Pythia8::WZPolarization Struct Reference

Convert all resonant W/Z boson decays to the angular distribution of a pure polarisation state. More...

Inheritance diagram for Pythia8::WZPolarization:

Collaboration diagram for Pythia8::WZPolarization:

Public Member Functions
	WZPolarization ()
bool	canVetoResonanceDecays ()
bool	doVetoResonanceDecays (Event &process)
double	sqr (double x)
double	rand01 ()

Public Attributes
Pythia8_UserHooks::UserSetting< int >	m_polmode

Detailed Description

Convert all resonant W/Z boson decays to the angular distribution of a pure polarisation state.

Definition at line 16 of file WZPolarization.cxx.

Constructor & Destructor Documentation

WZPolarization()

Pythia8::WZPolarization::WZPolarization ( )

inline

Definition at line 18 of file WZPolarization.cxx.

: m_polmode("WZPolarization:mode", 1) { }

Member Function Documentation

canVetoResonanceDecays()

bool Pythia8::WZPolarization::canVetoResonanceDecays ( )

inline

Definition at line 20 of file WZPolarization.cxx.

{ return true; }

doVetoResonanceDecays()

bool Pythia8::WZPolarization::doVetoResonanceDecays ( Event &  process )

inline

Definition at line 22 of file WZPolarization.cxx.

                                               {
      const int polmode = m_polmode(settingsPtr);
 
      for (int i = 1; i < process.size(); ++i) {
        // Select vector bosons
        Particle& v = process[i];
        if (v.id() != 23 && v.idAbs() != 24) continue;
        const Vec4 pv = v.p();
 
        // Find W/Z daughter particles
        Particle& d1 = process[v.daughter1()];
        Particle& d2 = process[v.daughter2()];
 
        // Get daughter momenta in the boson rest frame
        Vec4 pd1 = d1.p();
        Vec4 pd2 = d2.p();
        pd1.bstback(pv);
        pd2.bstback(pv);
 
        // Randomly reorient and rejection-sample decay configuration
        // (done inline here, rather than reboosting to the W/Z frame on each decay-hook iteration)
        while (true) {
 
          // Random reorientation
          const double dtheta = std::acos(2*rand01() - 1);
          const double dphi = 2*M_PI*rand01();
          pd1.rot(dtheta, dphi);
          pd2.rot(dtheta, dphi);
 
          // Angle w.r.t. W/Z flight direction, in rest-frame
          const double th = theta(pv, pd1);
 
          // Accept/reject the angle according to the polarisation being modelled
          if (polmode == 0) { // Isotropic
            break; // it's already been isotropically randomised
          } else if (polmode == 1) { // Longitudinal
            if (rand01() < sqr(std::sin(th))) break;
          } else if (polmode == 2) { // Trans-sum
            if (rand01() < (1 + sqr(std::cos(th)))/2) break;
          } else if (polmode == 3) { // Trans+
            if (rand01() < sqr(1 + std::cos(th))/4) break;
          } else if (polmode == 4) { // Trans-
            if (rand01() < sqr(1 - std::cos(th))/4) break;
          }
        }
 
        // Boost the vectors back to the lab frame
        pd1.bst(pv); d1.p(pd1);
        pd2.bst(pv); d2.p(pd2);
 
      }
 
      return false;
    }

rand01()

double Pythia8::WZPolarization::rand01 ( )

inline

Definition at line 79 of file WZPolarization.cxx.

{ return rndmPtr->flat(); }

sqr()

double Pythia8::WZPolarization::sqr ( double  x )

inline

Definition at line 77 of file WZPolarization.cxx.

{ return x*x; }

Member Data Documentation

m_polmode

Pythia8_UserHooks::UserSetting<int> Pythia8::WZPolarization::m_polmode

Definition at line 81 of file WZPolarization.cxx.

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

• WZPolarization.cxx