rivet is hosted by Hepforge, IPPP Durham

Rivet analyses reference

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
 1// -*- C++ -*-
 2#include "Rivet/Analysis.hh"
 3#include "Rivet/Projections/UnstableParticles.hh"
 4
 5namespace Rivet {
 6
 7
 8  /// @brief B -> Xs l+l-
 9  class BELLE_2016_I1283183 : public Analysis {
10  public:
11
12    /// Constructor
13    RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2016_I1283183);
14
15
16    /// @name Analysis methods
17    /// @{
18
19    /// Book histograms and initialise projections before the run
20    void init() {
21      // Initialise and register projections
22      declare(UnstableParticles(Cuts::abspid==521 || Cuts::abspid==511), "UFS");
23      // book the profile hist
24      book(_p,2,1,1);
25    }
26
27    void findDecayProducts(bool & charm, const Particle& mother,
28                           unsigned int& nK0, unsigned int& nKp,
29			   unsigned int& nKm, Particles & lp, Particles & lm) {
30      for (const Particle & p : mother.children()) {
31        int id = p.pid();
32	if(PID::isCharmHadron(p.pid())) charm = true;
33	else if ( id == PID::POSITRON || id == PID::ANTIMUON) lp.push_back(p);
34	else if ( id == PID::ELECTRON || id == PID::MUON    ) lm.push_back(p);
35        else if ( id == PID::KPLUS )    ++nKp;
36        else if (id == PID::KMINUS )    ++nKm;
37        else if (id == PID::K0S)        ++nK0;
38        else if (id == PID::PI0 || id == PID::PIPLUS || id == PID::PIMINUS) {
39	  continue;
40        }
41        else if ( !p.children().empty() ) {
42          findDecayProducts(charm, p, nK0, nKp, nKm,lp,lm);
43        }
44      }
45    }
46
47    /// Perform the per-event analysis
48    void analyze(const Event& event) {
49      // Loop over bottoms
50      for (const Particle& bottom : apply<UnstableParticles>(event, "UFS").particles()) {
51       	// remove mixing entries etc
52	if(bottom.children()[0].abspid()==bottom.abspid()) continue;
53	bool charm = false;
54	Particles lp,lm;
55	unsigned int nK0(0),nKp(0),nKm(0);
56	findDecayProducts(charm,bottom, nK0, nKp, nKm,lp,lm);
57	if(charm) continue;
58        unsigned int nk = nKp-nKm+nK0;
59	if( nk % 2 == 0) continue;
60	if (lp.size()!=1 || lm.size()!=1 || lp[0].pid()!=-lm[0].pid()) continue;
61	if(bottom.pid()>0) swap(lp,lm);
62	double q2 = (lp[0].momentum()+lm[0].momentum()).mass2();
63	// veto region valid for muons but not electrons
64	if(lm[0].pid()==PID::ELECTRON && ( (q2>7.3 && q2<8.1) || (q2>11.8 && q2<12.5) )) continue;
65	// first boost to bottom frame
66	const LorentzTransform boost  = LorentzTransform::mkFrameTransformFromBeta(bottom.momentum().betaVec());
67	FourMomentum plp = boost.transform(lp[0] .momentum());
68	FourMomentum plm = boost.transform(lm[0] .momentum());
69	FourMomentum pB  = boost.transform(bottom.momentum());
70	const LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta((plp+plm).betaVec());
71	plp = boost2.transform(plp);
72	pB  = boost .transform(pB );
73	double cTheta = plp.p3().unit().dot(pB.p3().unit());
74	_p->fill(q2, cTheta>0 ? 1 : -1);
75      }
76    }
77
78
79    /// Normalise histograms etc., after the run
80    void finalize() {
81    }
82
83    /// @}
84
85
86    /// @name Histograms
87    /// @{
88    Profile1DPtr _p;
89    /// @}
90
91
92  };
93
94
95  RIVET_DECLARE_PLUGIN(BELLE_2016_I1283183);
96
97}