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## Rivet analyses reference

### CELLO_1992_I345437

$\gamma\gamma\to\pi^+\pi^-$ for centre-of-mass energies between 0.75 and 1.7 GeV
Experiment: CELLO (Petra)
Inspire ID: 345437
Status: VALIDATED
Authors:
• Peter Richardson
References:
• Z.Phys.C 56 (1992) 381-390
Beams: 22 22
Beam energies: ANY
Run details:
Measurement of the differential cross section for $\gamma\gamma\to\pi^+\pi^-$. Both the cross section as a function of the centre-of-mass energy of the photonic collision, and the differential cross section with respect to the pion scattering angle are measured.
  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 // -*- C++ -*- #include "Rivet/Analysis.hh" #include "Rivet/Projections/FinalState.hh" namespace Rivet { /// @brief gamma gamma -> pi+pi- class CELLO_1992_I345437 : public Analysis { public: /// Constructor DEFAULT_RIVET_ANALYSIS_CTOR(CELLO_1992_I345437); /// @name Analysis methods ///@{ /// Book histograms and initialise projections before the run void init() { // Final state declare(FinalState(),"FS"); int ibin = (sqrtS()-0.70)/0.05; if(ibin>0&&ibin<19) book(_h_cTheta,2,1,ibin); if(inRange(sqrtS()/GeV,0.85,.95)) book(_h_cTheta2,2,1,19); else if(inRange(sqrtS()/GeV,1.15,1.25)) book(_h_cTheta2,2,1,20); else if(inRange(sqrtS()/GeV,1.25,1.35)) book(_h_cTheta2,2,1,21); book(_cPi, "/TMP/nPi"); } /// Perform the per-event analysis void analyze(const Event& event) { Particles part = applyProjection(event,"FS").particles(); if(part.size()!=2) vetoEvent; double cTheta(0.); bool foundP(false),foundM(false); for(const Particle & p : part) { if(p.pid()==PID::PIPLUS) { foundP=true; cTheta = abs(p.momentum().z()/p.momentum().p3().mod()); } else if(p.pid()==PID::PIMINUS) foundM=true; } if(!foundP || !foundM) vetoEvent; if(cTheta<=0.6) _cPi->fill(); if(_h_cTheta ) _h_cTheta ->fill(cTheta); if(_h_cTheta2) _h_cTheta2->fill(cTheta); } /// Normalise histograms etc., after the run void finalize() { double fact = crossSection()/nanobarn/sumOfWeights(); if(_h_cTheta ) scale(_h_cTheta ,fact); if(_h_cTheta2) scale(_h_cTheta2,fact); double sigma = _cPi->val()*fact; double error = _cPi->err()*fact; Scatter2D temphisto(refData(1, 1, 1)); Scatter2DPtr mult; book(mult, 1, 1, 1); for (size_t b = 0; b < temphisto.numPoints(); b++) { const double x = temphisto.point(b).x(); pair ex = temphisto.point(b).xErrs(); pair ex2 = ex; if(ex2.first ==0.) ex2. first=0.0001; if(ex2.second==0.) ex2.second=0.0001; if (inRange(sqrtS(), x-ex2.first, x+ex2.second)) { mult->addPoint(x, sigma, ex, make_pair(error,error)); } else { mult->addPoint(x, 0., ex, make_pair(0.,.0)); } } } ///@} /// @name Histograms ///@{ Histo1DPtr _h_cTheta,_h_cTheta2; CounterPtr _cPi; ///@} }; DECLARE_RIVET_PLUGIN(CELLO_1992_I345437); }