm_240_den", refData(1, 1, 4));
 39
 40      // Dielectron
 41      book(_hist_ee_100_num, "TMP/ee_100_num", refData(2, 1, 1));
 42      book(_hist_ee_125_num, "TMP/ee_125_num", refData(2, 1, 2));
 43      book(_hist_ee_150_num, "TMP/ee_150_num", refData(2, 1, 3));
 44      book(_hist_ee_240_num, "TMP/ee_240_num", refData(2, 1, 4));
 45
 46      book(_hist_ee_100_den, "TMP/ee_100_den", refData(2, 1, 1));
 47      book(_hist_ee_125_den, "TMP/ee_125_den", refData(2, 1, 2));
 48      book(_hist_ee_150_den, "TMP/ee_150_den", refData(2, 1, 3));
 49      book(_hist_ee_240_den, "TMP/ee_240_den", refData(2, 1, 4));
 50
 51      // Dilepton
 52      book(_hist_ll_100_num, "TMP/ll_100_num", refData(3, 1, 1));
 53      book(_hist_ll_125_num, "TMP/ll_125_num", refData(3, 1, 2));
 54      book(_hist_ll_150_num, "TMP/ll_150_num", refData(3, 1, 3));
 55      book(_hist_ll_240_num, "TMP/ll_240_num", refData(3, 1, 4));
 56
 57      book(_hist_ll_100_den, "TMP/ll_100_den", refData(3, 1, 1));
 58      book(_hist_ll_125_den, "TMP/ll_125_den", refData(3, 1, 2));
 59      book(_hist_ll_150_den, "TMP/ll_150_den", refData(3, 1, 3));
 60      book(_hist_ll_240_den, "TMP/ll_240_den", refData(3, 1, 4));
 61
 62      book(_s_mm_100, 1, 1, 1);
 63      book(_s_mm_125, 1, 1, 2);
 64      book(_s_mm_150, 1, 1, 3);
 65      book(_s_mm_240, 1, 1, 4);
 66      book(_s_ee_100, 2, 1, 1);
 67      book(_s_ee_125, 2, 1, 2);
 68      book(_s_ee_150, 2, 1, 3);
 69      book(_s_ee_240, 2, 1, 4);
 70      book(_s_ll_100, 3, 1, 1);
 71      book(_s_ll_125, 3, 1, 2);
 72      book(_s_ll_150, 3, 1, 3);
 73      book(_s_ll_240, 3, 1, 4);
 74    }
 75
 76
 77    double cosThetaCS(const Particle& l1, const Particle& l2) {
 78      const FourMomentum mom1 = l1.mom();
 79      const FourMomentum mom2 = l2.mom();
 80      const FourMomentum mom12 = mom1 + mom2;
 81      const double Q = mom12.mass();
 82      const double QT = mom12.pT();
 83      const double QZ = mom12.pz();
 84
 85      /// @todo Why include factors of sqrt2 which then get immediately multiplied then divided out?
 86      const double sqrt2 = sqrt(2.0);
 87      /// @todo Can be done more nicely via PID-ordered references to mom1, mom2
 88      const double P1p = ((l1.pid() > 0) ? (mom1.E() + mom1.pz()) : (mom2.E() + mom2.pz())) / sqrt2;
 89      const double P1m = ((l1.pid() > 0) ? (mom1.E() - mom1.pz()) : (mom2.E() - mom2.pz())) / sqrt2;
 90      const double P2p = ((l1.pid() > 0) ? (mom2.E() + mom2.pz()) : (mom1.E() + mom1.pz())) / sqrt2;
 91      const double P2m = ((l1.pid() > 0) ? (mom2.E() - mom2.pz()) : (mom1.E() - mom1.pz())) / sqrt2;
 92
 93      const double cosThetaCS = sign(QZ) * (2 / (Q * add_quad(Q, QT))) * (P1p*P2m - P1m*P2p);
 94      return cosThetaCS;
 95    }
 96
 97
 98    /// Perform the per-event analysis
 99    void analyze(const Event& event) {
100
101      const DileptonFinder& zfinder_el = apply<DileptonFinder>(event, "zfinder_el");
102      if (zfinder_el.bosons().size() > 0) {
103        const Particle& z  = zfinder_el.bosons()[0];
104        const Particle& l1 = zfinder_el.constituents()[0];
105        const Particle& l2 = zfinder_el.constituents()[1];
106
107        // Prepare variables for filling
108        const double rap = z.absrap();
109        const double costhetacs = cosThetaCS(l1, l2);
110        const double sgn = sign(costhetacs);
111
112        // Fill the histograms
113        if (rap < 1.0) {
114          _hist_ee_100_num->fill(z.mass(), sgn);
115          _hist_ll_100_num->fill(z.mass(), sgn);
116          _hist_ee_100_den->fill(z.mass());
117          _hist_ll_100_den->fill(z.mass());
118        } else if (rap < 1.25) {
119          _hist_ee_125_num->fill(z.mass(), sgn);
120          _hist_ll_125_num->fill(z.mass(), sgn);
121          _hist_ee_125_den->fill(z.mass());
122          _hist_ll_125_den->fill(z.mass());
123        } else if (rap < 1.50) {
124          _hist_ee_150_num->fill(z.mass(), sgn);
125          _hist_ll_150_num->fill(z.mass(), sgn);
126          _hist_ee_150_den->fill(z.mass());
127          _hist_ll_150_den->fill(z.mass());
128        } else if (rap < 2.40) {
129          _hist_ee_240_num->fill(z.mass(), sgn);
130          _hist_ll_240_num->fill(z.mass(), sgn);
131          _hist_ee_240_den->fill(z.mass());
132          _hist_ll_240_den->fill(z.mass());
133        }
134      }
135
136      const DileptonFinder& zfinder_mu = apply<DileptonFinder>(event, "zfinder_mu");
137      if (zfinder_mu.bosons().size() > 0) {
138        const Particle& z  = zfinder_mu.bosons()[0];
139        const Particle& l1 = zfinder_mu.constituents()[0];
140        const Particle& l2 = zfinder_mu.constituents()[1];
141
142        // Prepare variables for filling
143        const double rap = z.absrap();
144        const double costhetacs = cosThetaCS(l1, l2);
145        const double sgn = sign(costhetacs);
146
147        // Fill the histograms
148        if (rap < 1.0) {
149          _hist_mm_100_num->fill(z.mass(), sgn);
150          _hist_ll_100_num->fill(z.mass(), sgn);
151          _hist_mm_100_den->fill(z.mass());
152          _hist_ll_100_den->fill(z.mass());
153        } else if (rap < 1.25) {
154          _hist_mm_125_num->fill(z.mass(), sgn);
155          _hist_ll_125_num->fill(z.mass(), sgn);
156          _hist_mm_125_den->fill(z.mass());
157          _hist_ll_125_den->fill(z.mass());
158        } else if (rap < 1.50) {
159          _hist_mm_150_num->fill(z.mass(), sgn);
160          _hist_ll_150_num->fill(z.mass(), sgn);
161          _hist_mm_150_den->fill(z.mass());
162          _hist_ll_150_den->fill(z.mass());
163        } else if (rap < 2.40) {
164          _hist_mm_240_num->fill(z.mass(), sgn);
165          _hist_ll_240_num->fill(z.mass(), sgn);
166          _hist_mm_240_den->fill(z.mass());
167          _hist_ll_240_den->fill(z.mass());
168        }
169      }
170    }
171
172
173    /// Normalise histograms etc., after the run
174    void finalize() {
175      divide(_hist_mm_100_num, _hist_mm_100_den, _s_mm_100);
176      divide(_hist_mm_125_num, _hist_mm_125_den, _s_mm_125);
177      divide(_hist_mm_150_num, _hist_mm_150_den, _s_mm_150);
178      divide(_hist_mm_240_num, _hist_mm_240_den, _s_mm_240);
179      divide(_hist_ee_100_num, _hist_ee_100_den, _s_ee_100);
180      divide(_hist_ee_125_num, _hist_ee_125_den, _s_ee_125);
181      divide(_hist_ee_150_num, _hist_ee_150_den, _s_ee_150);
182      divide(_hist_ee_240_num, _hist_ee_240_den, _s_ee_240);
183      divide(_hist_ll_100_num, _hist_ll_100_den, _s_ll_100);
184      divide(_hist_ll_125_num, _hist_ll_125_den, _s_ll_125);
185      divide(_hist_ll_150_num, _hist_ll_150_den, _s_ll_150);
186      divide(_hist_ll_240_num, _hist_ll_240_den, _s_ll_240);
187    }
188
189
190  private:
191
192    /// Histograms
193    Histo1DPtr _hist_ee_100_num, _hist_ee_125_num, _hist_ee_150_num, _hist_ee_240_num;
194    Histo1DPtr _hist_ee_100_den, _hist_ee_125_den, _hist_ee_150_den, _hist_ee_240_den;
195    Histo1DPtr _hist_mm_100_num, _hist_mm_125_num, _hist_mm_150_num, _hist_mm_240_num;
196    Histo1DPtr _hist_mm_100_den, _hist_mm_125_den, _hist_mm_150_den, _hist_mm_240_den;
197    Histo1DPtr _hist_ll_100_num, _hist_ll_125_num, _hist_ll_150_num, _hist_ll_240_num;
198    Histo1DPtr _hist_ll_100_den, _hist_ll_125_den, _hist_ll_150_den, _hist_ll_240_den;
199    Estimate1DPtr _s_ee_100, _s_ee_125, _s_ee_150, _s_ee_240;
200    Estimate1DPtr _s_mm_100, _s_mm_125, _s_mm_150, _s_mm_240;
201    Estimate1DPtr _s_ll_100, _s_ll_125, _s_ll_150, _s_ll_240;
202
203  };
204
205  RIVET_DECLARE_PLUGIN(CMS_2013_I1122847);
206
207}