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Current status of the MC & Cosmic ray rates

Current status of the MC & Cosmic ray rates. Vlasios Vasileiou Milagro Collaboration Meeting Los Alamos 12/19/2006. Status of the Monte Carlo Simulation Bug fixes since last collaboration meeting. There was a deficit of high energy events in the milagro and future detector simulated data.

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Current status of the MC & Cosmic ray rates

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  1. Current status of the MC &Cosmic ray rates Vlasios Vasileiou Milagro Collaboration Meeting Los Alamos 12/19/2006

  2. Status of the Monte Carlo SimulationBug fixes since last collaboration meeting • There was a deficit of high energy events in the milagro and future detector simulated data. • “Max number of PEs for PMT” bug in milinda • When a PMT was hit with more than a max number of PEs, DataRead_MCASCII5 skipped that event and that MC file.  Almost all of the high energy events had these kind of huge hits • Geant4 couldn’t simulate events with more than thousands of particles  It would take forever to inject the particles from corsika to Geant4. • The response of the Geant4 collaboration: “This is a feature not a bug” • I modified Geant4 code to make it work

  3. New “universal” corsika library • New corsika library • Extended energy range: • Old : 30 GeV – 100 TeV • New: 5GeV – 500 TeV • Two observation levels 2650m and 4300m • Harder spectrum: -2.00 for gammas & hadrons

  4. Status of the Monte Carlo SimulationOther bugs • Corsika bug: Version 6.5001 had a bug • Showers from zenith angle<~10deg were completely empty. • I had verified this for hadronic showers. Gamma showers looked ok, but I still didn’t trust that version. • A big part of g4sim v2.0 data were produced with the broken Corsika version. • I have deleted all the buggy Corsika data and all v2.0 data produced with it. • G4sim bug in the simulation of hadronic physics • Some hadronic physics weren’t enabled (ex. neutron absorption) • Bug present in v1.2 and v2.0

  5. Improvements in the Geant4 simulation • PMT Optical Model + PMT corrections • Muon peak • A muon produces about 110PEs in the muon layer for both MC and data. Compare it with ~250pes of G3 and ~200pes of G4 with no PMT corrections. • mxpe and total pes distributions • Almost perfect agreement between MC and data • X2 and A4 distributions (see Aous’ talk)

  6. Improvements in the Geant4 simulation • Detailed modeling of the reflections in the pond • Incidence angle dependent reflectivities (cover, liner) • Photon-energy dependent reflectivities (tyvek, baffles) • Added support for partial air under cover (new in v2.1) • 20 stripes of air, total coverage can vary from 0-100% • Reflectivity of bottom increased by a 10% to account for the pipes (new in v2.1)

  7. Partial air under the cover

  8. Improvements in the Geant4 simulation • More accurate simulation of scattering in the water • Wrote code for simulation of Mie scattering • Forward and backward scattering available. (backward scattering new in v2.1) • Can control the scattering angle distribution separately for forward and backward scattering and the ratios between them (currently 80% forward)

  9. One of the remaining problemsCosmic ray rates • Low detector sensitivity predicted from the MC (low cosmic ray and Crab(?) rates ) • Andy’s Cosmic-Ray Rates memo • Sent to the milagro mailing list this summer. Not in the memos page • With an offline cut ntop>85 PMTs, the predicted cosmic ray rate from the simulation is about 60% of the one from data.

  10. One of the remaining problemsCosmic ray rates • I studied this problem in more detail • Plotted predicted rates for ntop, ntop2, nfit cuts • Examined the effects of: • Air under the cover • Corsika hadronic interaction models • g4sim versions • PMT corrections • Using the cosmic ray rates from different experiments (JACEE, BESS, ATIC) • Different Corsika datasets (30GeV-100TeV vs 5GeV- 500TeV)

  11. The analysis • Rates from Data • Data run 6200, same run Andy used in his memo. • Reconstructed raw data, using Epoch 5 (v71) reconstruction and 603 calibrations. • Data rate was increased by 10% to account for the dead time • Rates from the MC • Used both Protons and Helium • Used dead and non-calibrated PMTs from that run • Didn’t rescale the pes (because comparing to 603 calibs)

  12. Effects of air under cover • Mirror cover = 100% diffuse reflections • Reflected light doesn’t produce hits that participate in the fit

  13. Comparing g4sim v2.0 vs v2.1 with air under the cover The air under the cover reflects the increased upwards-going light of g4sim v2.1 causing an increase at the rates.

  14. Comparing g4sim v2.0 vs v2.1 with No air under the cover The upwards scattered light created by the improvements in g4sim v2.1 (backward scattering + increased reflectivity from the bottom) needs to be reflected from the cover in order to be detected

  15. Comparing different energy ranges Negligible amount of triggers from E<30GeV and E>100TeV

  16. Trigger energies Red: 5GeV – 500TeV Black: 30GeV – 100 TeV

  17. Using different hadronic physics in corsika • NeXus vs QGS • QGS looks better • We are using NeXus

  18. Using different experimental data for the CR flux

  19. Examining the effects of the noise Noise has a very small effect in the number of small hits

  20. Examining the effects of the PMT corrections • The PMT corrections do have a big effect on the rates but: • The PMT corrections helped to match many PE related quantities in the MC (muon peak, mxpes, total pes) • Even with the PMT corrections there is still a big deficit of high nfit events in the MC

  21. Comparing the past and the present • g4sim v2.0 vs v2.1 • No air under cover vs 50% air under cover • 30GeV – 100 TeV vs 5GeV vs 500TeV

  22. Conclusions • Latest Milagro MC predicts low sensitivity for big showers • Some factors that can affect the rates have been identified • The behavior of the rates with an nfit cut is different than the behavior of the rates with an ntop/ntop2 cut. • ntop/ntop2 cuts care just about hit pmts • nfit cut needs a hit to be in time with the shower, insensitive to reflected light • Identified factors don’t necessarily affect rate(ntop) & rate(ntop2) the same way as they affect rate(nfit)

  23. Conclusions • Factors that affect the rates: • Air under the cover. Strong effect on rate(ntop) & rate(ntop2) but not on rate(nfit) • Extra reflections from the bottom and water backscattering introduced in g4sim v2.1. Factor needs air under the cover to affect the rates. Doesn’t affect rate(nfit) • PMT corrections • Hadronic models in corsika • Factors that don’t affect the trigger rates • Inclusion of very low energy or very high energy showers • Noise • Choice of experimental data for the primary cosmic ray flux • Factors that need to be checked • Effects of different water absorption (currently 27m) • Heavier ions (Jordan?)

  24. Future • It would be nice if we knew why there aren’t so many big nicely fit events • I expect many bug fixes/improvements in the next versions of Geant4 & Corsika • Geant 4.8.2 was released this week and a new Corsika (with a new high energy hadronic physics package) was announced today (out next month)

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