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 //
 //
 // File: src/Top_Decaykin.cc
 // Purpose: Calculate some kinematic quantities for ttbar events.
 // Created: Jul, 2000, sss, based on run 1 mass analysis code.
 //
 // CMSSW File      : src/Top_Decaykin.cc
 // Original Author : Scott Stuart Snyder <snyder@bnl.gov> for D0
 // Imported to CMSSW by Haryo Sumowidagdo <Suharyo.Sumowidagdo@cern.ch>
 //
 
 /**
     @file Top_Decaykin.cc
 
     @brief A class to hold functions to calculate kinematic quantities
     of interest in \f$t\bar{t} \to \ell + 4 \mathrm{jets}\f$ events.
     See the documentation for the header file Top_Decaykin.h for details.
 
     @author Scott Stuart Snyder <snyder@bnl.gov>
 
     @par Creation date:
     Jul 2000.
 
     @par Modification History:
     Apr 2009: Haryo Sumowidagdo <Suharyo.Sumowidagdo@cern.ch>:
     Imported to CMSSW.<br>
     Nov 2009: Haryo Sumowidagdo <Suharyo.Sumowidagdo@cern.ch>:
     Added doxygen tags for automatic generation of documentation.
 
     @par Terms of Usage:
     With consent for the original author (Scott Snyder).
 
  */
 
 #include "TopQuarkAnalysis/TopHitFit/interface/Top_Decaykin.h"
 #include "TopQuarkAnalysis/TopHitFit/interface/Lepjets_Event.h"
 #include "TopQuarkAnalysis/TopHitFit/interface/fourvec.h"
 #include <cmath>
 #include <algorithm>
 #include <ostream>
 
 using std::abs;
 using std::ostream;
 using std::sqrt;
 using std::swap;
 
 namespace hitfit {
 
   namespace {
 
     /**
     @brief Sum the four-momenta of all leptons in an event.
 
     @param ev The event.
  */
     Fourvec leptons(const Lepjets_Event& ev)
     //
     // Purpose: Sum all leptons in EV.
     //
     // Inputs:
     //   ev -          The event.
     //
     // Returns:
     //   The sum of all leptons in EV.
     //
     {
       return (ev.sum(lepton_label) + ev.sum(electron_label) + ev.sum(muon_label));
     }
 
   }  // unnamed namespace
 
   bool Top_Decaykin::solve_nu_tmass(const Lepjets_Event& ev, double tmass, double& nuz1, double& nuz2)
   //
   // Purpose: Solve for the neutrino longitudinal z-momentum that makes
   //          the leptonic top have mass TMASS.
   //
   // Inputs:
   //   ev -          The event to solve.
   //   tmass -       The desired top mass.
   //
   // Outputs:
   //   nuz1 -        First solution (smaller absolute value).
   //   nuz2 -        Second solution.
   //
   // Returns:
   //   True if there was a real solution.  False if there were only
   //   imaginary solutions.  (In that case, we just set the imaginary
   //   part to zero.)
   //
   {
     bool discrim_flag = true;
 
     const Fourvec& vnu = ev.met();
     Fourvec cprime = leptons(ev) + ev.sum(lepb_label);
     double alpha1 = tmass * tmass - cprime.m2();
     double a = 2 * 4 * (cprime.z() * cprime.z() - cprime.e() * cprime.e());
     double alpha = alpha1 + 2 * (cprime.x() * vnu.x() + cprime.y() * vnu.y());
     double b = 4 * alpha * cprime.z();
     double c = alpha * alpha - 4 * cprime.e() * cprime.e() * vnu.vect().perp2();
     double d = b * b - 2 * a * c;
     if (d < 0) {
       discrim_flag = false;
       d = 0;
     }
 
     double dd = sqrt(d);
     nuz1 = (-b + dd) / a;
     nuz2 = (-b - dd) / a;
     if (abs(nuz1) > abs(nuz2))
       swap(nuz1, nuz2);
 
     return discrim_flag;
   }
 
   bool Top_Decaykin::solve_nu_tmass(
       const Lepjets_Event& ev, double tmass, double& re_nuz1, double& im_nuz1, double& re_nuz2, double& im_nuz2)
   //
   // Purpose: Solve for the neutrino longitudinal z-momentum that makes
   //          the leptonic top have mass TMASS, including the imaginary
   //          component of the z-component of the neutrino'somentum.
   //
   // Inputs:
   //   ev -          The event to solve.
   //   tmass -       The desired top mass.
   //
   // Outputs:
   //   re_nuz1 -     Real component of the first solution.
   //   im_nuz1 -     Imaginary component of the first solution (in the lower half of
   //                 the complex plane).
   //   re_nuz2 -     Real component of the second solution.
   //   im_nuz2 -     Imaginary component of the second solution (in the upper half of
   //                 the complex plane).
   //
   // Returns:
   //   True if there was a real solution.  False if there were only
   //   complex solutions.
   //
   {
     bool discrim_flag = true;
 
     const Fourvec& vnu = ev.met();
     Fourvec cprime = leptons(ev) + ev.sum(lepb_label);
     double alpha1 = tmass * tmass - cprime.m2();
     double a = 2 * 4 * (cprime.z() * cprime.z() - cprime.e() * cprime.e());
     // Haryo's note: Here a is equivalent to '2a' in the quadratic
     // equation ax^2 + bx + c = 0
     double alpha = alpha1 + 2 * (cprime.x() * vnu.x() + cprime.y() * vnu.y());
     double b = 4 * alpha * cprime.z();
     double c = alpha * alpha - 4 * cprime.e() * cprime.e() * vnu.vect().perp2();
     double d = b * b - 2 * a * c;
     if (d < 0) {
       discrim_flag = false;
     }
 
     if (discrim_flag) {
       re_nuz1 = (-b + sqrt(d)) / a;
       im_nuz1 = 0;
       re_nuz2 = (-b - sqrt(d)) / a;
       im_nuz2 = 0;
       if (abs(re_nuz1) > abs(re_nuz2)) {
         swap(re_nuz1, re_nuz2);
       }
 
     } else {
       // Take absolute value of the imaginary component of nuz, in case
       // a is negative, before multiplying by +1 or -1 to get the upper-half
       // or lower-half imaginary value.
       re_nuz1 = -b / a;
       im_nuz1 = -fabs(sqrt(-d) / a);
       re_nuz2 = -b / a;
       im_nuz2 = fabs(sqrt(-d) / a);
     }
 
     return discrim_flag;
   }
 
   bool Top_Decaykin::solve_nu(const Lepjets_Event& ev, double wmass, double& nuz1, double& nuz2)
   //
   // Purpose: Solve for the neutrino longitudinal z-momentum that makes
   //          the leptonic W have mass WMASS.
   //
   // Inputs:
   //   ev -          The event to solve.
   //   wmass -       The desired W mass.
   //
   // Outputs:
   //   nuz1 -        First solution (smaller absolute value).
   //   nuz2 -        Second solution.
   //
   // Returns:
   //   True if there was a real solution.  False if there were only
   //   imaginary solutions.  (In that case, we just set the imaginary
   //   part to zero.)
   //
   {
     bool discrim_flag = true;
 
     const Fourvec& vnu = ev.met();
     Fourvec vlep = leptons(ev);
 
     double x = vlep.x() * vnu.x() + vlep.y() * vnu.y() + wmass * wmass / 2;
     double a = vlep.z() * vlep.z() - vlep.e() * vlep.e();
     double b = 2 * x * vlep.z();
     double c = x * x - vnu.perp2() * vlep.e() * vlep.e();
 
     double d = b * b - 4 * a * c;
     if (d < 0) {
       d = 0;
       discrim_flag = false;
     }
 
     nuz1 = (-b + sqrt(d)) / 2 / a;
     nuz2 = (-b - sqrt(d)) / 2 / a;
     if (abs(nuz1) > abs(nuz2))
       swap(nuz1, nuz2);
 
     return discrim_flag;
   }
 
   bool Top_Decaykin::solve_nu(
       const Lepjets_Event& ev, double wmass, double& re_nuz1, double& im_nuz1, double& re_nuz2, double& im_nuz2)
   //
   // Purpose: Solve for the neutrino longitudinal z-momentum that makes
   //          the leptonic W have mass WMASS, including the imaginary
   //          component of the z-component of the neutrino'somentum.
   //
   // Inputs:
   //   ev -          The event to solve.
   //   wmass -       The desired W mass.
   //
   // Outputs:
   //   re_nuz1 -     Real component of the first solution.
   //   im_nuz1 -     Imaginary component of the first solution  (in the lower half of
   //                 the complex plane).
   //   re_nuz2 -     Real component of the second solution.
   //   im_nuz2 -     Imaginary component of the second solution  (in the upper half of
   //                 the complex plane).
   //
   // Returns:
   //   True if there was a real solution.  False if there were only
   //   complex solutions.
   //x
   {
     bool discrim_flag = true;
 
     const Fourvec& vnu = ev.met();
     Fourvec vlep = leptons(ev);
 
     double x = vlep.x() * vnu.x() + vlep.y() * vnu.y() + wmass * wmass / 2;
     double a = vlep.z() * vlep.z() - vlep.e() * vlep.e();
     double b = 2 * x * vlep.z();
     double c = x * x - vnu.perp2() * vlep.e() * vlep.e();
 
     double d = b * b - 4 * a * c;
     if (d < 0) {
       discrim_flag = false;
     }
 
     if (discrim_flag) {
       re_nuz1 = (-b + sqrt(d)) / 2 / a;
       im_nuz1 = 0.0;
       re_nuz2 = (-b - sqrt(d)) / 2 / a;
       im_nuz2 = 0.0;
       if (fabs(re_nuz1) > fabs(re_nuz2)) {
         swap(re_nuz1, re_nuz2);
       }
 
     } else {
       // Take absolute value of the imaginary component of nuz, in case
       // a is negative, before multiplying by +1 or -1 to get the upper-half
       // or lower-half imaginary value.
 
       re_nuz1 = -b / 2 / a;
       im_nuz1 = -fabs(sqrt(-d) / a);
       re_nuz2 = -b / 2 / a;
       im_nuz2 = fabs(sqrt(-d) / a);
     }
 
     return discrim_flag;
   }
 
   Fourvec Top_Decaykin::hadw(const Lepjets_Event& ev)
   //
   // Purpose: Sum up the appropriate 4-vectors to find the hadronic W.
   //
   // Inputs:
   //   ev -          The event.
   //
   // Returns:
   //   The hadronic W.
   //
   {
     return (ev.sum(hadw1_label) + ev.sum(hadw2_label));
   }
 
   Fourvec Top_Decaykin::hadw1(const Lepjets_Event& ev)
   //
   // Purpose:
   //
   // Inputs:
   //   ev -          The event.
   //
   // Returns:
   //   The higher-pT hadronic jet from W
   //
   {
     return ev.sum(hadw1_label);
   }
 
   Fourvec Top_Decaykin::hadw2(const Lepjets_Event& ev)
   //
   // Purpose:
   //
   // Inputs:
   //   ev -          The event.
   //
   // Returns:
   //   The lower-pT hadronic jet from W
   //
   //
   {
     return ev.sum(hadw2_label);
   }
 
   Fourvec Top_Decaykin::lepw(const Lepjets_Event& ev)
   //
   // Purpose: Sum up the appropriate 4-vectors to find the leptonic W.
   //
   // Inputs:
   //   ev -          The event.
   //
   // Returns:
   //   The leptonic W.
   //
   {
     return (leptons(ev) + ev.met());
   }
 
   Fourvec Top_Decaykin::hadt(const Lepjets_Event& ev)
   //
   // Purpose: Sum up the appropriate 4-vectors to find the hadronic t.
   //
   // Inputs:
   //   ev -          The event.
   //
   // Returns:
   //   The hadronic t.
   //
   {
     return (ev.sum(hadb_label) + hadw(ev));
   }
 
   Fourvec Top_Decaykin::lept(const Lepjets_Event& ev)
   //
   // Purpose: Sum up the appropriate 4-vectors to find the leptonic t.
   //
   // Inputs:
   //   ev -          The event.
   //
   // Returns:
   //   The leptonic t.
   //
   {
     return (ev.sum(lepb_label) + lepw(ev));
   }
 
   ostream& Top_Decaykin::dump_ev(std::ostream& s, const Lepjets_Event& ev)
   //
   // Purpose: Print kinematic information for EV.
   //
   // Inputs:
   //   s -           The stream to which to write.
   //   ev -          The event to dump.
   //
   // Returns:
   //   The stream S.
   //
   {
     s << ev;
     Fourvec p;
 
     p = lepw(ev);
     s << "lepw " << p << " " << p.m() << "\n";
     p = lept(ev);
     s << "lept " << p << " " << p.m() << "\n";
     p = hadw(ev);
     s << "hadw " << p << " " << p.m() << "\n";
     p = hadt(ev);
     s << "hadt " << p << " " << p.m() << "\n";
 
     return s;
   }
 
   double Top_Decaykin::cos_theta_star(const Fourvec& fermion, const Fourvec& W, const Fourvec& top)
   //
   // Purpose: Calculate cos theta star in top decay
   //
   // Inputs:
   //   fermion -     The four momentum of fermion from W
   //   W -           The four momentum of W from top
   //   top -         The four momentum of top
   // Returns:
   //   cos theta star
   //
   {
     if (W.isLightlike() || W.isSpacelike()) {
       return 100.0;
     }
 
     CLHEP::HepBoost BoostWCM(W.findBoostToCM());
 
     CLHEP::Hep3Vector boost_v3fermion = BoostWCM(fermion).vect();
     CLHEP::Hep3Vector boost_v3top = BoostWCM(top).vect();
 
     double costhetastar = boost_v3fermion.cosTheta(-boost_v3top);
 
     return costhetastar;
   }
 
   double Top_Decaykin::cos_theta_star(const Lepjets_Event& ev)
   //
   // Purpose: Calculate lepton cos theta star in top decay
   //
   // Inputs:
   //   ev -          A lepton+jets event
   // Returns:
   //   cos theta star of lepton
   //
   {
     return cos_theta_star(leptons(ev), lepw(ev), lept(ev));
   }
 
   double Top_Decaykin::cos_theta_star_lept(const Lepjets_Event& ev)
   //
   // Purpose: Calculate lepton cos theta star in top decay
   //
   // Inputs:
   //   ev -          A lepton+jets event
   // Returns:
   //   cos theta star of lepton
   //
   {
     return cos_theta_star(ev);
   }
 
   double Top_Decaykin::cos_theta_star_hadt(const Lepjets_Event& ev)
   //
   // Purpose: Calculate absolute value of cos theta star of
   //          one of the hadronic W jet from hadronic top.
   //
   // Inputs:
   //   ev -          A lepton+jets event
   // Returns:
   //   absolute value of cos theta star
   //
   {
     return fabs(cos_theta_star(hadw1(ev), hadw(ev), hadt(ev)));
   }
 
 }  // namespace hitfit

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