Rivet analyses

title: 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: - Phys. Lett. B 718 (2013) 752 - DOI: 10.1016/j.physletb.2012.10.082 - arXiv: 1207.3973

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

```c++ // -- C++ --

include "Rivet/Analysis.hh"

include "Rivet/Projections/DileptonFinder.hh"

include "Rivet/Projections/FinalState.hh"

namespace Rivet {

class CMS_2013_I1122847 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(CMS_2013_I1122847);


/// Book histograms and initialise projections before the run
void init() {

  Cut cuts_mu = Cuts::abseta < 2.4 && Cuts::pT > 20 * GeV;
  DileptonFinder zfinder_mu(91.2 * GeV, 0.0, cuts_mu && Cuts::abspid == PID::MUON, Cuts::mass > 40 * GeV);
  declare(zfinder_mu, "zfinder_mu");

  Cut cuts_el = Cuts::pT > 20 * GeV && Cuts::abseta < 2.4 && !Cuts::absetaIn(1.447, 1.57);
  DileptonFinder zfinder_el(91.2 * GeV, 0.0, cuts_el && Cuts::abspid == PID::ELECTRON,
                            Cuts::mass > 40 * GeV);
  declare(zfinder_el, "zfinder_el");


  /// Histograms
  // dimuon
  book(_hist_mm_100_num, "TMP/mm_100_num", refData(1, 1, 1));
  book(_hist_mm_125_num, "TMP/mm_125_num", refData(1, 1, 2));
  book(_hist_mm_150_num, "TMP/mm_150_num", refData(1, 1, 3));
  book(_hist_mm_240_num, "TMP/mm_240_num", refData(1, 1, 4));

  book(_hist_mm_100_den, "TMP/mm_100_den", refData(1, 1, 1));
  book(_hist_mm_125_den, "TMP/mm_125_den", refData(1, 1, 2));
  book(_hist_mm_150_den, "TMP/mm_150_den", refData(1, 1, 3));
  book(_hist_mm_240_den, "TMP/mm_240_den", refData(1, 1, 4));

  // Dielectron
  book(_hist_ee_100_num, "TMP/ee_100_num", refData(2, 1, 1));
  book(_hist_ee_125_num, "TMP/ee_125_num", refData(2, 1, 2));
  book(_hist_ee_150_num, "TMP/ee_150_num", refData(2, 1, 3));
  book(_hist_ee_240_num, "TMP/ee_240_num", refData(2, 1, 4));

  book(_hist_ee_100_den, "TMP/ee_100_den", refData(2, 1, 1));
  book(_hist_ee_125_den, "TMP/ee_125_den", refData(2, 1, 2));
  book(_hist_ee_150_den, "TMP/ee_150_den", refData(2, 1, 3));
  book(_hist_ee_240_den, "TMP/ee_240_den", refData(2, 1, 4));

  // Dilepton
  book(_hist_ll_100_num, "TMP/ll_100_num", refData(3, 1, 1));
  book(_hist_ll_125_num, "TMP/ll_125_num", refData(3, 1, 2));
  book(_hist_ll_150_num, "TMP/ll_150_num", refData(3, 1, 3));
  book(_hist_ll_240_num, "TMP/ll_240_num", refData(3, 1, 4));

  book(_hist_ll_100_den, "TMP/ll_100_den", refData(3, 1, 1));
  book(_hist_ll_125_den, "TMP/ll_125_den", refData(3, 1, 2));
  book(_hist_ll_150_den, "TMP/ll_150_den", refData(3, 1, 3));
  book(_hist_ll_240_den, "TMP/ll_240_den", refData(3, 1, 4));

  book(_s_mm_100, 1, 1, 1);
  book(_s_mm_125, 1, 1, 2);
  book(_s_mm_150, 1, 1, 3);
  book(_s_mm_240, 1, 1, 4);
  book(_s_ee_100, 2, 1, 1);
  book(_s_ee_125, 2, 1, 2);
  book(_s_ee_150, 2, 1, 3);
  book(_s_ee_240, 2, 1, 4);
  book(_s_ll_100, 3, 1, 1);
  book(_s_ll_125, 3, 1, 2);
  book(_s_ll_150, 3, 1, 3);
  book(_s_ll_240, 3, 1, 4);
}


double cosThetaCS(const Particle& l1, const Particle& l2) {
  const FourMomentum mom1 = l1.mom();
  const FourMomentum mom2 = l2.mom();
  const FourMomentum mom12 = mom1 + mom2;
  const double Q = mom12.mass();
  const double QT = mom12.pT();
  const double QZ = mom12.pz();

  /// @todo Why include factors of sqrt2 which then get immediately multiplied then divided out?
  const double sqrt2 = sqrt(2.0);
  /// @todo Can be done more nicely via PID-ordered references to mom1, mom2
  const double P1p = ((l1.pid() > 0) ? (mom1.E() + mom1.pz()) : (mom2.E() + mom2.pz())) / sqrt2;
  const double P1m = ((l1.pid() > 0) ? (mom1.E() - mom1.pz()) : (mom2.E() - mom2.pz())) / sqrt2;
  const double P2p = ((l1.pid() > 0) ? (mom2.E() + mom2.pz()) : (mom1.E() + mom1.pz())) / sqrt2;
  const double P2m = ((l1.pid() > 0) ? (mom2.E() - mom2.pz()) : (mom1.E() - mom1.pz())) / sqrt2;

  const double cosThetaCS = sign(QZ) * (2 / (Q * add_quad(Q, QT))) * (P1p * P2m - P1m * P2p);
  return cosThetaCS;
}


/// Perform the per-event analysis
void analyze(const Event& event) {

  const DileptonFinder& zfinder_el = apply<DileptonFinder>(event, "zfinder_el");
  if (zfinder_el.bosons().size() > 0) {
    const Particle& z = zfinder_el.bosons()[0];
    const Particle& l1 = zfinder_el.constituents()[0];
    const Particle& l2 = zfinder_el.constituents()[1];

    // Prepare variables for filling
    const double rap = z.absrap();
    const double costhetacs = cosThetaCS(l1, l2);
    const double sgn = sign(costhetacs);

    // Fill the histograms
    if (rap < 1.0) {
      _hist_ee_100_num->fill(z.mass(), sgn);
      _hist_ll_100_num->fill(z.mass(), sgn);
      _hist_ee_100_den->fill(z.mass());
      _hist_ll_100_den->fill(z.mass());
    }
    else if (rap < 1.25) {
      _hist_ee_125_num->fill(z.mass(), sgn);
      _hist_ll_125_num->fill(z.mass(), sgn);
      _hist_ee_125_den->fill(z.mass());
      _hist_ll_125_den->fill(z.mass());
    }
    else if (rap < 1.50) {
      _hist_ee_150_num->fill(z.mass(), sgn);
      _hist_ll_150_num->fill(z.mass(), sgn);
      _hist_ee_150_den->fill(z.mass());
      _hist_ll_150_den->fill(z.mass());
    }
    else if (rap < 2.40) {
      _hist_ee_240_num->fill(z.mass(), sgn);
      _hist_ll_240_num->fill(z.mass(), sgn);
      _hist_ee_240_den->fill(z.mass());
      _hist_ll_240_den->fill(z.mass());
    }
  }

  const DileptonFinder& zfinder_mu = apply<DileptonFinder>(event, "zfinder_mu");
  if (zfinder_mu.bosons().size() > 0) {
    const Particle& z = zfinder_mu.bosons()[0];
    const Particle& l1 = zfinder_mu.constituents()[0];
    const Particle& l2 = zfinder_mu.constituents()[1];

    // Prepare variables for filling
    const double rap = z.absrap();
    const double costhetacs = cosThetaCS(l1, l2);
    const double sgn = sign(costhetacs);

    // Fill the histograms
    if (rap < 1.0) {
      _hist_mm_100_num->fill(z.mass(), sgn);
      _hist_ll_100_num->fill(z.mass(), sgn);
      _hist_mm_100_den->fill(z.mass());
      _hist_ll_100_den->fill(z.mass());
    }
    else if (rap < 1.25) {
      _hist_mm_125_num->fill(z.mass(), sgn);
      _hist_ll_125_num->fill(z.mass(), sgn);
      _hist_mm_125_den->fill(z.mass());
      _hist_ll_125_den->fill(z.mass());
    }
    else if (rap < 1.50) {
      _hist_mm_150_num->fill(z.mass(), sgn);
      _hist_ll_150_num->fill(z.mass(), sgn);
      _hist_mm_150_den->fill(z.mass());
      _hist_ll_150_den->fill(z.mass());
    }
    else if (rap < 2.40) {
      _hist_mm_240_num->fill(z.mass(), sgn);
      _hist_ll_240_num->fill(z.mass(), sgn);
      _hist_mm_240_den->fill(z.mass());
      _hist_ll_240_den->fill(z.mass());
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  divide(_hist_mm_100_num, _hist_mm_100_den, _s_mm_100);
  divide(_hist_mm_125_num, _hist_mm_125_den, _s_mm_125);
  divide(_hist_mm_150_num, _hist_mm_150_den, _s_mm_150);
  divide(_hist_mm_240_num, _hist_mm_240_den, _s_mm_240);
  divide(_hist_ee_100_num, _hist_ee_100_den, _s_ee_100);
  divide(_hist_ee_125_num, _hist_ee_125_den, _s_ee_125);
  divide(_hist_ee_150_num, _hist_ee_150_den, _s_ee_150);
  divide(_hist_ee_240_num, _hist_ee_240_den, _s_ee_240);
  divide(_hist_ll_100_num, _hist_ll_100_den, _s_ll_100);
  divide(_hist_ll_125_num, _hist_ll_125_den, _s_ll_125);
  divide(_hist_ll_150_num, _hist_ll_150_den, _s_ll_150);
  divide(_hist_ll_240_num, _hist_ll_240_den, _s_ll_240);
}

private:

/// Histograms
Histo1DPtr _hist_ee_100_num, _hist_ee_125_num, _hist_ee_150_num, _hist_ee_240_num;
Histo1DPtr _hist_ee_100_den, _hist_ee_125_den, _hist_ee_150_den, _hist_ee_240_den;
Histo1DPtr _hist_mm_100_num, _hist_mm_125_num, _hist_mm_150_num, _hist_mm_240_num;
Histo1DPtr _hist_mm_100_den, _hist_mm_125_den, _hist_mm_150_den, _hist_mm_240_den;
Histo1DPtr _hist_ll_100_num, _hist_ll_125_num, _hist_ll_150_num, _hist_ll_240_num;
Histo1DPtr _hist_ll_100_den, _hist_ll_125_den, _hist_ll_150_den, _hist_ll_240_den;
Estimate1DPtr _s_ee_100, _s_ee_125, _s_ee_150, _s_ee_240;
Estimate1DPtr _s_mm_100, _s_mm_125, _s_mm_150, _s_mm_240;
Estimate1DPtr _s_ll_100, _s_ll_125, _s_ll_150, _s_ll_240;

};

RIVET_DECLARE_PLUGIN(CMS_2013_I1122847);

} ```