TPythia6Decayer.cxx

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// @(#)root/pythia6:$Id$
// Author: Christian Holm Christensen   22/04/06
// Much of this code has been lifted from AliROOT.

/*************************************************************************
 * Copyright (C) 1995-2006, Rene Brun and Fons Rademakers.               *
 * All rights reserved.                                                  *
 *                                                                       *
 * For the licensing terms see $ROOTSYS/LICENSE.                         *
 * For the list of contributors see $ROOTSYS/README/CREDITS.             *
 *************************************************************************/

/** \class TPythia6Decayer
    \ingroup pythia6

This class implements the TVirtualMCDecayer interface.  

The TPythia6 singleton object is used to decay particles.  Note, that since
this class modifies common blocks (global variables) it is defined as a
singleton.
*/

#include "TPythia6.h"
#include "TPythia6Decayer.h"
#include "TPDGCode.h"
#include "TLorentzVector.h"
#include "TClonesArray.h"

ClassImp(TPythia6Decayer)

TPythia6Decayer* TPythia6Decayer::fgInstance = 0;

////////////////////////////////////////////////////////////////////////////////
/// Get the singleton object.

TPythia6Decayer* TPythia6Decayer::Instance()
{
   if (!fgInstance) fgInstance = new TPythia6Decayer;
   return fgInstance;
}

////////////////////////////////////////////////////////////////////////////////
/// Constructor

TPythia6Decayer::TPythia6Decayer()
   : fDecay(kMaxDecay),
   fBraPart(501)
{
   fBraPart.Reset(1);
}

////////////////////////////////////////////////////////////////////////////////
/// Initialize the decayer

void TPythia6Decayer::Init()
{
   static Bool_t init = kFALSE;
   if (init) return;
   init = kTRUE;
   ForceDecay();
}

////////////////////////////////////////////////////////////////////////////////
/// Decay a particle of type IDPART (PDG code) and momentum P.

void TPythia6Decayer::Decay(Int_t idpart, TLorentzVector* p)
{
   if (!p) return;
   TPythia6::Instance()->Py1ent(0, idpart, p->Energy(), p->Theta(), p->Phi());
   TPythia6::Instance()->GetPrimaries();
}

////////////////////////////////////////////////////////////////////////////////
/// Get the decay products into the passed PARTICLES TClonesArray of
/// TParticles

Int_t TPythia6Decayer::ImportParticles(TClonesArray *particles)
{
   return TPythia6::Instance()->ImportParticles(particles,"All");
}

////////////////////////////////////////////////////////////////////////////////
/// Force a particular decay type

void TPythia6Decayer::SetForceDecay(Int_t type)
{
   if (type > kMaxDecay) {
      Warning("SetForceDecay", "Invalid decay mode: %d", type);
      return;
   }
   fDecay = EDecayType(type);
}

////////////////////////////////////////////////////////////////////////////////
/// Force a particle decay mode

void TPythia6Decayer::ForceDecay()
{
   EDecayType decay=fDecay;
   TPythia6::Instance()->SetMSTJ(21,2);
   if (decay == kNoDecayHeavy) return;

   //
   // select mode
   Int_t products[3];
   Int_t mult[3];

   switch (decay) {
   case kHardMuons:
      products[0] =     13;
      products[1] =    443;
      products[2] = 100443;
      mult[0] = 1;
      mult[1] = 1;
      mult[2] = 1;
      ForceParticleDecay(  511, products, mult, 3);
      ForceParticleDecay(  521, products, mult, 3);
      ForceParticleDecay(  531, products, mult, 3);
      ForceParticleDecay( 5122, products, mult, 3);
      ForceParticleDecay( 5132, products, mult, 3);
      ForceParticleDecay( 5232, products, mult, 3);
      ForceParticleDecay( 5332, products, mult, 3);
      ForceParticleDecay( 100443, 443, 1);  // Psi'  -> J/Psi X
      ForceParticleDecay(    443,  13, 2);  // J/Psi -> mu+ mu-

      ForceParticleDecay(  411,13,1); // D+/-
      ForceParticleDecay(  421,13,1); // D0
      ForceParticleDecay(  431,13,1); // D_s
      ForceParticleDecay( 4122,13,1); // Lambda_c
      ForceParticleDecay( 4132,13,1); // Xsi_c
      ForceParticleDecay( 4232,13,1); // Sigma_c
      ForceParticleDecay( 4332,13,1); // Omega_c
      break;
   case kSemiMuonic:
      ForceParticleDecay(  411,13,1); // D+/-
      ForceParticleDecay(  421,13,1); // D0
      ForceParticleDecay(  431,13,1); // D_s
      ForceParticleDecay( 4122,13,1); // Lambda_c
      ForceParticleDecay( 4132,13,1); // Xsi_c
      ForceParticleDecay( 4232,13,1); // Sigma_c
      ForceParticleDecay( 4332,13,1); // Omega_c
      ForceParticleDecay(  511,13,1); // B0
      ForceParticleDecay(  521,13,1); // B+/-
      ForceParticleDecay(  531,13,1); // B_s
      ForceParticleDecay( 5122,13,1); // Lambda_b
      ForceParticleDecay( 5132,13,1); // Xsi_b
      ForceParticleDecay( 5232,13,1); // Sigma_b
      ForceParticleDecay( 5332,13,1); // Omega_b
      break;
   case kDiMuon:
      ForceParticleDecay(  113,13,2); // rho
      ForceParticleDecay(  221,13,2); // eta
      ForceParticleDecay(  223,13,2); // omega
      ForceParticleDecay(  333,13,2); // phi
      ForceParticleDecay(  443,13,2); // J/Psi
      ForceParticleDecay(100443,13,2);// Psi'
      ForceParticleDecay(  553,13,2); // Upsilon
      ForceParticleDecay(100553,13,2);// Upsilon'
      ForceParticleDecay(200553,13,2);// Upsilon''
      break;
   case kSemiElectronic:
      ForceParticleDecay(  411,11,1); // D+/-
      ForceParticleDecay(  421,11,1); // D0
      ForceParticleDecay(  431,11,1); // D_s
      ForceParticleDecay( 4122,11,1); // Lambda_c
      ForceParticleDecay( 4132,11,1); // Xsi_c
      ForceParticleDecay( 4232,11,1); // Sigma_c
      ForceParticleDecay( 4332,11,1); // Omega_c
      ForceParticleDecay(  511,11,1); // B0
      ForceParticleDecay(  521,11,1); // B+/-
      ForceParticleDecay(  531,11,1); // B_s
      ForceParticleDecay( 5122,11,1); // Lambda_b
      ForceParticleDecay( 5132,11,1); // Xsi_b
      ForceParticleDecay( 5232,11,1); // Sigma_b
      ForceParticleDecay( 5332,11,1); // Omega_b
      break;
   case kDiElectron:
      ForceParticleDecay(  113,11,2); // rho
      ForceParticleDecay(  333,11,2); // phi
      ForceParticleDecay(  221,11,2); // eta
      ForceParticleDecay(  223,11,2); // omega
      ForceParticleDecay(  443,11,2); // J/Psi
      ForceParticleDecay(100443,11,2);// Psi'
      ForceParticleDecay(  553,11,2); // Upsilon
      ForceParticleDecay(100553,11,2);// Upsilon'
      ForceParticleDecay(200553,11,2);// Upsilon''
      break;
   case kBJpsiDiMuon:

      products[0] =    443;
      products[1] = 100443;
      mult[0] = 1;
      mult[1] = 1;

      ForceParticleDecay(  511, products, mult, 2); // B0   -> J/Psi (Psi') X
      ForceParticleDecay(  521, products, mult, 2); // B+/- -> J/Psi (Psi') X
      ForceParticleDecay(  531, products, mult, 2); // B_s  -> J/Psi (Psi') X
      ForceParticleDecay( 5122, products, mult, 2); // Lambda_b -> J/Psi (Psi') X
      ForceParticleDecay( 100443, 443, 1);          // Psi'  -> J/Psi X
      ForceParticleDecay(    443,13,2);             // J/Psi -> mu+ mu-
      break;
   case kBPsiPrimeDiMuon:
      ForceParticleDecay(  511,100443,1); // B0
      ForceParticleDecay(  521,100443,1); // B+/-
      ForceParticleDecay(  531,100443,1); // B_s
      ForceParticleDecay( 5122,100443,1); // Lambda_b
      ForceParticleDecay(100443,13,2);    // Psi'
      break;
   case kBJpsiDiElectron:
      ForceParticleDecay(  511,443,1); // B0
      ForceParticleDecay(  521,443,1); // B+/-
      ForceParticleDecay(  531,443,1); // B_s
      ForceParticleDecay( 5122,443,1); // Lambda_b
      ForceParticleDecay(  443,11,2);  // J/Psi
      break;
   case kBJpsi:
      ForceParticleDecay(  511,443,1); // B0
      ForceParticleDecay(  521,443,1); // B+/-
      ForceParticleDecay(  531,443,1); // B_s
      ForceParticleDecay( 5122,443,1); // Lambda_b
      break;
   case kBPsiPrimeDiElectron:
      ForceParticleDecay(  511,100443,1); // B0
      ForceParticleDecay(  521,100443,1); // B+/-
      ForceParticleDecay(  531,100443,1); // B_s
      ForceParticleDecay( 5122,100443,1); // Lambda_b
      ForceParticleDecay(100443,11,2);   // Psi'
      break;
   case kPiToMu:
      ForceParticleDecay(211,13,1); // pi->mu
      break;
   case kKaToMu:
      ForceParticleDecay(321,13,1); // K->mu
      break;
   case kWToMuon:
      ForceParticleDecay(  24, 13,1); // W -> mu
      break;
   case kWToCharm:
      ForceParticleDecay(   24, 4,1); // W -> c
      break;
   case kWToCharmToMuon:
      ForceParticleDecay(   24, 4,1); // W -> c
      ForceParticleDecay(  411,13,1); // D+/- -> mu
      ForceParticleDecay(  421,13,1); // D0  -> mu
      ForceParticleDecay(  431,13,1); // D_s  -> mu
      ForceParticleDecay( 4122,13,1); // Lambda_c
      ForceParticleDecay( 4132,13,1); // Xsi_c
      ForceParticleDecay( 4232,13,1); // Sigma_c
      ForceParticleDecay( 4332,13,1); // Omega_c
      break;
   case kZDiMuon:
      ForceParticleDecay(  23, 13,2); // Z -> mu+ mu-
      break;
   case kHadronicD:
      ForceHadronicD();
      break;
   case kPhiKK:
      ForceParticleDecay(333,321,2); // Phi->K+K-
      break;
   case kOmega:
      ForceOmega();
   case kAll:
      break;
   case kNoDecay:
      TPythia6::Instance()->SetMSTJ(21,0);
      break;
   case kNoDecayHeavy: break; // cannot get here: early return above
   case kMaxDecay: break;
   }
}

////////////////////////////////////////////////////////////////////////////////
/// Get the partial branching ratio for a particle of type IPART (a
/// PDG code).

Float_t TPythia6Decayer::GetPartialBranchingRatio(Int_t ipart)
{
   Int_t kc = TPythia6::Instance()->Pycomp(TMath::Abs(ipart));
   // return TPythia6::Instance()->GetBRAT(kc);
   return fBraPart[kc];
}

////////////////////////////////////////////////////////////////////////////////
/// Get the life-time of a particle of type KF (a PDG code).

Float_t TPythia6Decayer::GetLifetime(Int_t kf)
{
   Int_t kc=TPythia6::Instance()->Pycomp(TMath::Abs(kf));
   return TPythia6::Instance()->GetPMAS(kc,4) * 3.3333e-12;
}

////////////////////////////////////////////////////////////////////////////////
/// Read in particle data from an ASCII file.   The file name must
/// previously have been set using the member function
/// SetDecayTableFile.

void TPythia6Decayer::ReadDecayTable()
{
   if (fDecayTableFile.IsNull()) {
      Warning("ReadDecayTable", "No file set");
      return;
   }
   Int_t lun = 15;
   TPythia6::Instance()->OpenFortranFile(lun,
                                         const_cast<char*>(fDecayTableFile.Data()));
   TPythia6::Instance()->Pyupda(3,lun);
   TPythia6::Instance()->CloseFortranFile(lun);
}

// ===================================================================
// BEGIN COMMENT
//
// It would be better if the particle and decay information could be
// read from the current TDatabasePDG instance.
//
// However, it seems to me that some information is missing.  In
// particular
//
//   - The broadning cut-off,
//   - Resonance width
//   - Color charge
//   - MWID (?)
//
// Further more, it's not clear to me at least, what all the
// parameters Pythia needs are.
//
// Code like the below could be used to make a temporary file that
// Pythia could then read in.   Ofcourse, one could also manipulate
// the data structures directly, but that's propably more dangerous.
//
#if 0
void PrintPDG(TParticlePDG* pdg)
{
   TParticlePDG* anti = pdg->AntiParticle();
   const char* antiName = (anti ? anti->GetName() : "");
   Int_t color = 0;
   switch (TMath::Abs(pdg->PdgCode())) {
      case 1: case 2: case 3: case 4: case 5: case 6: case 7: case 8: // Quarks
      color = 1; break;
      case 21: // Gluon
      color = 2; break;
      case 1103:
      case 2101: case 2103: case 2203:
      case 3101: case 3103: case 3201: case 3203: case 3303:
      case 4101: case 4103: case 4201: case 4203: case 4301: case 4303: case 4403:
      case 5101: case 5103: case 5201: case 5203: case 5301: case 5303: case 5401:
      case 5403: case 5503:
      // Quark combinations
      color = -1; break;
      case 1000001: case 1000002: case 1000003: case 1000004: case 1000005:
      case 1000006: // super symmetric partners to quars
      color = 1; break;
      case 1000021: // ~g
      color = 2; break;
      case 2000001: case 2000002: case 2000003: case 2000004: case 2000005:
      case 2000006: // R hadrons
      color = 1; break;
      case 3000331: case 3100021: case 3200111: case 3100113: case 3200113:
      case 3300113: case 3400113:
      // Technicolor
      color = 2; break;
      case 4000001: case 4000002:
      color = 1; break;
      case 9900443: case 9900441: case 9910441: case 9900553: case 9900551:
      case 9910551:
      color = 2; break;
   }
   std::cout << std::right
             << " " << std::setw(9) << pdg->PdgCode()
             << "  " << std::left   << std::setw(16) << pdg->GetName()
             << "  " << std::setw(16) << antiName
             << std::right
             << std::setw(3) << Int_t(pdg->Charge())
             << std::setw(3) << color
             << std::setw(3) << (anti ? 1 : 0)
             << std::fixed   << std::setprecision(5)
             << std::setw(12) << pdg->Mass()
             << std::setw(12) << pdg->Width()
             << std::setw(12) << 0 // Broad
             << std::scientific
             << " " << std::setw(13) << pdg->Lifetime()
             << std::setw(3) << 0 // MWID
             << std::setw(3) << pdg->Stable()
             << std::endl;
}

void MakeDecayList()
{
   TDatabasePDG* pdgDB = TDatabasePDG::Instance();
   pdgDB->ReadPDGTable();
   const THashList*    pdgs  = pdgDB->ParticleList();
   TParticlePDG*       pdg   = 0;
   TIter               nextPDG(pdgs);
   while ((pdg = static_cast<TParticlePDG*>(nextPDG()))) {
      // std::cout << "Processing " << pdg->GetName() << std::endl;
      PrintPDG(pdg);

      TObjArray*     decays = pdg->DecayList();
      TDecayChannel* decay  = 0;
      TIter          nextDecay(decays);
      while ((decay = static_cast<TDecayChannel*>(nextDecay()))) {
        // std::cout << "Processing decay number " << decay->Number() << std::endl;
      }
   }
}
#endif
// END COMMENT
// ===================================================================

////////////////////////////////////////////////////////////////////////////////
/// write particle data to an ASCII file.   The file name must
/// previously have been set using the member function
/// SetDecayTableFile.
///
/// Users can use this function to make an initial decay list file,
/// which then can be edited by hand, and re-loaded into the decayer
/// using ReadDecayTable.
///
/// The file syntax is
///
///     particle_list : partcle_data
///                   | particle_list particle_data
///                  ;
///     particle_data : particle_info
///                   | particle_info '\n' decay_list
///                   ;
///     particle_info : See below
///                   ;
///     decay_list    : decay_entry
///                   | decay_list decay_entry
///                   ;
///     decay_entry   : See below
/// 
/// The particle_info consists of 13 fields:
///
///     PDG code             int
///     Name                 string
///     Anti-particle name   string  if there's no anti-particle,
///                                  then this field must be the
///                                  empty string
///     Electic charge       int     in units of |e|/3
///     Color charge         int     in units of quark color charges
///     Have anti-particle   int     1 of there's an anti-particle
///                                  to this particle, or 0
///                                  otherwise
///     Mass                 float   in units of GeV
///     Resonance width      float
///     Max broadning        float
///     Lifetime             float
///     MWID                 int     ??? (some sort of flag)
///     Decay                int     1 if it decays. 0 otherwise
///
/// The format to write these entries in are
///
///     " %9  %-16s  %-16s%3d%3d%3d%12.5f%12.5f%12.5f%13.gf%3d%d\n"
///
/// The decay_entry consists of 8 fields:
///
///     On/Off               int     1 for on, -1 for off
///     Matrix element type  int
///     Branching ratio      float
///     Product 1            int     PDG code of decay product 1
///     Product 2            int     PDG code of decay product 2
///     Product 3            int     PDG code of decay product 3
///     Product 4            int     PDG code of decay product 4
///     Product 5            int     PDG code of decay product 5
///
/// The format for these lines are
///
///    "          %5d%5d%12.5f%10d%10d%10d%10d%10d\n"
///

void TPythia6Decayer::WriteDecayTable()
{
   if (fDecayTableFile.IsNull()) {
      Warning("ReadDecayTable", "No file set");
      return;
   }
   Int_t lun = 15;
   TPythia6::Instance()->OpenFortranFile(lun,
                                         const_cast<char*>(fDecayTableFile.Data()));
   TPythia6::Instance()->Pyupda(1,lun);
   TPythia6::Instance()->CloseFortranFile(lun);
}

////////////////////////////////////////////////////////////////////////////////
/// Count number of decay products

Int_t TPythia6Decayer::CountProducts(Int_t channel, Int_t particle)
{
   Int_t np = 0;
   for (Int_t i = 1; i <= 5; i++)
      if (TMath::Abs(TPythia6::Instance()->GetKFDP(channel,i)) == particle) np++;
   return np;
}

////////////////////////////////////////////////////////////////////////////////
/// Force golden D decay modes

void TPythia6Decayer::ForceHadronicD()
{
   const Int_t kNHadrons = 4;
   Int_t channel;
   Int_t hadron[kNHadrons] = {411,  421, 431, 4112};

   // for D+ -> K0* (-> K- pi+) pi+
   Int_t iKstar0     =  313;
   Int_t iKstarbar0  = -313;
   Int_t products[2] = {kKPlus, kPiMinus}, mult[2] = {1, 1};
   ForceParticleDecay(iKstar0, products, mult, 2);

   // for Ds -> Phi pi+
   Int_t iPhi = 333;
   ForceParticleDecay(iPhi,kKPlus,2); // Phi->K+K-

   Int_t decayP1[kNHadrons][3] = {
      {kKMinus, kPiPlus,    kPiPlus},
      {kKMinus, kPiPlus,    0      },
      {kKPlus , iKstarbar0, 0     },
      {-1     , -1        , -1        }
   };
   Int_t decayP2[kNHadrons][3] = {
      {iKstarbar0, kPiPlus, 0   },
      {-1        , -1     , -1  },
      {iPhi      , kPiPlus, 0  },
      {-1        , -1     , -1  }
   };

   TPythia6* pyth = TPythia6::Instance();
   for (Int_t ihadron = 0; ihadron < kNHadrons; ihadron++) {
      Int_t kc = pyth->Pycomp(hadron[ihadron]);
      pyth->SetMDCY(kc,1,1);
      Int_t ifirst = pyth->GetMDCY(kc,2);
      Int_t ilast  = ifirst + pyth->GetMDCY(kc,3)-1;

      for (channel = ifirst; channel <= ilast; channel++) {
         if ((pyth->GetKFDP(channel,1) == decayP1[ihadron][0] &&
            pyth->GetKFDP(channel,2) == decayP1[ihadron][1] &&
            pyth->GetKFDP(channel,3) == decayP1[ihadron][2] &&
            pyth->GetKFDP(channel,4) == 0) ||
           (pyth->GetKFDP(channel,1) == decayP2[ihadron][0] &&
            pyth->GetKFDP(channel,2) == decayP2[ihadron][1] &&
            pyth->GetKFDP(channel,3) == decayP2[ihadron][2] &&
            pyth->GetKFDP(channel,4) == 0)) {
            pyth->SetMDME(channel,1,1);
         } else {
            pyth->SetMDME(channel,1,0);
            fBraPart[kc] -= pyth->GetBRAT(channel);
         } // selected channel ?
      } // decay channels
   } // hadrons
}

////////////////////////////////////////////////////////////////////////////////
///
///  Force decay of particle into products with multiplicity mult

void TPythia6Decayer::ForceParticleDecay(Int_t particle, Int_t product, Int_t mult)
{
   TPythia6* pyth = TPythia6::Instance();

   Int_t kc =  pyth->Pycomp(particle);
   pyth->SetMDCY(kc,1,1);

   Int_t ifirst = pyth->GetMDCY(kc,2);
   Int_t ilast  = ifirst + pyth->GetMDCY(kc,3)-1;
   fBraPart[kc] = 1;

   //
   //  Loop over decay channels
   for (Int_t channel= ifirst; channel <= ilast; channel++) {
      if (CountProducts(channel,product) >= mult) {
         pyth->SetMDME(channel,1,1);
      } else {
         pyth->SetMDME(channel,1,0);
         fBraPart[kc]-=pyth->GetBRAT(channel);
      }
   }
}

////////////////////////////////////////////////////////////////////////////////
///
///  Force decay of particle into products with multiplicity mult

void TPythia6Decayer::ForceParticleDecay(Int_t particle, Int_t* products,
                                         Int_t* mult, Int_t npart)
{
   TPythia6* pyth = TPythia6::Instance();

   Int_t kc     = pyth->Pycomp(particle);
   pyth->SetMDCY(kc,1,1);
   Int_t ifirst = pyth->GetMDCY(kc,2);
   Int_t ilast  = ifirst+pyth->GetMDCY(kc,3)-1;
   fBraPart[kc] = 1;
   //
   //  Loop over decay channels
   for (Int_t channel = ifirst; channel <= ilast; channel++) {
      Int_t nprod = 0;
      for (Int_t i = 0; i < npart; i++)
         nprod += (CountProducts(channel, products[i]) >= mult[i]);
      if (nprod)
         pyth->SetMDME(channel,1,1);
      else {
         pyth->SetMDME(channel,1,0);
         fBraPart[kc] -= pyth->GetBRAT(channel);
      }
   }
}

////////////////////////////////////////////////////////////////////////////////
/// Force Omega -> Lambda K- Decay

void TPythia6Decayer::ForceOmega()
{
   TPythia6* pyth = TPythia6::Instance();

   Int_t kc     = pyth->Pycomp(3334);
   pyth->SetMDCY(kc,1,1);
   Int_t ifirst = pyth->GetMDCY(kc,2);
   Int_t ilast  = ifirst + pyth->GetMDCY(kc,3)-1;
   for (Int_t channel = ifirst; channel <= ilast; channel++) {
      if (pyth->GetKFDP(channel,1) == kLambda0 &&
         pyth->GetKFDP(channel,2) == kKMinus  &&
         pyth->GetKFDP(channel,3) == 0)
         pyth->SetMDME(channel,1,1);
      else
         pyth->SetMDME(channel,1,0);
      // selected channel ?
   } // decay channels
}