************************************************************************ ATTEANTION ************************************************************************ 1) By comparing PYTHIA and PHOJET files of GEANT3, one has to take into account that cavern and LUBN scoring annulus are in PYTHIA but not in PHOJET and not in GEANT4 (I guess). 2) GEANT3 contains informations of particles at IP (excluded PHOJET setup: "Entire Experiment, single wall beampipe, aerogel). GEANT4 does not. ************************************************************************ ************************************************************************ OBSERVATIONS ************************************************************************ 0) Particle type ditributions at the IP for different experimental setup are compatible (p.1,4). Fine. 1) Primary photons (pions) are suppressed by more than 2 orders of magnitude (factor 4-5) in the entire experiment compared to the empty experiment in GEANT3 and GEANT4, both in PYTHIA and PHOJET (p.2,5,7,9). 2) What is the origin of such a large amount of secondary photons and neutrons at LUCID in an empty experiment in GEANT3 PYTHIA sample (p.3)? This happens in GEANT3 PYTHIA (p.3) and NOT in GEANT3 PHOJET (p.6), NOT in GEANT4 PYTHIA (p.8), NOT in GEANT4 PHOJET (p.10). This is due to the fact that in GEANT3 PYTHIA the "empty" experiment is not really "empty" (cavern and LUBN scoring annulus are present). The effect is better visible in GEANT3 PYTHIA-PHOJET comparison (p.15). Since a smiliar discrepancy can be observed in GEANT3-GEANT4 comparison in the "entire experiment", both in PYTHIA (p.11) and PHOJET (p.13), one possible conclusion is that cavern and LUBN scoring annulus are a MAJOR source of difference in the comparison between GEANT3 and GEANT4. 3) The beampipe is the major source of photons and electrons. The entire experiment is the major source of neutrons. This is valid for GEANT3 PYTHIA (p.3) and GEANT3 PHOJET (p.6) The same is true for GEANT4 PYTHIA (p.8) and GEANT4 PHOJET (p.10), with the only difference that in GEANT4 there are less neutrons. This might be due to missing cavern and LUBN scoring annulus in GEANT4. 4) One problem that remains is the discrepancy in secondary photons at LUCID between GEANT3 PHOJET and GEANT4 PHOJET in a "really empty" experiment (p.12). 5) The energy spectrum of primary pions and gamma at IP looks completely different in PHOJET and PYTHIA samples of GEANT3. PHOJET seems more realistic than PYTHIA (p.16,17). 6) The effect of the cavern and the LUBN scoring annulus in GEANT3 PYTHIA compared to GEANT3 PHOJET is to give lots of low energy secondary photons (p.19), mainly from the back (p.20). An excess of low energy pions is also visible (p.18). 7) Problem of piZero. There should be no piZero at LUCID. There are secondary piZero in GEANT3 PYTHIA (p.3) and GEANT3 PHOJET (p.6) There should be either primary piZero, or primary photons (from piZero decays), not both (p.14) ************************************************************************ A.Sbrizzi