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File indexing completed on 2021-02-14 14:21:07

0001 
0002 /*
0003 ________________________________________________________________________
0004 
0005  BetafuncEvtVtxGenerator
0006 
0007  Smear vertex according to the Beta function on the transverse plane
0008  and a Gaussian on the z axis. It allows the beam to have a crossing
0009  angle (slopes dxdz and dydz).
0010 
0011  Based on GaussEvtVtxGenerator
0012  implemented by Francisco Yumiceva (yumiceva@fnal.gov)
0013 
0014  FERMILAB
0015  2006
0016 ________________________________________________________________________
0017 */
0018 
0019 #include "IOMC/EventVertexGenerators/interface/BetafuncEvtVtxGenerator.h"
0020 #include "FWCore/Utilities/interface/Exception.h"
0021 #include "FWCore/ParameterSet/interface/ParameterSet.h"
0022 #include "FWCore/Framework/interface/EventSetup.h"
0023 #include "FWCore/Framework/interface/ESHandle.h"
0024 
0025 #include "CLHEP/Random/RandGaussQ.h"
0026 #include "CLHEP/Units/GlobalSystemOfUnits.h"
0027 #include "CLHEP/Units/GlobalPhysicalConstants.h"
0028 //#include "CLHEP/Vector/ThreeVector.h"
0029 #include "HepMC/SimpleVector.h"
0030 
0031 #include <iostream>
0032 
0033 BetafuncEvtVtxGenerator::BetafuncEvtVtxGenerator(const edm::ParameterSet& p) : BaseEvtVtxGenerator(p), boost_(4, 4) {
0034   readDB_ = p.getParameter<bool>("readDB");
0035   if (!readDB_) {
0036     fX0 = p.getParameter<double>("X0") * cm;
0037     fY0 = p.getParameter<double>("Y0") * cm;
0038     fZ0 = p.getParameter<double>("Z0") * cm;
0039     fSigmaZ = p.getParameter<double>("SigmaZ") * cm;
0040     fbetastar = p.getParameter<double>("BetaStar") * cm;
0041     femittance = p.getParameter<double>("Emittance") * cm;              // this is not the normalized emittance
0042     fTimeOffset = p.getParameter<double>("TimeOffset") * ns * c_light;  // HepMC time units are mm
0043 
0044     setBoost(p.getParameter<double>("Alpha") * radian, p.getParameter<double>("Phi") * radian);
0045     if (fSigmaZ <= 0) {
0046       throw cms::Exception("Configuration") << "Error in BetafuncEvtVtxGenerator: "
0047                                             << "Illegal resolution in Z (SigmaZ is negative)";
0048     }
0049   }
0050   if (readDB_) {
0051     beamToken_ = esConsumes<SimBeamSpotObjects, SimBeamSpotObjectsRcd, edm::Transition::BeginLuminosityBlock>();
0052   }
0053 }
0054 
0055 BetafuncEvtVtxGenerator::~BetafuncEvtVtxGenerator() {}
0056 
0057 void BetafuncEvtVtxGenerator::beginLuminosityBlock(edm::LuminosityBlock const&, edm::EventSetup const& iEventSetup) {
0058   update(iEventSetup);
0059 }
0060 
0061 void BetafuncEvtVtxGenerator::update(const edm::EventSetup& iEventSetup) {
0062   if (readDB_ && parameterWatcher_.check(iEventSetup)) {
0063     edm::ESHandle<SimBeamSpotObjects> beamhandle = iEventSetup.getHandle(beamToken_);
0064 
0065     fX0 = beamhandle->fX0;
0066     fY0 = beamhandle->fY0;
0067     fZ0 = beamhandle->fZ0;
0068     //    falpha=beamhandle->fAlpha;
0069     fSigmaZ = beamhandle->fSigmaZ;
0070     fTimeOffset = beamhandle->fTimeOffset;
0071     fbetastar = beamhandle->fbetastar;
0072     femittance = beamhandle->femittance;
0073     setBoost(beamhandle->fAlpha, beamhandle->fPhi);
0074   }
0075 }
0076 
0077 HepMC::FourVector BetafuncEvtVtxGenerator::newVertex(CLHEP::HepRandomEngine* engine) const {
0078   double X, Y, Z;
0079 
0080   double tmp_sigz = CLHEP::RandGaussQ::shoot(engine, 0., fSigmaZ);
0081   Z = tmp_sigz + fZ0;
0082 
0083   double tmp_sigx = BetaFunction(Z, fZ0);
0084   // need sqrt(2) for beamspot width relative to single beam width
0085   tmp_sigx /= sqrt(2.0);
0086   X = CLHEP::RandGaussQ::shoot(engine, 0., tmp_sigx) + fX0;  // + Z*fdxdz ;
0087 
0088   double tmp_sigy = BetaFunction(Z, fZ0);
0089   // need sqrt(2) for beamspot width relative to single beam width
0090   tmp_sigy /= sqrt(2.0);
0091   Y = CLHEP::RandGaussQ::shoot(engine, 0., tmp_sigy) + fY0;  // + Z*fdydz;
0092 
0093   double tmp_sigt = CLHEP::RandGaussQ::shoot(engine, 0., fSigmaZ);
0094   double T = tmp_sigt + fTimeOffset;
0095 
0096   return HepMC::FourVector(X, Y, Z, T);
0097 }
0098 
0099 double BetafuncEvtVtxGenerator::BetaFunction(double z, double z0) const {
0100   return sqrt(femittance * (fbetastar + (((z - z0) * (z - z0)) / fbetastar)));
0101 }
0102 
0103 void BetafuncEvtVtxGenerator::setBoost(double alpha, double phi) {
0104   //boost_.ResizeTo(4,4);
0105   //boost_ = new TMatrixD(4,4);
0106   TMatrixD tmpboost(4, 4);
0107 
0108   //if ( (alpha_ == 0) && (phi_==0) ) { boost_->Zero(); return boost_; }
0109 
0110   // Lorentz boost to frame where the collision is head-on
0111   // phi is the half crossing angle in the plane ZS
0112   // alpha is the angle to the S axis from the X axis in the XY plane
0113 
0114   tmpboost(0, 0) = 1. / cos(phi);
0115   tmpboost(0, 1) = -cos(alpha) * sin(phi);
0116   tmpboost(0, 2) = -tan(phi) * sin(phi);
0117   tmpboost(0, 3) = -sin(alpha) * sin(phi);
0118   tmpboost(1, 0) = -cos(alpha) * tan(phi);
0119   tmpboost(1, 1) = 1.;
0120   tmpboost(1, 2) = cos(alpha) * tan(phi);
0121   tmpboost(1, 3) = 0.;
0122   tmpboost(2, 0) = 0.;
0123   tmpboost(2, 1) = -cos(alpha) * sin(phi);
0124   tmpboost(2, 2) = cos(phi);
0125   tmpboost(2, 3) = -sin(alpha) * sin(phi);
0126   tmpboost(3, 0) = -sin(alpha) * tan(phi);
0127   tmpboost(3, 1) = 0.;
0128   tmpboost(3, 2) = sin(alpha) * tan(phi);
0129   tmpboost(3, 3) = 1.;
0130 
0131   tmpboost.Invert();
0132   boost_ = tmpboost;
0133   //boost_->Print();
0134 }
0135 
0136 void BetafuncEvtVtxGenerator::sigmaZ(double s) {
0137   if (s >= 0) {
0138     fSigmaZ = s;
0139   } else {
0140     throw cms::Exception("LogicError") << "Error in BetafuncEvtVtxGenerator::sigmaZ: "
0141                                        << "Illegal resolution in Z (negative)";
0142   }
0143 }
0144 
0145 TMatrixD const* BetafuncEvtVtxGenerator::GetInvLorentzBoost() const { return &boost_; }