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TPC_1986_I228072

$\gamma\gamma\to\pi^+\pi^-$ ($0.5<\sqrt{s}<3.25$ GeV) and $K^+K^-$ ($1.25<\sqrt{s}<3.5$ GeV)
Experiment: TPC (PEP)
Inspire ID: 228072
Status: VALIDATED
Authors:
  • Peter Richardson
References:
  • Phys.Rev.Lett. 57 (1986) 404, 1986
Beams: 22 22
Beam energies: ANY
Run details:
  • gamma gamma to hadrons

Measurement of the differential cross section for $\gamma\gamma\to\pi^+\pi^-$ ($0.5<\sqrt{s}<3.25$ GeV) and $K^+K^-$ ($1.25<\sqrt{s}<3.5$ GeV). The cross section as a function of the centre-of-mass energy of the photonic collision is measured

Source code: TPC_1986_I228072.cc
  1// -*- C++ -*-
  2#include "Rivet/Analysis.hh"
  3#include "Rivet/Projections/FinalState.hh"
  4#include "Rivet/Projections/FastJets.hh"
  5#include "Rivet/Projections/DressedLeptons.hh"
  6#include "Rivet/Projections/MissingMomentum.hh"
  7#include "Rivet/Projections/PromptFinalState.hh"
  8
  9namespace Rivet {
 10
 11
 12  /// @brief gamma gamma -> pi+pi-/K+ K-
 13  class TPC_1986_I228072 : public Analysis {
 14  public:
 15
 16    /// Constructor
 17    RIVET_DEFAULT_ANALYSIS_CTOR(TPC_1986_I228072);
 18
 19
 20    /// @name Analysis methods
 21    ///@{
 22
 23    /// Book histograms and initialise projections before the run
 24    void init() {
 25      // Final state
 26      declare(FinalState(),"FS");
 27      // check CMS energy in range
 28      if(sqrtS()<0.5*GeV || sqrtS()>3.5*GeV)
 29	throw Error("Invalid CMS energy for TPC_1986_I228072");
 30      book(_cPi[0],"/TMP/nPi_06");
 31      book(_cPi[1],"/TMP/nPi_03");
 32      book(_cK    ,"/TMP/nK"    );
 33    }
 34
 35
 36    /// Perform the per-event analysis
 37    void analyze(const Event& event) {
 38      Particles part = applyProjection<FinalState>(event,"FS").particles();
 39      if(part.size()!=2) vetoEvent;
 40      if(part[0].pid()!=-part[1].pid()) vetoEvent;
 41      double cTheta(0.);
 42      bool foundPi(false),foundK(false);
 43      for(const Particle & p : part) {
 44	if(p.pid()==PID::PIPLUS) {
 45	  foundPi=true;
 46	  cTheta = abs(p.momentum().z()/p.momentum().p3().mod());
 47	}
 48	else if(p.pid()==PID::KPLUS) {
 49	  foundK=true;
 50	  cTheta = abs(p.momentum().z()/p.momentum().p3().mod());
 51	}
 52      }
 53      if(!foundPi && !foundK) vetoEvent;
 54      if(cTheta>0.6) vetoEvent;
 55      if(foundPi) {
 56	_cPi[0]->fill();
 57	if(cTheta<0.3)
 58	  _cPi[1]->fill();
 59      }
 60      else if(foundK)
 61	_cK->fill();
 62    }
 63
 64
 65    /// Normalise histograms etc., after the run
 66    void finalize() {
 67      double fact = crossSection()/nanobarn/sumOfWeights();
 68      for (unsigned int ih=1;ih<6;++ih) {
 69	if(ih==2||ih==3) continue;
 70	double sigma(0.),error(0.);
 71	CounterPtr count;
 72	if(ih==1) {
 73	  count = _cPi[0];
 74	}
 75	else if(ih==4) {
 76	  count = _cPi[1];
 77	}
 78	else if(ih==5) {
 79	  count = _cK;
 80	}
 81	else
 82	  assert(false);
 83	if(count->numEntries()==0) continue;
 84	sigma = count->val()*fact;
 85	error = count->err()*fact;
 86	Scatter2DPtr cross;
 87	Scatter2D temphisto(refData(ih, 1, 1));
 88	book(cross, ih, 1, 1);
 89	for (size_t b = 0; b < temphisto.numPoints(); b++) {
 90	  const double x  = temphisto.point(b).x();
 91	  pair<double,double> ex = temphisto.point(b).xErrs();
 92	  pair<double,double> ex2 = ex;
 93	  if(ex2.first ==0.) ex2. first=0.0001;
 94	  if(ex2.second==0.) ex2.second=0.0001;
 95	  if (inRange(sqrtS(), x-ex2.first, x+ex2.second)) {
 96	    cross->addPoint(x, sigma, ex, make_pair(error,error));
 97	  }
 98	  else {
 99	    cross->addPoint(x, 0., ex, make_pair(0.,.0));
100	  }
101	}
102      }
103    }
104
105    ///@}
106
107
108    /// @name Histograms
109    ///@{
110    CounterPtr _cPi[2],_cK;
111    ///@}
112
113
114  };
115
116
117  RIVET_DECLARE_PLUGIN(TPC_1986_I228072);
118
119}