Rivet analyses

title: LHCB_2015_I1333223

Measurement of inelastic interaction cross-section in pp collisions at 7 TeV for LHCb fiducial phase-space.

Experiment: LHCB (Large Hadron Collider (LHC))

Inspire ID: 1333223

Status: VALIDATED

Authors: - Alex Grecu

References: - JHEP02:129,2015 - DOI: 10.1007/JHEP02(2015)129 - arXiv: 1412.2500

Beams: p+ p+

Beam energies: (3500.0, 3500.0)GeV

Run details: - Proton-proton interactions at sqrt(s) = 7 TeV. LHCb minimum bias, inelastic events (elastic processes may be turned off).

LhCb measurement of the cross-section for inelastic proton-proton collisions at $\sqrt{s} = 7$ TeV with at least one prompt stable charged particle of transverse momentum $p_T > 0.2$ GeV/$c$ and pseudorapidity ($\eta$) in the range $2.0 < \eta < 4.5$. A prompt stable charged particle is defined as having the true impact parameter relative to the true primary vertex smaller than 200 $\mu$m.

Source code:LHCB_2015_I1333223.cc

```c++ // -- C++ --

include "Rivet/Analysis.hh"

include "Rivet/Math/Units.hh"

include "Rivet/Projections/ChargedFinalState.hh"

include "Rivet/Tools/Logging.hh"

include

using namespace std;

namespace Rivet {

class LHCB_2015_I1333223 : public Analysis { public:

/// @name Constructors etc.
/// @{

/// Constructor
LHCB_2015_I1333223()
    : Analysis("LHCB_2015_I1333223") { }

/// @}

public:

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

/// Book histograms and initialise projections before the run
void init() {
  // Charged particles
  declare(ChargedFinalState(Cuts::eta > 2.0 && Cuts::eta < 4.5 && Cuts::pT > 0.2 * GeV), "CFS");
  // Reproducing only measurement for prompt charged particles
  book(_hInelasticXs, 1, 1, 1);
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  const ChargedFinalState& cfs = apply<ChargedFinalState>(event, "CFS");

  // eliminate non-inelastic events and empty events in LHCb
  if (cfs.particles().size() == 0) vetoEvent;

  // See if this event has at least one prompt particle
  for (const Particle& myp : cfs.particles()) {
    double dPV = getPVDCA(myp);
    // if IP > 200 microns the particle is not considered prompt
    if ((dPV < 0.) || (dPV > 0.2 * millimeter)) {
      MSG_DEBUG(" Vetoing " << myp.pid() << " at " << dPV);
      continue;
    }
    // histo gets filled only for inelastic events (at least one prompt charged particle)
    _hInelasticXs->fill(sqrtS());
    break;
  } //end loop on particles
}


/// Normalise histograms etc., after the run
void finalize() {
  scale(_hInelasticXs, crossSection() / sumOfWeights() / millibarn);
}

/// @}

private:

/// Compute distance of closest approach in z range for one particle.
/// Returns -1 if unable to compute the DCA to PV.
double getPVDCA(const Particle& p) {
  ConstGenVertexPtr vtx = p.genParticle()->production_vertex();
  if (0 == vtx) return -1.;

  // Unit vector of particle's MOMENTUM three vector
  const Vector3 u = p.momentum().p3().unit();

  // The interaction point is always at (0, 0,0,0) hence the
  // vector pointing from the PV to the particle production vertex is:
  Vector3 d(vtx->position().x(), vtx->position().y(), vtx->position().z());

  // Subtract projection of d onto u from d
  double proj = d.dot(u);
  d -= (u * proj);

  // d should be orthogonal to u and it's length give the distance of
  // closest approach
  return d.mod();
}


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

};

RIVET_DECLARE_PLUGIN(LHCB_2015_I1333223);

} ```