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MARKII_1984_I195739

$\gamma\gamma\to\pi^+\pi^-/K^+K^-$ for centre-of-mass energies between 1.6 and 2.5 GeV
Experiment: MARKII (PEP)
Inspire ID: 195739
Status: VALIDATED
Authors:
  • Peter Richardson
References:
  • Phys.Rev.D 30 (1984) 851, 1984
Beams: 22 22
Beam energies: ANY
Run details:
  • gamma gamma to hadrons

Measurement of the differential cross section for $\gamma\gamma\to\pi^+\pi^-/K^+K^-$ for $1.6 \text{GeV} < W < 2.5 \text{GeV}$.

Source code: MARKII_1984_I195739.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-/K+ K-
 9  class MARKII_1984_I195739 : public Analysis {
10  public:
11
12    /// Constructor
13    RIVET_DEFAULT_ANALYSIS_CTOR(MARKII_1984_I195739);
14
15
16    /// @name Analysis methods
17    ///@{
18
19    /// Book histograms and initialise projections before the run
20    void init() {
21      declare(FinalState(),"FS");
22      // check CMS energy in range
23      if(sqrtS()<1.6*GeV || sqrtS()>2.5*GeV)
24	throw Error("Invalid CMS energy for MARKII_1984_I195739");
25      book(_cPiK, "/TMP/nPiK_");
26    }
27
28
29    /// Perform the per-event analysis
30    void analyze(const Event& event) {
31      Particles part = applyProjection<FinalState>(event,"FS").particles();
32      if(part.size()!=2) vetoEvent;
33      if(part[0].pid()!=-part[1].pid()) vetoEvent;
34      double cTheta(0.);
35      bool foundPi(false),foundK(false);
36      for(const Particle & p : part) {
37	if(p.pid()==PID::PIPLUS) {
38	  foundPi=true;
39	  cTheta = abs(p.momentum().z()/p.momentum().p3().mod());
40	}
41	else if(p.pid()==PID::KPLUS) {
42	  foundK=true;
43	  cTheta = abs(p.momentum().z()/p.momentum().p3().mod());
44	}
45      }
46      if(!foundPi && !foundK) vetoEvent;
47      if(cTheta>0.3) vetoEvent;
48      _cPiK->fill();
49    }
50
51
52    /// Normalise histograms etc., after the run
53    void finalize() {
54      double fact = crossSection()/nanobarn/sumOfWeights();
55      double sigma = _cPiK->val()*fact;
56      double error = _cPiK->err()*fact;
57      Scatter2D temphisto(refData(1, 1, 1));
58      Scatter2DPtr cross;
59      book(cross, 1, 1, 1);
60      for (size_t b = 0; b < temphisto.numPoints(); b++) {
61	const double x  = temphisto.point(b).x();
62	pair<double,double> ex = temphisto.point(b).xErrs();
63	pair<double,double> ex2 = ex;
64	if(ex2.first ==0.) ex2. first=0.0001;
65	if(ex2.second==0.) ex2.second=0.0001;
66	if (inRange(sqrtS(), x-ex2.first, x+ex2.second)) {
67	  cross->addPoint(x, sigma, ex, make_pair(error,error));
68	}
69	else {
70	  cross->addPoint(x, 0., ex, make_pair(0.,.0));
71	}
72      }
73    }
74
75    ///@}
76
77
78    /// @name Histograms
79    ///@{
80    CounterPtr _cPiK;
81    ///@}
82
83
84  };
85
86
87  RIVET_DECLARE_PLUGIN(MARKII_1984_I195739);
88
89}