Rivet analyses
Forward pi0 meson production at HERA
Experiment: H1 (HERA)
Inspire ID: 504022
Status: VALIDATED
Authors: - Keila Moral Figueroa - Hannes Jung
References: - Phys.Lett.B462:440-452,1999 - DOI: 10.1016/S0370-2693(99)00906-5 - arXiv: hep-ex/9907030
Beams: p+ e-, e- p+
Beam energies: (820.0, 27.5); (27.5, 820.0)GeV
Run details: - π0 production in the forward region detected by H1 in DIS ep scattering events at HERA. Cuts:0.1 < y< 0.6, 2 < Q2< 70 GeV2, π0 transverse momentum in the hadronic CMS. pT* $ > $ 2.5 GeV, 5o < θ < 25o, where θ is the polar angle of the produced π0,xπ0 > 0.001 where $ x_{^0} = E_{^0}/ E_{proton}$ and Eproton = 820GeV is the proton beam energy. RAPGAP 26.7 configuration parameters: 10^6 events.
High transverse momentum π0 mesons have been measured with the H1 detector at HERA in deep-inelastic ep scattering events at low Bjorken-x, down to x ≈ 4 ⋅ 10−5 .The measurement is performed in a region of small angles with respect to the proton remnant in the laboratory frame of reference, namely the forward region, and corresponds to central rapidity in the centre of mass system of the virtual photon and proton. This region is expected to be particularly sensitive to QCD effects in hadronic final states. Differential cross-sections for inclusive π0 meson production are presented as a function of Bjorken-x and the four-momentum transfer Q2, and as a function of transverse momentum and pseudorapidity.
Source
code:H1_1999_I504022.cc
// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/UnstableParticles.hh"
#include "Rivet/Projections/DISKinematics.hh"
namespace Rivet {
/// @brief Forward pi0 meson production at HERA (H1)
class H1_1999_I504022 : public Analysis {
public:
/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(H1_1999_I504022);
/// @name Analysis methods
///@{
/// Book histograms and initialise projections before the run
void init() {
// Initialise and register projections
// The basic final-state projection:
declare(FinalState(Cuts::abseta < 7 ), "FS");
declare(DISKinematics(), "Kinematics");
declare(UnstableParticles(), "UFS");
// Book histograms
// take binning from reference data using HEPData ID (digits in "d01-x01-y01" etc.)
book(_h["p_T>2.5&x"], 1, 1, 1);
book(_h["Q:2.0-4.5-eta"], 2, 1, 1);
book(_h["Q:2.0-4.5-p_T"], 3, 1, 1);
book(_h["Q:4.5-15.0-x"], 4, 1, 1);
book(_h["Q:4.5-15.0-eta"], 5, 1, 1);
book(_h["Q:4.5-15.0-p_T"], 6, 1, 1);
book(_h["Q:15.0-70.0-x"], 7, 1, 1);
book(_h["Q:15.0-70.0-eta"], 8, 1, 1);
book(_h["Q:15.0-70.0-p_T"], 9, 1, 1);
book(_h["p_T>2.5&Q"], 10, 1, 1);
book(_h["p_T>3.5&x"], 11, 1, 1);
book(_h["p_T>3.5&Q"], 12, 1, 1);
}
/// Perform the per-event analysis
void analyze(const Event& event) {
/// @todo Do the event by event analysis here
const DISKinematics& dk = apply<DISKinematics>(event, "Kinematics");
// Get the DIS kinematics
double xbj = dk.x();
double ybj = dk.y();
double Q2 = dk.Q2()/GeV2;
// Q2 and inelasticity cuts
//cout << " after xbj " << xbj << endl;
if (!inRange(ybj, 0.1, 0.6)) vetoEvent;
//cout << " after ybj " << ybj << endl;
if (!inRange(Q2, 2.0*GeV2, 70.0*GeV2)) vetoEvent;
//cout << " after Q2 " << Q2 << endl;
const FinalState& fs = apply<FinalState>(event, "FS");
const size_t numParticles = fs.particles().size();
//cout << " Num all final state particles " << numParticles << endl;
//proton beam energy: 820 GeV
double e_proton = dk.beamHadron().E()/GeV;
// Even if we only generate hadronic events, we still need a cut on numCharged >= 2.
if (numParticles < 2) {
MSG_DEBUG("Failed leptonic event cut");
vetoEvent;
}
// Extracting the pi0
const UnstableParticles& ufs = apply<UnstableFinalState>(event, "UFS");
//Get the hadronic CMS kinematics
const LorentzTransform hcmboost = dk.boostHCM();
for (const Particle& p : ufs.particles(Cuts::pid==PID::PI0)) {
//cout << " Pid = " << p.pid() << endl;
//Get the LAB kinematics
double theta = p.theta();
double eta = p.pseudorapidity();
// double pT = p.pT()/GeV;
//Boost hcm
const FourMomentum hcmMom = hcmboost.transform(p.mom());
double pThcm = hcmMom.pT();
double e_pi0 = p.E()/GeV;
double x_pi0_proton = e_pi0/e_proton;
// epi0/e_proton, theta and pThcm cuts
if(x_pi0_proton < 0.01) continue;
//cout << " theta " << theta << " in deg " << theta/degree << endl;
if (!inRange(theta/degree, 5, 25)) continue;
if(pThcm < 2.5*GeV) continue;
//Three cuts for Q2:
if (Q2 > 2.0*GeV2 && Q2 < 4.5*GeV2){
_h["Q:2.0-4.5-eta"]->fill(eta);
_h["Q:2.0-4.5-p_T"]->fill(pThcm);
}
if (Q2 > 4.5*GeV2 && Q2 < 15.0*GeV2){
_h["Q:4.5-15.0-x"]->fill(xbj);
_h["Q:4.5-15.0-eta"]->fill(eta);
_h["Q:4.5-15.0-p_T"]->fill(pThcm);
}
if (Q2 > 15.0*GeV2 && Q2 < 70.0*GeV2){
_h["Q:15.0-70.0-x"]->fill(xbj);
_h["Q:15.0-70.0-eta"]->fill(eta);
_h["Q:15.0-70.0-p_T"]->fill(pThcm);
}
//Two cuts for p_T:
if (pThcm > 2.5*GeV){
_h["p_T>2.5&x"]->fill(xbj);
_h["p_T>2.5&Q"]->fill(Q2);
}
if (pThcm > 3.5*GeV){
_h["p_T>3.5&x"]->fill(xbj);
_h["p_T>3.5&Q"]->fill(Q2);
}
}
}
/// Normalise histograms etc., after the run
void finalize() {
const double sn = crossSection()/nanobarn/sumW();
const double sp = crossSection()/picobarn/sumW();
scale(_h["p_T>2.5&x"], sn);
scale(_h["Q:2.0-4.5-eta"], sp);
scale(_h["Q:2.0-4.5-p_T"], sp);
scale(_h["Q:4.5-15.0-x"], sn);
scale(_h["Q:4.5-15.0-eta"], sp);
scale(_h["Q:4.5-15.0-p_T"], sp);
scale(_h["Q:15.0-70.0-x"], sn);
scale(_h["Q:15.0-70.0-eta"], sp);
scale(_h["Q:15.0-70.0-p_T"], sp);
scale(_h["p_T>2.5&Q"], sp);
scale(_h["p_T>3.5&x"], sn);
scale(_h["p_T>3.5&Q"], sp);
}
///@}
/// @name Histograms
///@{
map<string, Histo1DPtr> _h;
///@}
};
RIVET_DECLARE_PLUGIN(H1_1999_I504022);
}