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Energy non-conservation in Geant4 LHEP model. Mikhail Kosov, Physics Validation 17.10.07. Quantum numbers & E/M conservation. The LHEP model was corrected in test19 : Momentum, Charge, Baryon Number are lost Test19 creates a missing residual to correct it
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Energy non-conservation in Geant4 LHEP model Mikhail Kosov, Physics Validation 17.10.07
Quantum numbers & E/M conservation • The LHEP model was corrected in test19: • Momentum, Charge, Baryon Number are lost • Test19 creates a missing residual to correct it • Energy is still not conserved. To what extend? • After the correction LHEP conserves charge and baryon number in all events. • “Corrected LHEP” conserves 3-momentum with the d-function accuracy by definition. • The energy of the added residual is small. M.Kosov. E non-conservation in LHEP
Energy conservation in the LHEP model • Range from 3.6 MeV/c to 1 TeV/c for • Protons (neutrons are roughly the same): Ein=Ekin • p- mesons (absorbed even at low energies): Ein=Etot • K+ mesons (multiplicity of K- is much smaller): Ein=Ekin • Even p- mesons and anti-protons have a threshold below which the number of secondaries is zero • At low energies the Efin is bigger than Ein because the binding energy is not taken into account. • In pA reactions below 5 MeV the Efin is negative. • <Efin>/Ein-1 is shown withs(Efin)/Efinerrors. M.Kosov. E non-conservation in LHEP
Energy spent to photons (p @ 90 MeV) • In PreCompound/Binary models: only one photon • Real gamma cascade is simulated only in Bertini • Gamma multiplicity increases with A increasing • Berini model provides up to 11 photons with total energy up to 19 (of 90) MeV • In LHEP & CHIPS No Gamma (more probable) • LHEP spends a lot of energy to only one photon • CHIPS does not have photons in pBi at all M.Kosov. E non-conservation in LHEP
Kinetic energy of secondaries (no binding) • For p and K+ the kinetic energy of the projectile is compared with the sum of kinetic energies of secondaries (even for mesons and anti-barions, which have a small contribution to low energies). • For p- the total energy of projectiles is compared with the sum of kinetic energy of baryons and hyperons, total energy of mesons, and “E+m” for anti-baryons. • In the first three pictures the sum is shown for LHEP only and on the last three pictures the LHEP sum is relative to the BERTINI sum, which more or less conserves the total energy. Statistics: 10000 ev./pt. M.Kosov. E non-conservation in LHEP
Conclusion • It is very dangerous to use LHEP for precise simulation of the calorimeter response and the calorimeter resolution. • Problems in LEP are relatively bigger than in HEP, so the QGS/FTF models do not help much. Bertini/Binary models can help a bit, but the 3-15 GeV model is still needed. • While the energy non-conservation is “compensated” (it is overestimated for one set of energies and materials and underestimated for another set), different shifts of responses can be obtained for different materials. In general the simulated LHEP response of calorimeters is below the real value. At high energies it is a bit “up-compensated” by HEP. • Energy non-conservation makes the simulated resolution worse, adding unphysical fluctuations of energy. • Enormous amount of energy transferred to photons leads to overestimation of local energy deposition (p0@High Energy?). M.Kosov. E non-conservation in LHEP
