Rivet analyses

Measurement of W charge asymmetry from D0 Run II

Experiment: D0 (Tevatron Run 2)

Inspire ID: 791230

Status: VALIDATED

Authors: - Andy Buckley - Gavin Hesketh

References: - Phys.Rev.Lett.101:211801,2008 - DOI: 10.1103/PhysRevLett.101.211801 - arXiv: 0807.3367

Beams: p- p+

Beam energies: (980.0, 980.0)GeV

Run details: - Event type: W production with decay to e νe only * for Pythia 6: MSEL = 12, MDME(206,1) = 1 * Energy: 1.96 TeV

Measurement of the electron charge asymmetry in pp̄ → W + X → eνe + X events at a center of mass energy of 1.96 TeV. The asymmetry is measured as a function of the electron transverse momentum and pseudorapidity in the interval (-3.2, 3.2). This data is sensitive to proton parton distribution functions due to the valence asymmetry in the incoming quarks which produce the W. Initial state radiation should also affect the pT distribution.

Source code:D0_2008_I791230.cc

// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/MissingMomentum.hh"
#include "Rivet/Projections/LeptonFinder.hh"
#include "Rivet/Projections/LeadingParticlesFinalState.hh"
#include "Rivet/Projections/IdentifiedFinalState.hh"

namespace Rivet {


  /// @brief D0 Run II measurement of W charge asymmetry
  ///
  /// @author Andy Buckley
  /// @author Gavin Hesketh
  class D0_2008_I791230 : public Analysis {
  public:

    RIVET_DEFAULT_ANALYSIS_CTOR(D0_2008_I791230);


    /// @name Analysis methods
    /// @{

    // Book histograms and set up projections
    void init() {

      // Projections
      declare("MET", MissingMomentum());
      LeptonFinder ef(0.2, Cuts::abseta < 5 && Cuts::pT > 25*GeV && Cuts::abspid == PID::ELECTRON);
      declare(ef, "Elecs");

      // Histograms (temporary +- charge histos and scatters to store the calculated asymmetries)
      for (size_t pmindex = 0; pmindex < 2; ++pmindex) {
        const string suffix = (pmindex == 0) ? "plus" : "minus";
        book(_hs_dsigpm_deta_25_35[pmindex] ,"TMP/dsigpm_deta_25_35_" + suffix, refData(1, 1, 1));
        book(_hs_dsigpm_deta_35[pmindex] ,"TMP/dsigpm_deta_35_" + suffix, refData(1, 1, 2));
        book(_hs_dsigpm_deta_25[pmindex] ,"TMP/dsigpm_deta_25_" + suffix, refData(1, 1, 3));
      }
      book(_h_asym1, 1, 1, 1);
      book(_h_asym2, 1, 1, 2);
      book(_h_asym3, 1, 1, 3);
    }


    /// Do the analysis
    void analyze(const Event & event) {

      // W reco, starting with MET
      const P4& pmiss = apply<MissingMom>(event, "MET").missingMom();
      if (pmiss.pT() < 25*GeV) vetoEvent;

      // Identify the closest-matching l+MET to m == mW
      const Particles& es = apply<LeptonFinder>(event, "Elecs").particles();
      const int ifound = closestMatchIndex(es, pmiss, Kin::mass, 80.4*GeV, 60*GeV, 100*GeV);
      if (ifound < 0) {
        MSG_DEBUG("No W candidates found: vetoing");
        vetoEvent;
      }

      // Get the e+- momentum, and an effective charge including the eta sign
      const Particle& e = es[ifound];
      const int chg_e = sign(e.eta()) * sign(e.charge());
      assert(chg_e == 1 || chg_e == -1);
      MSG_TRACE("Charged lepton sign = " << chg_e);

      // Fill histos with appropriate +- indexing
      const size_t pmindex = (chg_e > 0) ? 0 : 1;
      if (e.Et() < 35*GeV) _hs_dsigpm_deta_25_35[pmindex]->fill(e.abseta());
      else _hs_dsigpm_deta_35[pmindex]->fill(e.abseta());
      _hs_dsigpm_deta_25[pmindex]->fill(e.abseta());
    }


    /// @brief Finalize
    ///
    /// Construct asymmetry: (dsig+/deta - dsig-/deta) / (dsig+/deta + dsig-/deta) for each ET region
    void finalize() {
      asymm(_hs_dsigpm_deta_25_35[0], _hs_dsigpm_deta_25_35[1], _h_asym1);
      asymm(_hs_dsigpm_deta_35[0],    _hs_dsigpm_deta_35[1],    _h_asym2);
      asymm(_hs_dsigpm_deta_25[0],    _hs_dsigpm_deta_25[1],    _h_asym3);
      _h_asym1->scale(100.);
      _h_asym2->scale(100.);
      _h_asym3->scale(100.);
    }

    /// @}


  private:

    /// @name Histograms
    /// @{
    Histo1DPtr _hs_dsigpm_deta_25_35[2], _hs_dsigpm_deta_35[2], _hs_dsigpm_deta_25[2];
    Estimate1DPtr _h_asym1, _h_asym2, _h_asym3;
    /// @}

  };


  RIVET_DECLARE_ALIASED_PLUGIN(D0_2008_I791230, D0_2008_S7837160);

}

Aliases: - D0_2008_S7837160