Current status of Current status of the MC &the MC &

Cosmic ray ratesCosmic ray rates

Vlasios VasileiouVlasios Vasileiou

Milagro Collaboration MeetingMilagro Collaboration Meeting

Los Alamos 12/19/2006Los Alamos 12/19/2006

Status of the Monte Carlo Status of the Monte Carlo SimulationSimulation

Bug fixes since last collaboration meetingBug fixes since last collaboration meeting There was a deficit of high energy events in the There was a deficit of high energy events in the

milagro and future detector simulated data.milagro and future detector simulated data. ““Max number of PEs for PMT” bug in milindaMax number of PEs for PMT” bug in milinda

When a PMT was hit with more than a max number of PEs, When a PMT was hit with more than a max number of PEs, DataRead_MCASCII5 skipped that event and that MC file. DataRead_MCASCII5 skipped that event and that MC file. Almost all of the high energy events had these kind of huge Almost all of the high energy events had these kind of huge hitshits

Geant4 couldn’t simulate events with more than Geant4 couldn’t simulate events with more than thousands of particles thousands of particles It would take forever to inject It would take forever to inject the particles from corsika to Geant4. the particles from corsika to Geant4.

The response of the Geant4 collaboration: “This is a feature The response of the Geant4 collaboration: “This is a feature not a bug”not a bug”

I modified Geant4 code to make it workI modified Geant4 code to make it work

New “universal” corsika libraryNew “universal” corsika library

New corsika libraryNew corsika library Extended energy range: Extended energy range:

Old : 30 GeV – 100 TeVOld : 30 GeV – 100 TeV New: 5GeV – 500 TeV New: 5GeV – 500 TeV

Two observation levels 2650m and Two observation levels 2650m and 4300m 4300m

Harder spectrum: -2.00 for gammas & Harder spectrum: -2.00 for gammas & hadronshadrons

Status of the Monte Carlo Status of the Monte Carlo SimulationSimulation

Other bugsOther bugs Corsika bug: Version 6.5001 had a bugCorsika bug: Version 6.5001 had a bug

Showers from zenith angle<~10deg were completely empty. Showers from zenith angle<~10deg were completely empty. I had verified this for hadronic showers. Gamma showers I had verified this for hadronic showers. Gamma showers

looked ok, but I still didn’t trust that version. looked ok, but I still didn’t trust that version. A big part of g4sim v2.0 data were produced with the broken A big part of g4sim v2.0 data were produced with the broken

Corsika version. Corsika version. I have deleted all the buggy Corsika data and all v2.0 data I have deleted all the buggy Corsika data and all v2.0 data

produced with it.produced with it.

G4sim bug in the simulation of hadronic physicsG4sim bug in the simulation of hadronic physics Some hadronic physics weren’t enabled (ex. neutron Some hadronic physics weren’t enabled (ex. neutron

absorption)absorption) Bug present in v1.2 and v2.0 Bug present in v1.2 and v2.0

Improvements in the Geant4 Improvements in the Geant4 simulationsimulation

PMT Optical Model + PMT correctionsPMT Optical Model + PMT corrections Muon peak Muon peak

A muon produces about 110PEs in the muon A muon produces about 110PEs in the muon layer for both MC and data. Compare it with layer for both MC and data. Compare it with ~250pes of G3 and ~200pes of G4 with no PMT ~250pes of G3 and ~200pes of G4 with no PMT corrections. corrections.

mxpe and total pes distributions mxpe and total pes distributions Almost perfect agreement between MC and dataAlmost perfect agreement between MC and data

X2 and A4 distributions (see Aous’ talk)X2 and A4 distributions (see Aous’ talk)

Improvements in the Geant4 Improvements in the Geant4 simulationsimulation

Detailed modeling of the reflections in the Detailed modeling of the reflections in the pondpond Incidence angle dependent reflectivities (cover, Incidence angle dependent reflectivities (cover,

liner)liner) Photon-energy dependent reflectivities (tyvek, Photon-energy dependent reflectivities (tyvek,

baffles)baffles) Added support for partial air under cover Added support for partial air under cover (new (new

in v2.1)in v2.1) 20 stripes of air, total coverage can vary from 0-100% 20 stripes of air, total coverage can vary from 0-100%

Reflectivity of bottom increased by a 10% to Reflectivity of bottom increased by a 10% to account for the pipes account for the pipes (new in v2.1)(new in v2.1)

Partial air under the Partial air under the covercover

Improvements in the Geant4 Improvements in the Geant4 simulationsimulation

More accurate simulation of scattering More accurate simulation of scattering in the waterin the water Wrote code for simulation of Mie scatteringWrote code for simulation of Mie scattering

Forward and backward scattering Forward and backward scattering available. available. (backward scattering new in (backward scattering new in v2.1)v2.1)

Can control the scattering angle Can control the scattering angle distribution separately for forward and distribution separately for forward and backward scattering and the ratios backward scattering and the ratios between them (currently 80% forward)between them (currently 80% forward)

One of the remaining problemsOne of the remaining problemsCosmic ray ratesCosmic ray rates

Low detector sensitivity predicted from Low detector sensitivity predicted from the MC (low cosmic ray and Crab(?) the MC (low cosmic ray and Crab(?) rates )rates ) Andy’s Cosmic-Ray Rates memoAndy’s Cosmic-Ray Rates memo

Sent to the milagro mailing list this summer. Sent to the milagro mailing list this summer. Not in the memos pageNot in the memos page

With an offline cut ntop>85 PMTs, the With an offline cut ntop>85 PMTs, the predicted cosmic ray rate from the simulation predicted cosmic ray rate from the simulation is about 60% of the one from data.is about 60% of the one from data.

One of the remaining problemsOne of the remaining problemsCosmic ray ratesCosmic ray rates

I studied this problem in more detailI studied this problem in more detail Plotted predicted rates for ntop, ntop2, Plotted predicted rates for ntop, ntop2,

nfit cutsnfit cuts Examined the effects of:Examined the effects of:

Air under the cover Air under the cover Corsika hadronic interaction modelsCorsika hadronic interaction models g4sim versionsg4sim versions PMT correctionsPMT corrections Using the cosmic ray rates from different Using the cosmic ray rates from different

experiments (JACEE, BESS, ATIC)experiments (JACEE, BESS, ATIC) Different Corsika datasets (30GeV-100TeV Different Corsika datasets (30GeV-100TeV

vs 5GeV- 500TeV)vs 5GeV- 500TeV)

The analysisThe analysis Rates from DataRates from Data

Data run 6200, same run Andy used in his Data run 6200, same run Andy used in his memo.memo.

Reconstructed raw data, using Epoch 5 Reconstructed raw data, using Epoch 5 (v71) reconstruction and 603 calibrations.(v71) reconstruction and 603 calibrations.

Data rate was increased by 10% to account Data rate was increased by 10% to account for the dead timefor the dead time

Rates from the MCRates from the MC Used both Protons and HeliumUsed both Protons and Helium Used dead and non-calibrated PMTs from Used dead and non-calibrated PMTs from

that runthat run Didn’t rescale the pes (because comparing Didn’t rescale the pes (because comparing

to 603 calibs)to 603 calibs)

g4sim 2.1, 5GeV-500TeV

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Effects of air under coverEffects of air under coverg4sim 2.1, 5GeV-500TeV

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g4sim 2.1, 5GeV-500TeV

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Mirror cover

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50% air under cover

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o Mirror cover = 100% diffuse reflections

o Reflected light doesn’t produce hits that participate in the fit

Comparing g4sim v2.0 vs v2.1 with air under the coverComparing g4sim v2.0 vs v2.1 with air under the cover

Comparing different g4sim versions

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Comparing different g4sim versions

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Comparing different g4sim versions

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

Comparing g4sim v2.0 vs v2.1 with No air Comparing g4sim v2.0 vs v2.1 with No air under the coverunder the cover

Comparing different g4sim versions

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Comparing different g4sim versions

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Comparing different g4sim versions

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2.1, No Air under cover, 30GeV-100TeV

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

Comparing different energy ranges Comparing different energy ranges Comparing different corsika sets

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2.1, Air under cover, 30GeV-100TeV

Comparing different corsika sets

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Negligible amount of triggers from E<30GeV and E>100TeV

Comparing different corsika sets

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2.1, Air under cover, 30GeV-100TeV

Trigger energiesTrigger energies

Red: 5GeV – 500TeVBlack: 30GeV – 100 TeV

Using different hadronic physics in Using different hadronic physics in corsikacorsika

Examining the effects of different hadronic models

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2.1, No air under cover, 30GeV-100TeV, QGS

Examining the effects of different hadronic models

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Examining the effects of different hadronic models

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2.1, No air under cover, 30GeV-100TeV, QGS

NeXus vs QGS

• QGS looks better• We are using NeXus

Using different experimental data for the CR Using different experimental data for the CR fluxflux

Using different experimental data for the CR flux

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ATIC 2.1,50% Air under cover, 5GeV-500TeV

JACEE 2.1,50% Air under cover, 5GeV-500TeV

BESS, 2.1,50% Air under cover, 5GeV-500TeV

Using different experimental data for the CR flux

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ATIC 2.1,50% Air under cover, 5GeV-500TeV

JACEE 2.1,50% Air under cover, 5GeV-500TeV

BESS, 2.1,50% Air under cover, 5GeV-500TeV

Using different experimental data for the CR flux

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ATIC 2.1,50% Air under cover, 5GeV-500TeV

JACEE 2.1,50% Air under cover, 5GeV-500TeV

BESS, 2.1,50% Air under cover, 5GeV-500TeV

Examining the effects of the Examining the effects of the noisenoise

Examining the effects of the noise

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2.1,50% Air under cover, 5GeV-500TeV

Examining the effects of the noise

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Examining the effects of the noise

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2.1,50% Air under cover, 5GeV-500TeV

Noise has a very small effect in the number of small hits

Examining the effects of the PMT Examining the effects of the PMT correctionscorrections

Examining the effects of the PMT corrections

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Examining the effects of the PMT corrections

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Examining the effects of the PMT corrections

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2.1,50% Air under cover, 5GeV-500TeV

The PMT corrections do have a big effect on the rates but:

o The PMT corrections helped to match many PE related quantities in the MC (muon peak, mxpes, total pes)

o Even with the PMT corrections there is still a big deficit of high nfit events in the MC

Comparing the past and the Comparing the past and the presentpresent

Comparing past and present

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Comparing past and present

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Comparing past and present

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g4sim v2.0 vs v2.1 No air under cover vs 50% air under cover 30GeV – 100 TeV vs 5GeV vs 500TeV

ConclusionsConclusions Latest Milagro MC predicts low sensitivity for Latest Milagro MC predicts low sensitivity for

big showersbig showers Some factors that can affect the rates have been Some factors that can affect the rates have been

identifiedidentified The behavior of the rates with an nfit cut is different The behavior of the rates with an nfit cut is different

than the behavior of the rates with an ntop/ntop2 cut.than the behavior of the rates with an ntop/ntop2 cut. ntop/ntop2 cuts care just about hit pmtsntop/ntop2 cuts care just about hit pmts nfit cut needs a hit to be in time with the shower, nfit cut needs a hit to be in time with the shower,

insensitive to reflected lightinsensitive to reflected light Identified factors don’t necessarily affect rate(ntop) & Identified factors don’t necessarily affect rate(ntop) &

rate(ntop2) the same way as they affect rate(nfit)rate(ntop2) the same way as they affect rate(nfit)

ConclusionsConclusions Factors that affect the rates:Factors that affect the rates:

Air under the cover. Strong effect on rate(ntop) & rate(ntop2) Air under the cover. Strong effect on rate(ntop) & rate(ntop2) but not on rate(nfit)but not on rate(nfit)

Extra reflections from the bottom and water backscattering Extra reflections from the bottom and water backscattering introduced in g4sim v2.1. Factor needs air under the cover to introduced in g4sim v2.1. Factor needs air under the cover to affect the rates. Doesn’t affect rate(nfit)affect the rates. Doesn’t affect rate(nfit)

PMT correctionsPMT corrections Hadronic models in corsikaHadronic models in corsika

Factors that don’t affect the trigger ratesFactors that don’t affect the trigger rates Inclusion of very low energy or very high energy showersInclusion of very low energy or very high energy showers NoiseNoise Choice of experimental data for the primary cosmic ray fluxChoice of experimental data for the primary cosmic ray flux

Factors that need to be checkedFactors that need to be checked Effects of different water absorption (currently 27m)Effects of different water absorption (currently 27m) Heavier ions (Jordan?)Heavier ions (Jordan?)

FutureFuture It would be nice if we knew why there aren’t so It would be nice if we knew why there aren’t so

many big nicely fit eventsmany big nicely fit events I expect many bug fixes/improvements in the I expect many bug fixes/improvements in the

next versions of Geant4 & Corsikanext versions of Geant4 & Corsika Geant 4.8.2 was released this week and a new Corsika Geant 4.8.2 was released this week and a new Corsika

(with a new high energy hadronic physics package) was (with a new high energy hadronic physics package) was announced today (out next month)announced today (out next month)