Belle II Software light-2406-ragdoll
KlongCalculatorUtils Struct Reference

Utility class to calculate the Klong kinematics. More...

#include <KlongCalculatorUtils.h>

Static Public Member Functions

static bool calculateBtoKlongX (ROOT::Math::PxPyPzEVector &BMomentum, ROOT::Math::PxPyPzEVector &KMomentum, const std::vector< Particle * > daughters, const double m_b, int &idx)
 Calculate kinematics of two body B decays containing a K_L0.
 

Detailed Description

Utility class to calculate the Klong kinematics.

Definition at line 31 of file KlongCalculatorUtils.h.

Member Function Documentation

◆ calculateBtoKlongX()

static bool calculateBtoKlongX ( ROOT::Math::PxPyPzEVector &  BMomentum,
ROOT::Math::PxPyPzEVector &  KMomentum,
const std::vector< Particle * >  daughters,
const double  m_b,
int &  idx 
)
inlinestatic

Calculate kinematics of two body B decays containing a K_L0.

Parameters
BMomentum4-vector of B-meson that will be updated by this function
KMomentum4-vector of Klong that will be updated by this function
daughtersOriginal daughters of the B-meson
m_bPDG-mass of the B-meson
idxArray index of the other daughter. This will be assigned to the extraInfo, permID, of Klong.
Returns
true if the kinematics is physical

Definition at line 41 of file KlongCalculatorUtils.h.

46 {
47
48 bool k_check = false;
49 ROOT::Math::PxPyPzEVector klDaughters; // 4-vector of K_L
50 ROOT::Math::PxPyPzEVector pDaughters; // 4-vector of other daughters
51 double m_j = 0;
52 for (auto daughter : daughters) {
53 if (daughter->getPDGCode() == Const::Klong.getPDGCode()) {
54 if (k_check)
55 B2FATAL("More than one K_L is detected! This tool accepts only one K_L in the final state.");
56
57 const Belle2::KLMCluster* klm_cluster = daughter->getKLMCluster();
58 if (klm_cluster)
59 klDaughters = klm_cluster->getMomentum();
60 else {
61 const Belle2::ECLCluster* ecl_cluster = daughter->getECLCluster();
62 if (ecl_cluster) {
63 ClusterUtils clutls;
64 klDaughters = clutls.Get4MomentumFromCluster(ecl_cluster, ECLCluster::EHypothesisBit::c_neutralHadron);
65 } else {
66 B2ERROR("K_L candidate must have related KLM or ECL cluster!");
67 }
68 }
69 k_check = true;
70 } else {
71 pDaughters += daughter->get4Vector();
72
73 // if there is only two daughter (e.g. K_L J/psi), use the PDG mass of the other daughter.
74 m_j = daughter->getPDGMass();
75 idx = daughter->getArrayIndex() + idx * 100;
76 }
77 }
78
79 if (!k_check)
80 B2FATAL("This tool is meant to reconstruct decays with a K_L0 in the final state. There is no K_L0 in this decay!");
81
82 // if there are more than two daughters, use the invariant mass of sum of the other daughters.
83 if (daughters.size() == 3) {
84 m_j = pDaughters.M();
85 }
86
87 const double m_k2 = Const::Klong.getMass() * Const::Klong.getMass();
88
89 const double s_p = (klDaughters.Vect().Unit()).Dot(pDaughters.Vect());
90 const double m_sum = (m_b * m_b) - (m_j * m_j) - m_k2;
91
92 const double s_p2 = s_p * s_p;
93 const double m_sum2 = m_sum * m_sum;
94 const double s_pm = s_p * m_sum;
95 const double e_j2 = pDaughters.E() * pDaughters.E();
96
97 const double k_mag1 = (s_pm + std::sqrt(s_p2 * m_sum2 - 4 * (e_j2 - s_p2) * (e_j2 * m_k2 - m_sum2 / 4))) / (2 *
98 (e_j2 - s_p2));
99 const double k_mag2 = (s_pm - std::sqrt(s_p2 * m_sum2 - 4 * (e_j2 - s_p2) * (e_j2 * m_k2 - m_sum2 / 4))) / (2 *
100 (e_j2 - s_p2));
101
102
103 ROOT::Math::PxPyPzEVector missDaughters;
104
105 if (k_mag1 > 0)
106 missDaughters = k_mag1 * klDaughters / klDaughters.P();
107 else
108 missDaughters = k_mag2 * klDaughters / klDaughters.P();
109
110 missDaughters.SetE(std::sqrt(m_k2 + missDaughters.P2()));
111
112 if (isnan(missDaughters.P()))
113 return false;
114
115 ROOT::Math::PxPyPzEVector mom = pDaughters + missDaughters;
116 mom.SetE(std::sqrt(m_b * m_b + mom.P2()));
117 if (isnan(mom.P()))
118 return false;
119
120 KMomentum = missDaughters;
121 BMomentum = mom;
122
123 return true;
124 };
int getPDGCode() const
PDG code.
Definition: Const.h:473
double getMass() const
Particle mass.
Definition: UnitConst.cc:356
static const ParticleType Klong
K^0_L particle.
Definition: Const.h:678
ECL cluster data.
Definition: ECLCluster.h:27
@ c_neutralHadron
CR is reconstructed as a neutral hadron (N2)
KLM cluster data.
Definition: KLMCluster.h:28

The documentation for this struct was generated from the following file: