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 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 Why is neutron background hard to simulate?

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

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

6 u Usually only affect one layer, sometimes two, sometimes more.  At L =10 34, we expect at most 3% chance of a neutron per chamber, per BX. u We had thought that the trigger would suppress most of these, but it doesn’t! è We had thought suppression used LCTs, which require four layers r So we thought we should only add neutron hits to chambers that already have signal è In reality, it uses CLCT pretriggers, which only require two layers r Which means we need to simulate all chambers, and implement a more accurate zero suppression in the simulation CSC-specific issues

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

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