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ALEPH_2003_I626022

$\gamma\gamma\to\pi^+\pi^-$ ($2<\sqrt{s}<6$ GeV) and $K^+K^-$ ($2.25<\sqrt{s}<4$ GeV)
Experiment: ALEPH (LEP)
Inspire ID: 626022
Status: VALIDATED
No authors listed References:
  • Phys.Lett.B 569 (2003) 140-150
Beams: 22 22
Beam energies: ANY
Run details:
  • gamma gamma to hadrons

Measurement of the differential cross section for $\gamma\gamma\to\pi^+\pi^-$ ($2<\sqrt{s}<6$ GeV) and $K^+K^-$ ($2.25<\sqrt{s}<4$ GeV). The cross section as a function of the centre-of-mass energy of the photonic collision is measured, and the differential cross section with respect to the meson scattering angle are measured.

Source code: ALEPH_2003_I626022.cc
 1// -*- C++ -*-
 2#include "Rivet/Analysis.hh"
 3#include "Rivet/Projections/FinalState.hh"
 4#include "Rivet/Projections/FastJets.hh"
 5#include "Rivet/Projections/LeptonFinder.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 ALEPH_2003_I626022 : public Analysis {
14  public:
15
16    /// Constructor
17    RIVET_DEFAULT_ANALYSIS_CTOR(ALEPH_2003_I626022);
18
19
20    /// @name Analysis methods
21    ///@{
22
23    /// Book histograms and initialise projections before the run
24    void init() {
25      // check CMS energy in range
26      if (sqrtS()<2.*GeV || sqrtS()>6.*GeV)
27        throw Error("Invalid CMS energy for ");
28      // Final state
29      declare(FinalState(),"FS");
30      // histos
31      book(_h_Pi,1,1,1);
32      if (sqrtS()<4.)
33        book(_h_K,2,1,1);
34      book(_cPi, "/TMP/nPi_");
35      book(_cK , "/TMP/nK_" );
36    }
37
38
39    /// Perform the per-event analysis
40    void analyze(const Event& event) {
41      Particles part = apply<FinalState>(event,"FS").particles();
42      if (part.size()!=2) vetoEvent;
43      if (part[0].pid()!=-part[1].pid()) vetoEvent;
44      double cTheta(0.);
45      bool foundPi(false),foundK(false);
46      for (const Particle & p : part) {
47        if (p.pid()==PID::PIPLUS) {
48          foundPi=true;
49          cTheta = abs(p.momentum().z()/p.momentum().p3().mod());
50        }
51        else if (p.pid()==PID::KPLUS) {
52          foundK=true;
53          cTheta = abs(p.momentum().z()/p.momentum().p3().mod());
54        }
55      }
56      if (!foundPi && !foundK) vetoEvent;
57      if (foundPi&&_h_Pi) _h_Pi->fill(cTheta);
58      if (foundK &&_h_K ) _h_K ->fill(cTheta);
59      if (foundPi)     _cPi->fill();
60      else if (foundK)  _cK->fill();
61    }
62
63
64    /// Normalise histograms etc., after the run
65    void finalize() {
66      double fact = crossSection()/nanobarn/sumOfWeights();
67      if (_h_Pi) scale(_h_Pi, fact);
68      if (_h_K ) scale(_h_K , fact);
69      for (unsigned int ih=3; ih<5; ++ih) {
70        CounterPtr count = ih==3 ? _cPi : _cK;
71        double sigma = count->val()*fact;
72        double error = count->err()*fact;
73        // hist for axis
74        Estimate1DPtr cross;
75        book(cross, ih, 1, 1);
76        for (auto& b : cross->bins()) {
77          if (inRange(sqrtS(), b.xMin(), b.xMax())) {
78            b.set(sigma, error);
79          }
80        }
81      }
82    }
83
84    ///@}
85
86
87    /// @name Histograms
88    ///@{
89    Histo1DPtr _h_Pi,_h_K;
90    CounterPtr _cPi,_cK;
91    ///@}
92
93
94  };
95
96
97  RIVET_DECLARE_PLUGIN(ALEPH_2003_I626022);
98
99}