Rivet analyses

Strangeness Production at low Q2 in Deep-Inelastic ep Scattering at HERA

Experiment: H1 (HERA)

Inspire ID: 810046

Status: VALIDATED

Authors: - Andrii Verbytskyi

References: - Eur.Phys.J.C 61 (2009) 185-205 - DOI: 10.1140/epjc/s10052-009-0995-1 - arXiv: 0810.4036

Beams: p+ e-, p+ e+

Beam energies: (159.0, 159.0)GeV

Run details: - e+p deep inelastic scattering with p at 920~GeV, e+ at 27.5 GeV $\sqrt{s} = 318~\GeV$

The production of neutral strange hadrons is investigated using deep-inelastic scattering events measured with the H1 detector at HERA. The measurements are made in the phase space defined by the negative four-momentum transfer squared of the photon 2 < Q2 < 100GeV2 and the inelasticity 0.1 < y < 0.6. The Ks and Λ production cross sections and their ratios are determined. Ks production is compared to the production of charged particles in the same region of phase space. The Λ - anti-Λ asymmetry is also measured and found to be consistent with zero. Predictions of leading order Monte Carlo programs are compared to the data.

Source code:H1_2009_I810046.cc

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

namespace Rivet {


  /// @brief Cross-sections of \f$K_{0}$\f and \f$\Lambda$\f in DIS
  class H1_2009_I810046 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(H1_2009_I810046);


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

    /// Book histograms and initialise projections before the run
    void init() {
      const DISKinematics& diskin = DISKinematics();
      declare(diskin, "Kinematics");
      declare(UnstableParticles(), "UPS");

      book(_h_K0S_q2, 4, 1, 1);
      book(_h_K0S_x, 5, 1, 1);
      book(_h_K0S_pt, 6, 1, 1);
      book(_h_K0S_eta, 7, 1, 1);

      book(_h_LAMBDA_q2, 8, 1, 1);
      book(_h_LAMBDA_x, 9, 1, 1);
      book(_h_LAMBDA_pt, 10, 1, 1);
      book(_h_LAMBDA_eta, 11, 1, 1);

    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      /// DIS kinematics
      const DISKinematics& dk = apply<DISKinematics>(event, "Kinematics");
      const double q2  = dk.Q2();
      const double x   = dk.x();
      const double y   = dk.y();
      const int orientation = dk.orientation();

      if (!inRange(q2/GeV2, 2.0, 100.0)) vetoEvent;
      if (!inRange(y, 0.1, 0.6)) vetoEvent;
      const UnstableParticles& ufs = apply<UnstableParticles>(event, "UPS");

      for (const Particle& p: select(ufs.particles(), Cuts::abspid == abs(PID::K0S))) {
        if (!inRange(p.pt()/GeV, 0.5, 3.5)) continue;
        if (!inRange(p.eta(), -1.3, 1.3)) continue;
        _h_K0S_q2->fill(q2/GeV2);
        _h_K0S_x->fill(x);
        _h_K0S_pt->fill(p.pt()/GeV);
        _h_K0S_eta->fill(p.eta()*orientation);
      }

      for (const Particle& p: select(ufs.particles(), Cuts::abspid == abs(PID::LAMBDA))) {
        if (!inRange(p.pt()/GeV, 0.5, 3.5)) continue;
        if (!inRange(p.eta(), -1.3, 1.3)) continue;
        _h_LAMBDA_q2->fill(q2/GeV2);
        _h_LAMBDA_x->fill(x);
        _h_LAMBDA_pt->fill(p.pt()/GeV);
        _h_LAMBDA_eta->fill(p.eta()*orientation);
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      const double sf = crossSection()/nanobarn/sumOfWeights();
      scale( _h_K0S_pt, sf);
      scale( _h_K0S_eta, sf);
      scale( _h_K0S_q2, sf);
      scale( _h_K0S_x, sf/1000);

      scale( _h_LAMBDA_pt, sf);
      scale( _h_LAMBDA_eta, sf);
      scale( _h_LAMBDA_q2, sf);
      scale( _h_LAMBDA_x, sf/1000);
    }

    /// @}

    /// @name Histograms
    /// @}
    Histo1DPtr _h_K0S_pt, _h_K0S_eta, _h_K0S_x, _h_K0S_q2;
    Histo1DPtr _h_LAMBDA_pt, _h_LAMBDA_eta, _h_LAMBDA_x, _h_LAMBDA_q2;
    /// @}

  };


  RIVET_DECLARE_PLUGIN(H1_2009_I810046);

}