Rivet analyses
ZEUS dijet cross-sections in neutral-current DIS
Experiment: ZEUS (HERA)
Inspire ID: 875006
Status: VALIDATED
Authors: - Jacob Shannon
References: - Eur.Phys.J.C70:965-982,2010 - DOI: 10.1140/epjc/s10052-010-1504-2 - arXiv: 1010.6167v1
Beams: p+ e+
Beam energies: ANY
Run details: - Deep Inelastic Scattering events, 125 to 20000 GeV2
Single- and double-differential inclusive dijet cross sections in neutral current deep inelastic ep scattering have been measured with the ZEUS detector using an integrated luminosity of 374 pb−1. The measurement was performed at large values of the photon virtuality, Q2, between 125 and 20000 GeV2. The jets were reconstructed with the kT cluster algorithm in the Breit reference frame and selected by requiring their transverse energies in the Breit frame, ETB, jet, to be larger than 8 GeV. In addition, the invariant mass of the dijet system, Mjj, was required to be greater than 20 GeV. The cross sections are described by the predictions of next-to-leading-order QCD.
Source
code:ZEUS_2010_I875006.cc
// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/FastJets.hh"
#include "Rivet/Projections/DISKinematics.hh"
#include "Rivet/Projections/DISFinalState.hh"
#include <cmath>
namespace Rivet {
/// @brief DIS dijets in the Breit frame
class ZEUS_2010_I875006 : public Analysis {
public:
/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(ZEUS_2010_I875006);
/// @name Analysis methods
/// @{
/// Book histograms and initialise projections before the run
void init() {
// Initialise and register projections
declare(DISKinematics(), "Kinematics");
// All final state particles boosted to Breit frame then clustered
//using FastJet KT algorithm with jet radius parameter 1
const DISFinalState DISfs(DISFrame::BREIT);
FastJets DISjetfs(DISfs, JetAlg::KT, 1.0);
declare(DISjetfs, "DISjets");
// Book histograms
// specify custom binning
//Non-Grouped histgrams
book(_h_Q2, 1,1,1);
book(_h_XBj, 2,1,1);
book(_h_Et, 3,1,1);
book(_h_Mjj, 4,1,1);
book(_h_Eta, 5,1,1);
book(_h_Zeta, 6,1,1);
//Zeta values seperated into Q2 ranges
book(_h_ZetaQ2[0], 7,1,1);
book(_h_ZetaQ2[1], 8,1,1);
book(_h_ZetaQ2[2], 9,1,1);
book(_h_ZetaQ2[3], 10,1,1);
book(_h_ZetaQ2[4], 11,1,1);
book(_h_ZetaQ2[5], 12,1,1);
//Transverse jet energy seperated into Q2 ranges
book(_h_EtQ2[0], 13,1,1);
book(_h_EtQ2[1], 14,1,1);
book(_h_EtQ2[2], 15,1,1);
book(_h_EtQ2[3], 16,1,1);
book(_h_EtQ2[4], 17,1,1);
book(_h_EtQ2[5], 18,1,1);
}
/// Perform the per-event analysis
void analyze(const Event& event) {
//First Lorentz invariant quantities in Lab frame
DISKinematics dis = apply<DISKinematics>(event, "Kinematics");
double Q2 = dis.Q2();
double xbj = dis.x();
double y = dis.y();
//Perform required cut on Q2 and y
if (!inRange(Q2, 125*GeV2, 20000*GeV2)) vetoEvent;
if (!inRange(y, 0.2, 0.6)) vetoEvent;
//Get Lorentz transforms for Breit Boost and Lab Boost
const LorentzTransform breitboost = dis.boostBreit();
const LorentzTransform labboost = breitboost.inverse();
//Get jets clustered in Breit frame
Jets jets = apply<FastJets>(event, "DISjets").jetsByPt();
//Boost jets to lab frame
for(std::vector<int>::size_type i=0; i<jets.size(); i++){
jets[i].transformBy(labboost);
}
//Cut on Pseudorapidity in lab frame
const int orientation = dis.orientation();
vector<Jet> cutJets;
for(std::vector<int>::size_type i=0; i<jets.size(); i++){
double etaJet = jets[i].eta()*orientation;
if(etaJet < 2.5 && etaJet > -1){
cutJets.push_back(jets[i]);
}
}
//veto event if only single jet
if(cutJets.size()<2){
vetoEvent;
}
//Boost jets to Breit frame
for(std::vector<int>::size_type i=0; i<cutJets.size(); i++){
cutJets[i].transformBy(breitboost);
}
//Sort jets by et in descending order
std::sort(cutJets.begin(), cutJets.end(),[](const Jet& j1, const Jet& j2){
return j1.Et()>j2.Et();
});
//Ensure two hardest jets have Et>8GeV in Breit frame
const Jet& jet1 = cutJets[0];
const Jet& jet2 = cutJets[1];
if(jet1.Et()<8*GeV || jet2.Et()<8*GeV){
vetoEvent;
}
//Extract required quantities in Breit frame
//Dijet mean transverse energy
const double dijetEt = (jet1.Et() + jet2.Et())/2;
//Invariant dijet mass of hardest transverse jets > 20GeV
const double Mjj = FourMomentum(jet1.momentum() + jet2.momentum()).mass();
if(Mjj<20*GeV){
vetoEvent;
}
const double eta1 = orientation*jet1.eta();
const double eta2 = orientation*jet2.eta();
const double etastar = abs(eta1 - eta2)/2;
const double logZeta = log10(xbj*(1 + pow(Mjj,2)/Q2));
//Fill histograms
_h_Q2->fill(Q2);
_h_XBj->fill(xbj);
_h_Et->fill(dijetEt);
_h_Mjj->fill(Mjj);
_h_Eta->fill(etastar);
_h_Zeta->fill(logZeta);
//Fill histograms for different Q2 ranges
if(Q2>125*GeV2 && Q2<=250*GeV2){
_h_ZetaQ2[0]->fill(logZeta);
_h_EtQ2[0]->fill(dijetEt);
}else if (Q2>250*GeV2 && Q2<=500*GeV2){
_h_ZetaQ2[1]->fill(logZeta);
_h_EtQ2[1]->fill(dijetEt);
}else if (Q2>500*GeV2 && Q2<=1000*GeV2){
_h_ZetaQ2[2]->fill(logZeta);
_h_EtQ2[2]->fill(dijetEt);
}else if (Q2>1000*GeV2 && Q2<=2000*GeV2){
_h_ZetaQ2[3]->fill(logZeta);
_h_EtQ2[3]->fill(dijetEt);
}else if (Q2>2000*GeV2 && Q2<=5000*GeV2){
_h_ZetaQ2[4]->fill(logZeta);
_h_EtQ2[4]->fill(dijetEt);
}else if (Q2>5000*GeV2 && Q2<=20000*GeV2){
_h_ZetaQ2[5]->fill(logZeta);
_h_EtQ2[5]->fill(dijetEt);
}
}
/// Normalise histograms etc., after the run
void finalize() {
//Calculate scaling factor from cross section
const double sf = crossSection()/picobarn/sumW(); //Scale factor with cuts
scale(_h_Q2, sf);
scale(_h_XBj, sf);
scale(_h_Et, sf);
scale(_h_Mjj, sf);
scale(_h_Eta, sf);
scale(_h_Zeta, sf);
for(int i = 0; i<6;i++){
scale(_h_ZetaQ2[i], sf);
scale(_h_EtQ2[i],sf);
}
}
/// @}
/// @name Histograms
/// @{
Histo1DPtr _h_Q2;
Histo1DPtr _h_XBj;
Histo1DPtr _h_Et;
Histo1DPtr _h_Mjj;
Histo1DPtr _h_Eta;
Histo1DPtr _h_Zeta;
Histo1DPtr _h_ZetaQ2[6];
Histo1DPtr _h_EtQ2[6];
/// @}
};
RIVET_DECLARE_PLUGIN(ZEUS_2010_I875006);
}