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CSC Simulated Charge

CSC Simulated Charge. Tim Cox, Jay Hauser , Greg Rakness , Rick Wilkinson. The Problem. Simulated charge distributions are narrower than in data. Our Simulation. GEANT gives us an entry & exit point in the gas volume. We need to simulate the drift electrons: How many

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CSC Simulated Charge

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  1. CSC Simulated Charge Tim Cox, Jay Hauser, Greg Rakness, Rick Wilkinson CSC Charge Simulation

  2. The Problem • Simulated charge distributions are narrower than in data CSC Charge Simulation

  3. Our Simulation • GEANT gives us an entry & exit point in the gas volume. • We need to simulate the drift electrons: • How many • Where along the line they happen • Include delta ray electrons • Presented by Tim in more detail here: • https://indico.cern.ch/conferenceDisplay.py?confId=131685 • https://indico.cern.ch/conferenceDisplay.py?confId=a032316 CSC Charge Simulation

  4. Modeling the Energy Loss Used GEANT3 to construct a table of collisions Use the velocity and lowest threshold to generate a mean free path for a step Throw a random number between 0 and Ncollisions to get a “percentile” energy loss for that step CSC Charge Simulation

  5. Energy Loss Line is GEANT4 energy loss per gap Triangle is our simulation CSC Charge Simulation

  6. Modeling the Ionization • We use two parameters to convert energy loss to some number of ionizations • Ionization energy • Minimum energy to produce ionization • ~10 eV • Effective work function • Average energy loss per ionization • ~ tens of eV • Any deposit with two or more ionizations is considered a delta ray • We check range to see if it leaves gas volume CSC Charge Simulation

  7. Comparison with Sauli • We create, on average, 72 primary ionizations per gas gap, and 91 total. • Compare with Sauli’s 1977 paper on multiwire proportional chambers • http://lhcb-muon.web.cern.ch/lhcb-muon/documents/Sauli_77-09.pdf • He expects 34 primary ionizations per cm in CO2, 91 total, and 29 primary & 94 total for Ar. • Could this explain our charge distribution? CSC Charge Simulation

  8. Toy Monte Carlo Line is 80 primary ionization, 91 total Triangle is 34 primary, 91 total Fewer collisions and bigger delta rays lead to bigger fluctuations in charge CSC Charge Simulation

  9. Ionization Parameters • Sauli’s paper uses different ionization parameters than we do. • Usingthese parameters (weighted average) will lead to fewer primary ionizations, but bigger delta rays. • Maybe 10.4 eV was an excitation energy, not ionization? CSC Charge Simulation

  10. Comparison with Data Old New Data includes Greg’s gain corrections CSC Charge Simulation

  11. Electron Attachment • We had been modeling this by attenuating the signal by 50%. • Changed to using a 50% chance of killing the electron • Doesn’t broaden the distribution much. • Is attachment a function of drift time? CSC Charge Simulation

  12. Chargevs. Drift Time Data Sim • No obvious attenuation due to attachment • Don’t understand structure in far tails of timing More at http://rakness.web.cern.ch/rakness/internal/log/1104/log.html CSC Charge Simulation

  13. Conclusions • Simulation of energy loss looks good. • Going to standard ionization parameters gives much better agreement with data charge distributions. • Electron attachment is still an open question. CSC Charge Simulation

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