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Neutron Background Simulation

Neutron Background Simulation. R. Wilkinson. Neutron Background Simulation. 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.

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Neutron Background Simulation

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  1. Neutron Background Simulation R. Wilkinson

  2. Neutron Background Simulation • 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

  3. Why is neutron background hard to simulate? • 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

  4. GEANT Simulation • QGSP_BERT_HP physics tables • Other options needed to give long-lived, low energy particles • No pT cuts or eta cuts • Long tracking time • No neutron threshold

  5. Old Methods • Parametrization (UC Davis) • Database of Chamber Hit Patterns (Wilkinson) • Meant to be added only to chambers with signal

  6. CSC-specific issues • Usually only affect one layer, sometimes two, sometimes more. • At L =1034, we expect at most 3% chance of a neutron per chamber, per BX. • We had thought that the trigger would suppress most of these, but it doesn’t! • We had thought suppression used LCTs, which require four layers • So we thought we should only add neutron hits to chambers that already have signal • In reality, it uses CLCT pretriggers, which only require two layers • Which means we need to simulate all chambers, and implement a more accurate zero suppression in the simulation

  7. Workplan • Treat neutrons like regular pileup • Take SimHits with a high time of flight, change the TOF to 0-25 ns, and save the new hits in a different collection. • SimMuon/Neutron/src/NeutronProducer.cc • Keep relative timing for hits within the same chamber • Drop all data except the high-TOF hits from the events • Let the MixingModule mix in the new events. • Use the average number of interactions per bunch crossing, including gaps • Should get the correct occupancy, assuming steady-state running. • Should just work for DT & RPC

  8. CSC Workplan • Current Simulation: • Saves any layer which has signal • Only simulates and reads out groups of strips (CFEBs) containing or near signals • Doesn’t always make all the noise strips needed • What’s needed: • Create a transient container of unsuppressed digis • Neutron hits come from MixingModule • Run the L1 trigger primitive simulation • Move the module from the L1Trigger sequence to the SimMuon sequence • Code would still live in L1Trigger • Input is unsuppressed digis • Creates a new transient collection of pretrigger digis • Make a zero suppression module which produces the suppressed digis • Generating noise, if needed • Prototype in SimMuon/CSCDigitizer/src/CSCDigiSuppressor.cc

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