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## Rivet analyses reference

### BELLE_2008_I786560

Measurement of Semi-Leptonic Tau Decays into $\pi^\pm\pi^0$
Experiment: Belle (KEKB)
Inspire ID: 786560
Status: VALIDATED
Authors:
• Peter Richardson
References:
Beams: e+ e-
Beam energies: (3.5, 8.0) GeV
Run details:
• Tau production, can be any process but original data was in $e^+ e^-$ at the $\Upsilon(4S)$ resonance, with CoM boosts of 8.0 GeV ($e^-$) and 3.5 GeV ($e^+$)

High-statistics measurement of the branching fraction for $\tau\to\pi^-\pi^0\nu_\tau$ and the invariant mass spectrum of the produced $\pi^-\pi^0$ system using 72.2fb$^{-1}$of data recorded with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider.

Source code: BELLE_2008_I786560.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 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 // -*- C++ -*- #include "Rivet/Analysis.hh" #include "Rivet/Projections/UnstableParticles.hh" namespace Rivet { /// @brief BELLE tau lepton to pi pi /// @author Peter Richardson class BELLE_2008_I786560 : public Analysis { public: BELLE_2008_I786560() : Analysis("BELLE_2008_I786560") { } void init() { declare(UnstableParticles(), "UFS"); book(_hist_pipi , 1, 1, 1); book(_weight_total, "TMP/weight_total"); book(_weight_pipi, "TMP/weight_pipi"); } void analyze(const Event& e) { // Find the taus Particles taus; const UnstableParticles& ufs = apply(e, "UFS"); for (const Particle& p : ufs.particles()) { if (p.abspid() != PID::TAU) continue; _weight_total->fill(); Particles pip, pim, pi0; unsigned int nstable = 0; // find the decay products we want findDecayProducts(p, nstable, pip, pim, pi0); if (p.pid() < 0) { swap(pip, pim); } if (nstable != 3) continue; // pipi if (pim.size() == 1 && pi0.size() == 1) { _weight_pipi->fill(); _hist_pipi->fill((pi0[0].momentum()+pim[0].momentum()).mass2()); } } } void finalize() { if (_weight_pipi->val() > 0.) scale(_hist_pipi, 1. / *_weight_pipi); } private: //@{ // Histograms Histo1DPtr _hist_pipi; // Weights counters CounterPtr _weight_total, _weight_pipi; //@} void findDecayProducts(const Particle &mother, unsigned int & nstable, Particles& pip, Particles& pim, Particles& pi0) { for (const Particle &p : mother.children()) { long id = p.pid(); if (id == PID::PI0 ) { pi0.push_back(p); ++nstable; } else if (id == PID::K0S) ++nstable; else if (id == PID::PIPLUS) { pip.push_back(p); ++nstable; } else if (id == PID::PIMINUS) { pim.push_back(p); ++nstable; } else if (id == PID::KPLUS) { ++nstable; } else if (id == PID::KMINUS) { ++nstable; } else if (!p.children().empty()) { findDecayProducts(p, nstable, pip, pim, pi0); } else ++nstable; } } }; DECLARE_RIVET_PLUGIN(BELLE_2008_I786560); }