Rivet analyses

π+π− mass distribution in Λb*0(5920) → Λb0π+π− decays

Experiment: LHCB (LHC)

Inspire ID: 1114753

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Rev.Lett. 109 (2012) 172003

Beams: * *

Beam energies: ANY

Run details: - any process producing lambda_b(5920), original pp

Measurement of the production of excited Λb baryons by LHCb. The only interesting distribution from a simulation perspective is the mass disutribution of π+π− in Λb*0(5920) → Λb0π+π− decays which is sensitive to the decay model used for this decay mode.

Source code:LHCB_2012_I1114753.cc

// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {


  /// @brief pi+pi- mass in lambdab* decays
  class LHCB_2012_I1114753 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(LHCB_2012_I1114753);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      declare(UnstableParticles(Cuts::abspid==102154),"UFS");
      book(_h_mpipi,1,1,1);
    }

    void findDecayProducts(const Particle & mother,
               unsigned int & nstable,
               Particles& pip, Particles& pim,
               Particles & lambda) {
      for(const Particle & p : mother.children()) {
        int id = p.pid();
        if ( id == PID::PIMINUS) {
      pim.push_back(p);
      ++nstable;
    }
        else if (id == PID::PIPLUS) {
          pip.push_back(p);
          ++nstable;
        }
    else if (abs(id)==5122) {
      lambda.push_back(p);
      ++nstable;
    }
    else if ( !p.children().empty() ) {
      findDecayProducts(p,nstable,pip,pim,lambda);
    }
    else
      ++nstable;
      }
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      // loop over unstable particles
      for(const Particle& lb : apply<UnstableParticles>(event, "UFS").particles()) {
    unsigned int nstable(0);
    Particles pip, pim, lambda;
    findDecayProducts(lb,nstable,pip,pim,lambda);
    // check for lambda
    if(lambda.size() !=1 || nstable !=3 ||
       pip.size()!=1 || pim.size() !=1 ) continue;
    FourMomentum q = pip[0].momentum()+pim[0].momentum();
    _h_mpipi->fill(q.mass()/MeV);
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      normalize(_h_mpipi);
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h_mpipi;
    /// @}


  };


  RIVET_DECLARE_PLUGIN(LHCB_2012_I1114753);

}