doc/v626/vo007__PhysicsHelpers_8C.html

void vo007_PhysicsHelpers()

{

   // The DeltaPhi helper computes the closest angle between angles.

   // This means that the resulting value is in the range [-pi, pi].


   // Note that the helper also supports to compute the angle difference of an

   // RVec and a scalar and two scalars. In addition, the computation of the

   // difference and the behaviour at the boundary can be adjusted to radian and

   // degrees.

   ROOT::RVecF phis = {0.0, 1.0, -0.5, M_PI + 1.0};

   auto idx = Combinations(phis, 2);


   auto phi1 = Take(phis, idx[0]);

   auto phi2 = Take(phis, idx[1]);

   auto dphi = DeltaPhi(phi1, phi2);


   std::cout << "DeltaPhi(phi1 = " << phi1 << ",\n"

             << "         phi2 = " << phi2 << ")\n"

             << " = " << dphi << "\n";


   // The DeltaR helper is similar to the DeltaPhi helper and computes the distance

   // in the \f$\eta\f$-\f$\phi\f$ plane.

   ROOT::RVecF etas = {2.4, -1.5, 1.0, 0.0};


   auto eta1 = Take(etas, idx[0]);

   auto eta2 = Take(etas, idx[1]);

   auto dr = DeltaR(eta1, eta2, phi1, phi2);


   std::cout << "\nDeltaR(eta1 = " << eta1 << ",\n"

             << "       eta2 = " << eta2 << ",\n"

             << "       phi1 = " << phi1 << ",\n"

             << "       phi2 = " << phi2 << ")\n"

             << " = " << dr << "\n";


   // The InvariantMasses helper computes the invariant mass of a two particle system

   // given the properties transverse momentum (pt), rapidity (eta), azimuth (phi)

   // and mass.

   ROOT::RVecF pt3 = {40, 20, 30};

   ROOT::RVecF eta3 = {2.5, 0.5, -1.0};

   ROOT::RVecF phi3 = {-0.5, 0.0, 1.0};

   ROOT::RVecF mass3 = {10, 10, 10};


   ROOT::RVecF pt4 = {20, 10, 40};

   ROOT::RVecF eta4 = {0.5, -0.5, 1.0};

   ROOT::RVecF phi4 = {0.0, 1.0, -1.0};

   ROOT::RVecF mass4 = {2, 2, 2};


   auto invMass = InvariantMasses(pt3, eta3, phi3, mass3, pt4, eta4, phi4, mass4);


   std::cout << "\nInvariantMass(pt1 = " << pt3 << ",\n"

             << "              eta1 = " << eta3 << ",\n"

             << "              phi1 = " << phi3 << ",\n"

             << "              mass1 = " << mass3 << ",\n"

             << "              pt2 = " << pt4 << ",\n"

             << "              eta2 = " << eta4 << ",\n"

             << "              phi2 = " << phi4 << ",\n"

             << "              mass2 = " << mass4 << ")\n"

             << " = " << invMass << "\n";


   // The InvariantMass helper also accepts a single set of (pt, eta, phi, mass) vectors. Then,

   // the invariant mass of all particles in the collection is computed.


   auto invMass2 = InvariantMass(pt3, eta3, phi3, mass3);


   std::cout << "\nInvariantMass(pt = " << pt3 << ",\n"

             << "              eta = " << eta3 << ",\n"

             << "              phi = " << phi3 << ",\n"

             << "              mass = " << mass3 << ")\n"

             << " = " << invMass2 << "\n";

}

M_PI
#define M_PI
Definition Rotated.cxx:105

ROOT::VecOps::RVec< float >

ROOT::VecOps::InvariantMasses
RVec< T > InvariantMasses(const RVec< T > &pt1, const RVec< T > &eta1, const RVec< T > &phi1, const RVec< T > &mass1, const RVec< T > &pt2, const RVec< T > &eta2, const RVec< T > &phi2, const RVec< T > &mass2)
Return the invariant mass of two particles given the collections of the quantities transverse momentu...
Definition RVec.hxx:2873

ROOT::VecOps::Take
RVec< T > Take(const RVec< T > &v, const RVec< typename RVec< T >::size_type > &i)
Return elements of a vector at given indices.
Definition RVec.hxx:2242

ROOT::Math::VectorUtil::DeltaR
Vector1::Scalar DeltaR(const Vector1 &v1, const Vector2 &v2)
Find difference in pseudorapidity (Eta) and Phi betwen two generic vectors The only requirements on t...
Definition VectorUtil.h:110

ROOT::Math::VectorUtil::InvariantMass
Vector1::Scalar InvariantMass(const Vector1 &v1, const Vector2 &v2)
return the invariant mass of two LorentzVector The only requirement on the LorentzVector is that they...
Definition VectorUtil.h:246