Rivet Analyses Reference

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
 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
// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FinalState.hh"

namespace Rivet {


  /// @brief gamma gamma -> pi+pi-
  class PLUTO_1984_I204487 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(PLUTO_1984_I204487);


    /// @name Analysis methods
    ///@{

    /// Book histograms and initialise projections before the run
    void init() {
      // Final state
      declare(FinalState(),"FS");
      // check CMS energy in range
      if(sqrtS()<0.36*GeV || sqrtS()>1.72*GeV)
	throw Error("Invalid CMS energy for PLUTO_1984_I1260740");
      book(_cPi, "/TMP/nPi");
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      Particles part = applyProjection<FinalState>(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<=0.2)    _cPi->fill();
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      double fact = crossSection()/nanobarn/sumOfWeights();
      double sigma = _cPi->val()*fact/0.2;
      double error = _cPi->err()*fact/0.2;
      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<double,double> ex = temphisto.point(b).xErrs();
	pair<double,double> 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
    ///@{
    CounterPtr _cPi;
    ///@}


  };


  RIVET_DECLARE_PLUGIN(PLUTO_1984_I204487);

}