Rivet analyses

title: H1_2009_I810046

Strangeness Production at low $Q^2$ 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 \to $\sqrt{s} = 318~\GeV$

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 $2 < Q^2 < 100 GeV^2$ and the inelasticity $0.1 < y < 0.6$. The $K_s$ and $\Lambda$ production cross sections and their ratios are determined. $K_s$ production is compared to the production of charged particles in the same region of phase space. The $\Lambda$ - anti-$\Lambda$ 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++ // -- C++ --

include "Rivet/Analysis.hh"

include "Rivet/Projections/DISKinematics.hh"

include "Rivet/Projections/FinalState.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);

} ```