Rivet analyses

Measurement of the transverse momentum spectrum of the Higgs boson produced in ppcollisions at $\sqrt{s} = 8$ TeV using H to WW decays

Experiment: CMS (LHC)

Inspire ID: 1467451

Status: VALIDATED

Authors: - Lorenzo Viliani

References: - JHEP 1703 (2017) 032, 2017 - DOI:10.1007/JHEP03(2017)032 - arXiv: 1606.01522 - Expt page: CMS-HIG-15-010

Beams: p+ p+

Beam energies: (4000.0, 4000.0)GeV

Run details: - H->WW->lvlv, both ggH and XH (VBF anf VH) productions modes are included

The cross section for Higgs boson production in pp collisions is studied using the H → W+W− decay mode, followed by leptonic decays of the W bosons to an oppositely charged electron-muon pair in the final state. The measurements are performed using data collected by the CMS experiment at the LHC at a centre-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 19.4 fb−1. The Higgs boson transverse momentum (pT) is reconstructed using the lepton pair pT and missing pT. The differential cross section times branching fraction is measured as a function of the Higgs boson pT in a fiducial phase space defined to match the experimental acceptance in terms of the lepton kinematics and event topology. The production cross section times branching fraction in the fiducial phase space is measured to be 39 ± 8 (stat) ± 9 (syst) fb. The measurements are found to agree, within experimental uncertainties, with theoretical calculations based on the standard model. The fiducial region is defined at particle level (using Born level leptons) as: - emununu, leptons are required not to originate from leptonic tau decays - leading lepton pT > 20 GeV - subleading lepton pT > 10 GeV - psudorapidity of electrons and muons |η| < 2.5 - Invariant mass of the two charged leptons mll > 12 GeV - Charged lepton pair pT > 30 GeV - Invariant mass of the leptonic system in the transverse plane mTeμνν > 50 GeV Notes on reinterpretation: Major- Despite the existance of a “fiducial” cross section definition, it is not clear this can really be used to constrain any BSM signal other than an excess/deficit in SM Higgs->WW events. There is a b-jet veto is applied to suppress ttbar background, which is however not implemented in the fiducial cross section defintion, and so is extrapolated out during the unfolding. Even after this, the background remains very large and is subtracted using a fit to data. How all this might affect a hypothetical non-SM-H source of electrons and muons (on which the “fiducial” region is based) is very difficult to evaluate. Minor- The rivet routine uses dressed leptons even though the above (and the paper) say they are born level.

Source code:CMS_2017_I1467451.cc

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

namespace Rivet {


  /// Higgs -> WW -> emu + MET in 8 TeV pp collisions
  class CMS_2017_I1467451 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(CMS_2017_I1467451);


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

      const double lepConeSize = 0.1;
      const double lepMaxEta = 2.5;
      const Cut lepton_cut = (Cuts::abseta < lepMaxEta);

      MSG_WARNING("\033[91;1mLIMITED VALIDITY - check info file for details!\033[m");


      // Initialise and register projections
      FinalState fs((Cuts::etaIn(-2.5,2.5)));
      FinalState fsm((Cuts::etaIn(-5,5)));
      declare(fs, "FS");
      declare(fsm, "FSM");

      ChargedLeptons charged_leptons(fs);
      IdentifiedFinalState photons(fs);
      photons.acceptIdPair(PID::PHOTON);

      PromptFinalState prompt_leptons(charged_leptons);
      prompt_leptons.acceptMuonDecays(true);
      prompt_leptons.acceptTauDecays(false);

      PromptFinalState prompt_photons(photons);
      prompt_photons.acceptMuonDecays(true);
      prompt_photons.acceptTauDecays(false);

      LeptonFinder dressed_leptons(prompt_leptons, prompt_photons, lepConeSize, lepton_cut);
      declare(dressed_leptons, "LeptonFinder");

      MissingMomentum Met(fsm);
      declare(Met, "MET");


      // Book histograms
      book(histoPtH , 1,1,1);
      book(histoXsec, 2,1,1);
    }


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

      Particles leptons = apply<LeptonFinder>(event, "LeptonFinder").particlesByPt(10.0*GeV);
      if (leptons.size() < 2) vetoEvent;
      if (leptons[0].pT() < 20*GeV || leptons[1].pT() < 10*GeV) vetoEvent;
      if (leptons[0].charge() == leptons[1].charge()) vetoEvent;
      if (leptons[0].abspid() == leptons[1].abspid()) vetoEvent;

      FourMomentum LL = (leptons[0].momentum() + leptons[1].momentum());
      if (LL.mass() < 12*GeV) vetoEvent;
      if (LL.pT() < 30*GeV) vetoEvent;

      FourMomentum EtMiss = apply<MissingMomentum>(event,"MET").missingMomentum();
      FourMomentum P4H = LL + EtMiss;

      double dphi = deltaPhi(LL, EtMiss);

      double mT = sqrt(2*LL.pT()*EtMiss.pT()*(1-cos(dphi)));
      if (mT < 50*GeV) vetoEvent;

      histoPtH->fill(min(P4H.pT()/GeV, 199.));
      histoXsec->fill(8000); ///< @todo Should probably be a Counter
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      scale(histoPtH, crossSection()/sumOfWeights()/femtobarn);
      scale(histoXsec, (histoXsec->xMax()-histoXsec->xMin())*crossSection()/sumOfWeights()/femtobarn);
    }


  private:

    Histo1DPtr histoPtH, histoXsec;

  };


  RIVET_DECLARE_PLUGIN(CMS_2017_I1467451);

}