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PLUTO_1984_I204487

$\gamma\gamma\to\pi^+\pi^-$ for centre-of-mass energies between 0.36 and 1.72 GeV
Experiment: PLUTO (PETRA)
Inspire ID: 204487
Status: VALIDATED
Authors:
  • Peter Richardson
References:
  • Z.Phys.C 26 (1984) 199, 1984
Beams: 22 22
Beam energies: ANY
Run details:
  • gamma gamma to hadrons

Measurement of the differential cross section for $\gamma\gamma\to\pi^+\pi^-$. The cross section as a function of the centre-of-mass energy of the photonic collision is measured.

Source code: PLUTO_1984_I204487.cc
 1// -*- C++ -*-
 2#include "Rivet/Analysis.hh"
 3#include "Rivet/Projections/FinalState.hh"
 4
 5namespace Rivet {
 6
 7
 8  /// @brief gamma gamma -> pi+pi-
 9  class PLUTO_1984_I204487 : public Analysis {
10  public:
11
12    /// Constructor
13    RIVET_DEFAULT_ANALYSIS_CTOR(PLUTO_1984_I204487);
14
15
16    /// @name Analysis methods
17    ///@{
18
19    /// Book histograms and initialise projections before the run
20    void init() {
21      // Final state
22      declare(FinalState(),"FS");
23      // check CMS energy in range
24      if(sqrtS()<0.36*GeV || sqrtS()>1.72*GeV)
25	throw Error("Invalid CMS energy for PLUTO_1984_I1260740");
26      book(_cPi, "/TMP/nPi");
27    }
28
29
30    /// Perform the per-event analysis
31    void analyze(const Event& event) {
32      Particles part = applyProjection<FinalState>(event,"FS").particles();
33      if(part.size()!=2) vetoEvent;
34      double cTheta(0.);
35      bool foundP(false),foundM(false);
36      for(const Particle & p : part) {
37	if(p.pid()==PID::PIPLUS) {
38	  foundP=true;
39	  cTheta = abs(p.momentum().z()/p.momentum().p3().mod());
40	}
41	else if(p.pid()==PID::PIMINUS)
42	  foundM=true;
43      }
44      if(!foundP || !foundM) vetoEvent;
45      if(cTheta<=0.2)    _cPi->fill();
46    }
47
48
49    /// Normalise histograms etc., after the run
50    void finalize() {
51      double fact = crossSection()/nanobarn/sumOfWeights();
52      double sigma = _cPi->val()*fact/0.2;
53      double error = _cPi->err()*fact/0.2;
54      Scatter2D temphisto(refData(1, 1, 1));
55      Scatter2DPtr mult;
56      book(mult, 1, 1, 1);
57      for (size_t b = 0; b < temphisto.numPoints(); b++) {
58	const double x  = temphisto.point(b).x();
59	pair<double,double> ex = temphisto.point(b).xErrs();
60	pair<double,double> ex2 = ex;
61	if(ex2.first ==0.) ex2. first=0.0001;
62	if(ex2.second==0.) ex2.second=0.0001;
63	if (inRange(sqrtS(), x-ex2.first, x+ex2.second)) {
64	  mult->addPoint(x, sigma, ex, make_pair(error,error));
65	}
66	else {
67	  mult->addPoint(x, 0., ex, make_pair(0.,.0));
68	}
69      }
70    }
71
72    ///@}
73
74
75    /// @name Histograms
76    ///@{
77    CounterPtr _cPi;
78    ///@}
79
80
81  };
82
83
84  RIVET_DECLARE_PLUGIN(PLUTO_1984_I204487);
85
86}