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Rivet analyses reference

ZEUS_1997_I450085

Dijet photoproduction analysis
Experiment: ZEUS (HERA Run I)
Inspire ID: 450085
Status: VALIDATED
Authors:
  • Juan Jose Juan Castella
  • Jon Butterworth
  • Matthew Wing
References:
  • EEur. Phys. J C 1, (1998) 109–122
  • DESY-97-196
  • hep-ex/9710018
Beams: p+ e+
Beam energies: (820.0, 27.5) GeV
Run details:
  • 820 GeV protons colliding with 27.5 GeV positrons; Direct and resolved photoproduction of dijet events; Both jets $E_T > 6$ GeV; Jet pseudorapidity $-1.375 < |\eta| < 1.875$; Pseudorapidity difference between jets $|\eta| < 0.5$;

Dijet cross sections are presented using photoproduction data obtained with the ZEUS detector during 1994. These measurements represent an extension of previous results, as the higher statistics allow cross sections to be measured at higher jet transverse energy (ETJ). Jets are identified in the hadronic final state, and the cross sections compared to complete next-to-leading order QCD calculations. Agreement with these calculations is seen for the pseudorapidity dependence of the direct photon events with ETJ $>$ 6 GeV and of the resolved photon events with ETJ $>$ 11 GeV. Calculated cross sections for resolved photon processes with 6 GeV $<$ ETJ $<$ 11 GeV lie below the data. The paper also studied reconstructing the jets with two different types of legacy cone algorithm (EUCELL and PUCELL). Histograms for these are not generated by this rivet routine as focus was on the the KTCLUS data.

Source code: ZEUS_1997_I450085.cc 
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// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/Beam.hh"
#include "Rivet/Projections/DISKinematics.hh"
#include "Rivet/Projections/FastJets.hh"

namespace Rivet {
	// @brief ZEUS dijet photoproduction in different xgamma regions
  
	class ZEUS_1997_I450085 : public Analysis {
	public:

		// Constructor
		RIVET_DEFAULT_ANALYSIS_CTOR(ZEUS_1997_I450085);
		
		// Initialization, books projections and histograms
		void init() {
			
			// Projections
			// checking recombination scheme and radius checked with original code from M.Wing
			FinalState fs;
			declare(FastJets(fs, fastjet::JetAlgorithm::kt_algorithm, fastjet::RecombinationScheme::Et_scheme, 1.0), "Jets");
			declare(DISKinematics(), "Kinematics");

			//Histograms
			// Table 1
			book(_h_etabar_all[0], 1, 1, 1);
			book(_h_etabar_all[1], 2, 1, 1);
			book(_h_etabar_all[2], 3, 1, 1);
			book(_h_etabar_all[3], 4, 1, 1);
			// Table 6
			book(_h_etabar[1][0], 21, 1, 1);
			book(_h_etabar[1][1], 22, 1, 1);
			book(_h_etabar[1][2], 23, 1, 1);
			book(_h_etabar[1][3], 24, 1, 1);
			// Table 7
			book(_h_etabar[0][0], 25, 1, 1);
			book(_h_etabar[0][1], 26, 1, 1);
			book(_h_etabar[0][2], 27, 1, 1);
			book(_h_etabar[0][3], 28, 1, 1);

		}
		// Analysis
		void analyze(const Event & event) {

			// Determine kinematics, including event orientation since ZEUS coord system is for +z = proton direction
			const DISKinematics & kin = apply<DISKinematics>(event, "Kinematics");
		    if (kin.failed()) vetoEvent;
			const int orientation = kin.orientation();

			// Q2 and inelasticity cuts
			if (kin.Q2() > 4 * GeV2) vetoEvent;
			if (!inRange(kin.y(), 0.2, 0.8)) vetoEvent;

			// Jet calculation
			const Jets jets = apply<FastJets>(event, "Jets") \
				.jets(Cuts::Et > 6 * GeV && Cuts::etaIn(-1.375 * orientation, 1.875 * orientation), cmpMomByEt);
			MSG_DEBUG("Jet multiplicity = " << jets.size());
			//Dijet event selection
			if (jets.size() < 2) vetoEvent;
			const Jet & j1 = jets[0];
		    const Jet & j2 = jets[1];
	
			//Jet eta, average eta and eta difference calculation
			const double eta1 = orientation * j1.eta(), eta2 = orientation * j2.eta();
			const double etabar = (eta1 + eta2) / 2;
			const double etadiff = eta1 - eta2;

			//Cut in pseudorapidity difference
			if (abs(etadiff) > 0.5) vetoEvent;

			// Calculation of x_gamma^obs
			/// note Assuming Ee is the lab frame positron momentum, not in proton rest frame cf.
		    const double xyobs = (j1.Et() * exp(-eta1) + j2.Et() * exp(-eta2)) / (2 * kin.y() * kin.beamLepton().E());
			const size_t i_xyobs = (xyobs < 0.75) ? 0 : 1;

			//Classify events according to minimum jet energies
			size_t iE_min = 0;
			if (j1.Et() > 8 * GeV && j2.Et() > 8 * GeV)
				iE_min = 1;
			if (j1.Et() > 11 * GeV && j2.Et() > 11 * GeV)
				iE_min = 2;
			if (j1.Et() > 15 * GeV && j2.Et() > 15 * GeV)
				iE_min = 3;

			//Fill histograms
			for (size_t isel = 0; isel <= iE_min; ++isel) {

				//T1
				_h_etabar_all[isel]->fill(etabar);
				//T6, T7
				if (xyobs < 0.3) vetoEvent;
				_h_etabar[i_xyobs][isel]->fill(etabar);
			}
			

		}
		
		// Finalize
		void finalize() {
			const double sf = crossSection() / nanobarn / sumOfWeights();
			for (size_t ix = 0; ix < 2; ++ix) {
				for (auto& h : _h_etabar[ix]) scale(h, sf);

			}
			for (auto& h : _h_etabar_all) scale(h, sf);

		}


	private:
		//name Histograms
		Histo1DPtr _h_etabar_all[4], _h_etabar[2][4];

	};
	
	RIVET_DECLARE_PLUGIN(ZEUS_1997_I450085);

}