Rivet analyses

title: BELLE_2016_I1283183

Lepton Forward-Backward Asymmetry in $B\to X_s\ell^+\ell^-$

Experiment: BELLE (KEKB)

Inspire ID: 1283183

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Rev.D 93 (2016) 3, 032008

Beams: * *

Beam energies: ANY

Run details: - Any process producing B0, B+ mesons, original Upsilon(4S) decays

Measurement of the lepton forward-backward asymmetry in $B\to X_s\ell^+\ell^-$ in 4 $q^2$ bins.

Source code:BELLE_2016_I1283183.cc

```c++ // -- C++ --

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief B -> Xs l+l- class BELLE_2016_I1283183 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2016_I1283183);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  declare(UnstableParticles(Cuts::abspid == 521 || Cuts::abspid == 511), "UFS");
  // book the profile hist
  for (unsigned int ix = 0; ix < 4; ++ix) book(_p[ix], 1, 1, ix + 1);
}

void findDecayProducts(bool& charm,
                       const Particle& mother,
                       unsigned int& nK0,
                       unsigned int& nKp,
                       unsigned int& nKm,
                       Particles& lp,
                       Particles& lm) {
  for (const Particle& p : mother.children()) {
    int id = p.pid();
    if (PID::isCharmHadron(p.pid()))
      charm = true;
    else if (id == PID::POSITRON || id == PID::ANTIMUON)
      lp.push_back(p);
    else if (id == PID::ELECTRON || id == PID::MUON)
      lm.push_back(p);
    else if (id == PID::KPLUS)
      ++nKp;
    else if (id == PID::KMINUS)
      ++nKm;
    else if (id == PID::K0S)
      ++nK0;
    else if (id == PID::PI0 || id == PID::PIPLUS || id == PID::PIMINUS) {
      continue;
    }
    else if (!p.children().empty()) {
      findDecayProducts(charm, p, nK0, nKp, nKm, lp, lm);
    }
  }
}

/// Perform the per-event analysis
void analyze(const Event& event) {
  if (_edges.empty()) {
    for (unsigned int ix = 0; ix < 4; ++ix) _edges.push_back(_p[ix]->xEdges()[0]);
  }
  // Loop over bottoms
  for (const Particle& bottom : apply<UnstableParticles>(event, "UFS").particles()) {
    // remove mixing entries etc
    if (bottom.children()[0].abspid() == bottom.abspid()) continue;
    bool charm = false;
    Particles lp, lm;
    unsigned int nK0(0), nKp(0), nKm(0);
    findDecayProducts(charm, bottom, nK0, nKp, nKm, lp, lm);
    if (charm) continue;
    unsigned int nk = nKp - nKm + nK0;
    if (nk % 2 == 0) continue;
    if (lp.size() != 1 || lm.size() != 1 || lp[0].pid() != -lm[0].pid()) continue;
    if (bottom.pid() > 0) swap(lp, lm);
    double q2 = (lp[0].momentum() + lm[0].momentum()).mass2();
    // veto region valid for muons but not electrons
    if (lm[0].pid() == PID::ELECTRON && ((q2 > 7.3 && q2 < 10.5) || (q2 > 11.8 && q2 < 12.5))) continue;
    // first boost to bottom frame
    const LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(
        bottom.momentum().betaVec());
    FourMomentum plp = boost.transform(lp[0].momentum());
    FourMomentum plm = boost.transform(lm[0].momentum());
    FourMomentum pB = boost.transform(bottom.momentum());
    const LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta((plp + plm).betaVec());
    plp = boost2.transform(plp);
    pB = boost.transform(pB);
    double cTheta = plp.p3().unit().dot(pB.p3().unit());
    if (q2 > 0.2 && q2 < 4.3)
      _p[0]->fill(_edges[0], cTheta > 0 ? 1 : -1);
    else if (q2 > 4.3 && q2 < 8.1)
      _p[1]->fill(_edges[1], cTheta > 0 ? 1 : -1);
    else if (q2 > 10.2 && q2 < 12.5)
      _p[2]->fill(_edges[2], cTheta > 0 ? 1 : -1);
    else if (q2 > 14.3 && q2 < 25.0)
      _p[3]->fill(_edges[3], cTheta > 0 ? 1 : -1);
  }
}


/// Normalise histograms etc., after the run
void finalize() { }

/// @}


/// @name Histograms
/// @{
BinnedProfilePtr<string> _p[4];
vector<string> _edges;
/// @}

};

RIVET_DECLARE_PLUGIN(BELLE_2016_I1283183);

} ```