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Neutron Background Simulation: Infrastructure and Validation

Neutron Background Simulation: Infrastructure and Validation. Vadim Khotilovich, Rick Wilkinson, with help from Piet Verwilligen, Alexei Safonov, Tim Cox. Simulation Meeting August 30, 2010. Outline. Intro N eutron simulation infrastructure Basic S im H it level results for muon systems

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Neutron Background Simulation: Infrastructure and Validation

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  1. Neutron Background Simulation: Infrastructure and Validation Vadim Khotilovich, Rick Wilkinson, with help fromPiet Verwilligen, Alexei Safonov, Tim Cox Simulation Meeting August 30, 2010

  2. Outline • Intro • Neutron simulation infrastructure • Basic SimHit level results for muon systems • From high-stat samples produced in 3_6_3QGSP_BERT_HP physics list • Comparison to older results • Plans • Validation of QGSP_BERT_HP_EML and QGSP_BERT_EMLSN physics lists • low stat samples in 3_9_0_pre2

  3. Intro From Rick’s previous presentation: http://indico.cern.ch/conferenceDisplay.py?confId=55712 • Long-lived neutrons created, diffuse around collision hall • They get captured by nuclei, emitting a photon • Compton scattering or photoelectric effect makes MeV electrons, which cause hits in muon chambers

  4. Why neutrons are hard to simulate? From Rick’s previous presentation: http://indico.cern.ch/conferenceDisplay.py?confId=55712 • Because neutrons can live up to a second before making a signal • They can’t be treated like ordinary minimum-bias pileup, because millions of collisions in the past can contribute • log10TOF vs log10Ekin • Plot made in 2001

  5. New Neutron Simulation Infrastructure MinBias simulated with:- special physics list- tracking time up to 1s - no pt and neutron cuts generator “Pythia6GeneratorFilter” generatorNeutrons “Pythia6GeneratorFilter” g4SimHits “OscarProducer” g4SimHitsNeutrons “OscarProducer” MinBiasPileupSample Transform TOFs of >250ns SimHits into25ns wide time intervalwhile preservinghits’ time ordering cscNeutronWriter “CSCNeutronWriter” rpcNeutronWriter “RPCNeutronWriter” dtNeutronWriter “DTNeutronWriter” SimMuon/Neutron Special utility modulesto standardize collectionsfor MixingModule generator “EmptyHepMCProducer” generator Any desired generator g4SimHits “NeutronHitsCollector” f = fraction of filled BXs in LHC orbit g4SimHits “OscarProducer” NPU NeutronPileupSample mix “MixingModule” f*NPU signal to digitizers

  6. Neutron SIM Samples • CMSSW_3_6_3 • QGSP_BERT_HP physics list • MinBias generated @ 14 TeV • ~105K events • Geometries • Current detector geometry • Most of results: TDR RPC & YE4 shielding • Along with transformed neutron SimHit collections keep the original ones produced by GEANT

  7. Muon SimHits TOF vs. Ekin • TDR geometry with YE4 • CSC&DT have lots of low energy hits • RPCs are not so sensitive

  8. CSC: hits vs. clusters of hits • Simple clustering of CSC hits in a chamber layer: • Sort by closes wire group, strip, TOF • Take first hit • Cluster other hits around it requiring DWG ≤ 1 & DS ≤ 3 & DTOF < 2 ns • Repeat recursively… • Very low energy hits are from secondary interactions

  9. Fractions of evt. with n-hits: YE4 effect Geometry:currentTDR with YE4 • Fraction of events with neutron simhits • Can be used for probabilistic interpretations • Comparing two geometries: • Current • TDR with YE4 • ME4/2 gets ~4.4 times more neutron hits without YE4 shielding • There is smaller effect in other ring=2 stations • Should expect similar magnitude effect in RPC’s RE4/2 & RE4/3 9

  10. Fractions of evt. with hits: MB vs. neutrons SimHits from:MinBiasNeutrons SimHits from:MinBiasNeutrons • SimHits from regular minbias vs. SimHits from neutrons • TDR geometry with YE4 • CSC: • Most stations get hits from neutrons more often then from MinBias (except ME1/1) • Even with shielding ME4/2 is dominated by neutron hits • RPCf: • MinBias contribution is higher in most of stations (except RE 4/3, 4/2, 3/3) • b/c neutron hits energies are lower 10

  11. Fractions of events with neutron hits TDR geometry with YE4 11

  12. Neutron Hits Fluxes at Nominal L SimHits from:MinBiasNeutrons SimHits from:MinBiasNeutrons SimHits from:MinBiasNeutrons SimHits from:MinBiasNeutrons TDR geometry with YE4 NPU=25 Fraction of filled BXs = 0.795 Only neutron bars have text markers DT&CSC n-cluster fluxes ~2 times lower then n-hits fluxes 12

  13. Neutron Hits Fluxes: Trigger TDR • CMS Trigger TDR results: • Full circles = Neutron hits • Solid lines + open circles = MinBias • Current estimates for neutron rates are • ~2-6 times lower in CSC • ~4-30 times lower in DT • Reason not clear • Current estimates for MinBias rates are • CSC • Somewhat higher, especially for closer to beamline stations • DT • Reasonably similar • Slightly higher in outer stations • Plan to produce somewhat similar plot for easier comparison 13

  14. Plans • Neutron simulation infrastructure: • Extending the configuration for heavy ion simulation • With help from Catherine Silvestre • Consolidation of all relevant modules in SimMuon/Neutron • Maybe adding an option to cmsDriver • Adopting new physics lists • Possibly: employ endcaps’ rotational and +-z symmetry to effectively increase neutron samples statistics x34 for trigger rates studies • Plans for studies: • Comparison to data • Special runs with 1-layer CSC pretrigger are planned to be taken soon • Will need 7 TeV neutron sample simulated • DIGI level • Preliminary: fraction of events with CSC digis from neutrons is ~5 times lower than fraction of events with neutron simhits • Trigger primitives level • Preliminary: • Without YE4, ME4/2 gets ~40% more of LCTs b/c of neutrons • Much lower effect in other chamber types • GMT • Combining CSC and RPCf in high pileup environment 14

  15. Physics Lists Validation 15

  16. Physics Lists • Standard one for use in CMS simulation: • QGSP_BERT_EML • Too crude for neutron modelling • Special “high precision” lists for modeling of long-lived neutrons: • QGSP_BERT_HP • Older detailed multiple scattering model • QGSP_BERT_HP_EML • New simplified/faster multiple scattering model • Special parameterized neutron cross section table: • QGSP_BERT_EMLSN • The newest parameterization 16

  17. Validation Samples • For each physics list: • 2K events sample • Produced with CMSSW_3_9_0_pre2 in the same conditions • Standard geometry • GEANT settings: g4SimHitsNeutrons.Physics.type = 'SimG4Core/Physics/QGSP_BERT_***‘g4SimHitsNeutrons.Physics.FlagBERT = Trueg4SimHitsNeutrons.StackingAction.NeutronThreshold = 0.g4SimHitsNeutrons.StackingAction.MaxTrackTime = 1e9g4SimHitsNeutrons.SteppingAction.MaxTrackTime = 1e9# the following two enable simulation in the Quad regiong4SimHitsNeutrons.StackingAction.MaxTrackTimes[2] = 1e9g4SimHitsNeutrons.SteppingAction.MaxTrackTimes[2] = 1e9# no cuts on generator-level particlesg4SimHitsNeutrons.Generator.ApplyPCuts = Falseg4SimHitsNeutrons.Generator.ApplyEtaCuts = False 17

  18. Timing (min/evt) QGSP_BERT_HP 17.2 QGSP_BERT_HP_EML 16.2 QGSP_BERT_EMLSN 1.4 QGSP_BERT_EML 1.2 • For HP lists Most of time is spent in transport of neutrons from quad regions • EMLSN timing: too good to be true?... 18

  19. Fraction of Events with n-hits in CSC • ~x4 lower for EMLSN • HP and HP_EML: within stat errors • Except ME4/2 wherequad region simulationis important • DT & RPC: • Small statistics • x2-5 lower for EMLSNin DT 19

  20. Validation: TOF vs. Ekin in CSC QGSP_BERT_HP QGSP_BERT_HP_EML QGSP_BERT_EMLSN QGSP_BERT_EML Both exhibitTOF cut-offat 104 ns _ 20

  21. Validation: Ekin & TOF in CSC P 21

  22. Conclusions • QGSP_BERT_HP and QGSP_BERT_HP_EML show close results, except for ME4/2 station • QGSP_BERT_EMLSN • Neutron hit yield lower by x4 • It doesn’t track particles longer then 104 ns 22

  23. BAckup

  24. CSC # of layers with hits MinBias Neutrons Neutrons leave hits in 1-2 layers most of time By chamber type (no YE4 schielding): 24

  25. r-z Neutron hits Heatmap Endcap in currentgeometry TDR geometry with YE4

  26. x-y Neutron hits Heatmap in Barrel 26

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