Neutron Background SimulationNeutron Background Simulation

R. WilkinsonR. Wilkinson

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Neutron Background SimulationNeutron Background Simulation

Long-lived neutrons created, Long-lived neutrons created, diffuse around collision diffuse around collision hallhall

They get captured by nuclei, They get captured by nuclei, emitting a photonemitting a photon

Compton scattering or Compton scattering or photoelectric effect makes photoelectric effect makes MeV electrons, which MeV electrons, which cause hits in muon cause hits in muon chamberschambers

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Because neutrons can live Because neutrons can live up to a second before up to a second before making a signalmaking a signal

They can’t be treated like They can’t be treated like ordinary minimum-bias ordinary minimum-bias pileup, because millions of pileup, because millions of collisions in the past can collisions in the past can contributecontribute

Why is neutron background hard to Why is neutron background hard to simulate?simulate?

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QGSP_BERT_HP physics tablesQGSP_BERT_HP physics tables

Other options needed to give long-lived, low energy particlesOther options needed to give long-lived, low energy particles No pT cuts or eta cutsNo pT cuts or eta cuts Long tracking timeLong tracking time No neutron thresholdNo neutron threshold

GEANT SimulationGEANT Simulation

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Old MethodsOld Methods

Parametrization (UC Davis)Parametrization (UC Davis)

Database of Chamber Hit Patterns (Wilkinson)Database of Chamber Hit Patterns (Wilkinson) Meant to be added only to chambers with signalMeant to be added only to chambers with signal

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Usually only affect one layer, sometimes two, Usually only affect one layer, sometimes two, sometimes more.sometimes more.

At At L L =10=103434, we expect at most 3% chance of a , we expect at most 3% chance of a neutron per chamber, per BX.neutron per chamber, per BX.

We had thought that the trigger would suppress We had thought that the trigger would suppress most of these, but it doesn’t!most of these, but it doesn’t!

We had thought suppression used LCTs, We had thought suppression used LCTs, which require four layerswhich require four layers

So we thought we should only add neutron So we thought we should only add neutron hits to chambers that already have signalhits to chambers that already have signal

In reality, it uses CLCT pretriggers, which In reality, it uses CLCT pretriggers, which only require two layersonly require two layers

Which means we need to simulate all Which means we need to simulate all chambers, and implement a more chambers, and implement a more accurate zero suppression in the accurate zero suppression in the simulationsimulation

CSC-specific issuesCSC-specific issues

Events to add, 10^34, 24 bx

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Shielded G3

G4

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Treat neutrons like regular pileupTreat neutrons like regular pileup

Take SimHits with a high time of flight, change the TOF to 0-25 ns, and save Take SimHits with a high time of flight, change the TOF to 0-25 ns, and save the new hits in a different collection.the new hits in a different collection.

SimMuon/Neutron/src/NeutronProducer.ccSimMuon/Neutron/src/NeutronProducer.cc Keep relative timing for hits within the same chamberKeep relative timing for hits within the same chamber

Drop all data except the high-TOF hits from the eventsDrop all data except the high-TOF hits from the events

Let the MixingModule mix in the new events.Let the MixingModule mix in the new events. Use the average number of interactions per bunch crossing, including gapsUse the average number of interactions per bunch crossing, including gaps Should get the correct occupancy, assuming steady-state running.Should get the correct occupancy, assuming steady-state running.

Should just work for DT & RPCShould just work for DT & RPC

WorkplanWorkplan

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Current Simulation:Current Simulation: Saves any layer which has signalSaves any layer which has signal Only simulates and reads out groups of strips (CFEBs) containing or near Only simulates and reads out groups of strips (CFEBs) containing or near

signalssignals Doesn’t always make all the noise strips neededDoesn’t always make all the noise strips needed

What’s needed:What’s needed: Create a transient container of unsuppressed digisCreate a transient container of unsuppressed digis

Neutron hits come from MixingModuleNeutron hits come from MixingModule Run the L1 trigger primitive simulationRun the L1 trigger primitive simulation

Move the module from the L1Trigger sequence to the SimMuon sequenceMove the module from the L1Trigger sequence to the SimMuon sequence Code would still live in L1TriggerCode would still live in L1Trigger

Input is unsuppressed digis Input is unsuppressed digis Creates a new transient collection of pretrigger digisCreates a new transient collection of pretrigger digis

Make a zero suppression module which produces the suppressed digisMake a zero suppression module which produces the suppressed digis Generating noise, if neededGenerating noise, if needed Prototype in SimMuon/CSCDigitizer/src/CSCDigiSuppressor.ccPrototype in SimMuon/CSCDigitizer/src/CSCDigiSuppressor.cc

CSC WorkplanCSC Workplan