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Neutron Background Simulation: Infrastructure and Validation

This presentation outlines advancements in neutron simulation infrastructure, highlighting the challenges of tracking long-lived neutrons produced in collision environments. Key findings include basic SimHit level results for muon systems derived from high-statistics samples using the QGSP_BERT_HP physics list, and comparisons to older results. Planned improvements focus on validating new physics lists, extending simulation for heavy ions, and enhancing data collection methodologies. The session emphasizes the importance of effective neutron simulation for accurate detection and analysis in particle physics experiments.

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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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